A computational model based on finite element method is derived to examine how the recorded time-dependent signals are related to the basic optical properties of a slab at both excitation and emission wavelengths. The model is based on a set of two time-dependent photon diffusion equations: -the transport of the pulsed laser source light (1 ps) and -the transport of the induced fluorescent light excited by the source. The coupling between these equations is due to a source term directly proportional to the scattered fluence rate at the same location. To solve this problem, the method proceeds following the Galerkin formulation, added to implicite finite difference scheme (Backward Euler) to integrate the resulting matrix formulation with respect to time. The meshed domain is two dimensional and takes into account the available boundary conditions relative to air-tissue interface (Robin boundary conditions). The computations are first carried out for a slab in which fluorophores are uniformly distributed, and afterwards devoted to the localization in depth of a fluorescent object (like a tumor) embedded within the slab.

The concepts of time refraction was introduced in recent years, as the temporal analogue of the usual (space) refraction, for waves propagating in non-stationary optical media. We discuss possible experimental configurations for time refraction of low intensity and short laser pulses propagating in optical fibers, and their eventual use in photonics. We generalize our previous work to the case of guided propagation. The expected frequency shifts, amplitudes and shapes of the secondary pulses resulting from time refraction are calculated.

Frequency conversion technique using nonlinear optical crystals is indispensable to solid-state laser applications. It is well known that the conversion efficiency is very sensitive to temperature change of crystal, which is caused by laser absorption. We have been analyzing problems of second harmonic generation (SHG) by coupling the electric field to the temperature field. In this study, temporal pulse-shape dependence of SHG was investigated theoretically, and Gaussian pulse and rectangular pulse were compared. Main conclusions obtained are as follows: (1) Both conversion efficiencies with Gaussian pulses and rectangular pulses fluctuate with irradiation time, however the former fluctuation is slower and more gentle. (2) Pulse of output second harmonic fluctuates most remarkably at the center, where power density of incident fundamental is highest, in the Gaussian pulse. (3) As a result, pre-pulse and post-pulse are generated before and after the main pulse. (4) Such distortion of output pulse shape becomes more remarkable as power density increases.

Electromagnetic theory of open laser resonators is formulated in the domain of partially coherent optics. The theory is then used to find out the electromagnetic degree of coherence of the field in various situations. It is shown that if only one transverse mode is present in the steady-state condition, then the field is necessarily completely coherent in view of the recently introduced degree of coherence for electromagnetic fields [Opt. Express. 11, 1137 (2003)].

No abstract available.

In wave-optical engineering the propagation of light through an optical system can be simulated by using several physical approximations. Independent of the used method it is necessary to have full access to the complete electromagnetic field information in the desired regions. In this article we firstly go into the question what the required information is to get access to the whole electromagnetic field and as a second step we give some insights into physical modeling accuracy and numerical accuracy which is of high importance to evaluate the quality of the calculated results.

We present an extremely efficient rigorous vector electromagnetic analysis of field distribution and power flow in grating coupled surface emitting structures. The developed technique is based on constructing an artificially periodic structure of identical grating coupled device cells separated by anisotropic magnetic/electric perfect matching layers. The resulting periodic multi-layered structure is analyzed using the RCWA combined with a very efficient scattering matrix recursive technique. Calculated distributions of the electric and magnetic field components within the structure as well as the fields coupled into the output regions and into the substrate for typical devices are presented. Field distribution and power flow in the longitudinal and in the transverse directions in the structure are determined for the first time to our knowledge.

We demonstrate the possibility of using periodically poled lithium niobate crystals (PPLN) as a direct source of entangled photon pairs. Two configurations are studied. The first enables the generation of polarization-entangled states from a one-dimensional PPLN structure at different frequencies; the second is dedicated to the production of frequency-entangled states from a bi-dimensional PPLN structure. The engineering of both of these PPLN structures are described from a theoretical perspective.

Computers are routinely used to design illumination systems. Automating the design process is enhanced through the use of optimization procedures. This paper describes some of the underlying illumination optimization fundamentals: parameterization, merit functions, and optimization algorithms. Numerous interesting examples of illumination design problems that benefit from optimization are shown. These examples illustrate illumination optimization through use of ray aiming, computing illuminance using flux tubes, and computing illuminance using Monte Carlo simulations.

