Defence Research and Development Canada (DRDC) and the Canadian Space Agency (CSA) are collaborating to place a microsatellite in low earth orbit to perform optical detection and tracking of both inner-earth orbiting asteroids and earth-orbiting satellites and debris (i.e., "Resident Space Objects", RSOs). The "Near Earth Object Surveillance Satellite (NEOSSat)" will be the first mission for the CSA multi-mission microsatellite bus program, and is intended by DRDC to demonstrate the military utility of this small and inexpensive class of spacecraft. The mission will obtain metric positions, for geosynchronous satellites, to within ±500 m, timestamps accurate to within a millisecond, and be sensitive to objects in geosynchronous orbit down to 14th magnitude. The asteroid tracking mission will repeatedly survey the area from ±45-70° solar elongation with the aim of finding >50% of all inner-earth asteroids having diameters greater than 1 km.

We have developed a method to estimate both the original objects and the blurring function from a sequence of noisy blurred images, simultaneously collected at different wavelengths (wavelength diversity). The assumption of common path-length errors across the diversity channels allows for a parallel deconvolution procedure that exploits this coupling. In contrast with previous work, no a priori assumptions about the object's intensity distribution are required. The method is described, and preliminary results for both synthetic computer-generated images and real images collected with a bench-scale imaging system are presented, demonstrating the promise of the algorithm.

INO is supporting research on ferrofluidic deformable mirror (FDM) adaptive optics technologies. INO research activities include development and characterization of FDM as well as development and characterization of high resolution (ExAO) adaptive optics systems using such FDM. The trend towards advanced adaptive optics systems is driving the need for deformable mirrors with a large number of low cost actuators. Liquid mirrors have long been recognized a potential low cost alternative to conventional solid mirrors. We present experimental results updated with a new INO’ FDM prototype (371 actuators, 50 um stroke) as well as theoretical model of surface behaviors.

Recent advances in photosensitive glass and holographic recording technologies open new possibilities for astronomical instrumentation. We have developed novel instrument concepts using thick Volume Phase Holographic gratings: a multiband filter for OH line suppression and a single order, widely tunable filter. We present these technologies along with other current and future uses of these promising holographic gratings.

The Canadian National Research Council (NRC), and the Association of Canadian Universities for Research in Astronomy (ACURA) have been collaborating on the development of Large Optical Telescope concepts. Our work has led to a partnership agreement with the Association of Universities for Research in Astronomy (AURA), Caltech, and the University of California to design and build a Thirty Meter Telescope (TMT). In this paper I will summarize the Canada's participation in the TMT project, and will present the science drivers and technical challenges related to the design and development of this facility.

Coupling of optical signal into a single mode waveguide has been a difficult problem for a long time. An advanced fibre coupling device (AFCD) is a high performance fibre coupling system that provide wavefront correction, vibration isolation and alignment. We will discuss two AFCD, one for a ground to space communication link an a second for astronomical interferometric application (DARWIN and VLTI interferometer).

The scanning Fabry Perot interferometer may be tuned over a considerable spectral waveband by adjusting the gap between the mirrors. However, a wide tuning range places significant demands on the design of the mirror coatings. The coatings should be all-dielectric for low absorption. They must also provide good reflectance and phase control over the tuning range. In general, both the reflectance and the phase-shift on reflection of dielectric mirrors are dispersive. This dispersion, left uncontrolled, changes the spectral resolution of a scanning Fabry Perot interferometer over the operating waveband. The mirror phase dispersion also reduces the free spectral range must be controlled in the design process to achieve operation with a reasonable number of blocking filters. However, some phase dispersion will always be present in the mirror design. It is, therefore, desirable to tune the reflectance dispersion and the remaining phase dispersion so that the combination stabilizes the spectral resolution. This paper describes a suitable optimization method. It takes advantage of some features of the Fabry Perot equations to provide error terms for mirror optimization that target a specific spectral resolution value. The paper includes the theory and provides some numerical examples.

Einstein's General Theory of Relativity predicts waves in spacetime caused by oscillating masses. Such waves, known as gravitational waves, are predicted to be created by binary black hole or neutron star inspirals, super-nova, or other catastrophic astronomical events. Even with such large masses moving so repidly, the expected size of the waves is extremely small, typically of order 10^-21 in unitless strain as seen on Earth. LIGO, the Laser Interferometer Gravitational Wave Observatory, is a basic physics experiments designed to detect and study these waves. The next generation interferometers, known as Advanced LIGO, are currently being designed. Thermal noise from mechanical loss in the optical coatings of the mirrors is expected to be an important limiting noise source. Reducing this noise by developing lower mechanical loss coatings, while preserving optical and thermal properties needed in the interferometer, is an area of active research.

We present an improved model for a spectrographic survey telescope with a kilometer scale diffraction grating collector. Refining the initial public disclosures, the new model quantifies flux collection for telescopes of this type. An option in the new model allows a trade of reduced spectral bandwidth for increased flux collection. We provide experimental evidence to demonstrate an earlier prediction of Ångstrom spectral resolution with relaxed tolerances for grating flatness. This model also posits a kilometer focal length secondary parabolic mirror and details its secondary spectrometer. Terrestrial installations for telescopes of this type can be at the ground level, presenting a near-zero wind profile despite the unprecedented kilometer scale aperture. The secondary, consisting of a parabolic reflector, is mechanically independent of the primary and completely static. The resulting open frame eliminates the need for a secondary spyder and has no obstructions in the active ray path. The grating primary can be combined with zenith tube liquid mirrors to provide full coverage of right ascension and all angles of declination. A folding mirror can be used as adaptive wave front correction. In space-based deployment, the kilometer length primary can be stowed as a membrane and unfurled in orbit using simple inertial forces.

Biomedical applications of MOEMS are limited only by the humankind imagination. Precision measurements are minute amounts of biological material could be performed by optical means with a remarkable accuracy. Although available in medical laboratories, such analyzers are making their way directly to the users. Such an example is the test kit to detect the existence of cardiac enzymes in the blood stream. Apart from the direct users, the medical personnel will make use of such tools given the practicality of the kit. In a large proportion of patients admitted to hospital suspected of Acute Myocardial Infarction (AMI), the symptoms and electrocardiographic changes are inconclusive. This necessitates the use of biochemical markers of myocardial damage for correct exclusion or conformation of AMI. New cardiac-specific markers have recently been introduced into the detection of AMI. The cardiac troponins, because of their extraordinary high specificity for myocardial cell injury, have gained particular interest. Experimental setup involves the use of a rectangle shaped AFM cantilevers, optical lenses, laser source, oscilloscope and a charged coupled device (CCD) to detect the cantilever deflection. When specific biomolecular binding occurs on one surface of a microcantilever beam, intermolecular nanomechanics bend the cantilever, which can be detected optically. Based upon the above concept, troponin I was detected optically by depositing it on the microcantilever containing anti-troponin I. The laser beam was directed on the cantilever and the deflection noted on the CCD.

