This PDF file contains the front matter associated with SPIE Proceedings Volume 8770, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Laser-matter interaction is a unique and simple approach to structure materials or locally modify their properties at the micro and nanoscale level. Playing with the pulse duration and the laser wavelength, a broad range of materials and applications can be addressed. Direct irradiation of surfaces with laser beam through a standard optical beam setup allows an easy and fast structuring of these surfaces in the range of few micrometers. However, the irradiation of materials through an array of dielectric nanospheres provides a unique opportunity to break the diffraction limit and to realize structures in the range of hundred of nanometers. This simple, fast and low-cost near-field nanolithography technique is presented and discussed, as well as its great potential. The theoretical aspects of the near-field enhancement effects underneath the particles have been studied with a simple model based on the Mie theory. A commercial FDTD software has also been used to study the influence of the substrate and the surrounding media, on the energy profile of the photonic jet generated under the sphere. A specific study has been dedicated to the influence of the dispersion of the sphere diameter on the morphology of the ablation craters. This technique has been used for patterning bi-layer substrates. The process leads to the formation of a nanoporous membrane which has been used to realize an array of gold nanodots on silicon. We have also associated the Laser-Induced Forward Transfer (LIFT) process with the near-field nanolithography to print, in a single laser shot, an array of metallic nanobumps.

One of the most prominent nonlinear optical (NLO) material among A^IIIB^VI class of crystals is GaSe (gallium selenide), which is called by the scientific community in the world as an ″outstanding″ NLO material or material with an ″outstanding″ NLO properties. NLO properties of GaSe has been investigated first in 1972 and may be summurized as follows: i) very high NLO coefficient d₂₂ = 86 ± 17 pm/V; ii) wide transparency range of 0.7 - 18 μm with the linear absorption coefficient less than α ≤ 0.3 cm^-1; iii) high birefringence Δn = n_o - n_e ≈ 0.28 (λ = 1.06 μm); iv) nonlinearity in the phase-matched direction: d_eff = -d₂₂cosθsin3φ (e = e + o) (where θ is angle between the wave vector K of the pump radiation and the optical c-axis and φ-is the angle between the crystal planes XZ and KZ; e and o is for extraordinary and ordinary wave, respectively); v) phase-matching angle θ for the second harmonic generation (SHG) at the pump wavelength λ = 2.36 μm is θ = 18°40' ± 10'; θ = 10°10' ± 20' (λ = 5.3 μm); θ = 12°40' ± 20'; (λ = 10.6 μm); vi) high value of the two photon absorption (TPA) coefficient (≈10^-7 cm/W at λ = 1.06 μm; vii) high power threshold for optical damage of ≈ 2 x 107 W/cm² (λ = 0.694 μm, τ p = 25 ns), ≈ 3.5 x 107 W/cm² (λ = 1.06 μm, τ p = 10 ns), ≈ 25 MW/cm² (λ = 9.3 μm, f = 20 Hz), ≈ 100 W/cm² (λ = 0.8 μm). The NLO properties of A^III B^VI compounds and some of their solid solutions including perspectives for future research and applications in the THz range of spectra are considered in the present article with emphasis on GaSe bulk crystals as well as nanoparticles.

We investigate the non-linear absorption of 1.3 μm femtosecond laser pulses strongly focused inside silicon and fused silica. Through transmission diagnostics, multiphoton initiated energy deposition is clearly observed inside these two materials with nanojoules laser pulse energy when using 0.3 numerical aperture objective. For silicon, the non-linear interaction is strongly dependent on the focusing depth due to the presence of spherical aberration contrarily to fused silica. Below the surface, we find a difference of three orders of magnitude between the intensity thresholds for non-linear absorption at 1.3 μm wavelength inside the two tested materials due to the difference of number of photons required for non-linear absorption. By measuring the transmission of the ionizing pulses during multiple pulse irradiation, irreversible modifications of the material are monitored inside fused silica in accordance with previous studies at 800 nm. For similar laser energy deposition, the response of bulk silicon remains unchanged over more than twenty thousands pulses suggesting no irreversible modifications are initiated.

Theoretical analysis on the electromagnetic field properties in vicinity of noble metal nanostructures is presented. The study is done on the basis of numerical simulation using Finite Difference Time Domain approach. The systems under consideration are two- and three-dimensional arrays composed of gold or silver nanoparticles. The near field intensity distribution and its enhancement are calculated for structures with different characteristics – particle size, inter-particle distance, and at different conditions related to the incident irradiation – polarization, and geometry of excitation. This analysis is used for definition of some optimal parameters for such structures from the viewpoint of application in Surface Enhancement Raman Spectroscopy (SERS). It is shown that the manipulation of the geometry of excitation of the nanoparticle system could be used as a crucial parameter for improving the efficiency of the classical configuration in SERS. The predicted influences of the nanoparticle system properties on the Raman signal enhancement are confirmed experimentally.

Pulsed laser deposition was used together with a glancing angle deposition technique in order to produce suitable metal substrates for surface enhanced Raman scattering (SERS) applications. The surface morphology, crystallinity, optical properties, and enhancement factor of these substrates were investigated. Rodamine-6G was used as a SERS active molecule pumped at 785 nm. The Au nanorods with average lengths of 50 – 70 nm having diameter in the range of 10 – 20 nm exhibited a SERS enhancement factor of 10⁵. The as-prepared metal substrates were found to meet the criteria of a sensitive, uniform, and easily produced SERS substrate.

The composite nanostructures of double layer, multilayer and mosaic Ag/ZnO containing nano-sized particles have been produced by laser deposition and annealing procedures. The samples are investigated and the results indicated that laser annealing of Ag or Ag/ZnO layer is a feasible method to tune the optical properties of the nanostructures. Their morphology and optical absorption were investigated as a function of annealing regime and preparation procedure, leading to different silver arrangement. All annealed samples showed surface plasmon resonance (SPR) properties. The red shifted SPR was observed with the increase of the number of layers and is associated with the reduction of the interparticle distance. The absorption minimum of a mosaic samples broadens towards the longer wavelengths with reducing the thickness, due to the broader NPs size distribution. A ZnO excitonic feature visible in the spectra of double layer and multilayer structures disappear in the spectrum of a mosaic sample. The X-ray photoelectron spectroscopy was used to study the composition and chemical state of the double layer Ag/ZnO nanocomposites on the surface and in depth. The binding energy of Ag3d_5/2 shifts to the lower values compared to the pure metallic Ag due to the interaction between Ag and ZnO.

