This PDF file contains the front matter associated with SPIE Proceedings Volume 6606, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

In this paper, we review the history of laser space propulsion from its earliest theoretical conceptions to modern practical applicatons. Applications begin with the "Lightcraft" flights of Myrabo and include practical thrusters for satellites now completing development as well as proposals for space debris removal and direct launch of payloads into orbit. We consider laser space propulsion in the most general sense, in which laser radiation is used to propel a vehicle in space. In this sense, the topic includes early proposals for pure photon propulsion, laser ablation propulsion, as well as propulsion using lasers to detonate a gas, expel a liquid, heat and expel a gas, or even to propagate power to a remote conventional electric thruster. We also discuss the most recent advances in LSP. For the first time, it is possible to consider space propulsion engines which exhibit thrust of one to several newtons while simultaneously delivering 3,000 seconds, or greater, specific impulse. No other engine concept can do both in a compact format. These willl use onboard, rather than remote, lasers. We will review the concept of chemically augmented electric propulsion, which can provide overall thrust efficiency greater than unity while maintaining very low mass to power ratio, high mean time to failure and broad operating range. The main advantage of LSP is exhaust velocity which can be instantaneously varied from 2km/s to 30km/s, simply by varying laser pulsewidth and focal spot size on target. The laser element will probably be a diode-pumped, fiber master-oscillator-power-amplifier (MOPA) system. Liquid fuels are necessary for volumetric efficiency and reliable performance at the multi-kW optical power levels required for multi-N thrust.

It was shown that metals such as gallium, indium and bismuth heated above melting temperature can be used as a target for 10 Hz femtosecond laser plasma highly stable hard x-ray source.

Modern technologies such as DWDM (Dense Wavelength Division Multiplex) need precise stability of laser frequencies. According to this fact, requirements of new etalons of optical frequencies in the telecommunication band is rapidly growing. Lasers working in near infrared telecommunication band (1500-1600 nm) can be stabilized to ¹²C₂H₂ or ¹³C₂H₂ (acetylene) gas absorption lines. The acetylene gas absorption has been widely studied and accepted by international bodies of standardization as a primary wavelength reference in the near infrared band around 1550 nm. Our aim was to design and develop a compact fibre optics laser system generating coherent light in near-IR band with high frequency stability (at least 1.10^-8). This system should become a base for realization of a primary frequency standard for optical communications in the Czech Republic. Such an etalon will be needed for calibration of wavelengthmeters and spectral analysers for DWDM communication systems. We are co-operating with CMI (Czech Metrology Institute) on this project. We present stabilized laser system based on a single frequency DFB (Distributed Feedback) laser diode with a narrow spectral profile. The laser is pre-stabilized by means of the FM-spectroscopy on a passive resonator. Thanks to a fast feed-back loop we are able to improve spectral characteristics of the laser. The laser frequency is locked by a relatively slow second feed-back loop on an absorption line of acetylene vapour which is sealed in a cell under the optimised pressure.

Diode edge-pumped microchip Yb:YAG/YAG laser with a special design of the optical resonator was combined with LBO crystal in the nonlinear mirror configuration to obtain high power mode locking operation. 84.8 MHz pulse repetition rate of mode-locking oscillation was obtained with an average power of 30-W in quasi-CW operation with 10% duty factor.

We present an extended cavity laser system based on a tunable high-power laser diode optimized for maximum efficiency of the optical pumping process of Rb atoms. The aplication of the laser system is orineted to employment in an experimental arrangement for production of hyperpolarized gasses (HpG), namely Xenon. It is designed to operate in medical and industrial applications to come. We concentrated on the laser diode emission linewidth reduction because of the efficiency of the optical pumping process. The emission linewidth was reduced approximately from 1 THz to 69 GHz with only half of the total optical power loss and quadruple increase of the power spectral density at the wavelength of desire.

We simulated chirped and apodized fiber Bragg gratings (fiber gratings with modulation of the amplitude and with modulation of the spacing) the same as uniform fiber gratings. Results of our simulations are presented. Apodization of fiber Bragg gratings (FBG) has many advantages in comparison to other types of FBGs. Main improvement is suppressing of the side lobes in the grating spectral properties. The difference of side lobes suppression for uniform and Gaussian apodized grating is more than 110dB. On the basis of these results we designed a special fiber Bragg grating with apodization especially for using to stabilize semiconductor lasers for high precision laser applications with central wavelength 760nm. We present application of methods for calculation of parameters of apodized fiber Bragg gratings (FBG). We used combination of methods based on layered dielectric media (LDM) and the transfer matrix. On the contrary to the other calculation techniques the LDM method is based on sequence of thin films of dielectric media assembled in the direction of wave propagation. The combination of the LDM method and the transfer matrix method can be used to the calculation of arbitrary fiber gratings with high precision. For this designed apodized FBG we calculated the phase mask to manufacture by interference patterns. The phase mask and the fixation bottom of the fiber were made by e-beam lithography to achieve highly precise stability during manufacturing. We present the set-up of this system for writing FBG by pulsed UV laser with wavelength 266nm. Measurement of commercially available FBG with comparison to our calculated FBG is presented.

