This PDF file contains the front matter associated with SPIE Proceedings Volume 7747, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

This paper describes two topics of our recent studies on ultrafast strong-field interactions with atoms, molecules and solid surfaces. One is concerned with the high-order harmonic generation (HHG) from molecules nonadiabatically aligned with intense femtosecond (fs) laser pulses in a pump and probe experiment. The HHG is very sensitive to the molecular orbital and its spatial orientation with respect to the laser polarization. Experimental and theoretical studies demonstrate the characteristic properties of HHG from coherently rotating molecules. The other topic is the periodic nanostructure formation observed in fs laser ablation of dielectric materials. The major interest is in the ultrafast interaction process of nanostructuring on solid surfaces, for the purposes of potential applications of fs lasers to nanoprocessing. The experimental results have shown that enhanced near-field initiates the ablation of surface area much smaller than the laser wavelength and the origin of nanoscale periodicity can be attributed to the excitation of surface plasmon polaritons in the surface layer.

Catheters and medicals tubes are widely used to introduce pharmaceuticals and nutrients into arteries and veins, and to drain fluids or urine from urethra or the digestive organs. It is well known that illuminated TiO₂ photocatalysts can decompose most noxious or toxic organic compounds. We studied the properties of titanium dioxide layers created by pulsed laser deposition from pure titanium and titanium dioxide targets with the goal to develop urethral catheter using TiO2 coated plastic tube. To reach crystalline structure at low substrate temperatures the radio-frequency discharge between the target and the substrate was implemented. The crystalline structure of layers was determined by X-ray diffraction and Fourier Transform Infrared Spectroscopy. Morphology was studied by atomic force microscopy (AFM). Using RF discharge, mixture of anatase and rutile was found at substrate temperature of 90°C (which was reached only by RF discharge).

This preliminary work explores a technique for processing collagen thin films by femtosecond Ti:Sapphire laser ablation in order to provide a structured matrix support for cell growth and other tissue engineering applications. The laserinduced structuring of collagen easily yields an expanded micro foam material with interconnected pores and properties that mimics the native collagen-based extracellular matrix. The obtained structured matrix is formed by a cavitation and bubble growth mechanism. The surface properties of collagen thin films before and after Ti-sapphire irradiation with 800 nm were investigated by means of Field Emission Scanning Electron Microscope (FESEM) technique. FESEM analysis showed that with a single pulse of ultra-short laser radiation is capable of inducing morphological changes in the irradiated collagen films. The size of the observed features can be controlled by selection of laser fluence and pulse number. Collagen-based biomaterials were developed and explored for the purposes of tissue engineering. Biomaterials are expected to function as cell scaffolds to replace native collagen. The ultra-short laser ablation induced nanofoaming of biomaterials will improve currently available techniques. Artificial collagen nanofibers are increasingly significant in numerous tissue engineering applications and seem to be ideal scaffolds for cell growth and proliferation.

Lasers can provide a precious tool to conservation process due to their accuracy and the controlled energy they deliver, especially to fragile organic material such as paper. The current study concerns laser modification such as paper cleaning, initially of test papers artificially soiled and then of an original book of the early 20^th Century. The test objects were A4 copier paper, newspaper, and paper Whatman No.1056. During the experiments, ink of a pen, pencil and ink from a stamp was mechanically employed on each paper surface. Laser cleaning was applied using a Q-switched Nd:YAG operating at 532 nm and CO₂ laser at 10.6 μm for various fluences. The experimental results were presented by using optical microscopy. Eventually, laser cleaning of ink was performed to a book of 1934, by choosing the best conditions and parameters from cleaning the test samples, like Nd:YAG laser operating at 532 nm.