Thin TiO₂ films prepared by pulsed laser deposition (PLD) in the O₂ gas ambient using the bulk metal Ti or pressed TiO₂ powder targets were characterized using spectroscopic methods. Films were deposited on SiO₂ (001) and SiO₂ glass substrates heated up to 300 °C. The deposition process was investigated at laser fluencies from the range of 1 – 3 J/cm² and at oxygen pressure of 0.1 – 3.2 Pa. The μ-Raman and X-ray diffraction (XRD) spectra of the TiO₂ films revealed consistently both the anatase and rutile crystalline phases and a strong dependence of the phase content ratio on target material and deposition conditions. The range of crystallite size determined from XRD bandwidths was between (2-30) nm and (6-14) nm for anatase and rutile, respectively. The film thickness values between 0.74 and 1.65 μm depending on the deposition time were obtained from the transmittance and ellipsometric measurements. Values of the band gap of 3.5-4.1 eV derived from absorption spectra were higher than that of 3.2 eV corresponding to anatase and this difference was ascribed to the relatively small size of the anatase crystallites and presence of rutile, too. The SEM images of films produced under similar conditions from Ti and TiO₂ targets revealed porous structures. The highest anatase content was observed for films deposited by ablation of the TiO₂ target at moderate laser fluencies below 2 J/cm² and at oxygen pressure around 1.9 Pa.

In this paper we present a study of the photoinduced anisotropy in novel nanocomposite films of azopolymers doped with ZnO nanoparticles with different sizes – 50 and 100 nm. The photoresponse was evaluated by classical polarimetric setup with two crossed polarizers, recording laser with wavelength 473 nm and probe He-Ne laser. Our experimental results indicate that doping with both 50 and 100 nm sized particles improves the response time, however the smaller size nanoparticles provide increase of Δn_max with up to 40%, as the 100 nm particles reduce the saturated value of the birefringence, due to the higher scattering.

The object of the present work is investigation of the role of the actual conditions of illumination on the magnitude of photo-darkening for a specific material (the incident photon flux and the penetration depth of absorbed photons). It was found that the photo-induced changes in the thin As₂S₃ film depend on the light intensity and they are affected by heating of the material at higher laser intensities. The influence of the deposition rate on the film’s microstructure was investigated. The conditions for deposition of coatings with columnar structure were determined. The photo-induced changes of the optical properties of the obliquely deposited thin As_40-xGexS₆₀ films are examined. It was established that the microstructure of thin As-Ge-S films can a play significant role in photo-induced volume changes.

In this work the time-resolved Laser-Induced Plasma Spectroscopy (LIPS) is applied for investigation of samples containing calcium carbonate (CaCO₃) which represents a marker in the identification of historical stone and pigment materials. The relatively broad bands in the range of 547-560 nm and between 580 nm and 650 nm ascribed to the CaO molecular emission are clearly observed together with the collection of sharp peaks characteristic for the atomic Ca I and ionic Ca II lines. For suppressed oxide formation processes by means of recording the spectra in the N₂ environment a marked change in the time evolution of the CaO bands is observed and reaction kinetics different from that observed in air is concluded. This supports the CaO assignment and is confirmed by values of the decay time constant of 2,49 μs for nitrogen and 0,81μs for air derived from fitting of the experimental decay curves of the molecular emission. The case of CaO confirms that the time-resolved LIPS analysis provide useful supplementary data and contribute to reliability of the material identification.

Stretching of laser pulses allows to improve eximer laser output characteristics and to prolong a laser lifetime. Two methods of laser pumping are proposed in this paper for stretching of laser pulses. Using a special electric circuit in a pumping generator scheme allowed to double a pulse duration for a small ArF-laser. For the first time a pumping mode with periodically damping voltage across a discharge gap was successfully realized for increasing of KrF-laser pulse duration.

In this paper results on laser nanostructuring of Au/Ag and Au/Ni thin films are presented. The nanostructuring leads to formation of arrays of bimetallic nanoparticles. The fabrication of the these structures is made using a two step procedure. Initially, thin films are deposited on quartz substrates by classical pulsed laser deposition method. In order to produce Au/Ag or Au/Ni thin films, targets with two sections consist the different metals are used. Thin films with different concentrations of the two metals are obtained by changing the area of the different sections in the target. The as prepared films are then annealed by nanosecond laser pulses delivered by Nd:YAG laser system operated at λ = 355 nm. It is found that the laser annealing may lead to nanostructuring of the deposited films as at certain conditions decomposition into monolayers of nanoparticles with narrow size distribution is obtained. The performed EDX analyses indicate that the fabricated particles are composed by a bimetallic system of the basic metals used. The transmission spectra of the obtained structures show evidences of plasmon excitations. The bimetal nanostructures are covered with Rhodamine 6G and then tested as active substrates for Surface Enhanced Raman Spectroscopy (SERS).

In present work we report the analysis of thin films and targets from new stilbazolium dye E-4-(2-(4- hydroxynaphthalen-1-yl)vinyl)-1-octylquinolinium iodide (D1) deposited by Pulsed Laser Deposition (PLD) technique using high power UV TEA N2 laser. The thin films are deposited onto substrates – KBr, 316L SS alloy, optical glass and aluminum foil. The films were characterized by FTIR spectroscopy, bright field microscopy, fluorescence microscopy and atomic force microscopy (AFM) analysis. FTIR spectroscopic analysis of thin films and target material shows small differences between deposited films and native substance. The films are found to be homogeneous by AFM results and without any cracks and droplets on the surfaces. The present study demonstrates the ability of PLD technique to provide thin films from new stilbazolium dyes with good quality when they are applied as non-linear optical (NLO) organic materials on different type of substrates.

A novel approach for one-step synthesis of hybrid inorganic-organic nanocomposite coatings by new modification of Pulsed Laser Deposition technology called Laser Adaptive Ablation Deposition (LAAD) is presented. Hybrid nanocomposite coatings including Mg- Rapamycin and Mg- Desoximetasone were produced by UV TEA N₂ laser under low vacuum (0.1 Pa) and room temperature onto substrates from SS 316L, KCl and NaCl. The laser fluence for Mg alloy was 1, 8 J/cm² and for Desoximetasone 0,176 J/cm² and for Rapamycin 0,118 J/cm² were respectively. The threedimensional two-segmented single target was used to adapt the interaction of focused laser beam with inorganic and organic material. Magnesium alloy nanoparticles with sizes from 50 nm to 250 nm were obtained in organic matrices. The morphology of nanocomposites films were studied by Bright field / Fluorescence optical microscope and Scanning Electron Microscope (SEM). Fourier Transform Infrared (FTIR) spectroscopy measurements were applied in order to study the functional properties of organic component before and after the LAAD process. Energy Dispersive X-ray Spectroscopy (EDX) was used for identification of Mg alloy presence in hybrid nanocomposites coatings. The precise control of process parameters and particularly of the laser fluence adjustment enables transfer on materials with different physical chemical properties and one-step synthesis of complex inorganic- organic nanocomposites coatings.