In the paper we will show that formation of a phase-conjugated wave in a self-pumped phase-conjugate mirror can be considerably (6 - 20 times faster) accelerated by a special training procedure. Efficiency of some static and dynamic training procedures will be compared and analyzed.

A phase-locked three-channel Nd:YAG laser system based on phase-conjugate loop oscillators is designed and studied. The Nd:YAG laser system had three laser outputs as the self-Q-switched laser 100-mJ monopulses interfering with an interference pattern contrast tending to unity giving a sixfold interferential increase of the laser brightness. A new opportunity to apply the Nd:YAG laser systems based on phase-conjugate loop oscillators for drilling of the super-deep (up to 27 mm deep) holes of small 100-micron diameter for the most perspective metals, alloys and ceramics with different composition is shown.

High peak power and high energy laser pulse from 2 at% Nd:YAG and 1 at.% Nd:GdVO₄ diode pumped at 808nm laser and passively Q-switched by Cr⁴⁺:YAG is reported. Pulse energy as large as 45&mgr;J, 10kHz repetition rate and 1.7MW peak power has been demonstrated for Nd:YAG while Nd:GdVO4 results are 4.4&mgr;J, 160kHz, 180kW.

In the contribution we present a system for measurement of iodine purity by means excitation of a selected strong transition, measurement of induced fluorescence and evaluation by the Stern-Volmer formula. The arrangement is based on a pumping Ar-ion laser tuned to the transition of interest but its linewidth far exceeds the transition. Frequency noise of the laser is effectivelly reduced by monitoring the fluorescence in a second, reference iodine cell and together with monitoring of the laser power enables cancelation of the frequency noise influence which generates errors by demodulating on the absorption profile. The level of the scattered light is subtracted as well. All the measured data are digitally processed and the experiment is fully computer controlled.

We report preliminary measurements on the catastrophic damage threshold and also on the maximum fluence/irradiance for non-damage of a 355 nm high reflectance mirror, by using a new optical arrangement. Our goal was two-fold: to determine the ability of a new, variable spot size (zoom) optical system (named VariSpot^®) to be used in laser-induced damage measurements, and also to characterize the damage properties of the mirror under test. The classical measurement scheme maintains a constant spot size on the target by using a fixed-focus optical system, and the laser fluence/irradiance on the target is varied by appropriately attenuating the laser beam before the focusing optics. In contrast, our scheme maintains constant the energy/power of the incoming beam before the focusing optics and uses a zoom-type optical system to continuously change the spot size and correspondingly the fluence/irradiance on the target, while keeping constant the working distance (from optics to target). A 355 nm beam representing the third harmonic of an electro-optically Q-switched, unstable cavity Nd:YAG laser was used as incoming beam. Its spatial diagnostics was done by using a CMOS-type beam profiler and following the definitions and recommendations of the ISO 11146 standard. The VariSpot optical system represents a prototype with a working distance of approximately 100 mm and delivering a round and adjustable spot size with diameters from 0.085 mm to 4.3 mm at that distance for the specific 355 nm incoming laser beam. The results show the advantages of using the VariSpot system for such type of measurements and also reveal reasonable good damage properties of the tested mirror. We briefly discuss the major sources of errors in the obtained results and also suggest several ways to improve the future measurements using similar arrangements.

In the present paper a coupled cavities filter with potential applications in photonic crystal microcircuits is studied. The analysis is based on "coupled mode theory in time" which is an approximate method that allows relatively simple derivations of optimal design parameters. Coupled cavities appear everywhere in optical circuits. In many cases they induce parasitic effects like big reflections back to the source. In other situations, if carefully designed, a device consisting of two micro cavities can act as a bandpass filter.

The study of dynamics of spatial solitons in nonlinear and unidimesional fotonic crystals, with a periodical and nonlinear fotonic network which is generated by Dirac function is presented. Are analysed comparisons and differences which appear in development of periodical models describes by nonlinear Schrödinger equation. Also, is developed theory of couple models for periodical modulation of refractive index. Fudamental theory of spatial solitons are based to obtain discrete nonlinear Schrödinger equation with analyze of stationary solutions on discrete models.

Experimental results are reported on the surface nanoablation of diamond single crystal induced by nanosecond pulses (&tgr;=15 ns) of KrF excimer laser (&lgr;=248 nm) at fluence below a graphitization threshold of diamond. The relatively low etching rate (less 1nm/1000 pulses) in this regime has been studied depending on both laser fluence and external experimental conditions (ambient gas and temperature). The photochemical mechanism is proposed to explain the nanoablation of diamond surface.

The fundamental mechanisms and dynamics of laser ablation are reviewed, based on experiments with femtosecond laser pulses to exclude secondary effects like the interaction of the incident laser light with the ablation plume or with a target preconditioned during the initial slope of the laser pulse. It is shown that the incident energy drives the target into a state of instability, far from thermodynamic equilibrium. The subsequent ultra-rapid relaxation results in the formation of self-organized regular nanostructures in the irradiated and ablated area.

Laser ablation of materials in air is able to introduce long living modification of the gas environment in vicinity of the exposed area. Such a modification implies formation and residence of small particles of the material and of ablation products. If the material is exposed to multipulse laser action, which is normally the case for micro-mashining, ignition of laser plasma at such particles is able to create significant screening of incident radiation, influencing this way formation rates and morphology of ablated structures. Effect of this low-threshold air breakdown is especially pronounced in long drilled channels, where convection is poor.