An illumination can be generally understood as a light transformation where an input field is transformed into a specified output field. There are several approaches to achieve the desired illumination. These approaches differ with respect to the used concept as well as the realization done by the optical system. For illumination tasks the usage of diffusers is very promising. The concept and the realization by an optical system are presented and discussed. The functionality of a diffuser is not restricted to coherent light but it is also applicable to partially coherent light. This seems to be of special interest for illumination tasks. Beyond that, some experimental results of the usage of a non-paraxial diffuser in combination with a light emitting diode are presented.

Mostly, the typical light distribution of a light source, as a LED or an excimer laser, is not suitable for the application. The excimer laser beam for example shows a distinct elliptical Gaussian profile. As another example the layout of the light emitting chip and the reflector of a LED form an extremely inhomogeneous luminescent area. To achieve a better adapted beam profile a homogenizing setup with beam shaping qualities can be used. In this talk two setups for homogenization with the help of refractive micro lens arrays are shown and compared. The main attention is turned on the influence of the numerical aperture of the micro lenses, the limitations due to the spatial coherence degree and the difficulties of the alignment of the systems. In addition, a diffractive solution of homogenization for spatial partially coherence is presented.

Introduction of diffractive optical elements (DOEs) opened the possibilty to control amplitude-phase distribution in the cross-section of laser beam. In fact, by use of DOE one can form the beam with pregiven behaviour during propagation through waveguide medium. The diffractive microrelief can be realized either on the separated substrate or directly on the waveguide surface. This work is devoted to the theoretical and experimental investigation of diffractive microrelief intended for waveguiding beam control. Experimental results of step-like optical waveguide mode excitation and selection by DOE are presented. Different approaches for synthesis of high-efficient DOEs matched with waveguide modes are discussed. The strategy of the search of waveguide mode with amplitude distribution closed to the illuminating beam amplitude distribution is presented. The phase of found mode can be chosen as DOE phase function.

Photon management stands for the generation of tailored electromagnetic radiation. It demands optical systems which perform general light transformations. Consequently, optical engineering for photon management requires a generalization of established optical engineering which mainly addresses imaging problems. It turns out that the consequent inclusion of wave optics becomes fundamental in this context. Optics simulation and design software must take this development into account. Of special concern is the thorough use of an electromagnetic field model in all simulation techniques. Moreover, various propagation techniques must be available. Each of them must allow its assignment to any part of the optical system. Furthermore, a generalization of the ideal lens concept is needed to offer a efficient design technique. The wave-optical engineering software package VirtualLab implements these generalized optical engineering concepts.

One of the most important properties of a laser resonator is the highly collimated or spatially coherent nature of the laser output beam. The spatial beam quality of the output beam, namely beam diameter and propagation factor M² are critical parameters in a wide range of practical laser applications. This is because the spatial beam quality determines how tightly the beam can be focused or how well the beam propagates over long distances without significant spreading. It was investigated by many authors in previous years how to define and on how to measure the laser beam quality. An ISO working Draft Committee has also been organized to set-up a standard for definitions and test methods of the laser beam quality. In this work, the quality factor is studied with different methods.

Analogue Optical Signal Processing is a very important area in optics and central to it, is the implementation of the Optical Fourier Transform (OFT). There are many bulk optical arrangements for implementing the OFT however one which is particularly popular is the Scaled Optical Fourier Transform (SOFT) because it offers the user to the ability to change the size or scale of the output Fourier distribution. In this paper we examine the some of the practical limits introduced by the use of a cylindrical lens of finite aperture. We examine the phase and intensity deviations and provide simple rules of thumb, which allows the cautious user to, not only avoid, but also to quantify the worst case errors arising due to diffraction.

The reshaping of laser beams to intensity distributions with high homogeneity is of practical interest for a lot of applications. Often the generation of intensity distributions with high resolution, very small or large diameters is of practical interest. These intensities correspond typically with waves with high divergence angles. For the generation of these intensities non-paraxial beam shaping systems are needed. The authors will explain how known paraxial beam shaping techniques can be extended for the design of systems creating non-paraxial output fields. The systems, explained in this article, will consist of a paraxial diffractive element together with a non-paraxial lens. This new extended design concept will be explained on the example of the shaping of a circular Top Hat from a Gaussian beam.