Drug-eluting medical implants are active implants whose function is to create healing effects. The current requirements for active medical coatings for Drug-eluting medical implants are to be biocompatible, biodegradable, polymer free, mechanically stable and enable a controlled release of one or more drugs and defined degradation. This brings hybrid nanocomposite coatings into focus especially in the field of cardiovascular implants. We studied the properties of Metal (Mg alloy)-Paclitaxel coatings obtained by novel Laser Adaptive Ablation Deposition Technique (LAAD) onto cardiovascular stents from 316 LVM stainless steel material. The morphology and topology of coatings were studied by Bright field / Fluorescence optical microscope and Scanning Electron Microscope (SEM). Comparative measurements were made of the morphology and topology of hybrid, polymer free nanocomposite coatings deposited by LAAD and polymerdrug coatings deposited by classical spray technique. The coatings obtained by LAAD are homogeneous without damages and cracks. Metal nanoparticles with sizes from 40 nm to 230 nm were obtained in drug matrixes. Energy Dispersive X-ray Spectroscopy (EDX) was used for identification of metal nanoparticles presence in hybrid nanocomposites coatings. The new technology opens up possibilities to obtain new hybrid nanocomposite coatings with applications in medicine, pharmacy and biochemistry.

This paper presents the recent results of the TrapRad/Francium collaboration whose final aim is the measurement of the Atomic Parity Non-Conservation effect (APNC) in Francium atoms stored in a Magneto – Optical Trap (MOT) built at the Laboratori Nazionali di Legnaro (LNL) of the National Institute for Nuclear Physics (INFN). Current developments and new strategies to enhance the trapping efficiency of Francium isotopes and to detect new spectroscopic features are reported.

Atom-wall interactions play an unexpectedly important role in the atomic spectroscopy. J.L. Cojan was the first who observed and then interpreted the effects of the atom-wall interactions on the reflection spectra in the vicinity of the atomic spectral line. His observation was made on the mercury vapors of such a low concentration that the Doppler width was much larger than the homogeneous width of the atomic transition. Surprisingly, the width of the spectral line he observed in reflection was much smaller than the Doppler width. He pointed out that the atoms those leave the window posses a transient rather than the stationary polarization. This is the reason why their contribution to the reflected field differs from what was expected. M. Ducloy employed the tiny distortions of these narrow resonances in reflection spectra to measure for the first time the van der Waals constants in the excited atomic states. In our work we considered reflection from a narrow slice of atomic vapors and found a manifold of spectral line shapes depending on the width of the vapor slice that have nothing in common with the Fabri-Perot resonances. It was not until the invention of an Extremely Thin Cell (ETC) by D. Sarkisyan that the observation of these effects becomes possible in the optical domain. In the subsequent years ETC proved to be a very powerful tool of modern spectroscopy.

We show that a thermal vapor confined in a nanostructure is of spectroscopic interest. We perform reflection spectroscopy on a Cs vapour cell whose window is covered with a thin opal film (typically, 10 or 20 layers of ~ 1μm diameter spheres). Sub-Doppler structures appear in the optical spectrum in a purely linear regime of optical excitation and the signal is shown to originate from the interstitial regions of the opal. These narrow spectral structures, observable for a large range of oblique incidence angles (~ 30-50°), are an original feature associated to the 3-D vapor confinement. It remembers a Dicke narrowing, i.e. a Doppler broadening suppression when the atomic motion is sub-wavelength confined. This narrowing, commonly observed in the r.f. domain when a buffer gas ensures a collision confinement effect, had remained elusive in the optical frequency. Also, we describe preliminary experiments performed in a pump-probe technique, intended to elucidate the spatial origin of the narrow contribution. We finally discuss how our results allow envisioning micron-size references for optical frequency clocks, and high resolution spectroscopy of weak and hard-to-saturate molecular lines.

We report simultaneous observation of the N- and EIT- resonances formation using multi-region (MR) cell, which contains micrometric –thin region with the thickness L varying in the range of 1μm - 90μm. MR cell is filled with natural Rb and 150 Torr neon gas. To form N- and EIT- resonances in Λ-system, two lasers are used: the probe (with tunable frequency), and the coupling (with the fixed frequency) with λ ≈ 795 nm wavelength and 1MHz- line-width. Although, the best parameters of N-resonance could be obtained for a cell thickness about 1cm, the use of MR cell with the thickness 30-40 μm still allows to obtain a good contrast and a narrow line-width. The N-resonance demonstrates subnatural increase of the probe absorption and is formed when probe frequency ν_P1 is in resonance with the ⁸⁵Rb transition F_g=2 →5P_1/2, while for the coupling frequency the condition υ_C = υ_P1 + Δ₁ (Δ₁=3036 MHz) is fulfilled. The EITresonance is formed when ν_P2 scans the transition ⁸⁷Rb, F_g=2 →5P_1/2 and for the same coupling frequency the condition υC = υ_P2 +Δ₂ (Δ₂=6835 MHz) should fulfill. The frequency separation between N- and EIT-resonances is equal to Δ₂-Δ₁≈ 3.8 GHz. We also detected the low-frequency beating signal when the condition υ_C ≈ ν_P' is fulfilled, which allows a directly determine the coupling frequency υ_C. Splitting of N-resonance in the external longitudinal magnetic field into five components is detected. Possible applications are addressed.

We demonstrate a bi-chromatic pump-probe spectroscopy comparison between conventional cm-size Cs-filled cell and cells with thickness miniaturized down to 5.2 μm and 700 μm. In the 5.2 μm cell very-good-contrast enhancedtransparency- resonances were obtained that can be efficiently suppressed (controlled) with small about 31 MHz detuning of the pump laser frequency. The resonances do not move their spectral position with the pump frequency detuning like it is in the classical cm-size cells. Miniaturization down to 700 μm does not compromise the enhanced-transparencyresonances. In addition, at that level of miniaturization, the probe beam transmission spectra show as narrow features as in classical cm-size cells. Comparison of the obtained coherent resonances in 700 μm cell with that in 2.5 cm shows no broadening and both have resonance width limited by the emission linewidth of the used pump and probe lasers.

We present here the behavior of Electromagnetically Induced Transparency (EIT), Velocity Selective Optical Pumping (VSOP) resonances and Velocity Selective Excitation (VSE) resonances observed in Cs vapor confined in а micrometric optical cell (MC) with thickness L = 6λ, λ = 852nm. For comparison of behavior of VSE resonance another conventional optical cell with thickness L=2.5 cm is used. Cells are irradiated in orthogonal to their windows directions by probe beam scanned on the Fg = 4 → Fe= 3, 4, 5 set of transitions and pump beam fixed at the Fg = 3 → Fe = 4 transition, on the D2 line of Cs. The enhanced absorption (fluorescence) narrow VSOP resonance at the closed transition transforms into reduced absorption (fluorescence) one with small increase of atomic concentration or light intensity. A striking difference appears between the VSE resonance broadening in L = 6λ and conventional L = 2.5cm cells.