Pulsed laser deposition in an inert ambient gas allows for producing cluster-assembled films whose constituent building blocks are atom aggregates with size ranging from a few to several thousands of atoms. The choice of the deposition parameters, such as gas pressure, laser energy density and target to substrate distance, affects cluster size and size distribution. By controlling these critical parameters the features of film surface can be managed at the scale of tens of nanometers, or less. We introduce a mixed propagation model, based on a modification of the diffusion and the drag models to calculate the size of clusters formed in the plume during its propagation. Model ingredients are quantities directly deduced from available values of process parameters. The mixed propagation model is applied to interpret experimental results on the synthesis of clusters of different elements.

Carbon-made materials have been the field of major discoveries with the identification of new phases, which have stimulated a huge effort to understand their properties. Laser pyrolysis of hydrocarbons is based on a high temperature C/H/O/... system of well-established composition and allows obtaining carbon nanostructures from the almost amorphous carbon and particles with a turbostratic structure up to those characterized by a high degree of curvature. The variation of the gas composition and experimental parameters controls the final particle morphology providing useful functional properties. Gas-phase hydrocarbons were used either in resonant or non-resonant laser pyrolysis processes. The formation of different nanostructures is related to the presence of heteroatom in the reactants. Focusing, in the context of necessary presence of this heteroatom in the gas composition, on the present questions concerning the rational synthesis of nanostructures with controlled dimensionality, size and potentially properties, the work presents some significant changes in soot morphology produced by the variation of the experimental parameters and these, sometimes unavoidable, heterogeneous atoms.

Because of their quantum-scale dimensions, nanoparticles exhibit properties different from those of the bulk. As a result of their unique properties, numerous efforts have been made to disperse nanoparticles in polymers to enhance or modify their structural and magnetic properties. A new in situ synthesis method was used to incorporate small iron nanoparticles into a polyoxocarbosilane polymer matrix. Nano-magnetic iron-based composites were obtained by a one-step procedure consisting of the IR laser co-pyrolysis of a sensitized (with ethylene) gaseous mixture containing gaseous iron pentacarbonyl and hexamethyldisiloxane in argon. The simultaneously occurring formation of iron from iron pentacarbonyl and that of organosilicon polymer from hexamethyldisiloxane yield iron nanoparticles surrounded by an organosilicon polymer shell. The particles become superficially oxidized in the atmosphere. They were characterized by Raman analysis, electron microscopy and magnetic measurements. The properties of the nanocomposite particles depend on the experimental synthesis parameters such as flow rates of precursors, total pressure and laser power. Magnetization curves, exchange bias Hex at T = 5 K and AC susceptibility were studied in the temperature range 5-400 K. It was found that the nanocomposite should be in a ferromagnetic blocked state with a minor superparamagnetic contribution of the smallest nanoparticles.

Nanocrystalline powders of Y₂SiO₅ doped with Eu³⁺ ions were obtained by a sol-gel technique. The morphologic changes produced by thermal treatments were monitored using X-Ray Diffraction (XRD), Fourier- Transform Infrared Spectroscopy (FT-IR) and luminescence spectroscopy.

The dynamics and the spectral kinetic characteristics of the plume emerging in the vicinity of graphite targets, pressed pellets consisting of zirconium oxide powder stabilized with yttrium (YSZ) and of garnet stock with neodymium (YAG:Nd) are studied. The targets are irradiated in air at room temperature using a repetitively pulsed CO₂ laser with a wavelength of 10.6mm, a peak power of up to 9 kW, a pulse energy of up to 1.69 J, and a pulse duration of 330ms at a level of 0.1. The plume propagates normally to the target surface at an angle of 45° relative to the laser radiation. The spectral kinetic characteristics of the plume luminescence are discretely measured along the entire length. It is demonstrated that the plumes of all targets represent the "ows of a weakly nonequilibrium gas plasma with a temperature of 10 kK (graphite) and 3.1...4.7 kK (YSZ and YAG:Nd pressed pellets). The plume size is determined by the peak power of the laser pulse. The luminescence of the two-atom radicals (C₂ in graphite; ZrO and YO in YSZ; and YO, AlO, and NdO in YAO:Nd) dominates in all of the plumes. A relatively high temperature of the graphite plume is maintained owing to the energy of the exothermic reaction involving the association of carbon atoms and the energy of the vibrationally excited molecules resulting from this reaction. The dynamics of plasma plume was studied by luminescence imaging and shadowgraphy.

The surface charge of a silicon nanoparticle in solution of weak silver nitrate electrolyte was studied. The charge was determined by electrophoretic method in colloidal system strongly diluted with water. The physical model was offered, which combined electrostatics, hydrodynamics and optics, to describe our method. With the help of our model the approximate value of nanoparticle charge was calculated. The total surface charge of a silicon nanoparticle was determined by a number of silver surface adsorbed ions. The method gave the value of Q ≈ 65•10^-19 ≈ 40e for the particles of about 20 nm in diameter. The layer of counterions located in liquid near the nanoparticle to neutralize its charge, the colloidal system was in dynamical balance. Applying electric field to the colloidal system can disturbed the balance. Thus the nanoparticles may start to move to one of the electrodes depending on value and sign of their charge. The threshold of electric field intensity, which was necessary to disrupt dynamical equilibrium and begin the nanoparticle movement was found in our work. To describe the nature of this threshold behavior of the colloidal system the theoretical model was offered.