Recently, the development of Si-based optical sensors for protein and other biochemicals has become of great interest. Here, we examine the protein and Si-based substrate interaction by studying the BSA interaction with surface derivatized porous Si (pSi). The pSi fabricated through electrochemical anodization of crystalline silicon in hydrofluoric acid showed an average pore diameter of ~ 10 nm. Chemically functionalization of pSi by thermal reaction with undecylenic acid produced an organic monolayer covalently attached to the silicon surfaces. Bovine serum albumin (BSA) was then adsorbed onto the acid-terminated pSi surfaces. The resulting surfaces were characterized using scanning electron microscopy (SEM), ellipsometry and Fourier transform infrared spectroscopy (FTIR). Ellipsometry and SEM both showed that the BSA molecule penetrated more than 1 μm into the porous structure. SEM further revealed the damaged and partially lifted-off porous film from the silicon substrate after a prolonged BSA adsorption. It is caused by the BSA penetrating deep into the porous structure and anchoring itself tightly through strong electrostatic interaction with the acid-covered pSi sidewalls. A change in surface tension during BSA film formation then causes the pSi layer to buckle and lift-off from the underlying Si substrate. FTIR results from the undecylenic acid-modified pSi surfaces after BSA adsorption showed strong characteristic Amide I, II and III vibrational bands. The role of the surface chemistry, wetting properties, substrate porosity and topography will be discussed.

A DNA aptamer sensor using a long-period grating (LPG) is proposed for the sensitive detection of the interaction between the DNA aptamer and its target. The DNA aptamer can be immobilized on the surface of the LPG, and the detection of the specific interaction between the DNA aptamer and its target is monitored optically. This sensor operates on the evanescent field interacting with the DNA aptamer immobilized over the grating region. The reaction between the DNA aptamer and its target alter the refractive index and thus change the LPG transmission spectrum, which can be monitored in real time. This technology eliminates the labeling of the DNA aptamer. In this paper, for the first time, the dependence of the LPG transmission spectrum on the characteristic of the LPG and the property of the immobilized DNA aptamer are studied both theoretically and experimentally. Experimental demonstration of the immobilization of DNA aptamer on LPG and its real-time effect on the transmission spectrum are reported.

Photodynamic therapy of recurrent prostate cancer is currently undergoing Phase II clinical trials with the vascular targeting drug TOOKAD. Proper PDT dosage requires sound estimates of the light fluence and drug concentration throughout the organ. The treatment requires multiple diffusing light delivery fibers placed in position according to a light dose treatment plan under ultrasound guidance. Fluence rate is monitored by multiple sensor fibers placed throughout the organ and in sensitive organs near the prostate. The combination of multiple light delivery and fluence sensor fibers is used to estimate the optical properties of the tissue and to provide a general fluence map throughout the organ. This fluence map is then used to estimate extent of photodynamic dose. Optical spectroscopy is used to monitor drug pharmacokinetics in the organ and blood plasma and blood hemodynamics within the organ. Further development of these delivery and monitoring techniques will permit full online monitoring of the treatment that will enable real-time patient-specific delivery of photodynamic therapy.

The ability to customize photodynamic therapy (PDT) parameters with regards to timing and dosing of administered drug and light can be beneficial in determining target specificity and mode of cell death. Sustained, low level PDT or metronomic PDT (mPDT) may afford enhanced apoptotic cell death. This is of particular importance when considering PDT for the treatment of brain tumors as unlike apoptosis, necrotic cell death often leads to inflammation with increased intracranial pressure. The ability, therefore, to 'fine tune' PDT in favour of apoptosis is paramount. We have studied both acute (one time treatment) PDT (aPDT) and mPDT delivery strategies in combination with nicotinamide (NA) in an attempt to maximize the number of tumor cells dieing by apoptosis. Using several different glioma cell lines (9L, U87-MG and CNS-1) we now confirm that NA provides a dose-dependent (0.1-0.5 mM) increase in apoptotic cells following d-aminolevulinic acid-mediated aPDT or mPDT. Furthermore, using the 9L cell line stably transfected with the luciferase gene, NA was shown to delay the depletion of bioluminscence signal in aPDT and mPDT treated cells, inferring that adenosine triphosphate levels are maintained for longer following NA treatment. NA has previously been reported as promoting neuronal and vascular cell survival in normal brain following a number of neurological insults in which reactive oxygen species are implicated including, stroke, Alzheimer's disease and toxin-induced lesions. It is likely that the effects of NA reflect its capacity as an antioxidant as well as its ability to inhibit poly (adenosine diphosphate-ribose) polymerase-mediated depletion of ATP. Our results indicate that NA may prove therapeutically advantageous when used in combination with PDT treatment of brain tumors.

The potential for the use of photodynamic therapy (PDT) after resection of brain tumors is currently limited by the ensuing side effects. These include direct non-specific tissue damage due to the photodynamic action and elevated intracranial pressure as a result of edema and subsequent indirect tissue damage. Erythropoietin (EPO) has been recognized to confer resistance to apoptosis of neurons and endothelial cells in the brain. Here we present preliminary results of the combination of Photofrin – PDT and EPO in the treatment of rat brain astrocytomas in vivo and its ability to increase the therapeutic ratio versus stand alone PDT. The effects of the combination treatment are characterized in normal rat brain based on tissue damage (using TTC as a live cell stain) and monitoring intracranial pressure (ICP) for 24 hours following surgery, using a piezoelectric transducer. To access tumor cell kill, EGFP transduced astrocytoma cell line, CNS-1_gfp, is implanted in the cortex of Lewis rats through a craniotomy, allowed to grow to a diameter of 3mm. Immediately after PDT tumors are excised with the aid of a fluorescence microscope, desaggregated, counted under fluorescence and plated for colony forming assays. Tumor cell kill due to PDT is compared in the presence and absence of EPO.

Recent advances in imaging technology have contributed greatly to biological science. Confocal fluorescence microscopy (CFM) facilitates high-contrast 2D and 3D images of biological samples such as living cells, and frozen or fixed tissue sections. However, to date, imaging with existing confocal microscopes has been limited by practicality, especially when samples are large and overfill the field of view (FOV) of typical microscope objectives (e.g., ~10 mm2 tissue section). In this case, image-tiling must be employed to cover the entire specimen. This can be time consuming and cause artifacts in the composite image. The MACROscope® system (Biomedical Photometrics Inc, Waterloo, Canada), is a confocal device with a 2x7 cm2 FOV, and is ideal for imaging large tissue sections in a single frame. The system used in this work is a prototype capable of simultaneous acquisition from two detection channels. Reflected light (RL), transmitted light (TL) and differential phase contrast (DPC) images of whole cut mouse tumor xenografts were collected with the same system. Preliminary results demonstrate that the MACROscope® can produce high quality images of large tissue samples; comparable in resolution and contrast to those obtained with conventional CFM using low-power (5-10x) objectives, but at increased imaging speeds (>10x), and FOV (>20x). This new device avoids the need for image-tiling and provides simultaneous imaging of multiple tissue-specific fluorescent labels in large biological samples with high resolution and contrast; thereby allowing time- and cost-efficient high-throughput screening of immunohistopathological samples. This device may also serve in the imaging of high-throughput DNA and tissue arrays.