We introduce a method for designing high-efficiency paraxial-domain diffractive elements working over a broad frequency range. The design method is based on the theory of dielectric polarization gratings, in which the local state of polarization is controlled by means of form-birefringent diffractive structures. We show that any scalar transmission function can be easily converted to a corresponding broadband design.

A position difference from a theoretical one by ray tracing on the imaging plane has taken place due to a distortion by using f θ lens in this optical system, which has been able to be compensated by returning a correction value acquired from accurate theoretical calculations to the control system. This paper will describe the system and control of this equipment.

Twisted nematic liquid crystal displays (TN-LCD) are commercially available and have found a widespread use for displaying dynamic diffractive elements. Usually these devices are inserted between two polarizers but then a strong amplitude-phase coupling is obtained. In this paper we show that by using elliptically polarized light at the entrance and detecting elliptically polarized light at the output, it is possible to obtain a pure phase-only modulation. The complete device then consists on a polarizer, a waveplate, the TN-LCD, another waveplate and another polarizer. This technique is particularly useful for newer LCDs which are thinner devices and require short wavelengths to achieve a 2π phase modulation depth. If a phase-only diffractive element is displayed by an LCD which does not produce this perfect phase-only modulation, different diffraction orders are generated. We include a model to evaluate the diffraction efficiency, which accounts for a phase modulation depth less than 2π, non-linearities in the phase modulation or a coupled amplitude modulation. We derive the expression to evaluate the amplitude of these diffraction orders which are related with the light efficiency that can be obtained. It is demonstrated that a good efficiency can be obtained even though the maximum phase modulation depth is less than 2π. For instance, this is the situation if a thin display is illuminated with a long wavelength. The diffraction efficiency is higher than 90% when the modulation depth is 1.4π, and higher than 40% (the equivalent for a binary phase element) when the modulation depth is 0.7π.

The development of an inexpensive, reproducible and highly accurate method for the production of microlens arrays is of vital importance to the next generation of optics based technologies. One of the fabrication techniques used to produce microlens arrays, the photoresist reflow method, will be discussed. When lenses are produced using this method they are often found to have aspherical profiles. Aspheric lenses have applications that include beam shaping, power transfer and fiber coupling. The fabrication of these aspheric lenses currently requires an iterative experimental process as there is currently no model that accurately predicts the lens profiles from first principles. One model that shows promise is the Curvature Correction Model, CCM. In this paper we propose a novel mathematical method to solve approximately the CCM, thus enabling predictions of the expected microlens profile. This technique can then be used to determine a starting range for the fabrication parameters to design a specific lens. This novel method also provides a framework within which a number of polynomial models, that have been presented in the literature, can be examined in the context of the CCM.

Recently a new technique has been proposed for laser-assisted generation of phase microrelief to manufacture diamond diffractive lenses for the far IR range. In the present paper the realization of diamond diffractive optical elements (DOEs) is considered, able to focus an incoming CO2 laser beam into certain pregiven focal domains. Exemplarily, two completely different DOEs for different tasks of laser beam focusing have been designed by different methods, manufactured and finally investigated by means of optical experiment and computer simulation. Measured intensity distributions in the DOEs' focal planes as well as measured diffraction efficiencies have been compared with related results of computer simulation, and have been found to be in good mutual concordance. Obtained first results indicate that technique of laser-assisted ablation can be effectively used for manufacturing of high quality diamond DOEs for laser beam focusing.

We describe an aperture-coded hybrid (optical-digital) imaging system to achieve super-resolution for an a priori known class of binary objects. This super-resolution is achieved by aligning the singular functions of a paraxial imaging gathering module and the eigenfunctions of the covariance matrix of this class of binary objects. This work and particularly its potential extension to high numerical aperture vectorial imaging are of interest to optical data storage imaging applications.

Retinal Scanning Display (RSD) is a near-to-eye scanned beam display technology. An exit pupil expander (EPE) or numerical aperture (NA) expander is used in RSDs to create a large display exit pupil. A novel EPE approach that uses two microlens arrays (MLA) is presented in this paper. The approach is based on cascading two identical microlens arrays spaced precisely at one focal length distance with sub-micron registration tolerances relative to each other. We demonstrated a dual MLA based EPE that produced excellent exit pupil uniformity and better than 90% diffraction efficiency for all three wavelengths in a color display system. Registration was performed with sub-micron precision using farfield alignment techniques. Both numerical and experimental results are presented, and three fabrication technologies: grayscale lithography, photoresist reflow, and isotropic etching, are compared.