We report experimental and theoretical examinations of the peculiarities in Velocity Selective Optical Pumping (VSOP) resonance behavior at open and closed hyperfine transition spectra of Cs atoms (on the D2 line), confined in optical cell with thickness L = 6λ, where λ = 852 nm. For linear and circular polarizations of the irradiating light, open transitions exhibit reduced absorption (fluorescence) VSOP resonances whose contrast increases with atomic concentration and light intensity. However, in case of closed transition the situation is different, the enhanced absorption (fluorescence) VSOP resonance reverses its sign with the atomic concentration and light intensity. Theoretical analysis based on the density matrix formalism, taking into account the statistical tensors describing atomic population and longitudinal alignment, shows that the VSOP resonance sign reversal at the closed transition can be attributed to the efficiency reduction of population transfer by the spontaneous decay with atomic source temperature.

An investigation of the influence of light-induced atomic desorption (LIAD) on the transmission spectra from point of view of LIAD application for miniaturization of magneto-optical sensors and anti-relaxation coatings diagnostics is reported. With reduction of the dimensions of the cells, the amplitude of the signals decreases and it can be compensated by increasing the atomic density with temperature using special high temperature anti-relaxation coatings, or by LIAD. LIAD is a non-thermal process in which atoms adsorbed at a surface are released under illumination. It is investigated in various papers and has different applications - vapor density stabilization, MOT loading, surface nanostructuring etc. In this work the dependence of the shape of the absorption spectra on the laser power and blue light power is measured and analysis of the influence of different factors is done. All measurements are performed on the Rb D2 line in 3 different vacuum cells (uncoated, paraffin coated and SC-77 coated) with a 460 nm light emitting diode illumination. The good knowledge of the factors influencing the alkali atom spectra will be useful not only for the development of new alloptical sensors, but for study atom-dielectric surface interactions and development of new all-optical methods for surface and coating diagnostics.

The velocity distribution of atoms in a thermal gas is usually described through a Maxwell-Boltzman distribution of energy, and assumes isotropy. As a consequence, the probability for an atom to leave the surface under an azimuth angle θ should evolve as cos θ, in spite of the fact that there is no microscopic basis to justify such a law. The contribution of atoms moving at a grazing incidence towards or from the surface, i.e. atoms with a small normal velocity, here called "slow" atoms, reveals essential in the development of spectroscopic methods probing a dilute atomic vapor in the vicinity of a surface, enabling a sub-Doppler resolution under a normal incidence irradiation. The probability for such "slow" atoms may be reduced by surface roughness and atom-surface interaction. Here, we describe a method to observe and to count these slow atoms relying on a mechanical discrimination, through spatially separated pump and probe beams. We also report on our experimental progresses toward such a goal.

We have simulated spectra of weak probe absorption from one of two hyperfine structure (hfs) components of an atomic ground state, to a hfs manifold of an upper state. A stronger coupling transition was assumed to bind the other hfs component of the ground state with the same upper hfs manifold. The purpose of this simulation was to study the impact on the spectral features in probe absorption from the presence of a state to which the electric-dipole transition is allowed for coupling, but forbidden for probing. In relation to our other (experimental) work, we considered the D2-line transitions for ⁸⁵Rb. With coupling from the 5S_1/2(F=2) state, as in our experiment, the 5P_3/2(F'=1) state is coupled but not-probed from the 5S_1/2(F=3) state. In calculations we searched for steady-state solutions of optical Bloch equations assuming a 5-level model and RWA. The collisionless (cold) atoms were considered, and we assumed that decoherence was entirely due to natural decay and exciting lasers' linewidths. We investigated probe absorption spectra as a function of both coupling-field-induced Rabi frequency Ω_c, and coupling field detuning from the atomic resonances. The 5-level model spectra were compared with the corresponding spectra result of 4-level model calculations performed by omission of the 5P_3/2(F'=1) level. Even for small Ω_c values close to the natural linewidth, for some detunings a considerable influence of the 5P_3/2(F'=1) state on the spectra was observed which cannot be ignored in interpretations.

Pattern projection profilometry is a powerful tool to reconstruct three-dimensional (3D) surface of diffuse objects. A variety of pattern projection methods for 3D capture of objects is based on the generation of sinusoidal fringes. A sinusoidal phase grating under divergent coherent illumination with a point source produces high visibility and high spectral purity sinusoidal fringes in a large longitudinal region. In the present work we study the speckle suppression in the fringes by using a polychromatic light source. Such an approach makes use of the fact that the lateral fringe spacing does not depend on the wavelength of the illuminating light. The wavelength has an impact on the locations and the number of the Talbot planes, where self-imaging of the grating occurs, and on variation of the contrast and the frequency content of fringes along the distance from the grating. We analyze the multi-wavelength illumination of the grating by solving the Fresnel diffraction integral for a point source illumination in paraxial approximation. We verified the obtained results by experiments with a thin holographic grating recorded on a silver-halide holographic plate under illumination with a laser diode operating in single mode and multimode regimes.

The phenomenon of laser speckle can be used for detection and visualization of physical or biological activity in various objects (e.g. fruits, seeds, coatings) through statistical description of speckle dynamics. The paper presents the results of non-destructive monitoring of bread cooling by co-occurrence matrix and temporal structure function analysis of speckle patterns which have been recorded continuously within a few days. In total, 72960 and 39680 images were recorded and processed for two similar bread samples respectively. The experiments proved the expected steep decrease of activity related to the processes in the bread samples during the first several hours and revealed its oscillating character within the next few days. Characterization of activity over the bread sample surface was also obtained.

The interest in quantum dots fluorescence is connected with the problem of implementing new protective luminescence markers and labels. We studied the luminescence spectra of multi-sized quantum dots fluorescent labels and quantum dots fluorescent labels with different matrix pore size.

A compact and stable phase-stepping four-channels one-beam interferometer for full field displacement measurement in static and “real time” operation mode can be built through incorporation of a four-exposure reflection holographic optical element, which reconstructs four reference planes under illumination with two pairs of laser diodes positioned in the horizontal and the vertical planes. Such a multi-channel system is prone to misalignment errors and their estimation is crucial for its successful operation. The present work gives analysis of the error due to misalignment in illumination directions of the laser sources for the case of the out-of-plane (normal) displacements under double symmetrical illumination. First, analysis of the misalignment error observed in the experimental data is provided. Second, computer simulation of the system was made for estimation of the out-of-plane (normal) component of the displacement vector at each point of the tested object, and quantitative analysis of the errors caused by the misalignment was performed.