En-face OCT acquired simultaneously with paired confocal ophthalmoscopic (CO) images provides unprecedented point-to-point correlation between surface and subsurface anatomy of the retina. An advanced prototype of a dual channel OCT/CO instrument was developed in terms of signal to noise ratio and image size. The system can operate in A, B and C-scan regimes. The design is such that there is a strict pixel to pixel correspondence between the OCT and confocal images. An extensive array of clinic pathologies were studied including macular degeneration, central serous retinopathy (CSR), macular hole, macular pucker, cystoid macular edema (CME), diabetic maculopathy, and macular trauma. We report observation of reoccurring patterns in the en-face OCT images which could be identified with different diseases. The system can also simultaneously produce en-face OCT and indocyanine green (ICG) fluorescence images where the same source is used to produce the OCT image and excite the ICG. The system is compact and assembled on a chin rest and it enables the clinician to visualise the same area of the eye fundus in terms of both en face OCT slices and ICG angiograms, displayed side by side. The images are collected by fast en-face scanning (T-scan) followed by slower scanning along a transverse direction and depth scanning. The system is capable of providing chosen OCT B-scans at selected points from the ICG image.

Three-dimensional magnification of a diffusing surface can be achieved using profilometry based on holographic chirped frequency gratings and laser line projection. The recently patented method being investigated both supplants earlier 3-D microscopy methods using diffraction range finders [Thomas D. DeWitt and Douglas A. Lyon, Three-dimensional microscope using diffraction gratings, Three-Dimensional and Unconventional Imaging for Industrial Inspection and Metrology, SPIE, Vol. 2599, pp. 228-239] and also competes favorably with extant confocal microscopy in coverage area, speed of acquisition and unit cost. The geometry of grazing incidence in a diffraction range finder shows an intrinsic anamorphic magnification. A narrow waist of input rays is expanded to the full width of the grating itself. The spatial magnification is simply the ratio of the length of the grating to the waist of the input column of rays. As the column of input rays approaches the grating plane, this magnification ratio approaches infinity. We develop a theory that predicts a limit to resolution as a function of illumination wave length and grating pitch of the primary objective. A simple microscope can achieve near micron resolution over several centimeters of depth in the visible light regime. An empirical demonstration is made using silver halide holograms.

Optical coherence tomography (OCT) is a new biomedical imaging technique in resent year. It has some good qualities, such as non-ionizing radiation, non-invasive, high resolution and sensitivity. High-speed OCT imaging is very important for obtaining the cross-sectional images of the internal microstructure of living tissue. Increasing the imaging speed can produce imaging real time. To study high speed OCT, a new method of OCT imaging technique has been designed in this paper--replacing the point-focus mode with line-focus mode in the sample arm. Cylindrical lens can be used for focusing the incident light into a line in the sample. And a 2D OCT imaging can be obtained in one dimension scanning. In the paper we analyze the interference principle of line-focus imaging mode.

An optical system injecting light directly to skin and collecting spectrally modified within skin backscattered portion of light has been designed and fabricated. This method reduces the noise generated by specular component nearly to zero. Seven clinical tests performed on patients with suspect skin lesions have been tested with our device and later biopsy was taken as a “gold standard” procedure. Three cases proved to be melanoma and our spectra indicated differences from those collected from non-melanoma lesions. The process of collecting spectral data was too time consuming. To accelerate the process of data collection from the skin, using the same principle of diffuse spectroscopy, an imaging device was conceived which is able to collect skin spectral response at once from a relatively sizeable skin area. The requirement of a negligible specular component was considered of paramount importance. Two approaches can satisfy this requirement: 1. Collection of backscattered light directly from the skin 2. Injection of illuminating light directly to the skin without creating reflections directly from the skin. We decided to use the second approach and construct a circular, circumferential illuminator with angled light injection. Before fabricating this illuminator, a thorough analysis was performed to optimize its radius and angle of injection in order to receive the highest uniformity of diffuse light in the skin. Monte-Carlo simulation was applied to a three layer skin approximation.The results of the simulation will be presented.

Skin grafts and flaps form the basis of plastic and reconstructive surgery. Transplanted tissue such as a skin graft or free flap can experience a range of perfusion related complications. A number of adjunctive monitoring techniques have been suggested, however, none have met with clinical acceptance. A simple optical spectroscopic method is investigated and is shown to be superior to blood flow based methods for detecting and distinguishing between arterial insufficency and venous congestion in free flaps. The work suggests that this simple method may have clinical utility.

Cell parameters such as size and density may provide crucial information on issues such as aging and cancer. Measurement of these parameters in bulk, in a cells natural environment are therefore important. For bulk samples light diffusion measurements using transmission spatial profiles and correlation function analysis provide information on the mean free path, absorption and refractive index. Speckle fractal analysis can also provide cell structure information. For cells in suspension forward scattering is used to provide size information via the Mie theory for spherical objects. Two types of live yeast cells were measured in bulk and in suspension at various densities. The bulk samples were compacted by centrifuge into fractions whose mass and volume was measured. The parameter values obtained by optical diffusion were used to infer the density and size variations. The measurement detected density variation of about 10% for yeast grown under normal conditions. The size variation is also about 10% but it contained more uncertainty due to the constant density assumption used in the Mie theory for spherical objects. High resolution optical microscopy confirmed the cell size and showed that it followed a lognormal distribution. The density variation resulted mainly from size differences with a smaller contribution from mass structure such as protein. The results indicate that diffusion measurement is consistent with density measurement and could possibly be used as a cell density probe in clinical applications.

Based on the unique properties of the Volume Phase Holographic (VPH) Grating, P&P Optica has developed a high-performance imaging spectrometer system that has many uses in biophotonic and other research. These fields include, but are not limited to, optical transillumination spectroscopy for breast cancer detection, photodynamic therapy and other medical optical imaging. Since the spectrometer is able to image multiple channels simultaneously, there are a multitude of non-biophotonic applications as well, including process control and particulate detection for environmental research. This paper will outline the unique properties of the spectrometer and why it is valuable for the above applications. The discussion will include information on what Volume Holographic Gratings are and how they allow for the separation of the input and imaging parts of a spectrometer system. The result is a fiber optic spectrometer with superior SNR and efficiency compared to most currently available instruments. The paper will also highlight research results that have obtained using the high-performance, multi-channel imaging spectrometer.

In 1985, the discovery of chirped-pulse amplification (CPA) by G. Mourou and D. Strickland led to ultrashort and high energy pulse lasers. Since energy deposition of ultrashort pulses occurs with limited heat transfer and damages, potential applications of femtosecond lasers to corneal surgery are very promising. By focusing a femtosecond laser on a solid surface, matter is ablated and this process is strongly laser parameter dependent. The goal of the experiment presented here was to measure the femtosecond laser ablation thresholds for different corneal layers and hydrogels. Experiments have been realized with the INRS Ti:Sapphire laser (60fs-400ps, 800nm, 10Hz) and they constitute an initial step toward the development of a new type of high precision surgical tool for corneal microsurgery. Results will be compared to theoretical calculation for light-tissue interaction and propagation using the hydrodynamic code developed at INRS. Grant Identification: NSERC, FRSQ Research in Vision Network and China Scholarship 22836034.