Gold nanoparticles were prepared by laser ablation in water. Size separation was realized by sedimentation and centrifuging. The interaction of the protein (bull serum albumin - BSA) and gold nanoparticles was investigated in water solution. The obtained samples were characterized by approximation of optical absorption spectra in terms of Drude model for metal cores with dielectric shells.

At fluences well below the threshold for plasma formation, we have characterized the direct desorption of atomic ions from fused silica surfaces during 157-nm irradiation by time-resolved mass spectroscopy. The principal ions are Si⁺ and O⁺. The emission intensities are dramatically increased by treatments that increase the density of surface defects. Molecular dynamics simulations of the silica surface suggest that silicon ions bound at surface oxygen vacancies (analogous to E' centers) provide suitable configurations for the emission of Si⁺. We propose that emission is best understood in terms of a hybrid mechanism involving both antibonding chemical forces (Menzel- Gomer-Redhead model) and repulsive electrostatic forces on the adsorbed ion after laser excitation of the underlying defect.

The reversibility of phase-structure modifications of glass-ceramics (photosensitive and in-photosensitive) has already been experimentally demonstrated with the use of CO₂-laser. It has been demonstrated that CO₂-laser radiation resulted in a crystallization of glass and a subsequent reverse amorphization of as FS-1 and ST-50 glass-ceramics. The rates of such structural modification under laser heating are about 10² − 10³ times higher than under conventional heating with the use of a furnace. The laser technology of structural modification of glass-ceramics is very attractive for development and fabrication of new optical components, different microstructures and microdevices.

The use of direct-write techniques might revolutionize the way microelectronic devices such as interconnects, passives, IC's, antennas, sensors and power sources are designed and fabricated. The Naval Research Laboratory has developed a laser-based microfabrication process for direct-writing the materials and components required for the assembly and interconnection of the above devices. This laser direct-write (LDW) technique is capable of operating in subtractive, additive, and transfer mode. In subtractive mode, the system operates as a laser micromachining workstation capable of achieving precise depth and surface roughness control. In additive mode, the system utilizes a laser-forward transfer process for the deposition of metals, oxides, polymers and composites under ambient conditions onto virtually any type of surface, thus functioning as a laser printer for patterns of electronic materials. Furthermore, in transfer mode, the system is capable of transferring individual devices, such as semiconductor bare die or surface mount devices, inside a trench or recess in a substrate, thus performing the same function of the pick-and-place machines used in circuit board manufacture. The use of this technique is ideally suited for the rapid prototyping of embedded microelectronic components and systems while allowing the overall circuit design and layout to be easily modified or adapted to any specific application or form factor. This paper describes the laser direct-write process as applied to the forward transfer of microelectronic devices.

On-line diagnostics of hot plasma induced by superintense femtosecond laser pulses in a cavity during the deep hole drilling of solid target has been developed. Such a plasma is characterized by higher values of hard X-ray yield and hot electron temperature in comparison with the same parameters measured for flat nearsurface plasma. Dynamics of X-rays yield in the cavity during the deep hole drilling demonstrates several repetitive stages. The yield and energy of X-rays from plasma ignited in a cavity depend on the beam waist position respect to the target surface plane, i.e. focusing regime. We have detected strong second harmonic signal that correlated with hard X-Ray yield in the time of cavity formation. Depth resolved elemental analysis of compound targets, based on this diagnostics technique, has been proposed.

Two laser-based methods were used for the deposition of narrow band gap semiconductor films based on iron oxides. The first one is laser chemical vapor deposition (LCVD) from iron carbonyl Fe(CO)₅ vapors using Ar⁺ laser radiation. The width of the band gap of the films depends on the film thickness and the applied electrical field. The film thickness was varied from 10 to 18 nm and consequently the band gap width (E_g) varied from 0.46 to 0.66 eV. The longer the exposure time of the Si substrate to Ar⁺ laser radiation, the higher the content of iron oxides, the larger the width of the band gap in the deposited semiconductor materials. The second method is the reactive pulsed laser deposition (RPLD) of an iron target in low pressure oxygen atmosphere using a KrF excimer laser (&lgr;=248 nm, &tgr; congruent to 30 ns) at the fluence of 4 J/cm² and the repetition rate of 10 Hz. A number of pulses (3000-8500) increasing with oxygen ambient pressure (0.05-1 Pa) was used for each deposition with the aim of depositing films with almost equal thickness (~100 nm). The width of the band gap (E_g) varied in the range 0.13-0.34 eV, depending on the oxygen pressure: the higher the oxygen pressure, the higher the iron oxide content in the deposited film, the larger the width of the band gap in the deposited semiconductor material. It is shown that both LCVD and RPLD methods are appropriate technologies for the deposition of narrow variable band gap semiconductor thin films.