Recently we proposed a novel PLD arrangement, termed inverse pulsed laser deposition (IPLD). Being able to produce thin films of better surface morphology without any complex instrumentation, this method can represent an alternative to the traditional PLD technique while preserving versatility. Two configurations of this new target-substrate arrangement, namely static and co-rotating IPLD were developed. In the static IPLD configuration, the substrate is stationary with respect to the ablated spot; while in the co-rotating IPLD configuration the substrate is fixed to the target surface and rotates simultaneously with the target. Co-rotating IPLD proved to be capable of homogenizing the film thickness. Here we report a model calculation supported by experimental results to describe the radial growth rate variation of corotating IPLD films. To characterize the homogeneity of CNx, TiOx, and Ti co-rotating IPLD films, a thickness inhomogeneity index (TII) was introduced, which allows the comparison of thickness homogeneity between films of different lateral dimensions. The presented semi-analytical, semi-numerical model derives the radial variation of the growth rate of co-rotating IPLD films from the lateral growth rate distributions measured along the symmetry axes of the static IPLD films. The laterally averaged growth rate (LAGR) was used to describe how the ambient pressure affects thin film growth in the 0.5-50 Pa domain. As an example, the absolute error between the measured and calculated radial growth rate variation of CNx layers grown by co-rotating IPLD at 5 Pa, was less than 3%, while the LAGR was predicted with 20% accuracy.

μInterest to the narrow band gap semiconductors for example Pb_1-xCd_xSe is connected with problem of creation of new sources of IR radiation. Possibility of control of the properties of polycrystalline films of the lead chemical compounds by luminescent and Raman methods is considered.

Colloidal solutions of gold and silver nanoparticles (NPs) were prepared using a method pulsed laser ablation of target in liquid media. A gold and silver targets immersed in double distilled water are irradiated for 20 min by laser pulses with duration of 15 ns and repetition rate of 10 Hz. In order to investigate influences of laser wavelength and fluence on the particle size, shape and optical properties the experiments were preformed by using two different wavelength - the fundamental and the second harmonic (SH) (λ = 1064 and 532 nm, respectively) of a Nd:YAG laser system. Two different values of the laser fluence for each wavelength at the experimental conditions chosen were used and thus it was changed from several J/cm2 to tens of J/cm2. For characterization of the NPs shape and size distribution were used transmission electron microscope (TEM) and optical transmission spectroscopy in the near UV and in the visible region. Spherical shape of the nanoparticles at the low laser fluence and appearance of aggregation and building of nanowires at the SH and high laser fluence is seen. Dependence of the mean particle size at the SH on the laser fluence was established. The mean diameter of gold NPs became smaller with decrease in laser wavelength.

Modulated optical reflectance (MOR) technique is employed for defectoscopy and structural analysis of La_2/3Sr_1/3MnO₃(LSMO) ferromagnetic nanolayers. The optical reflectance is affected by the change of free charge carrier density due to periodic photothermal modulation described by Drude effect. A dual wavelength setup of a pulsed heating laser and a probe CW laser, whereas the laser focal spots are precisely aligned on the scanned sample surface, provides electrical signal proportional to the variation of optical reflectance at each measurement point. The probe beam is modulated selectively by reflection without interference by the substrate properties or external fields. It is shown theoretically and experimentally that MOR signal is proportional to the thermal derivative of magnetoresistance. The described contactless measurement may find important application in investigation of a range of new magnetoelectric devices.

Photomultiplier tubes are widely used detectors of low level light signals; however their performance is often limited, especially at long wavelengths. Input signals are reduced both by surface reflection and by transmission through the photocathode layer. Earlier methods of overcoming these weaknesses are summarized. New predictive modelling of the reflectivity and absorption reveals dependencies that are a function of angle of incidence, cathode thickness and polarization. Improvements on normal usage using extremely simple and low cost techniques are effective. These are demonstrated using retrofits that can improve the overall sensitivity of many types of photomultiplier. Examples include a simple external conical torch reflector, which has raised the efficiency of an S20 multialkali photocathode by between 20 to 10% across the blue to red spectral range. A second example, of a semi-cylindrical glass coupler, improved the absorption efficiency by exploiting 60 degree, rather than normal incidence of the light. Enhancements are up to 500% at longer wavelengths. Such gains are particularly valuable as this is the region of lowest quantum efficiency for the standard operation of the tubes.