This research project investigates the specifications of phase modulators for the treatment of presbyopia (accommodation loss). Correction of presbyopia is simulated using a pixilated phase modulator directly in front of a human eye model. The results show that maximal phase modulation depth of 17.5l (550nm) is required for a 2 Diopter change in a 6 mm pupil. The same phase retardation provides 7 Diopters of correction for a 3 mm pupil as opposed to 1.2 Diopters for 8 mm pupil. The impact of diffraction due to pixelation of the phase array on image quality is measured using encircled energy, where a well-focused point is defined as having 75% of its energy within a 15 mm radius. For a 2 Diopter correction in a 6 mm pupil, pixelation effects are important at low pixel density and decrease asymptotically with increasing density, stabilizing at about 51 x 51 pixels. In smaller pupils, the equivalent optical correction requires less pixel density to provide equal image quality. In conclusion, a phase modulator with a maximal phase change of 17.5l and 64 x 64 pixels could provide up to 2 Diopters of accommodation in a 6 mm pupil and significantly more in a smaller pupil, thus providing an excellent correction.

At laser pulse treatment of skin, the radiation intensity decreases exponentially versus depth; the exponent index includes the biotissue absorption coefficient. The intensity is maximal at the surface leading to preferential heating of superficial layers of skin and if the temperature rises to about 300 C° then both liquid and hard components of the upper layer boil and evaporate. The major part of the incident energy is spent on evaporation of the upper layers rather than deep bulk layers since during a laser pulse the heat front doesn’t spread inside the medium due to a limited thermal conductivity. However, in present work the study was carried out of the case when a nanosecond pulse of near IR optical range strikes the inhomogeneous biotissue like skin comprising substructures with differing optical and physical properties, such a parameter as volume energy density becomes a decisive one for its damage. Its magnitude reaches the damage threshold value only within the substructure whereas the surrounding tissue stays undisturbed.

An acute problem to protect human skin against harmful UV solar rays emerged in recent years because of increased occasions of skin cancer. The aim of this research is to evaluate, how optical properties of the horny layer of human skin can be changed by imbedding the titanium dioxide (TiO₂) fine particles in order to achieve the maximal attenuation of the UV solar radiation. In-depth distribution in the skin of TiO₂ particles typically achieved with the sunscreens is determined experimentally by the tape-stripping technique. Computer code implementing the Monte Carlo method is used to simulate photon migration within 20-mm thick horny layer partially filled with nano-sized TiO₂ spheres. Dependencies of absorbed by and reflected from, as well as transmitted through the horny layer UV radiation of two wavelengths (310 and 400 nm) on the concentration of TiO₂ particles are obtained and analyzed.

We have developed a new instrument for non-invasive assessments of biological materials. A new technique was implemented to measure the light-tissue interaction in samples using an efficient light delivery and detection method. The optical properties measured were, transmitted, forward scattered, diffusely reflected and specularly reflected light. Measurements were made using a white light source, as well as with spectrally-resolved signals. Using artificial, human, and rabbit corneas as models, measurements were made to determine correlations of the above optical properties in the different tissues. The instrument repeatability using non-biological controls, was between 0.1% and 0.2% for the measured optical properties. The repeatability was consistent even at low light conditions of 0.01 to 0.05 relative intensity. The instrument repeatability was better than the variability of samples within a test group. For both transmitted and reflected non-specular light, there was an equivalent correlation measured between artificial and human corneas. The instrument also proved useful in tracking time-dependant responses of biological tissues subjected to various insults. This new instrument is a reliable tool for measuring static and dynamic optical properties of various biological tissues. The ability to measure small relative changes in optical properties of tissues make it an invaluable diagnostic tool.

Possible approach to monitoring of the thermal-mediated cartilage reshaping can be based on application of the polarization-sensitive speckle-correlometry. This method deals with correlation analysis of spatial-temporal fluctuations of laser light scattered by modified tissue under the condition of polarization discrimination of detected speckle-modulated scattered optical signals. In the presented paper, various techniques of correlation analysis of polarization-dependent speckle intensity fluctuations are discussed. Experimental results obtained for tissue phantoms and partially denaturated in-vitro tissue samples are presented. The sensitivity of the polarization-dependent correlation functions of the intensity fluctuations of scattered light to the content of denaturated tissue fraction ("amorphous phase") is demonstrated.

We present characterization of a surface micro-machined microbolometer featuring a number of unique features. The active resistor layer is amorphous Ge_xSi_1-xO_y grown by reactively co-sputtering Ge and Si in an oxygen background. Complete control over Ge, Si, and O content using this technique allows control of both temperature coefficient of resistance and resistivity of the material, enabling optimization of material characteristics for bolometer applications. The resistor layer is combined with top and bottom NiCr metalization to form a tuned absorber for 10 μm radiation, eliminating requirements for additional absorber layers or for carefully controlled air gap thickness. Characterization of device noise and performance is presented.

Quantum well infrared photo-detectors (QWIP) have found numerous application as sensitive fast photo-detectors. Applications for fast detectors include laser diagnostics, telecommunications and Compton scattering measurements. The high speed potential of QWIPs is enabled by a short carrier lifetime in the order of 5 pS. This short lifetime permit's design of a 40 GHz bandwidth detector. In this paper we report on the development of a QWIP with an integrated electrical co-planar waveguide. The QWIP is a 100 well structure that is almost completely absorbing over the wavelength range of 9 to 11 microns. Free space radiation at 105 GHz has been observed from these QWIPs, but devices made to exploit this speed have not yet been developed. It is necessary to integrate an electrical co-planar waveguide with the QWIP mesa. In this work we report on a QWIP fabricated with a gold air bridge to connect the top of the mesa to the center line of a gold co-planar waveguide. The co-planar waveguide is tapered to allow direct connection to 2.4 mm and smaller electrical cable. Initial tests indicate that the device has a 40 GHz or greater bandwidth.

In this work, we have investigated and modeled an anomalous transient behaviour of the hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) in a time scale (of the order of hundreds of seconds) where the threshold voltage shift is not prominent. Such a long term transient in the terminal characteristics can be critical in analog applications of the TFT, such as in pixel driver circuits of organic light emitting diode (OLED) displays. The reproducibility of the transient behaviour regardless of the presence or absence of any thermal annealing cycle suggests that the behaviour is not related to the metastable creation of defects in a-Si:H. The underlying mechanism that we believe is a configurational relaxation of Si dangling bond (D) defects after change in their charge states. Other possible effects including the properties of the source and drain contacts are carefully considered. Based on the defect relaxation mechanism, we have proposed a time dependent drain current model to describe the transient response of the TFT in the forward above threshold regime of operation. The parameters associated with the model are physically based and have strong dependence on the TFT geometry. The measurement data are in good agreement with the simulation results with a discrepancy of less than 5%, thus validating the model.

Damage in CMOS image sensors caused by heavy ions with moderate energy (~10MeV) are discussed through the effects on transistors and photodiodes. SRIM (stopping and range of ions in matter) simulation results of heavy ion radiation damage to CMOS image sensors implemented with standard 0.35μm and 0.18μm technologies are presented. Total ionizing dose, displacement damage and single event damage are described in the context of the simulation. It is shown that heavy ions with an energy in the order of 10 MeV cause significant total ionizing dose and displacement damage around the active region in 0.35μm technology, but reduced effects in 0.18μm technology. The peak of displacement damage moves into the substrate with increasing ion energy. The effect of layer structure in the 0.18 and 0.35 micron technologies on heavy ion damage is also described.