The melting of carbon at a pressure of about 1 atm is observed. The escape of liquid carbon from the heating region and its spread over the sample surface are observed in the experiments. The structural change in graphite occurring in the melting region are determined from scanning tunneling microscope (STM) images obtained by means of an atomic force microscope and from Raman spectra. The STM images exhibit significant rearrange¬ment of the structure of the graphite surface in the region of the escape of liquid carbon. The Raman spectra show that the graphite ordering degree increases significantly. A method for reconstructing the surface relief from the video image is proposed and realized. The method is based on the measurement of the angular distribution of the light intensity scattered by the graphite sample surface. The surface relief of the graphite sample changing in time is reconstructed. The relative change in the relief height during laser excitation is measured. The statistical characteristics of the reconstructed graphite surface shape and their variation during laser irradiation are studied.

Wavelength, pulse energy, repetition rate of excimer lasers as well as beam profile and beam delivery system are highly important parameters for precision machining. In this paper we report features of our excimer lasers and excimer laser systems that have been designed for micromachining. The examples of treatment of different materials are presented. In particular, we provide some new results of microstructuring of the surface of fused silica and also formation of up to 10 mm long microchannels with extremely high aspect ratio. We discovered some liquid forming under certain circumstances due to drilling of microchannels in PMMA. This liquid remains unchanged in the microchannels after the treatment.

We describe a field non-destructive Digital Speckle Pattern Interferometry diagnosis method to be applied in art conservation works, using as the light source a home-made single-frequency pulsed micro-laser oscillator-amplifier system. The green nanosecond laser-pulses are directed towards an interferometer set-up, where a beam splitter cube divides the incoming beam to define the object, respectively the reference beams. The object beam illuminates the artwork target and a CCD camera records the scattered light. The reference beam is directly coupled into the camera head. The operation of the integrated system is governed by dedicated software, able to acquire and process the speckle pattern images as to detect and locate the defects on the investigated artwork. The method was successfully applied inlab and in-situ conditions. The results are illustrated for a variety of investigated artworks.

Systematic investigation of ablation harmonics are performed for silver and indium targets, using the 40 mJ, 25 fs output from the Advanced Laser Light Source. Optimum pre-pulse and main pulse conditions for ablation harmonics are studied.

The laser microdrilling of steel samples by nanosecond single pulses and pulse trains was compared in wide range of repetition rates (up to 200 kHz). It was found that drilling by the short trains, or just by pairs of pulses can be more effective compared to conventional pico- and nanosecond (100ps÷100ns) laser processing in vacuum or drilling using ultra-high repetition rate lasers.

We show that the interaction between very intense laser beams and atoms is accompanied by oscillations of the electrons in very intense electromagnetic fields, at relatively long distances, of the order of tens of nanometers and lead to two effects: the above threshold ionization and the high order harmonics generation. Two components of the kinetic energy of the electrons appear at the interaction between very intense laser beams and atoms, molecules and materials. The first component is a multiple of the energy of the field quanta and is due to a quantum electrodynamics effect, while the second component is a variable one, due to a classical quiver motion of the electron in the very high electrical field. In a recent paper we proved that the Klein-Gordon equation which describes these interactions has a solution at the classical limit. We show that this result could lead to a strong simplification of the modeling of the above effects.

The results of experimental studies of formation and evolution of a multiply ionized (multicharged) laser microplasma produced in gases (air, helium, nitrogen and argon) with high intensity ( I ~ 10¹⁷ W/cm² ) ultrashort (τ ~ 100 fs ) 800-nm laser pulses tightly focused in a region of diameter ~ 2-3 μm are presented. The measuring technique and experimental setup for generation and precise optical diagnostics of laser-induced plasma are described. The spatiotemporal distribution of the refractive index and the free electron density was studied by the interferometric pump-probe method with a spatial resolution of ~ 1.5 μm and a temporal resolution of ~ 100 fs. An almost complete ionization of the initial gas (down to the nuclei) was shown to occur even in the initial stage of gas plasma formation.

In this paper we investigate experimentally the dynamical response of a class B microchip laser submitted to optical feedback. Based on the theoretical model for a laser with optical feedback, we demonstrate how the effects of the optical reinjection of the laser beam reflected by an object situated in front on the laser can be used in determining the characteristics of the object (reflectivity and distance to the laser). In this purpose we have constructed a laser system, which we further use in an optical feedback experimental setup. The laser we use in our experiment is a class B Nd:YAG microchip laser, which has a damping rate of the laser cavity γ_c much higer than the damping rate of the population inversion γ₁. The laser has a cavity lenght L=0.8mm, operating at λ=1,064&mgr;m. In order to obtain the laser emission, the active medium is pumped by a system of laser diodes emitting at 810nm. This type of laser has the relaxation oscillations at a characteristic frequency, named relaxation frequency. For the maximum pump parameter η≈6 the maximum output power of the laser is P_out≈130mW and the relaxation frequency f_r≈1MHz. The value obtained for ^γc/_γ1≈1,7X10⁶>>1 proves that our laser is a class B laser and also that it can be successfully utilized for optical reinjection. Based on this laser system, we develop a method for exploiting the sensivity of the Nd:YAG laser to the optical reinjection. We demonstrate that the optical feedback modifies the steady state of the laser and changes the laser characteristics. This method is based on the high sensitivity of this type of laser to the optical reinjection. In order to analyse the effects of the optical feedback on the laser behaviour, we placed an object at the distance d in front of the laser and the retro reflected beam was reinjected into the laser cavity. We use a beam splitter to send a small fraction of the laser beam to a photodiode. The signal provided by this photodetector is sent to an oscilloscope, where we observe the signal and the power spectrum of the laser. Our experimental results show that the optical feedback modifies the laser characteristics. We observe that the optical feedback induces a significant amplification of the laser signal and also a deplacement of the relaxation frequency to smaller values. Our experimental results are in good agreement with the mathematical model. By introducing the reinjected electric field into the equations for the dynamical behavior of a class B laser, it can be shown that the reinjection of a wave with the same pulsation as the laser beam determines a changement of the steady state values for the population inversion, for the electric field and also for the optical frequency of the laser. Based on the the equations for laser intensity and for the relaxation pulsation in the presence of the optical feedback, we determine experimentally the reflectivity of the object and the distance between laser and object. We conclude that the class B lasers present a high sensitivity to the optical feedback, which induces the change of the steady state of the laser. This modifications can be succesfully used for determining the characteristics of differents objects submitted to laser irradiation.