Laser spectroscopy experiments are reported on rubidium atoms by using two or three external cavity diode lasers to study multiple resonance transitions in Λ- and V-type systems as well as on (Λ+V)-type system. Electromagnetically induced transparency (EIT) peaks having sub-natural line-widths are found on the Doppler broadened transmission backgrounds with velocity selective enhanced absorption dips. In the presence of a pump laser, probe spectrum shows enhancement of EIT signal by tuning the control laser frequency when the Λ- and V-type EIT signals are made to overlap. Theoretical analysis is carried out by solving the optical Bloch equations for five-level atomic model under Λ configuration. With the numerically simulated spectra, variation of EIT transmission peak with ground state decay rate and excited state spontaneous decay rate are investigated. Effect of pump Rabi frequency on the transmission peak is also shown.

Comparison of absorption and fluorescence in a nano-cell containing Rb vapor with other Rb nano-cells with addition of neon gas is presented. It is shown that the effect of collapse and revival of Dicke-type narrowing occurs for Rb nanocells containing N2 as buffer gas under 6 and 20 Torr pressure for the thickness L = λ /2 and L = where λ is the resonant λ, laser wavelength 794 nm (D1 line). Particularly for 6 Torr the line-width of the transmission spectrum for the thickness L =λ/2 is 2 times narrower than that for L = λ. For an ordinary Rb cell with L = 0.1 - 10 cm with addition of buffer gas, the velocity selective optical pumping/saturation (VSOP) resonances in saturated absorption spectra are fully suppressed when the buffer gas pressure > 0.5 Torr. A spectacular difference is that for L = λ, VSOP resonances located at the atomic transitions are still observable even when Ne pressure is ≥ 6 Torr. Narrowband fluorescence spectra of a nano-cell with L = λ/2 can be used as a convenient tool for online buffer gas pressure monitoring for the conditions when ordinary pressure gauges are unusable. Comparison of electromagnetically induced transparency (EIT) effect in a nano-cell filled with pure (without a buffer gas) Rb with another nano-cell, where buffer gas nitrogen is added, is presented. The use of N2 gas inside Rb nano-cells strongly extends the range of coupling laser detunings in which it is still possible to form EIT resonance.

We present in this paper recent results on Light - Induced Atom Desorption (LIAD) in sealed and open coated cells. LIAD is defined via the description of an experiment on rubidium atoms stored in a dry - film coated cell, where a few milliwatts of even non coherent and non resonant light are able to increase the alkali atomic density for more than one order of magnitude. Modeling of the effect is given. New features become relevant in the case of LIAD in porous glasses: in fact, although the photodesorption efficiency per unit area in bare glass is much lower, photoatomic sources can be prepared, due to the huge inner surface of porous samples. We applied LIAD from organic coatings to the stabilization of alkali densities out of equilibrium: sodium case is here discussed. Finally, we report on fully original, preliminary measurements of rubidium Magneto - Optical Trap loading via LIAD from a dry - film coated cell.

We present Hanle electromagnetically induced transparency (EIT) resonances obtained from the outer parts of the Gaussian laser beam. The signal from the outer parts only was obtained by placing circular opaque masks of different diameters in the center of the laser beam just in front of the detector. The Hanle EIT resonances obtained in that way are narrower and for high laser intensities even more contrasted. Suggested explanation for the line narrowing is based on lower power broadening in the wings of the Gaussian laser beam as well as on the traversing of the coherently prepared atoms through the beam. The resonance contrast to linewidth ratio, when the central part of the beam is blocked, is higher or equal to the ratio obtained when the whole laser beam is detected, for all laser intensities used in the experiment. Due to high ratio of contrast and linewidth, resonances obtained in proposed way could be useful in frequency metrology and magnetometry.

In this paper we present our spectroscopic studies on Coherent Population Trapping (CPT) in micro-fabricated Caesium cells and our evaluation of its application in miniature atomic frequency standards (atomic clocks). We observe the CPT signal on the Cs D1-line by coupling two hyperfine ground-state Zeeman sub-levels to a common excited state using two coherent electromagnetic fields created with a modulated DFB laser. Contrarily to double resonance, CPT does not require any microwave cavity, which should facilitate the miniaturization of a future atomic clock device. We study and report here on the light shift phenomena at different cell temperatures and laser wavelength. We also present resonance shifts due to cell temperature variations and clock frequency stability measurements. To the best of our knowledge, this article is the first report on light shift with Cs D1 line in a CPT vapour-cell atomic clock.