Studies of some optical materials, like fluored glass, crystals or polymers, show an important luminescence in the visible spectrum, near UV, due to high energy radiation (α, β, n, X-rays or γ). This phenomenon, known as radioluminescence or scintillation, is especially used for medical physics and dosimetry. Those materials can be doped by heavy metal ions, like rare-earth elements. Recent studies show that the irradiation of such rare-earth doped scintillators, can emit visible spectral rays. Those are corresponding to rare-earth transitions, in addition to the normal radioluminescence of the undoped material. Those peaks cannot correspond to the propagation of the self-trapped exciton in the inorganic scintillator. We actually believe the rare-earth ions are just excited by the light (blue) emitted by the scintillator, and that finally this phenomenon is not electronic but photonic, thus a kind of radioluminofluorescence.

A concept is described for the detection and location of transient objects, in which a "pixel-binary" CMOS imager is used to give a very high effective frame rate for the imager. The sensitivity to incoming photons is enhanced by the use of an image intensifier in front of the imager. For faint signals and a high enough frame rate, a single "image" typically contains only a few photon or noise events. Only the event locations need be stored, rather than the full image. The processing of many such "fast frames" allows a composite image to be created. In the composite image, isolated noise events can be removed, photon shot noise effects can be spatially smoothed and moving objects can be de-blurred and assigned a velocity vector. Expected objects can be masked or removed by differencing methods. In this work, the concept of a combined image intensifier/CMOS imager is modeled. Sensitivity, location precision and other performance factors are assessed. Benchmark measurements are used to validate aspects of the model. Options for a custom CMOS imager design concept are identified within the context of the benefits and drawbacks of commercially available night vision devices and CMOS imagers.

A CMOS image sensor with pixel level analog to digital conversion is presented. Each 16µm x 16µm pixel area contains a photodiode, with a fill factor of 22%, a comparator and an 8-bit DRAM, resulting in a total of 44 transistors per pixel. A digital to analog converter is used to deliver a voltage reference to compare with the pixel voltage for the analog to digital conversion. This sensor is required by a visual cortical stimulator, primarily to capture the image which is dedicated to stimulate the visual cortex of a blind patient. An active range finder system will be added to the implant, requiring the difference information between two images, in order to obtain the 3D information useful to the patient. For this purpose, three selectable operation modes are combined in the same pixel circuit. The linear integration, resulting from image capture at multiple exposure times, allows a high intrascene dynamic range. Random accessibility, in space and time, of the array of sensors is possible with the logarithmic mode. And the new differential mode makes the difference between two consecutive images. The circuit of a pixel has been fabricated in CMOS 0.18µm technology and it is under test to validate the full operation of the 3 modes. Also, a matrix of 45 x 90 pixels is currently being implemented for fabrication.

An optical beam combined with an array detector in a suitable geometrical arrangement is well-known to provide a range measurement based on the image position. Such a 'triangulation' rangefinder can measure range with short-term repeatability below the 10^-5 level, with the aid of spatial and temporal image processing. This level of precision is achieved by a centroid measurement precision of ±0.02 pixel. In order to quantify its precision, accuracy and linearity, a prototype triangulation rangefinder was constructed and evaluated in the laboratory using a CMOS imager and a collimated optical source. Various instrument, target and environmental conditions were used. The range-determination performance of the prototype instrument is described, based on laboratory measurements and augmented by a comprehensive parametric model. Temperature drift was the dominant source of systematic error. The temperature and vibration environments and target orientation and motion were controlled to allow their contributions to be independently assessed. Laser, detector and other effects were determined both experimentally and through modeling. Implementation concepts are presented for a custom CMOS imager that can enhance the performance of the rangefinder, especially with regards to update rate.

The usage of cellular camera phones and digital cameras is rapidly increasing. but camera imaging application is not so expanded due to the lack of practical camera imaging technology. Especially the acquisition environments of camera images are very different from those of scanner images. The status of light condition, viewing distance and viewing angles constantly varies in case of cameras. The variations of light condition and viewing distance make it difficult to extract character areas from images through binarization and the variation of camera viewing angles makes the images distorted geometrically. Therefore, the extraction of character areas for camera document images is far more complex and difficult than for scanner images. In this paper, these problems are totally discussed and the resolving methods are suggested for better image recognition. The solutions such as adaptive binarization, color conversion, correction of lens distortion and geometrical distortion correction are discussed and the correction methods are suggested for accurate document image recognition. In experiment, we use the various types of document images captured by mobile phone cameras and digital cameras. The results of distortion correction show that our image processing methods are efficient to increase the accuracy of character recognition for camera based document image.

We demonstrate a non-orthogonal image sensor architecture, called pyramid architecture in which the 2D sampling co-centric rings replaces the 1D row sampling in the classical imager architectures and the diagonals output busses replaces the classical vertical column busses. As the imager fixed pattern noise (FPN) is distributed on the output busses, the noise in the classical CMOS imagers will be distributed vertically leading to vertical strips. In our imager, this noise strips will be distributed diagonally. It is a well known fact that the human visual system is less sensitive to obliquely ordered contrast than to the orthogonal contrast. This characteristic is a very important feature of the human visual system which is therefore more sensitive to orthogonally distributed noise than to the diagonally generated noise of our pyramidal imager. So our pyramidal imager is benefiting from this limitation of human vision system sensitivity to diagonal contrast to make its inherent noise (FPN) not apparent to the human eye. Moreover, we proposed a scanning scheme in which instead of rolling over to the first ring (or row) at the end of image scanning it bounces off each time it reaches the two edges of the pyramid imager and samples back the image to the starting ring and continues on. This leads to a two scenes of rings’ integration time profiles that after being fused results in foveated dynamic range.

A general purpose FPGA architecture for real-time thresholding is proposed in this paper. The hardware architecture is based on a weight-based clustering threshold algorithm that takes the thresholding as a problem of clustering background and foreground pixels. This method employs the clustering capability of a two-weight neural network to find the centriods of the two pixel groups. The image threshold is the average of these two centriods. The proposed method is an adaptive thresholding technique because for every input pixel the closest weight is selected for updating. Updating is based on the difference between the input pixel gray level and the associated weight, scaled by a learning rate factor. The hardware system is implemented on a FPGA platform and consists of two pipelined functional blocks. While the first block is obtaining the threshold value for current frame, another block is applying the threshold value to the previous frame. This parallelism and the simple hardware component of both blocks make this approach suitable for real-time applications, while the performance remains comparable with the Otsu technique frequently used in off-line threshold determination. Results from the proposed algorithm are presented for numerous examples, both from simulations and experimentally using the FPGA. Although the primary application of this work is to centroiding of laser spots, its use in other applications will be discussed.

This paper presents the design, fabrication process, and performance evaluation of a two-dimensional hydrogenated amorphous silicon (a-Si:H) n-i-p photodiode array, developed specifically for low-level light sensor applications. The design of the device is simpler than conventional active-matrix-arrays with thin-film transistor (TFT) addressing electronics, owing to the utilization of the a-Si:H switching diodes for signal readout. Since both sensor diodes and switching diodes are formed simultaneously through dry etching the entire wafer area, the mask count required for lithography is reduced to six. The most challenging problem associated with the fabrication of these devices is the excess leakage current, which inherently limits the output signal-to-noise ratio and dynamic range. The reverse dark current in the photodiodes were minimized by tailoring the defects at the i-p interface. The junction-edge leakage current in the switching diodes is associated with damage caused by ion bombardment, and can be reduced by optimizing of the plasma processing conditions. A 3×4 pixels array prototype was tested using a specially designed test board which performs pre-amplification, double sampling and final amplification for each column of the array. Details of the signal readout process along with detector performances are presented and discussed.