In this paper we investigate the vibrations of a square aluminium plate by speckle interferometry means. Modes of vibration of this plate are shown as speckle interferograms. As usually is the case with such interferograms, enhancement and filtering of these images is needed after recording. The speckle index and the signal-to-noise ratio (SNR) of the preprocessed interferograms before and after filtering are calculated. An improvement of the SNR between 1.37 and 1.81 is obtained for the vibration modes presented here.

This paper is concerned with the determination of in-plane displacements and deformations, by using digital speckle correlation. A special algorithm for determining the position of the maximum of the correlation function is presented. An example on how to apply this method is presented.

We offer a model of induced gratings describing a stationary transverse periodical distribution of FF and SH amplitudes by trigonometrical functions risen to the definite power. Dependences of a lattice contrast, and peak amplitude on the spatial period of the structure as well as the phase mismatch are found. The least period of the gratings corresponds with a critical value of period, at which the periodic structure degenerates into a plane wave. We obtain also that such lattices except the high contrast structures are unstable at long distances of about tens of the diffraction lengths. The modulation instability of the lattices under the effect of the low frequency amplitude noise was investigated. Moreover, all-optical switching effects for such structures in the quadratically nonlinear media were obtained.

A new approach based on the use of the double laser pulse was proposed to improve the crystallinity of carbon nitride films producing by PLD method. A pairs of laser pulses with time delay of 10 µs were used for graphite ablation in nitrogen gas. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods were utilized for characterisation of carbon nitride films synthesised by common (single pulse) PLD and double pulse PLD techniques.

Low Coherence Doppler Flowmetry (LCDF) measurement produces a signal, which frequency domain characteristics are in connection to the speed of the flow. In this study performances of Artificial Neural Network (ANN) and Multilinear Regression (MLR) methods in prediction of pulp flow speed from the LCDF measurement data were compared. In the study the pulp flow speed was estimated distinctly from consecutive frequency bands of the LCDF data with both methods. The smallest estimation error in flow speed with the ANN method was 20% and with the MLR method 30%, depending on the selected frequency band. The results indicate the relationship between characteristics of the LCDF measurement and pulp flow speed includes remarkable number of nonlinear components. The result is in line with theoretical calculations about the Doppler shifts occurrence in the LCDF data.

An old type HOLOBEAM type Nd:YAG laser system was upgraded to reach technical requirements for diamond and diamond like materials drilling. A particular alignment protocol was tested to assure the best quality of the hole geometry. Various processing procedures were tested and important differences in bore quality are noticed for different materials and laser operating regimes. Dedicated user friendly software was made to drive the laser beam and holder actuators, for different hole drilling geometries.

We describe our low spectral resolution Raman system that allows us to directly appreciate the quality of YBa₂Cu₃O_7-δ (YBCO) films, obtained by pulsed laser deposition on LaAlO₃ substrate. We identify the basic features of YBCO films' spectral fingerprints, validated by high spectral resolution analysis, described in previous reports. This fast and nondestructive valuable analytical tool functions at a convenient time and environment after deposition.

Neodymium-Iron-Boron (NdFeB) is a material with important magnetic properties, mostly used in permanent magnet fabrication. Thin layers of NdFeB are needed for miniaturization in electrical engineering, electronics, and for high-tech devices. We applied pulsed lased deposition (PLD) and radio frequency plasma assisted pulsed lased deposition (RFPLD) in vacuum for obtaining thin films and nanostructures of NdFeB from stoichiometric targets, at different temperatures. The influence of the laser parameters (wavelengths and fluence), radio-frequency discharge power and substrate temperature on the NdFeB structures, composition and magnetic properties has been investigated. The obtained structures have been characterized by Auger electron spectroscopy (AES), Atomic Force Microscopy (AFM) and optical microscopy. Vibrating Sample Magnetometer (VSM) studies have been performed for specific magnetic characterization.