In laser drilling of sheet materials, the minimum diameter of the hole processed is determined by the laser machine used. Then, the purpose of this study is to develop a system for minimizing the diameter of the hole and evaluate the performance of the system. A CO₂ laser machine, maximum output power of 500 W in single mode, was used in the experiment. This beam includes an area with low power density at the peripheral portion hindering the drilling of a smaller diameter hole. To cope with this problem, an aperture was applied to the system to remove the area described. Metal sheets (0.5 mm thick mild steel and 0.6 mm thick stainless steel) and a ceramic sheet (0.6 mm thick Al₂O₃) were used as the materials to be processed. The effect of the aperture, together with the effect of pulse conditions such as peak power, frequency and duty, on the diameter and shape of the drilled hole was discussed. Results showed that the diameters of drilled holes are reduced as much as 50%(for mild steel) and 30%(for Al₂O₃) by the usage of the aperture. It was also found that the drilling of a taper-controlled micro hole is possible by changing the diameter of the aperture used.

Optical microparticle manipulation using laser fields of various configurations has found wide use in a variety of fields: for retardation, deflection, cooling, and localization of atoms; in biology and medicine for non-invasive trapping and examination of various types of bacteria, cells, viruses, and molecules; in nanotechnologies and micromechanical components control. Recent years have seen an increased interest in enhanced capabilities of microparticle manipulation thanks to special properties of the laser beams. For example, rotating the microparticles trapped by the laser field due to the spin or orbital angular momentum of the beam. In this paper, the fifth-order Bessel beam is produced using only a single optical element - a diffractive helical axicon. This beam was successfully used to trap and rotate 5-10 μm biological microobjects (yeast particles) and polystyrene beads of diameter 5 μm.

Photopolymers are considered one of the most interesting materials for holographic storage applications. The search for optimum chemical formulations to improve the quality of the final polymer materials has yielded a great deal of experimental work. different theoretical models have also been developed by different authors to clarify the mechanism of hologram formation inside photopolymer materials. These advances in both experimental and theoretical fields permit obtaining suitable compositions of photopolymer materials for data storage purposes. In this work we present the results of an optimization of a PVA/acrylamide recording material with a high thickness (over 1 mm) to obtain holographic memories. Diffraction gratings of 1125 lines/mm were recorded in this material by using the peristrophic multiplexing technique and using the light from an Argon laser at a wavelength of 514 nm.

Two extensions of the Nonlocal Polymer Driven Diffusion model (NPDD) describing grating formation in photopolymers are proposed. The inclusion of a nonlocal spatial response function has been shown to predict high spatial frequency cutoff in photopolymers. Here the nature of the temporal response of photopolymer is discussed and a nonlocal temporal response function proposed. A number of different possible spatial response functions are also examined. The extended model is then solved using a finite element technique and the results compared to the purely spatial response case. The kinetics of photosensitive polymer holographic recording are then examined. Assuming primary termination dominates the chain formation process a model is proposed based on a quadratic relationship which is shown to exist between the monomer concentration and polymerisation rate. The model is solved using a four-harmonic expansion. Results are then fitted numerically to growth curves of experimentally monitored diffraction efficiencies of gratings recorded in an acrylamide-based photopolymer system. Physical parameters such as diffusion constant and polymerisation rate are extracted and compared to the literature.

Phase holograms can, in principle, route light with zero photon loss. This property makes them ideal for applications with tight power constraints such as free space interconnects and optical tweezers. Both applications require that the deflection angle is varied accurately and smoothly over a certain range. For example, in a free space switch, the output would be a single mode fibre with core diameter of 9μm and the beam has to be centred accurately on it. If an adaptive link is used the beam will be scanned near the output and the optimum position will be determined. Any quantisation effects on the deflection angle may cause instabilities in the feedback loop of the link. In optical tweezers the quantisation effects on the deflection angle will cause the particle to move in discrete steps. This may release the particle from the optical tweezers due to the large acceleration. The quantisation effects on the deflection angle may be difficult to observe because of the very small changes involved. However, these effects can be very important. In this paper we derive the quantisation effects introduced to the deflection angle due to hologram quantisation. We evaluate the minimum number of pixels required in order to achieve a certain resolution on the deflection angle, and finally we suggest methods for enhancing the performance of the hologram by taking into account these effects.