The chromatic method of diffraction range finding can be exploited to construct localizers that track the 3-D positions of light sources. A spectrogram is made using a diffraction grating as the primary objective of an optical system that views broadband emitters such as a tungsten filaments or white phosphor L.E.D.’s. Computer image processing on spectra captured through the grating converts each spectrum at the input into a 3-D position at the output. The behavior conforms to the Diffraction Equation. This novel technique has unique advantages over prior art. Resolution is proportional to distance, because the number of samples increases with target distance. The plurality of samples overcomes occlusion liability, since multiple distinct paths exist between emitter and sensor. The grating can be made from inexpensive embossed plastic, and a wave length sensor can be constructed from a garden variety color 2-D array or ganged line scan IC’s. The method is robust at a grazing exodus angles that allow for a compact configuration of the receiver.In this paper we disclose the theory of operation including a mathematical model, and we demonstrate the method empirically using a simple example of tracking a light as a 3-D input method for a workstation.

Watermark bar code is one of the latest anti-counterfeiting technologies, which is applicable to the security of various financial documents, especially banknotes. With the machine-readable watermark bar code, we can not only distinguish the genuine from the fake, but also recognize different face values of banknotes. So it is necessary to develop an effective method to read it. With watermark bar codes embedded in euro banknotes as samples, we design a system for watermark bar code recognition based on light transmission theory. An 808nm LD serves as light source. By receiving the transmitted light from behind the banknote with a high-speed photodetector, light transmission curves in different parts of different face value euro banknotes are obtained and analyzed in order to get the unique characteristic of watermark bar code. The correlation coefficient is then introduced for two reasons. For one thing, the high correlation coefficient derived from the light transmission curves shows the coherence of vertically placed watermark bar code area in different horizontal parts of the same face value banknote, which testifies the consistency and repeatability of the experiment. For another, the low correlation coefficient shows the irrelevance of watermark bar code area and other area of banknotes. What’s more, it also shows the difference of watermark bar code area of different face value banknotes. As a result, the machine-readable watermark bar code is made the unique characteristic of certain face value banknotes, which can distinguish them from both the counterfeit ones and other face value genuine banknotes.

Conventional medical x-ray imaging, based on the transmission of primary photons, works well to distinguish between hard and soft tissues. Up to 90% of the photons that reach the image receptor, however, are coherently or incoherently scattered, and so there is growing interest in utilizing scattered x rays for diagnosis. The semi-analytical model developed by our group predicts better contrast and signal-to-noise ratio for scatter imaging than for primary for some diagnostic examinations such as distinguishing white versus gray brain matter, and for mammography. Low-angle scattered photons can only be distinguished from primary on the basis of direction and consequently a well-collimated x-ray system is required. A hexagonal array of seven 1.5 mm diameter pinholes is designed and tested to record the diffraction pattern of plastic and water phantoms. These materials are amorphous solids and result in rotationally-symmetric diffraction patterns which are characteristic of the materials. The intensities of the diffraction patterns are numerically integrated over concentric rings and the scatter images are made by assigning the ring sums as the pixel values. For these measurements the tube is operated with technique factors ranging from 70 kV 2500 mAs to 120 kV 500 mAs. The scatter patterns are recorded on a storage phosphor image plate. Test images are made of 1 cm thick targets in air and in a water tank. The ultimate goal is to make scatter images of different kinds of tissues for better diagnostic information.

The capture of a wide field of view (FOV) scene by dividing it into multiple sub-images is a technique with many precedents in the natural world, the most familiar being the compound eyes of insects and arthropods. Artificial structures of networked cameras and simple compound eyes have been constructed for applications in robotics and machine vision. Previous work in this laboratory has explored the construction and calibration of sensors which produce multiple small images (of ~150 pixels in diameter) for high-speed object tracking. In this paper design options are presented for electronic compound eyes consisting of 10¹ - 10³ identical 'eyelets'. To implement a compound eye, multiple sub-images can be captured by distributing cameras and/or image collection optics. Figures of merit for comparisons will be developed to illustrate the impact of design choices on the field of view, resolution, information rate, image processing, calibration, environmental sensitivity and compatibility with integrated CMOS imagers. Whereas compound eyes in nature are outward-looking, the methodology and subsystems for an outward-looking compound-eye sensor are similar for in an inward-looking sensor, although inward-looking sensors have a common region viewable to all eyelets simultaneously. The paper addresses the design considerations for compound eyes in both outward-looking and inward-looking configurations.

One of the biggest clues in specularity detection algorithms is the color of the specular highlights. There is a prevalent assumption that the color of specular highlights for materials like plastics and ceramics can be approximated by the color of the incident light. We will show that such an assumption is not generally appropriate because of the effects of the Fresnel reflectance coefficient and its dependence on wavelength. Our theoretical analysis shows that the sensitivity of the Fresnel term to the wavelength variations of the refractive index can be at least as large as 15%. Our experiments demonstrate that, even with traditional RGB color cameras, the recorded color of specular highlights is distinct from the color of the incident light. Furthermore, we will show that by computing the spectral gradients (i.e. the partial derivatives of the image with respect to wavelength) at specular regions we can isolate the Fresnel term up to an additive illumination constant. Our theory is supported by experiments performed on multispectral images of different colored plastic tiles. The refractive indices of the opaque plastics were measured using a Nano-View SE MF 1000 Spectroscopic Ellipsometer. The computed spectral gradients of the tile specularities exhibited a less than 2.5% deviation from the predicted theoretical values.

The advances at the semiconductor fabrication cause a need for three-dimensional measurements within the micro- and nanometer range. A method to derive lateral measuring information from height profiles with nanometer resolution is shortly introduced. Thereby, measurements are taken with a high resolution, point-wise working laser sensor. The paper discusses in detail the analysis of the measuring signal as observed at different height standards. At height standards with discontinuities smaller than the coherence length of the laser the measuring signal overshoots. This effect is called batwing effect. The novel approach comprises the utilisation of the batwing effect to determine the edge position. The characteristic signal curve is modelled with an appropriate mathematical function. Thus, edge detection algorithms well known from optical precision measurements are modified and applied to calculate the location of the edge along the scan line of the laser sensor. Exemplary, an experimental standard deviation (k=2) of 16 nm of the width of a 69 nm high height standard is attained. Based on measurements with an AFM at the same height standards the accuracy of size of the proposed method is evaluated. The presented work results from the collaborative research centre (SFB) 622 supported by the German Research Foundation (DFG).

A novel compound prism device consisting of a cubic polarizing beam splitter (PBS) and a non-polarizing dichroic prism is configured as the core component of the illumination unit of a full color projection display system of three pieces of reflective type liquid crystal imaging panels. When the in-coming light beam impinging on the PBS at 45 deg. of incidence, the beam component polarized perpendicularly to the plane of incidence is reflected and directed toward a LCD panel of red-image signal addressed after transmitted through a red-passing dichroic filter. The beam component polarized in parallel with the plane of incidence of the PBS is transmitted and passing through a red-cut dichroic filter. The rest portion of the light beam is then got the blue and green color bands separated by the dichroic filter at 30 deg. of incidence and directed to a blue and green signal addressed LCD panel respectively. All the dichroic filters are designed polarization independent and the PBS has a high contrast ratio of 1000 for the on/off states of teh addressed pixels of the image panels. The color separation and re-combination prism unit will provide a screen uniformity of d(u',v') <0.01 when it is accomodated in the projector with a projection lens assembly of F/#2.4.