A review is presented of the research on high resolution imaging of the eye based on en-face OCT. This can provide a dual display of images with different depth resolutions, where the two images are OCT and the other confocal. Two applications are presented: (i) OCT/ICG systems where the confocal channel is tuned to the fluorescence of indocyanine green and (ii) aberration corrections in both OCT and confocal channels using closed loop adaptive optics for enhanced contrast and transversal resolution.

In present paper we describe the development of advanced laser stereolithography (LS) methodology based on photopolymerisation of a new liquid mixture of polyfunctional acrylic monomers and osteoinductive hydroxyapatite powder. Supercritical carbon dioxide treatment of LS samples introduced both surface and bulk microporosity for enhanced primary cell attachment and to remove toxic additives improving biocompatibility of the materials. The results of in vitro tests comprising human osteoblast cells attachment, spreading and proliferation on the implants demonstrate low level of their cytotoxicity and high level of biocompatibility. We also present a novel Surface Selective Laser Sintering (SSLS) technique for biodegradable polymer scaffolds fabrication from thermosensitive poly(D,L-lactic) - and poly(D,L-lactic-co-glycolic) acids - polymers, which have a wide spread occurrence in biomedical applications. Unlike conventional Selective Laser Sintering (where the powder particles melt because of their volumetric absorption of the laser radiation), in SSLS initiation of the sintering occur due to near IR laser beam absorption by a small amount (<0.1wt.%) of biocompatible carbon black microparticles uniformly distributed along the polymer powder surface. This technique enable to prevent any significant changes in polymer initial structures and even incorporate bioactive enzymes into the samples. The results of our in vitro studies using 3T3 fibroblast, C2C12 myoblast and ovine meniscal chondrocyte cells cultures hold great promise for use of produced scaffolds and developed technique in tissue engineering.

In dental hard tissue ablation, ultra-short laser pulses have proven sufficiently their potential for material ablation with negligible collateral damage providing many advantages. The absence of micro-cracks and the possibility to avoid overheating of the pulp during dental cavity preparation may be among the most important issues, the latter opening up an avenue for potential painless treatment. Beside the evident short interaction time of laser radiation with the irradiated tissue, scanning of the ultra-short pulse trains turned out to be crucial for ablating cavities of required quality and shape. Additionally, long-pulsed laser systems have demonstrated successfully their suitability for decontamination purposes. In this paper, an overview of different indications for laser application in dental therapies in both pulse regimes is presented. A special focus is set on the decontamination of dental implants in periimplantitis therapy. Having employed commercially available long pulse systems for dental applications and ultra-short 330 fs pulses, we present first results for temperature development and corresponding ablation thresholds for dental implants, as in the future more gentle implant cleaning by ultra-short laser pulses could become of interest.

Mobility and intermoleculare interaction of blood serum proteins - in water solutions containing the ions with different ionic radii were investigated by Rayleigh-Debye light scattering (RDLS), photon-correlation spectroscopy (PCS) and fluorescence methods.

Luminescent silicon nanocrystals (nc-Si) are shown to be efficient photosensitizers of singlet oxygen (SO) generation. Photoluminescence (PL) spectroscopy method is used to study the mechanism and efficiency of the SO photosensitization in gaseous and aqueous ambiences. In vitro experiments demonstrated that the SO, photosensitized by nc-Si dispersed in nutrient solutions, could kill cancer cells. This finding opens a broad opportunity for biomedical applications of nc-Si, e.g. for the photodynamic therapy of cancer or antibacterial treatments.

We demonstrate two- and three-dimensional patterning of biological molecules. For the two-dimensional patterning we employ Laser-Induced Forward Transfer of materials in solution. For the three-dimensional patterning we employ femtosecond-laser induced three-photon polymerization, a technique which enables the construction of arbitrary 2D and 3D structures of submicron resolution. Biotin is subsequently attached to the 3D structures via UV-activated crosslinking. The integrity of the photolytically immobilized biotin is confirmed by detecting the binding of fluorescently labeled avidin via fluorescence microscopy.

Photodynamic therapy is a method that provides a reasonable alternative to other treatment modalities for patients with certain cancers, and in some cases may be the preferred treatment. The therapy implies the intravenous administration of a light-sensitive substance, the photosensitizer. The used sensitizer must absorb at long wavelength. For these purposes, the carbon dioxide laser, He-Ne and the argon laser are particularly suitable. In this study we evaluate in vitro the cytotoxic activity of three synthesized metallo-phthalocyanines with absorption bands in the red part of the spectrum: zinc-di-sulphonated phthalocyanine (ZnS₂Pc), zinc-tri-sulphonated phthalocyanine (ZnS₃Pc) and zinc-tetrasulphonated phthalocyanine (ZnS₄Pc). Some cellular models have been used in this paper, in order to optimize the conditions of this method, as we are presenting in this paper (LSR-SF(SR) - transplantable sarcoma in rat induced by Rous sarcoma virus strain Schmidt-Ruppin; LSCC-SF(Mc29) - transplantable chicken hepatoma induced by the myelocytomatosis virus Mc29, MCF-7 cell line (human breast adenocarcinoma) derived from a patient with metastatic breast cancer, 8-MG-BA - glioblastoma multiforme 8-MG-BA, K562 - lymphoblastic human cell line, LLC-WRC 256 - Walker epithelial carcinoma. Activation of these photosensitizers retained in the cancerous cells, by red light emitted from a He-Ne laser at &lgr;= 632.8 nm laser system, or by a diode laser emitting at 672 nm, produces a photochemical reaction that results in the selective destruction of tumor cells.