The fast development of CPT applications and the need of good magnetooptical sensors result in an increased interest in the Coherent Population Trapping (CPT) resonances and the processes that determine their shape. In this work the shape and width of the CPT resonances are investigated in two different paraffin-coated Rb vapor cells from point of view of understanding the processes influencing the shape of the resonances and building of miniature and sensitive detector. The dependence of the shape of the resonances on the laser power is measured. Narrow resonances on three hyperfine transitions of the D1 ⁸⁷Rb line are registered. For explanation of the bright structure in the resonance shapes at low laser powers analysis of the influence of different processes is made.

In this communication we report the first observation of a narrow, reduced fluorescence dip in the profile of the completely closed transition on the D₂ line of ¹³³Cs vapor, confined in Extremely Thin Cell with nanometric thickness. The theoretical modeling of the fluorescence based on the Optical Bloch Equation for two-level atomic system, shows that the narrow dip in the fluorescence could be attributed to a very small loss in the excitation process of the examined degenerate transition. While the population in the atomic system remains constant, the depolarization of the excited level can lead to some loss in the efficiency of the optical transition excitation. Under the conditions of our experiment, no dip in the fluorescence is registered for the cell thickness where a well pronounced Dicke peak in the absorption takes place. For the cells with nanometric thickness, the previous investigations demonstrate that the fluorescence profiles of optical transitions differ significantly from the absorption profiles. However, our experiment shows that some traces of the coherent Dicke process contributing to the absorption line still remain in the fluorescence, which is result of non-coherent processes.

Electromagnetically induced transparency (EIT) and Autler-Townes (A-T) effect were studied under conditions of strong coupling of the hyperfine manifold 5P_3/2 (F') with the 5S _1/2 (F=2) ground state of cold 85Rb atoms in MOT. Transmission spectra of a weak probe beam, at the frequency scanned in the vicinity of the 5S_1/2(F=3)→5P3/2(F') resonances were registered at various frequency settings of the coupling beam. The spectra were interpreted by applying optical Bloch equations. As a starting point, a 5-level model, accounting for F=2, 3 and F'=1, 2, 3 states was assumed (the noncoupled state F'=4 being neglected, but the F'=1 state, coupled but not directly probed, included, as its presence was found to be imprinted in the spectra). Such a model alone does not reproduce all the spectral features observed. Therefore we have considered the existence of the polarized light induced transitions between Zeeman substates, involving (F'=2, m') and (F'=3, m') upper states. In order to indirectly account for the m→m' absorption transitions to the non-coupled m' states, and to the pairs of states with incomplete coupling, we have complemented the results of the 5-level model with the ones of its reduced versions. Satisfactory agreement of the positions of respective modeled and experimental spectral peaks was achieved.

An analysis is presented of the high resolution Autler-Townes spectra in a pump-probe cascade 5S_1/2(F=3)→5P_3/2(F'=4) → 5D_5/2(F") experiment in a working ⁸⁵Rb-MOT. It is shown that despite the complex nature of the spatially varying interactions of individual atoms with MOT fields, the probed region of the atomic cloud in MOT can be characterized by effective Rabi frequency, at least for the customary used range of detuning and intensity of the trapping field. This effective value which relates to the averaged atom interactions, is directly dependent on the trapping laser power and practically does not depend of detuning. The applied procedure is based on predictions of a three-level model. The procedure can be used as a method for determination of the effective Rabi frequency experienced by atoms in MOT, and it also indicates applicability limits of the approach for a given MOT implementation.

The paper presents a holographic optical element (HOE) for a phase-stepping digital electronic speckle pattern interferometry with double symmetrical illumination of the object both in vertical and horizontal planes for precision full-field displacement measurement of objects under loading . More specifically, the proposed HOE allows for simultaneous reconstruction of four virtual and parallel to the HOE surface reference planes for off-axis illumination with two pairs of diode lasers emitting at two different wavelengths. In this way we transform a two-beam interferometer into a multiple beam interferometer with four separate channels. The HOE is constructed as a sandwich structure of two reflection (Denisuyk type) holograms of a diffuse metal screen illuminated at 30 degrees to the normal. Each of the holograms comprises two holographic reflection records made successively on a single holographic plate. Recording is performed in the visible part of the spectrum, and through additional chemical treatment the spectral maximum of the developed holograms is shifted into the IR region to achieve correct reconstruction for illumination at 790 nm and 830 nm. Super high resolution silver halide emulsion with resolution over 6000 line/mm is used for recording of holograms. The reconstructed four reference beams interfere with the beam reflected from the object, thus forming four independent optical channels for two laser beams at 790 nm with S and P polarizations, as well as for two S and P polarized beams at 830 nm.