A computer vision based new method for the measurement of the length of pedestrian crossings using a single camera is described. The main objective of this research is to develop a travel aid for the blind people. In a crossing, the usual black road surface is painted with constant width periodic white bands. In Japan, this width is 45 cm. The crossing region as well as its length is detected using this concept. At first, the crossing direction is determined from the power spectrum using fast Fourier transform. The periodic white and black bands are detected using integration along the crossing direction and then differentiation of the integral data perpendicular to crossing. This detection may be erroneous due to adverse effects of the neighboring region of crossing, as the intensity of the whole image is used for bands detection. To remove the neighboring effects, the crossing region is extracted. Then the crossing bands are detected from the image intensity using the crossing region only. Experiment is performed using 32 real road scenes with pedestrian crossing. The rms error is found 2.28 m. The technique determines the crossing length with good accuracy for crossings marked clearly with white paintings as well as fine image resolution.

We have built a customized vertical scanning white light interferometer (SWLI) for characterization of freely suspended (no substrate) transparent 5 µm thick monolayer polymer films. These films that are used by the electronics industry are found in e.g. film capacitors. Quality control (QC) of such films is important with regards to capacitance accuracy and process yield. Devices currently used to characterize polymer films scan the surface point by point whereas we measure, using wide-field SWLI, the total focal volume (0.9 mm by 0.7 mm by 0.01 mm, with 1.5 μm lateral resolution using 6x magnification.) in one rapid (1 s) scan. The thickness profile of the sample is obtained as the difference between the first and second surface profiles. Inclusions, e.g. defects or intentionally introduced entities also carry interest with regards to the QC of polymer (capacitor) films. We obtained the inclusion distribution within the film volume (with a depth resolution of 20 nm and a lateral resolution comparable to that on the surface) from the changes in the refractive index observed within the film. The measurement generates data presented in multiple formats: 3-D picture of the scanned volume (revealing inclusions), surface topographic plots, cross-section of the surface, and depth profiles.

We report on using a Scanning White Light Interferometer (SWLI) for quality control of aluminum lead single-point Tape Automated Bonding (spTAB). A spTAB process was used to connect 14 μm thick, 42 μm wide aluminum leads on a 12 μm thick polyimide layer to a micro chip. Three different bonding process parameters were varied in order to maximize the pull force: bond force, ultrasonic power, and ultrasonic time. A custom built SWLI was used to measure the topography of the bonds in order to find features that correlate with the tensile bond force. This force was obtained in a destructive way by a pull test. By keeping the bond height within 3±1.5 μm, bonds with acceptable tensile forces in excess of 54 mN were obtained. This was verified by a separate validation measurement where the pull force of bonds complying with the height requirement was recorded.

We present a new concept of optical spectrometer based on a plane holographic grating having a spatially variable period (chirped grating) used as the component for spectral selection. The chirped grating is made through a holographic technique. We have developed a mathematical model to predict the properties of the grating, as a function of the writing beam parameters. The experimental results confirmed the predictions from the model. The spatially variable period provides focusing properties to the grating which eliminate the need for the usual curved mirrors in the spectrometer. Once calibrated, this spectrometer has a resolution comparable to the one of a high-resolution commercial device, considering their different dimensions. This comparison is achieved with the help of a performance criterion we have introduced. The new concept would make it possible to reduce the optical dimensions of usual spectrometers approximately by half, for a given resolution. The aberrations produced by the chirped grating, the spectral range that can be analyzed and the positioning control of the detected image will be discussed.

Ablation of fused silica using the Gaussian irradiance profile of the TEM00 mode of a CO₂ laser is a very efficient way for micromachining features up to ten times smaller than the beam diameter. A series of laser-etched V-grooves sequentially shifted in a given fashion can be used to micromachine simple or structured patterns on the surface of fused silica substrates. Surface gratings with a periodicity of 12 μm were produced using a CO₂ laser beam of 100 µm (1/e2) in diameter. Rectangular wells 50 μm wide and 50 μm deep were also micromachined using the same technique with a radius of curvature of roughly 8 µm at the bottom edges. Although the resolution of the periodic pattern is not fully understood, it appears to be partly governed by the amount of material removal by the top portion of the Gaussian beam (tip processing), as well as a carefully controlled shifting of the etched V-grooves on the fused silica substrate. Physical mechanisms that could be at the origin of the V shape of the grooves are also discussed.

Femtosecond laser ablation technique has been used to process Si and Au targets in vacuum, air and water environment. The threshold of ablation was found to be much lower for Si compared to Au and that was related to much better radiation absorption of Si. The values of the threshold were almost identical for vacuum, air and water in the case of Si (0.4 J/cm² 0.2 J/cm² in the single and multi-pulse irradiation regime, respectively) and Au (0.9 J/cm² and 0.3 J/cm²). Craters on the surface of Si and Au were essentially similar for low fluences, suggesting an involvement of the same radiation-related mechanism of material removal, whereas for high fluences significant differences could take place. In particular, quite different crater morphologies were observed during the laser ablation in water, including ones with nanoporous layers for Si and ones with concentric spheres for Au. The differences of morphologies for high laser fluences were explained by the involvement of plasma-related effects under the processing in relatively dense media.

Submicron surface-relief gratings were fabricated in ultrathin dielectric films by F2-laser ablation. Projection mask imaging by a Schwarzschild objective applying nanosecond duration pulses from a high-resolution 157-nm optical processing system generated 780-nm-period gratings in various thin oxide layers. The grating modulation depths were controlled within tens of nanometers by applying suitable energy densities and number of pulses. Thus, high-resolution laser ablation proves to be a promising alternative approach to well-known lithographic methods for the fabrication of submicron-period gratings in thin films. Such gratings are the most critical component of grating waveguide structures (GWS) that comprise of a substrate, a thin waveguide, and a grating layer in a planar multilayer structure. Interference effects in a GWS will provide high reflection efficiency under resonance conditions for an ideal grating with no absorption losses. The resonance spectral responses of the F2-laser ablated gratings have been investigated using an ultrashort-pulse titanium-sapphire laser. Their potential for optical applications will be shown and discussed. GWS are attractive for optical switches or modulators, narrow-band spectral filters, high reflectivity mirrors, bio-sensor chips and many other applications.

MIcro machining of materials with high power ultra-short-pulsed lasers is becoming a preferred technique to obtain cleaner surface characteristics. Due to the short duration of the pulse, there is insufficient time to establish the thermal equilibrium. Consequently, ablation does not pass through the melting phase. Instead, it proceeds mainly with direct removal of the material at the molecular level. To fully benefit from these properties, a high quality beam profile is required. However, during processing the optical wave front suffers distortions while passing through the medium such as air. Passage through the medium causes the beam to self-focus and the gas breaks down, thus generating plasma, which distorts the geometrical and energy profiles of the beam. This phenomenon offsets the advantages of the procedure to a certain extent. For these reasons, processing is usually conducted in vacuum with associated inconvenience and expense. As a step towards improvement over the technique, we develop a numerical scheme to determine the beam profile in air medium. The profile of the beam is then used to determine the shape of the processed surface by a geometrical method developed recently. The calculated surface profile is compared with the experimental observations with good agreement. This provides a method to develop an understanding of the interactions of the laser beam, air and the material.