In the present work we study the effect of the length of fluorescent dye-filled micro-capillaries on the fluorescence spectra. Two types of micro-capillaries have been studied: a 100 μm inner diameter fused silica capillary with a transparent coating and one of the holes of a fiber optic glass ferrule with 125 μm inner diameter. The tubes were filled with solutions of Rhodamine 6G dissolved in ethanol and then in glycerin. Experimental data show that the maximum fluorescence and the largest spectral widths are observed for a sample length of about 0.25 mm for the used concentration. This results show that miniature tunable fiberized dye lasers can be developed using available standard micro-and fibre-optic components.

The aim of this study is investigation of gray component replacement (GCR) levels on reflectance spectrum for different overprints of the inks and color reproduction accuracy. The most commonly implemented method in practice for generation of achromatic composition is gray component replacement (GCR). The experiments in this study, have been performed in real production conditions with special test form generated by specialized software. The measuring of reflection spectrum of printed colors, gives a complete conception for the effect of different gray component replacement levels on color reproduction accuracy. For better data analyses and modeling of processes, we have calculated (converted) the CIEL^*a^*b^* color coordinates from the reflection spectra data. The assessment of color accuracy by using different GCR amount has been made by calculation of color difference ΔE^* ab. In addition for the specific printing conditions we have created ICC profiles with different GCR amounts. A comparison of the color gamuts has been performed. For a first time a methodology is implemented for examination and estimation of effect of GCR levels on color reproduction accuracy by studying a big number of colors in entire visible spectrum. Implementation in practice of the results achieved in this experiment, will lead to improved gray balance and better color accuracy. Another important effect of this research is reduction of financial costs of printing production by decreasing of ink consumption, indirect reduction of emissions during the manufacture of inks and facilitates the process of deinking during the recycling paper.

The paper presents investigation of the effect of different values of total area coverage of inks (TAC) on reflection spectra and color gamut. Total area coverage is a key factor for achieving of maximal volume of color gamut. The reflection spectra of color surfaces in entire visible spectrum are used for determination the effect of different values of TAC. For study the effect of TAC values on color gamut, we have used special test form that contains many components and test charts with over 1500 color patches. According to measurement of reflectance spectrum of test charts, we have compared the color gamuts with different values of TAC to obtain comprehensive information of all colors, which could be reproduced in the specific conditions. In addition we have converted the reflection spectra data to CIE L^*a^*b^* coordinates, and we have calculated the color difference ΔE^* _ab to determine the effect of TAC on color reproduction accuracy. The main goal of this study is development of methodology, which gives objective and analytical assessment, for determining the optimal value of total area coverage (TAC). A practical implementation of the correct and optimal value of total area coverage should improve the printability, better ink layers adhesion, biggest number of trapping values and reduce the quantity of process inks. The optimal value of the TAC determined by this new methodology helps to achieve a significant reduction of ink cost and a maximal color gamut volume, i.e. improve the quality of printed image and reduce financial costs.

In this work we present results of lidar remote sensing of aerosol layers in the atmosphere above Sofia during an episode of Sahara dust transport, 02-07 April, 2012. The investigations were made using two lidar systems, one equipped with a CuBr-vapor laser, emitting at wavelength 510.6 nm, and a second one - with Nd:YAG laser, at wavelengths 1064 nm and 532 nm. The results of lidar measurements are presented in terms of vertical atmospheric backscatter coefficient profiles and color maps of the aerosol stratification evolution. The involved into discussions ceilometer data (CHM 15k ceilometer) and satellite data from CALIPSO lidar, enhance the synergy of observations. Conclusion about atmospheric aerosol’s origin was made upon analyses of the information of weather-forecast maps provided by the Forecast system of Barcelona Supercomputing Centre, which are accessible via Internet. Additional information was provided by calculations of the backward air mass trajectories, using online software of NOAA about HYSPLIT model. The comparison between the data from the two lidars and the ceilometer showed similar behavior of aerosol layers development in the atmosphere above Sofia. All information about aerosol layers origin, their altitude above ground, persistence during lidar observations, confirmed the conclusion of observation of a long-distance Sahara dust transport beyond Balkans and Sofia. An interesting completion of CALIPSO lidar and ground based lidars results of measurement is presented in case of thick opaque cloud layer in the atmosphere, which slices the path of lidar sensing in both directions.

Results of remote measurements and characterization of biomass burning aerosols observed in the low troposphere over Sofia, Bulgaria, are presented and discussed. Measurements are accomplished by using two-wavelength elastic-scatter lidar, operating at 1064 nm and 532 nm. The aerosols are identified as to be consisted mainly of aged smoke of wildfires raging in the USA in the last third of July 2012. The long-range transport of the smoke aerosols, taking place from 24 July to 6 August 2012, is determined to be driven by the Northern hemisphere Polar jet stream. Spatial distribution of the observed aerosols is displayed by retrieving averaged vertical profiles of the aerosol backscatter coefficients. The temporal evolution of the aerosol layers during the period of measurement is shown by height-time coordinate colormaps of range-corrected lidar data. In order to characterize qualitatively the size range of the aerosol particles, the vertical profile of the backscatter-related Ǻngström exponent (BAE) is also retrieved. As an accent of the work, distributions of BAE corresponding to distinguished aerosol layers, as well as the overall one, are obtained and analyzed, representing qualitative counterparts of the real particle size distributions. In the case of the fire smoke layer, BAE values vary in the range 1.0-1.3, indicating processes of considerable aggregation of the finest particle size mods during the aging period. The reliability of the results and conclusions concerning the fire smoke BAE distributions and their evolution are indirectly validated by the obtained typical distribution ranges of the observed urban- and water aerosols.

A procedure to approach synthesized profile of lidar returns from hypothetical Rayleigh atmosphere to real lidar data is described in this work. The procedure is used in preprocessing of lidar data to determine the magnitude of background noise which should be removed before starting inversion processing (by Klett, or Fernald algorithm) to retrieve atmospheric backscatter or extinction profiles. Some applications of Rayleigh-fit procedure on real lidar data are discussed. After removing background noise from the lidar data, atmospheric backscatter profiles at two nearby laser wavelengths 510.6 nm and 578.2 nm (CuBr-vapor laser) are calculated. The ratio of these two backscatter profiles is used as justification of the results of Rayleigh-fit procedure for background noise removal.