Static and dynamic light scattering are used to measure molecular parameters of collagen in solutions. Isoelectric point, coefficients of intermolecular interactions and molecular weight of type I collagen were determined by static light scattering. Using photon correlation spectroscopy we obtained the dependence of the translational diffusion coefficient as a function of pH and concentration of collagen in solutions.

Generally, the beam distribution in the tissue in interaction with a pulsed laser is defined by optical properties (effective scattering and absorption coefficient). In 2900 nm range, the effective scattering coefficient is much smaller than the absorption coefficient. An Er:YAG skin puncher is presented. Thermal action of a laser beam can be described as one of three types: hyperthermia, coagulation and volatilization, depending on the degree and the duration of tissue heating. We are interested in the volatilization process that means a loss of material. The various constituents of the tissue disappear in smoke at above 100⁰C in a relatively short time of around one tenth of a second. At the edges of the volatilization zone there is a region of coagulation necrosis. In presented case of an Er:YAG laser operating in a free generation mode, the mechanical effects can result from explosive vaporization. When the exposure time of the laser is lower than the characteristic time of the thermal diffusion in the tissue, it produces a thermal containment with an accumulation of heat without diffusion and an explosive vaporization of the target. The Er:YAG laser device has the pulse length of about 160 microseconds and four emitted energy levels. This device is used to punch the skin for blood sampling for different kinds of analysis. The front panel of the device has four keys to select the desired energy according to the skin type.

Molecular methods of diagnostics of widespread diseases including oncological pathology on the base static and dynamic laser light scattering in serum blood solution are testified. Rayleigh - Debye laser light scattering method are used to measure molecular parameters of blood serum. Dynamical parameters of macromolecules can be measured by photon correlation spectroscopy method. We obtained that the parameter of intermolecular interaction B for serum blood solution of oncological patients is considerably less then B for serum blood solution of healthy persons and in a number of cases has even a negative value. The effective mass of scattering particles in serum water solutions for samples of oncology diseases patients increase in comparison to control samples. As follows from our experimental results, there is the difference between dynamic molecular parameters for control samples and ones with oncological pathology.

Some dental ceramics were coated with a bioactive glass and resulted the formation of a stable and well bonded with the ceramic substrate thin layer. After immersion in a solution with ion concentrations similar to those of human blood plasma the development of hydroxy carbonate apatite layer on the surface of bioactive glass may be observed. The objective of this study was to investigate structural surface changes of bioactive glass, after exposure in a simulated body fluid for a different number of days. The roughness and topography of the hydroxyapatite surface were investigated by Confocal Scanning Laser Microscopy. The chemical composition was analyzed by Energy Dispersive Spectroscopy measurements.

Low Coherence Doppler Flowmetry (LCDF) measurement produces a signal, which frequency domain characteristics are in connection to the speed of the flow. In this study a LCDF measurement data of pulp flow in a capillary was analyzed with a simple Artificial Neural Network (ANN) method to estimate the flow speed. The accuracy of the method proved to be good, validation of the method resulted in absolute error of 14 ± 11 percentage units (mean±std) in flow speed estimation. The results of the study can be utilized in development of industrial pulp flow speed measurement instruments.

Different accuracy enhancement devices have been and are being developed in order to improve the manipulation accuracy of microsurgeons. The paper presents a one-degree-of-freedom proof of concept of a laser deflection system for acousto-optic compensation of hand tremor. A recording of physiological tremor acquired in vivo during vitreoretinal surgery in a rabbit model was used for the present experiment. When operating with a hand motion input tremor amplitude of 4 microns rms, the average overall canceling error is 0.8 microns rms. The results obtained demonstrate the general feasibility of the concept of tremor cancellation in laser surgery by using acousto-optic deflection.

In the present paper, a study concerning the in-vitro behaviour of Hydroxyapatite films obtained by Pulsed Laser Deposition technique on titanium under different conditions was performed. The structures were immersed in Hank's Solution for 21 days in accurately controlled environment conditions. Both film and immersion solution changes were analyzed by means of XRD, SEM, EDX and X-Ray fluorescence respectively. The obtained results point to an excellent behaviour of the obtained films as bioactive structures, recommending this type of covering for further analysis in view of its use in orthopedic and dental implantology.

A blue laser system for eye diseases (age related macular degeneration, sub-retinal neo-vascularisation in myopia and presumed ocular histoplasmosis syndrome - POHS) photo-dynamic therapy, based on riboflavin as photosensitive substance, has been developed. A CW diode laser at 445 nm wavelength was coupled through an opto-mechanical system to the viewing path of a bio-microscope. The laser beam power in the irradiated area is adjustable between 1 mW and 40 mW, in a spot of 3-5 mm diameter. The irradiation time can be programmed in the range of 1-19 minutes. Currently, the laser system is under clinic tests.

It will be shown that stability of the Henyey-Greenstein phase function gives a possibility to solve quickly a multiple-scattering light propagation problem with the use of the same a priori information about the interaction processes as in the primary problem definition.