Coherent illumination of a diffuse object yields a randomly varying interference pattern, which changes over time at any modification of the object. This phenomenon can be used for detection and visualization of physical or biological activity in various objects (e.g. fruits, seeds, coatings) through statistical description of laser speckle dynamics. The present report aims at non-destructive full-field evaluation of bread by spatial-temporal characterization of laser speckle. The main purpose of the conducted experiments was to prove the ability of the dynamic speckle method to indicate activity within the studied bread samples. In the set-up for acquisition and storage of dynamic speckle patterns an expanded beam from a DPSS laser (532 nm and 100mW) illuminated the sample through a ground glass diffuser. A CCD camera, adjusted to focus the sample, recorded regularly a sequence of images (8 bits and 780 x 582 squared pixels, sized 8.1 × 8.1 μm) at sampling frequency 0.25 Hz. A temporal structure function was calculated to evaluate activity of the bread samples in time using the full images in the sequence. In total, 7 samples of two types of bread were monitored during a chemical and physical process of bread's staling. Segmentation of images into matrixes of isometric fragments was also utilized. The results proved the potential of dynamic speckle as effective means for monitoring the process of bread staling and ability of this approach to differentiate between different types of bread.

The electron-hole states in the molecular beam epitaxy grown GaAs/In0.5Ga0.5As quantum well, placed into space charge region, have been studied by photoreflectance spectroscopy. The energies of electrons and holes have been calculated in the envelope function model including deformation-induced changes in the band structure of quantum well. It is shown that the best accordance between experimental and theoretical data is achieved in the case of band offset Q = ;Ec/;Ev = 0.62/0.38 at GaAs/In0.5Ga0.5As heterojunction. The most intense transition is observed in this case between 1 electron and 1 light hole energy. This fact is connected with the indium segregation in the GaAs/In0.5Ga0.5Asquantum well. In this case one could obtain the flat bands in the quantum well and realize the parity selection rules for the rectangular potential. The model of the nonsymmetrical rectangular potential is applied to describe the energies of electronic levels in the quantum well. The segregation parameters have been calculated from the segregation-induced shift of the energies of interband transitions in the GaAs/In0.5Ga0.5As quantum well.

An interferometric phase-shifting photoelasticity is an effective approach to separate the stress components in engineering structures with mechanical and geometrical complexity, especially when the photoelastic coating method is applied. A series of photoelastic fringe patterns are recorded with a circular polariscope to obtain the phase map proportional to the difference of the principal stresses in the tested specimen. In addition, holographic recording of fringe patterns is applied for retrieval of isopachic fringes which give the sum of the principal stresses. The easiest way to perform a combined polariscopic and holographic measurement for full-field stress analysis is to use a laser light source. However, the speckle noise at coherent illumination could severely violate the requirement for high signal-tonoise ratio in the recorded patterns. Thus, task-oriented preprocessing and denoising algorithms become mandatory for accurate phase estimation and unwrapping. Development of such algorithms is impossible without an adequate signaland- noise model, which is the goal of this paper. The paper presents simulation of an interferometric photoelastic measurement that is based on calculation of the complex amplitudes at the output of a Mach-Zender interferometer combined with a circular polariscope. The model is used for simulation of speckled fringe patterns for an epoxy disk under concentrated diametral compression. Comparison with experimental fringe patterns which have been recorded at pure tensile load for PhotoStress coated samples with a hole as a mechanical stress concentrator is also included.