The actual performance of a miniature mechanism significantly depends on the geometric quality of the machined part and specific features therein. To fabricate functional parts and features with accuracy and precision within +/- 1 μm or less, the laser micromachining system requires the capabilities of following the desired toolpath trajectories with minimum dynamic errors, high positional repeatability, and synchronization of laser firing events at precise time-and-location to ablate the material. The major objectives of this study are to fabricate miniature functional mechanisms using precision laser micromachining method, explore the machining challenges and evaluate the geometrical quality of the machined parts in terms of accuracy, precision and surface quality. Two functional mechanisms based on electro-thermal actuation have been studied. Several machining challenges related to the corner accuracy, the asynchronization of motions and, the laser-on/off events in space and time with respect to the part geometry have been addressed. The source of inaccuracies primarily stems from the geometric complexity of the mechanism that consists of several features, such as, arcs, radii, lines, curvatures, segments and pockets, along with their dimensional aspect ratio. Such a complex design requires a large number of inconsecutive trajectories to avoid thermal deformations. Copper and nickel foils with a thickness of 25 and 12.5 µm respectively were used in the fabrication of the prototypes. The machining challenges were successfully tackled and the geometrical performance of the fabricated prototypes was evaluated. Local feature accuracies within 0.1 - 0.2 µm have been recorded.

Beam shaping at the output of optical fibers is required in a variety of applications including optical sensors, telecommunication devices and medical applications. We present a laser micro-machining technique for the fabrication of micro-lenses directly upon the end face of silica fibers using a F2-laser processing station. Ablation is performed in a mask projection arrangement with 25x demagnification. A mask with an occluded circular beam shape is imaged perpendicular to the fiber axis. The fiber is rotated axially while the laser cuts through the fiber, yielding a spherically shaped tip with radius defined by the mask dimensions. Strong 157 nm absorption by the silica glass facilitates precise structuring without micro-crack formation. The quality of the fiber-lenses is characterized by AFM, SEM and by analysing the beam profile at the fiber output.

We used an excimer laser (193 nm), a femtosecond laser (775 nm) and a CO₂ laser (10.6 µm) to drill cylindrical holes in fused silica optical fibers and in glass micro-pipettes. CO₂ laser-drilling using tip processing results in tapered holes with larger diameters than the holes drilled with the excimer and the femtosecond laser. Although routing of holes of various shapes results in sharper edges and a higher aspect ratio when the femtosecond laser is used, the CO₂ laser could still be used to route rectangular holes in fused silica optical fibers. Albeit hole dimensions and details are smaller when micromachined with the excimer and the femtosecond lasers, the optical fibers are very brittle at the end of the process. CO₂ lasers offer the advantage of producing higher fused silica ablation rates with much better polished surfaces and a better mechanical integrity, which are usually more suitable in some applications.

Volume phase hologography is used for the recording of refractive index patterns with the symmetry of a photonic crystal. As a recording material solid plates of PMMA, containing up to 10 wt% of residual monomer MMA doped with the photoinitiator titanocendichloride have been used. The mechanism for the formation of the desired refractive index pattern is the photoinduced residual polymerisation. The 2-dimensional patterns have been recorded in 2 subsequent steps using a 2-beam holgaphic setup. In a first step the recording process has been characterized for a single volume phase holographic grating with the grating constant Λ1. The recording procedure is optimized towards a short term exposure period of the order of a few seconds, followed by self-developing period. While the first pattern is developing the sample may be turned by an arbitrary angle Φ and a second volume phase grating with a different lattice constant Λ2 can be recorded. If e.g. an orthogonal crystalline symmetry is desired, the angle Φ will be chosen as Φ = 90°. After recording of the second grating the sample is developed and fixed by a thermal treatment. The obtained 2-D crystals are characterized using a goniometer with 2 rotary stages by the evaluation of the diffraction patterns. The different diffracted orders may be indexed according to their (h,k) Miller´s indices.

A laser direct write process has been developed for turning patterned bimetallic Sn/In film into a indium tin oxide layer. Sn over In films (15-120nm thick) with a 1:10 thickness ratio were deposited by DC sputtering. An argon laser beam (0.1 - 0.9 W, spot size: 2 micron, scan speed: 1 cm/s) exposes the film into patterns. These Sn/In films' optical absorption changed from 3 OD at deposition to 0.24 OD after exposure (at 356 nm). XRD, SEM, EDX, and Auger have been used to investigate the film's microstructure and composition suggesting ITO like characteristics. XRD indicated a preferred In₂O₃ (222) orientation which is similar to ITO films deposited by other methods. Four-point probe tests showed a converted film resistivity of 0.26x10^-3 to 9.7x10^-3 ohm-cm depending on the laser power and Sn concentration. Hall tests indicated that the bulk carrier concentration was in the range of 10¹⁸ to 10²⁰ cm^-3. Developed in a wet HCl: H₂O₂: H₂O =1:1:48 solution removes unexposed Sn/In leaving patterned ITO films created at much lower laser power levels than needed for ablative patterning of ITO. Developed films are also resistant to KOH anisotropic etching at a 1:700 ratio producing <111> trenches in Si (100). The large change in optical density means Sn/In films can be used as a material of the direct write photomasks.

The analysis of entrapped debris provides a useful complementary method of investigating the laser ablation mechanism in laser processing of polycrystalline metal samples using a femtosecond laser (Clark MXR, CPA2001). Morphological investigations of the laser- processed areas, for a range of laser fluences and pulse number, were recorded using optical and scanning electron microscopies (SEM) and white light interferometry. Data obtained on ablation rates, ejected particle sizes, and crater morphologies prove that ablation changes from a smooth to an explosive process at high fluences, as identified with changes in the material removal mechanisms. The build-up of laser-induced mechanical stresses, due to the heating and cooling of the samples between successive laser shots, plays an important role in the material modification process, leading to the observed dependence of ablation threshold on shot number. The strength of the dependence is governed by the incubation coefficient, S, which has been measured for all materials studied. In this paper, additional insight is derived from the analysis of the debris generated for metal samples, which can be attributed to laser ablation mechanisms based on vaporization, spallation, phase explosion, and fragmentation.

This paper describes an alternative way of sealing an optical fiber at a much lower cost than soldering, with an equal to or lower susceptibility to creep and misalignment of the fiber, and higher reliability. It involves the use of a low temperature (320C) glass preform which seals directly to the bare fiber without the need for the costly metallization required for soldering. Various processing methods are outlined, along with cross sections of the sealed fiber in a ferrule. The key variables of the seal length, inside diameter of the tube, and the tube material itself are discussed in reference to their impact on designing a reliable, stress controlled hermetic seal. Reliability information is presented to demonstrate the viability of this technique for hermetically sealing optical fibers in a package feed-through tube.

SiO_x microforest-like structures have been produced on Si (100) surfaces by pulsed excimer laser irradiation in air. Scanning electron microscopic observations have indicated these structures, which are composed of aggregated nanoparticles, to be 1-5 μm in diameter and 10-20 μm high, and to have the appearance of trees. XPS analysis has shown them to be composed of a-SiO_x (1