Aerosols, clouds and aerosol-cloud interactions are recognized as the key factors influencing the climate. Clouds are the primary modulators of the Earth’s radiative budget. This paper focuses on the detection of high-altitude aerosol layers in the troposphere over mid-latitude lidar station in Sofia, Bulgaria. They are situated in the height-region 6 km÷16 km, with thickness in the range 0.2 km÷5 km and have varying optical characteristics. On the basis of the general utilized classification of the Cirrus clouds, high values of the calculated atmospheric backscatter coefficient and Angströmexponent estimation results we conclude that the registered strongly scattered aerosol layers are Cirrus clouds. Lidar measurements are performed with an aerosol lidar, equipped with Nd:YAG laser at wavelengths 532 nm and 1064 nm. Mainly, lidar data are presented in terms of vertical atmospheric backscatter coefficient profiles. We also include 2Dcolormap in height-time coordinates build on the basis of so called range corrected signals. It shows in general changes of the aerosol stratification over the lidar station during the measurement period. We employed HYSPLIT backward trajectories and DREAM forecasts to analyze the lidar profile outlines and characterize the events during which Cirrus cloud samples were observed. So was remarked that most of the results were obtained during Saharan dust long-way transport over the city of Sofia. Reported experimental examples are extracted from regular lidar investigations of the atmosphere within the frame of European project EARLINET.

The rms errors are investigated, analytically and by computer simulations, in the determination by Thomson scattering lidar of the electron temperature T_e and concentration n_e and the pressure in fusion plasmas, using fitting approach. Unlike previous such studies, we have taken into account the correlation between the fluctuations of the statistical estimates of the electron temperature and concentration. Analytical expressions of the errors as functions of the electron temperature are derived for the cases of log-linear and non-linear fitting procedures at a high measurement signal-tonoise ratio. Also performed are computer simulations of the nonlinear fitting procedure, which confirm the analytical results. It is shown that in the log-linear fitting procedure the correlation between the estimates of the electron temperature and concentration leads to an increase in the rms errors in determining the concentration and the pressure compared to the case of no correlation. In the non-linear fitting procedure, the same correlation increases the n_e– measurement error while influencing only slightly the error in the determination of the pressure.

In this paper we derive interference equations and present theoretical models for a variety of cases of interfering mode pairs: non-degenerate and non-degenerate; non-degenerate and degenerate as well as degenerate and degenerate even/odd LP modes assuming a Gaussian approximation and an identical polarization. For 2x2 fiber couplers of different coupling ratios and single mode at 1310/1550nm, we measure the coupling ratio in a few mode regime of operation at 650nm and record the pattern distributions. We find a very good correspondence between theoretical and experimental results which will be used for optimizing a CCD array used for the analysis of the external disturbances along an optical fiber intrusion sensor.

The mechanical properties of cells, as well as their dysfunction, have been implicated in many aspects of human physiology and patho-physiology. Hence, new biophysical techniques, as optical tweezers, are of great importance for biomechanical measurements in both cells and cell simulators (e.g. liposomes). Liposomes are used, among other applications, as drug delivery nanosystems in cancer therapy. In this work, experimental measurements of the optical forces exerted by line optical tweezers on trapped cells (erythrocytes) and liposomes, using the dielectrophoresis method for calibration, are presented. Folding and elongation of trapped red blood cells was observed, in the direction of the electric field of incident beam, while, upon removal of the optical trap, the red blood cells were observed to unfold to their original biconcave shape. By measuring the folding and unfolding times, membrane elasticity properties such as bending modulus were estimated. Shear and bending modulus of liposomes were also estimated by measuring the liposome deformations, induced by optical forces along the beam long axis. The optical force is quasi-linearly increased with the increase of liposome diameter. In the elasticity regime, when the laser was turned off, the liposome acquired gradually its initial shape without any hysteresis.

Photodynamic therapy (PDT) is a clinically approved non-invasive and curative procedure for different oncological and non-oncological applications. PDT is still under development due to several limitations which lead to partially successful photodynamic response. The crucial steps in PDT procedure are binding of the photosensitizer to outer cell membrane, its penetration and subcellular localization which envisage the target sites of reactive oxygen species generated during irradiation. Since the surrounding normal cells are also exposed to the photosensitizer and the ambient daylight can be harmful for healthy tissues after therapeutic light application, the challenging task in PDT research is to optimize the procedure in a way to reach tumor cell selectivity. The present study outlines the influence of a light exposure pre-treatment (prior therapeutic light) with specific wavelengths (365 nm and 635 nm) on the uptake, the localization and further re-localization of galactose-substituted Zn(II) phthalocyanines into MDA-MB-231 breast cancer cells. The in vitro photodynamic effect towards tumor cells was studied in comparison to the normal cell line Balb/c 3T3 (clone 31) after pre-irradiation with UV light (365 nm) and red LED (635 nm). The results suggest that the galactose functional groups of Zn(II) phthalocyanine and the harmless UV light at 365 nm favor the selective PDT response.

The ability to produce idealized cellular constructs is essential for understanding and controlling intercellular processes and ultimately for producing engineered tissue replacements. Preliminary results have been obtained on collagen modification by irradiation with single and multiple pulses of femtosecond laser with variable pulse duration. Irradiation of collagen thin film by single pulses of femtosecond duration results in creation of foam layer with micrometer thickness. The structure and thickness of the layer strongly depends on the number of the applied laser pulses. The surface properties of collagen thin films before and after Ti-sapphire irradiation with 800 nm were investigated by means of the technique Field Emission Scanning Electron Microscope (FESEM). Based on the FESEM results, it was possible to identify an energy density range as the ablation threshold for collagen thin films. The laser-induced foam formation was characterized over the intensity range 3 – 4.2x10¹¹ W/cm². The results of the field emission scanning electron microscopy, showed that by tailoring the laser pulse duration, improved the uniformity of the pore network. Examination of the interaction of ultra-short laser pulses with collagen films is useful for controlling the chemical and microstructural modification of the created foam layer.

The aim of this work is to investigate the effect of UV solid state laser radiation on intraocular lens (IOL) polymer surfaces as an alternative method to conventional surface shaping techniques for IOLs customization. Laser ablation experiments were performed on PMMA plates and commercially available hydrophobic and hydrophilic acrylic IOLs with the 5^th harmonic of a Q-switched Nd:YAG laser (λ=213 nm). Circular arrays of holes were drilled on the polymer surface, covering the centre and the peripheries of the IOL. The morphology of the ablated IOL surface was examined with a conventional optical microscope (Leitz GMBH Wetzlar) and with a scanning electron microscope (SEM, Fei - Innova Nanoscope) at various laser parameters. Quantitative measurements of ablation rates were performed with a contact profilometer (Dektak-150), in which a mechanical stylus scanned across the surface of gold-coated IOLs (after SEM imaging) to measure variationsF in surface height. Laser interaction with IOLs depends on optical and mechanical material properties, in addition to laser radiation parameters. The exact ablation mechanism is discussed. Some polymer materials, depending on their properties, are more susceptible to the photothermal mechanism than the photochemical one or vice versa. In summary, every IOL polymer exhibits specific attributes in its interaction with the 5^th harmonic of Nd:YAG laser.