Holography has become of increasing commercial interest in recent years with significant technological developments in many areas such as data storage. Photopolymer materials such as acrylamide-based photopolymers are practical materials for the recording of holographic optical elements, as they are inexpensive and self-processing. A great deal of experimental data is available in the literature describing the diffraction efficiencies, growth curves and the angular selectivity of gratings recorded in various materials. Such testing is often carried out so as to allow a better understanding of the holographic recording processes to be developed and therefore allow material improvement. However, the majority of these discussions are based on the performance of the holographic optical element after the recording stage, once exposure is completed or using a probe beam during recording. It has been noted however, that sometimes, during recording, the recording beams are seen to vary in intensity during the fabrication of the grating. In this paper we discuss some of our recent experimental and theoretical results that attempt to explain the modulation of the transmitted exposing beams during grating formation and offer an explanation for this behaviour.

A large number of plane-wave holograms were recorded in Agfa-Gevaert 8E75HD holographic plates, at a wide range of bias exposures and fringe visibilities. The plates were processed by various combinations of developers (AAC, Pyrogallol and Catechol) and bleaching agents (R-9 and EDTA). A pair of absorption and phase holograms was recorded at each value of the recording parameters. Optical densities before bleaching were determined using the absorption holograms. Then each phase grating was studied by phase-contrast microscopy, using a high-power immersion (100 X) objective. Thus modulation of the refractive index as a function of the bias exposure and the visibility of the recording interference pattern could be determined. To characterize the processing, the modulation of the refractive index of the processed phase holograms was related to the amplitude of the optical density modulation obtained at the development step. These characteristics are especially useful for the comparison of various bleaching agents used with the same developer. Characteristics of similar forms were obtained for all the processing types, with significant differences in the slope and extent of the curves, so that sensitivity, linearity and dynamic range of the processes could be compared directly.

In the biomedical field, the laser Doppler flowmetry (LDF) technique is a non-invasive method to monitor skin perfusion. On the skin of healthy humans, LDF signals present a significant transient increase in response to a local and progressive pressure application. This vasodilatory reflex response may have important implications for cutaneous pathologies involved in various neurological diseases and in the pathophysiology of decubitus ulcers. The present work analyses the dynamic characteristics of these signals on young type 1 diabetic patients, and on healthy age-matched subjects. To obtain accurate dynamic characteristic values, a de-noising wavelet-based algorithm is first applied to LDF signals. All the de-noised signals are then normalised to the same value. The blood flow peak and the time to reach this peak are then calculated on each computed signal. The results show that a large vasodilation is present on signals of healthy subjects. The mean peak occurs at a pressure of 3.2 kPa approximately. However, a vasodilation of limited amplitude appears on type 1 diabetic patients. The maximum value is visualised, on the average, when the pressure is 1.1 kPa. The inability for diabetic patients to increase largely their cutaneous blood flow may bring explanations to foot ulcers.

In this work we explore the application of volume effects given by holographic optical elements (HOEs) to image processing operations. Bragg diffraction, exhibited by HOEs, modifies the impulse response of an imaging system, facilitating spatial filtering operations with no need for a physical Fourier plane. Both the holographic recording material we use and the specific HOE we design are important parameters. In the present communication we report our last results using a polyvinyl alcohol/acrylamide (PVA/AA) photopolymer. This compound combines good optical properties, ease of fabrication, and self-development capability. We are able to produce layers as thick as 1 millimeter (mm) with a diffraction efficiency higher than 80%. Using layers with a thickness of 0.1 mm and 1 mm we have recorded both holographic diffraction gratings and holographic lenses. When using the holographic gratings we can obtain image edge enhancement as demonstrated in previous works. As a novelty, in this work we show that when using the holographic lenses we obtain a space-variant image edge enhancement. We analyse the properties of this space-variant operation in terms of the reconstruction geometry and the local grating structure exhibited by the lens across its aperture.