We present the results of an experimental study of Coherent Population Trapping (CPT) in potassium, obtained by means of modulation of laser light amplitude with kHz frequency. The radiation from an external cavity diode laser, matching the D₁ line of K, is modulated by an acousto-optical modulator. In the cell containing buffer gas, the CPT resonance width is reduced more than three orders of magnitude as compared to the cell containing pure potassium vapor. In K this resonance narrowing occurs with high resonance contrast; such behavior is not observed in buffered cells containing Rb or Cs, where the optical pumping to the non-interacting with the light ground level is very effective and depletes the population of the working ground Zeeman sublevels. The narrow CPT resonance of reduced fluorescence transforms to the one of enhanced fluorescence with the cell temperature rising. The transformed resonance exhibits higher contrast and lower width than those of the reduced fluorescence resonance. Hence, beside its scientific importance the resonance sign reversal can be used for the improvement of the CPT resonance parameters.

This paper and corresponding seminar given on 20 September 2010 at the 16th International School for Quantum Electronics in Nesebar, Bulgaria, will describe the key hardware aspects of the Raman-shifted Eye-safe Aerosol Lidar (REAL) and recent advances in extracting two-component wind vector fields from the images it produces. The REAL is an eye-safe, ground-based, scanning, elastic aerosol backscatter lidar operating at 1.54 microns wavelength. Operation at this wavelength offers several advantages compared to other laser wavelengths including: (1) maximum eye-safety, (2) invisible beam, (3) superior performance photodetectors compared with those used at longer wavelengths, (4) low atmospheric molecular scattering when compared with operation at shorter wavelengths, (5) good aerosol backscattering, (6) atmospheric transparency, and (7) availability of optical and photonic components used in the modern telecommunations industry. A key issue for creating a high-performance direct-detection lidar at 1.5 microns is the use of InGaAs avalanche photodetectors that have active areas of at most 200 microns in diameter. The small active area imposes a maximum limitation on the field-of-view of the receiver (about 0.54 mrad full-angle for REAL). As a result, a key requirement is a transmitter that can produce a pulsed (>10 Hz) beam with low divergence (<0.25 mrad full-angle), high pulse-energy (>150 mJ), and short pulse-duration (<10 ns). The REAL achieves this by use of a commercially-available flashlamp-pumped Nd:YAG laser and a custom high-pressure methane gas cell for wavelength shifting via stimulated Raman scattering. The atmospheric aerosol features in the images that REAL produces can be tracked to infer horizontal wind vectors. The method of tracking macroscopic aerosol features has an advantage over Doppler lidars in that two components of motion can be sensed. (Doppler lidars can sense only the radial component of flow.) Two-component velocity estimation is done by computing two-dimensional cross-correlation functions (CCFs) and noting the displacement of the peak of the CCF with respect to the origin. Motion vectors derived from this method are compared with coincident sonic anemometer measurements at 1.6 km range. Preliminary results indicate the method performs best when the atmosphere is stable with light winds.

Aerosols and clouds have significant impact on global climate. In this work experimental results from regular lidar investigations of tropospheric aerosols and clouds are presented. Examples of calculated atmospheric backscatter coefficient profiles extracted from four years lidar dataset collected in the city of Sofia (Bulgaria) are offered and analyzed. They illustrate remote detection of aerosol fields and clouds at different altitudes including Saharan dust intrusion over the city and highly situated cirrus clouds. The mass temporal evolution and the spatial distribution of registered atmospheric layers are visualized by 2D-colormaps in height-time coordinates. The ground-based measurements are performed with a newly developed lidar in the Laser Radar Lab, Institute of Electronics, Bulgarian Academy of Sciences. The good parameters of all the laser, telescope, photo-receiving modules and software make it possible the developed lidar to be utilized for carrying out fast and accurate remote atmospheric measurements with high spatial and temporal resolution.

Second half of April and beginning of May 2010, were remembered by a big trouble in the airplane traffic over Europe, due to the eruption of the volcano Eyjafjallajokull in Iceland. The volcanic ash propagated quickly in the atmosphere traversing most of European countries. Its trajectories were forecasted and observed by many meteorological stations to prevent unintended consequences of the airplane transport The lidar stations of the European lidar network EARLYNET-ASOS [1] performed a large campaign of measurements to identify the position, the height above ground level (AGL) and the thickness of the volcanic aerosols transported in the air. It was an appreciable work to update meteorological forecasting and to study volcanic distribution directions, power and sedimentation in continental scale. As partner in EARLINET-ASOS project, Sofia lidar station performed measurements of the atmospheric aerosol profiling which results where quickly presented on the WEB-page of the Institute of Electronics - BAS [2]. A more detailed discussion and comments concerning only Sofia-lidar measurements of the volcanic dust layers observed over the town we present in this work.