The value of relative oxyhemoglobin concentration (saturation) in arterial (SаO₂) and venous blood (SvO₂) plays a significant role in the oxygen exchange in tissue and is used as criterion of delivery of oxygen adequate to the needs of tissue cells. Reduction of the volume of blood flows as well as reduction of oxygen concentration in arterial blood causes hypoxia - deficit of oxygen in tissue. One of the main mechanisms of elimination of hypoxia is based on compensation of the oxygen deficit by increasing the oxygen extraction from arterial blood, which leads to reduction of oxygen in the venous blood ¹. In this report two optical techniques for measurement of venous blood saturation are presented. The first one is based on the pulseoximetry with artificial mechanical modulation of the tissue volume and the second one on the spectrophotometry of human respiratory rhythm. Good correlation between the results obtained with both techniques is observed.

In recent years, lasers for optical trapping and micromanipulation of microscopic particles or cells and sub cellular structures, both in vivo and in vitro, have gained remarkable interest in biomedical research and applications. Although the principles and the mechanisms of pulsed laser ablation have been well described for macroscopic interventions, the microbeam operation under microscopic guidance necessitates further investigation. In this work, we present the research and development efforts towards a pulsed ultraviolet microbeam laser system, the design and realization efforts towards a near infrared laser trapping device and the results obtained on yeast cells and algae by the combined system. We investigated the optical dissection of the cells versus the presence of optical trapping forces and the presence of rhodamine dye. We characterized the optical ablation of the cell walls and resulting cavitation as plasma formation effects which create shock waves due to their occurrence only in nanosecond pulse irradiation mode. We estimated the minimum energy of the microbeam for optical dissection of yeast cell, under the influence of optical trapping forces, as lower as 3 μJ, while in the presence of rhodamine as lower as 2 μJ. Lastly, using the techniques of optical microsurgery we demonstrated the minimum energy value for sub cellular dissection on an algae cell equal to 27 μJ.

By using the developed by us approaches and instrumentation, we have obtained and presented series of systematized data, which are important for the use of the laser light in infrared (IR) spectral region. The obtained data include: 1) reflectivity of the human tooth dentin; 2) the spatial intensity distribution in the cross-section of the light beam penetrating the tooth’s dentin; 3) the absorbed and the diffused parts of the laser light that have been determined separately through combination of optical and calorimetric techniques. The last result is the most important because it permits to calculate the dentin absorption and scattering coefficients. The study is performed for the laser light at two easily generated wavelengths – 1.06 μm and 1.36 μm, emitted by the Nd:YAG laser that is well known, commercially available, economical and widely used in many laboratories and medical institutions. The study is made on the basis of fresh in-vitro teeth samples from the persons of Bulgaria, Sofia region.

We present the results from numerical simulation of the interaction of laser optical radiation with myoglobin (Mb) and oxymyoglobin (MbO₂) in muscle tissue. It is shown that the photodissociation of MbO₂ can modify the concentration of oxygen (O₂) in the muscle tissue directly at the irradiation zone. The criteria of the effectiveness of the combined effect of biological tissue oxygenation by two-wavelength laser radiation are considered.

The limitations of standard endoscopy for detection and evaluation of cancerous changes in gastrointestinal tract (GIT) are significant challenge and initiate development of new diagnostic modalities. Therefore many spectral and optical techniques are applied recently into the clinical practice for obtaining qualitatively and quantitatively new data from gastrointestinal neoplasia with different level of clinical applicability and diagnostic success. One of the most promising approaches is fluorescence detection using naturally existing fluorescent molecules or added fluorescent markers. Deltaaminolevulinic acid / protoporphyrin IX is applied for exogenous fluorescent tumor detection in the upper part of gastrointestinal tract. The 5-ALA is administered per os six hours before measurements at dose 20mg/kg weight. Highpower light-emitting diode at 405 nm is used as a source and the excitation light is passed through the light-guide of standard video-endoscopic system to obtain 2-D visualization. Both kinds of spectra – autofluorescence signals and protoporphyrin IX signal are recorded and stored using a fiber-optic microspectrometer, as in endoscopy instrumental channel a fiber is applied to return information about fluorescence signals. In such way 1-D detection and 2-D visualization of the lesions’ fluorescence are received. The results from in vivo detection show significant differentiation between normal and abnormal tissues in 1-D spectroscopic regime, but only moderate discrimination in 2-D imaging.

We review recent advances on the emission of tailored intense THz pulses from 2-color femtosecond laser filaments in gases. Extended tunability of the THz pulses is achieved via filamentation molding and the use of cleverly engineered metamaterials.

We investigate the nonlinear propagation of intense Bessel and Airy beams forming filaments in transparent media. We identify two propagation regimes separated by the relative importance of multiphoton absorption and self-focusing of the main Bessel or Airy lobe, due to the Kerr effect. We show that intense Bessel or Airy beams are reshaped into stationary nonlinear beams whose propagation is sustained by a continuous energy flux to the main lobe from its neighbors. The stationary propagation regime is obtained for Bessel cone angles exceeding a certain threshold; by focusing a Gaussian beam of sufficient power with an axicon. With respect to linear Bessel beams, stationary nonlinear Bessel beams exhibit ring compression and attenuation of contrast. For small cone angles, the nonlinear Bessel beams become unstable leading to an unsteady propagation regime. We demonstrate similar physics for intense Airy beam freely propagating in a Kerr medium: stationary nonlinear Airy beams are demonstrated in a planar geometry. These beams preserve the intensity profile and the transverse acceleration of the Airy peak. For powers in the main Airy lobe exceeding a certain threshold, this stationary propagation regime becomes unstable. In the 2-dimensional case, Airy beams with high powers in the main lobe reshape into a multifilamentary pattern induced by Kerr and multiphoton nonlinearities. The nucleation of new filaments and their interaction, affects the acceleration of the main Airy lobes.

Second harmonic generation microscopy has recently become an important tool for studying materials. In this article, we use a recently developed analytical method, for second-harmonic generation microscopy, to determine the point group symmetry of micro crystals of enantiomerically pure 1,1’-bi-2-naphtol.