The object of these article is the conception, the realization and the used of a new imaging process based on the study of the polarization in the light-media interaction. In this investigation, a polarization-based imaging system is developed and described that measures the two-dimensional effective backscattering Mueller matrix of a sample. As is well known, a Mueller matrix can provide considerable information on the makeup and optical characteristics of a sample (depolarization,retardance, diattenuation...), but The reliability of measure and the reconstruction of the mueller matrix require the analysis of the error and the calibration of a Mueller polarimetre.Simulations enabled us, first, to determine the measurement error on each element of the Mueller matrix without a sample and, second, to adopt a method of calibration. therefore, the precision of experimentals results given by the Mueller matrix is drastically improved.The studies presented were performed with cancerous tissues and another non cancerous.The results demonstrate how these techniques could provide information that may be of diagnostic value in the physical detection of lesion.

A large number of plane-wave holograms were recorded in Agfa-Gevaert 8E75HD holographic plates, at a wide range of bias exposures and fringe visibilities. The plates were processed by various combinations of developers (AAC, Pyrogallol and Catechol) and bleaching agents (R-9 and EDTA). The phase gratings were studied by phase-contrast microscopy, using a high-power immersion (100 X) objective. The phase contrast photomicrographs were Fourier-analyzed. Thus first- second- and third-order modulation of the refractive index as a function of the bias exposure and the visibility of the recording interference pattern could be determined. The ratio of the amplitudes of the higher-order modulations to that of the first-order one can serve as a measure of the nonlinearity of the holographic recording.

Beam propagation factor (usually referred to as M2 factor) and brightness of high-order symmetrical Laguerre Gauss (LG) beams that diffract upon a hard-aperture are investigated. We demonstrate that a circular aperture is able to decrease the M2 factor of a high-order symmetrical LG beam and also to enhance its brightness although induced losses.

The description of the light propagation in or between planar diffractive optical elements is done with the angular spec-trum method. That means, the confinement to the paraxial approximation is removed. In addition it is not necessary to make a difference between Fraunhofer and Fresnel diffraction as usually done by the solution of the of the Rayleigh Sommerfeld formula. The diffraction properties of slits of varying width are analysed first. The transitional phenomena between Fresnel and Fraunhofer diffraction will be discussed from the view point of metrology. The transition phenomena is characterised as a problem of reduced resolution or low pass filtering in free space propagation. The light distributions produced by a plane screens, including slits, line and space structures or phase varying structures are investigated in detail.

A two-step technique of fabricating blazed holographic grating is presented. The grating fabrication includes two exposures and two developments. In the first step, two collimated laser beams with symmetrical incidence about the normal of the holographic plate generate a grating with quasi-sinusoidal groove profile after the first development. In the second step only one collimated laser beam irradiates on the plate with a selected incident angle, resulting in a change of groove profile into quasi-triangular after the second development. A blazed holographic grating with 65% relative diffraction efficiency under non-auto-collimation was obtained in the experiment. The scanning electron micrographs clearly show the quasi-triangular groove profile of the grating. The factors that affect the groove profile are discussed.

In order to achieve higher diffraction efficiencies of the volume gratings stored in acrylamide based photopolymer, we introduce in the photopolymer a crosslinker (N,N'methylene-bis-acrylamide). The presence of this component increase the rate polymerization and the modulation of refraction index. The recording was performed using a holographic copying process. The original was a grating of 1000 lines/mm processed using silver halide sensitized gelatine, with diffraction efficiency around 50 % for a reconstruction wavelength of 532 nm. The main beam was split in two secondary beams by the original grating, with an intensity ratio 1:1. The results obtained using the new composition of material are compared with the composition without crosslinker. In the other hand the no linearity of the material's response is also studied comparing the energetic sensitivity, diffraction efficiencies and index modulation of gratings recorded with pulsed and continuous laser. This study is realized fitting the angular scan of each grating using Kogelnik's theory. The gratings are recorded with wavelength of 532 nm when pulsed exposure is used and with wavelength of 514 nm when continues exposure is used. Using pulsed laser at 532 nm the photopolymer without crosslinker presents the diffraction efficiencies lightly smaller than 60%. In the other hand when the crosslinker has been introduced in photopolymer composition, the diffraction efficiencies achieves are higher than 85 %.

Off-axis holographic Fresnel lenses were designed and fabricated, with the aim of using them as multiplexer/demultiplexer in optical networks. The reduction of third-order aberrations was the main consideration. The theoretical analysis indicates that third-order aberration can be effectively reduced if the condition tanα_C/tanα_R = -λ2/λ1 is applied in geometry design and long object distance is selected. The experimental results verify the theoretical analysis.

We present the promising properties of a very simple binary Diffractive Optical element which is a phase slit. The latter is made up of two plates of glass in which a phase step has been produced with ion-etching equipment. The two phase steps are set parallel and are able to slide each on the other so that the width of the phase shifting zone is continuously adjustable. The adjustable phase slit has been used for 1-D laser beam tailoring in which the key parameters that govern the shape of the far-field intensity distribution is the phase step height and the ratio of incident beam and slit widths. The phase slit is able to convert a Gaussian beam into a super-Gaussian or a hollow profile having a central depression whose depth can be continuously adjusted.

We present investigations of self-focusing and screening soliton formation processes in photorefractive Bi₁₂TiO₂₀ (BTO) crystals for two different cuts in dependence on both the magnitude of the applied external voltage and additional illumination intensity. We study also temporal behavior of soliton growth and the possibility of stable soliton existence in BTO crystals of the cut [111][112][110].

Multilevel Diffractive Optical Elements for high-power laser beam shaping have been designed and produced. The originality of the proposed approach rests on the realization of four phase levels reflection elements with a single etching step. Thus, if the phase change of 270° is obtained by etching a pixel element, intermediary phase difference is obtained by etching subwavelength structures of the same height with appropriate filling factor. Sizing of the subwavelength gratings required with this theory has been carry out for TE and TM polarized radiation with a rigorous electromagnetic model, the Finite Difference Time Domain method. In a first step, a test component has been realized using photolithography to validate the sizing of the subwavelength gratings. In a second step we have adapted a specific fabrication tool based on laser ablation and direct writing for greater flexibility. Characterization has been carried out with Coherence Probe Microscopy. The technique has been applied to the fabrication of a diffractive element used with a high-power CO₂ laser beam for surface marking.

It is shown that a specific position of an axial object point can be found for every optical element, where the spherical aberration is either zero or minimal. If we image this point with an optical element, then its point spread function will be almost identical to the point spread function of the diffraction limited optical system. It can be used for testing of centricity of very precise very precise optical elements, because we can simply detect unsymmetry of the point spread function, which is caused by the decentricity of the tested optical element. Furthermore, one can also use this method for testing optical elements in connection with a cementing process. It is also derived a simple equation for calculation of the coefficient of third order coma, which is caused by a decentricity of the optical surface due to a tilt of the surface with respect to the optical axis.

The work deals with an influence of aberrations of optical systems that are used in optical information processing systems. A detailed analysis of the influence of aberrations on the image formed using the optical system is carried out. Furthermore, the effect of aberrations of the wave field, which illuminates the object, is also studied. A theoretical analysis is carried out using the third order aberration theory, and several examples are shown for an object of a circular shape.

In this work we make a comparative study between different theories to predict the efficiencies of the different orders that propagate inside a volume phase grating. For the case of a pure sinusoidal grating, transmission and reflection, the theories of Rigorous Coupled Wave Theory (RCW), Coupled Wave Theory (CW) and Kogelnik's Theory are compared. This comparison allows establishing the range of physical values where the more approximate theories, CW and Kogelnik´s Theory are applicable. On the other hand for the case of a general dielectric grating, transmission and reflection, the RCW, CW, and a thin matrix decomposition method (TMDM) are also compared. The theoretical study is also validated by comparing the theoretical results with experimental data obtained in volume phase diffraction gratings recorded on photographic emulsions. To record the volume phase diffraction gratings BB-640 emulsions were exposed to an interference pattern of light from a He-Ne laser (633 nm).

Photopolymers are systems of organic molecules that rely on photoinitiated polymerization to record volume phase holograms. Characteristics such as good light sensitivity, large dynamic range, good optical properties and relatively low cost make photopolymers one of the most promising materials for write-one, read-many (WORM) holographic data storage applications. Thus, it is interesting to understand the mechanisms that control the way information is stored in photopolymer materials. Different authors have demonstrated that two processes play the main role in hologram formation: monomer polymerization and monomer diffusion. A number of models based on these two processes have been proposed and their prediction capability has been validated. In this work we extend the capabilities of the existent models by introducing another important characteristic: the attenuation of light through the depth of the material which happens in the recording process. In order to check the validity of the theoretical model that we propose, volume phase transmission gratings are recorded in a PVA/Acrylamide photopolymer with different spatial frequencies. Using the Rigorous Coupled Wave Theory (RCWT) we show that we can obtain information about the higher harmonics in the recorded refractive index modulation. Comparison between simulated and experimental results validates the interpretation provided by the proposed model.