We investigate the propagation in air of laser pulses in linear and nonlinear regime. The mathematical model presented in the paper describes the propagation of pulses with narrow-band spectrum, as well as the evolution of broad-band ones. It is shown that the diffraction of pulses with super-broad spectrum or pulses with a few cycles under the envelope is closer to wave type. For such pulses, a new physical mechanism of balance between non-paraxial diffraction and third order nonlinearity appears. We investigate in more detail the nonlinear third order polarization, taking into account the carrier to envelope phase. This additional phase transforms the third harmonic term to GHz terms, which start to generate radiation when the pulse duration reaches the femtosecond range.

We study by computer simulations the initial stage of bright background beam self-focusing initiated by the energy density redistribution due to the presence of optical vortex and/or ring dark wave. Local self-focusing Kerr nonlinear medium is considered. When a single ring dark wave is nested on the background, ring radius-to-width ratio Δ=2 promises up to 4 times peak intensity increase at a propagation distance of 2 dark beam diffraction lengths. Δ=6 seems adequate when flat-toped super-Gaussian beam is desired. Self-focusing in bright rings of different radii and even in two coaxial rings (at Δ=3) is observed when initially optical vortex and ring dark wave are simultaneously nested on the background. The detailed numerical analysis of the evolution of azimuthal perturbations confirmed the physical intuition that self-focusing rings of small radii suffer much less (when at all) from ring filamentation, because the spatial frequency of the perturbations on the inner rings appear higher than the critical one.

The emission spectra of the upconversion fluorescence of Er³⁺/Yb³⁺ co doped transparent oxyfluoride glass ceramics have been studied. The decay rates and excited states life times are measured at room temperature. The kinetic scheme is derived by measuring independently the life times of the excited states of both Er³⁺ and Yb³⁺ ions.

In the present work is being reviewed the evolution of one-dimensional femtosecond optical pulses with large spectral bandwidth in a single-mode fiber. The corresponding scalar nonlinear amplitude equation is used which describes the propagation of such pulses. It significantly differs from the ordinary Nonlinear Schrodinger equation. It appears that nonlinear term oscillates at a frequency proportional to the difference between the group and phase velocity of the pulse. This equation includes a term containing the first order of dispersion of the group velocity and the second derivatives of the coordinate z and the time t. It is assumed that the losses in the fiber are not significant and they will not be counted. An accurate analytical solution of this equation is found. It describes the evolution of soliton-like pulses in single-mode fiber. This soliton has different characteristics from those of the soliton obtained by solving the nonlinear Schrodinger equation.

In this work we study the evolution and interaction of semi-infinite dark beams carrying edge-screw phase dislocations in self-focusing and self-defocusing local Kerr nonlinear media aiming to find appropriate conditions to control the process of fusion/crossing the dark beams in a way suitable for probe-beam cross-switching. We show that a quasi-infinite vortex dipole (dipole much longer than the background beam) evolves into a one-dimensional dark spatial soliton with vanishing transverse velocity. Single semi-infinite fractional dipole develops snake instability near the dark beam end. Depending on their phase profiles, four parallel semi-infinite fractional vortex dipoles aligned to initially form two dark stripes can evolve into two different ‘cross-connects’ able to branch and route probe optical beams. Perpendicular probe beam propagation in the optically-induced guiding structures is modeled and analyzed with respect to the branching efficiency to respective virtual output channels for both self-focusing and self-defocusing conditions.

Experimental determination of electron temperature and electron density in the discharge period of nanosecond pulsed longitudinal discharges, exciting high-power Cu⁺ Ne-CuBr, He-Hg⁺ and He-Sr⁺ lasers, is carried out, using a simple method based on the time-resolved measurement of electrical discharge parameters, such as tube voltage and discharge current.

The polycrystalline LiNbO₃ films were grown by the ion-beam sputtering method on (001)Si substrates. Dielectric losses of the grown (001)Si-LiNbO₃ arises from conductivity of LiNbO³ films and increases when temperature rises. Ac conductivity of the studied heterostructures is described by the correlated-barrier hopping (CBH) model and it is induced by the jumps of charge carries between charge centers with concentration D = 3,5·10₂₂ m_-3.

The depth profile of the complex refractive index of silicon ion (Si⁺) implanted polymethylmethacrylate (PMMA) is studied, in particular PMMA implanted with Si⁺ ions accelerated to a relatively low energy of 50 keV and at a fluence of 3.2 × 10¹⁵ cm^-2. The ion-modified material with nano-clustered structure formed in the near(sub)surface layer of a thickness of about 100 nm is optically characterized by simulation based on reflection ellipsometry measurements at a wavelength of 632.8 nm (He-Ne laser). Being of importance for applications of ion-implanted PMMA in integrated optics, optoelectronics and optical communications, the effect of the index depth profile of Si⁺-implanted PMMA on the profile of the reflected laser beam due to laser-induced thermo-lensing in reflection is also analyzed upon illumination with a low power cw laser (wavelength 532 nm, optical power 10 – 50 mW).

Experiments of focusing coherent laser beams being diffracted on annular aperture are carried out in order to verify issues of a two-dimensional Fast Fourier Transform simulation of coherent pure (dark) annular flat beams done and published before. The beam pattern at focal plane (aka the far-field pattern) is a prominent central peak and faint concentrical rings around it. In the course of simulation we calculate the fraction of the central peak power to the whole power of beam that gives a notion of power spread within the focal spot. This fraction is a function of beam annularity i.e. ‘inside diameter /outside diameter’ ratio. The experimentally-measured dependence of the central peak power to the whole power of beam versus the annularity of pure annular laser beams was the major target of the report. The purpose was to verify experimentally the issues of our earlier simulation. We found that from the five experimental points four of them are within 16% error as to the simulated dependence which is tolerable in such a measurement.

We report for first time, to our best knowledge, experimental measurement of the degree of spatial coherence of a λ532 nm laser source (of a DPSS type - frequency doubled Nd:YVO4 laser) by reversal shear interferometers developed in our laboratories not so long. The degree of a full-sized non-apertured laser beam turned out to be quite high viz. up to 0.6 which is comparable with the degree of spatial coherence of λ510 nm copper lasers we had measured repeatedly for last decade.

On the base of our previous experience in the dual-color lasers we present our actual development - experimental realization, theory of a flash-lamp pumped Nd³⁺:YAG laser, that produces output at two desired (tunable) lines in the spectral range of 1μm -1.44 μm in free lasing and Q-switching operation. The laser operation avoids the wave’s competition effect for the two generations operating in two different parts of the active volume of an active single crystal and two closely disposed prism-selected resonators. Also, as we have shown, varying the partial laser volumes and the losses at each resonator in combination, it is possible to produce the generation at the two desired wavelengths with near equal output energy, peak power simultaneously or at desired time interval. We have found and treated some peculiarity of the formation of the generation, such as the actually used parts of the partial volumes.