We report on the efficient spectral control of ultrashort sub-nanojoule violet laser pulses by means of cross-phase modulation (XPM) with a pump pulse in a highly nonlinear photonic crystal fiber (PCF). Spectra of the output pulses were recorded as a function of pump-probe delay for different pump central wavelengths. For fiber lengths that are much longer than the pulse walk-off distance, we consistently observe simultaneous downshifted and upshifted bands in the output pulses, associated with the frequency shift induced by both the leading and trailing edges of the pump as it sweeps over the probe pulses. These features can only be observed with pump pulses propagating in the anomalous dispersion region of the PCF, where pump pulse compression occurs and provides the necessary pump asymmetry.

In this work, we apply a recently introduced electromagnetic degree of coherence to address the coherence properties of random, stationary electromagnetic fields. In particular, we consider the limit of complete coherence in space-frequency and space-time domains. We show that in both domains the (electric) coherence tensor is analogous, in its spatial and temporal structure, to the coherence function of fully coherent scalar fields. The results are important in the rigorous electromagnetic theory of optical coherence, as encountered, e.g., in non-paraxial near fields and diffractive optics.

The fractional Fourier transform (FRT) is a recently developed tool for linear space-frequency (or time-frequency) signal processing. It is a generalisation of the Fourier transform, FT, has a simple optical implementation and can potentially find use wherever the FT is used. We discuss and compare the most popular fast algorithms currently being used (in the area of optical signal processing, OSP) to calculate the digital FRT. We develop theory for the discrete Linear Canonical Transform (LCT) of which the FRT is a special case. We then derive the Fast Linear Canonical Transform (FLCT), a fast algorithm for its implementation using a similar approach as was done with the derivation of the Fast Fourier Transform (FFT) for implementation of the Discrete Fourier Transform (DFT). The new algorithm is entirely independent of the FFT and is based purely on the properties of the LCT and FRT.

Three different topics concerning the Zernike polynomials are investigated. First, the Zernike expansion of a function only of the coordinate x is considered. Second, a set of functions orthogonal for an electromagnetic optical system of high aperture are developed. Third, the effect of Zernike aberrations on the three-dimensional optical transfer function (OTF) is described.

Diffractive components in X-ray and UV regions have several attractive applications, but analysis in those regions has not been thoroughly investigated. Besides, in the X-ray and UV regions the complex refractive indices of metals differ substantially from the values in the visible region of the spectrum. The consequences of this phenomenon are analyzed for metallic structures illuminated by wavelengths ranging from infrared to soft X-rays. The rigorous diffraction theory and the thin element approximation is applied to study the behavior of both wire-grid polarizers and inductive grid filters. Single layer film theory is used to enhance the reliability of the thin element approximation.

The apodization of diffractive optical elements can be realized by a local change of their diffraction efficiency. In the case of lithographic elements with step-like structure of the period, the variable diffraction efficiency can be achieved by a gradual transformation of the 2^m step kinoform into its conjugate counterpart across the apodization region. In the present contribution we show experimental results confirming this idea, which until now was verified only by simulations. The apodized quaternary grating with locally varying diffraction efficiency was obtained on a SLM device as a programmable diffractive optical element by changing gradually the period's profile. Knowledge of the phase heights of the SLM's pixels is required for successful implementation of the apodization function. It was determined from Fresnel images of the binary phase gratings with different phase step height programmed on the SLM. The Fresnel images become then binary and their visibility depends on the phase height of the grating in a known way, what makes possible to calibrate the SLM.

In the present communicate the experimental results are shown, which deal with the interference pattern created by superposition of multiple Bessel beams. They confirm our earlier results obtained analytically as well as by simulations. The interfering Bessel beams were obtained in a standard way, i.e., a field produced by a set of concentric annular apertures of narrow width illuminated by a plane wave was transformed by a lens into a set of Bessel beams.