In this work we present an analysis of the response of a compact, simple and inexpensive optoelectronic sensor system intended to detect spectral shifts of a long-period fiber grating (LPG). The system makes use of a diffraction grating and a couple of receiving optical fibers that pick up signals at two different wavelengths. This differential detection system provides the same useful information from an LPG-based sensor as with a conventional laboratory system using optical spectrum analyzers for monitoring the minimum offset of LPG. The design of the fiber detection pair as a function of the parameters of the dispersion grating, the pick-up fiber and the LPG parameters, is presented in detail. Simulation of the detection system responses is presented using real from spectral shifts in nano-coated LPGs caused by the evaporation of various liquids such as water, ethanol and acetone, which are examples of corrosive, flammable and hazardous substances. Fiber optic sensors with similar detection can find applications in structural health monitoring for moisture detection, monitoring the spillage of toxic and flammable substances in industry etc.

The potentialities are investigated, by statistical modeling, of deconvolution techniques for high-resolution restoration of electron temperature profiles in fusion plasma reactors like Joint European Torus (JET) measured by Thomson scattering lidar using the center-of-mass wavelength approach. The sensing laser pulse shape and the receiving-system response function are assumed to be exponentially-shaped. The plasma light background influence is taken into account as well as the Poisson fluctuations of the photoelectron number after the photocathode enhanced in the process of cascade multiplying in the employed microchannel photomultiplier tube. It is shown that the Fourier-deconvolution of the measured long-pulse (lidar-response-convolved) lidar profiles, at relatively high and low signal-to-noise ratios, ensures a higher accuracy of recovering the electron temperature profiles with three times higher range resolution compared to the case without deconvolution. The final resolution scale is determined by the width of the window of an optimum monotone sharp-cutoff digital noise-suppressing (noise-controlling) filter applied to the measured lidar profiles.

Time-resolved measurements of the distribution and dynamics of aerosols in atmospheric layers over complex terrains differing in their orographic characteristics, performed at two or more wavelengths, offer an opportunity for revealing peculiarities and evolution of different aerosol fractions, in view of their importance for local climate, air circulations, rainfalls, ecology, etc. In this work, an investigation of dynamical characteristics of the atmospheric aerosol over adjacent city-, plain-, and mountain zone is reported. Measurements are carried out at two wavelengths (1064 nm and 532 nm) by using two channels of an aerosol lidar based on a powerful Nd:YAG laser. Representative results of lidar measurements over the zone of investigation are described, obtained during a winter day. Range profiles of the atmospheric backscattering coefficient, range-corrected lidar signal, normalized standard deviation, and backscattering-related Angstrom exponent are presented and analysed, as averaged over the time and/or range of measurements, as well as in their temporal evolution. Taking advantage of the two-wavelength lidar sounding, statistical quasi-quantitative analysis of the spatial density distribution and temporal dynamics of both the fine-mode and coarse-mode aerosol fractions is accomplished in orographic aspect. Domains of most intensive dynamics are determined for the two aerosol fractions. Obtained results show the strong impact of the heterogenic orography on the atmospheric dynamics, as well as the ability of the utilised lidar system for investigating the distribution and dynamics of aerosol fractions over large areas with high spatial and temporal resolution.

The use of intraocular lenses (IOL) is the most promising method for restoring excellent vision in cataract surgery. In addition, multifocal intraocular lenses for good distant and near vision are investigated. Several new materials, techniques and patterns are studied for the formation and etching of intraocular lenses in order to improve their optical properties and reduce the diffractive aberrations. As pulsed laser ablation is well established as a universal tool for surface processing of organic polymer materials, this study was focused in using laser ablation with short and ultra short laser pulses for surface modification of PMMA and intraocular lenses, instead of using other conventional techniques. The main advantage of using very short laser pulses, e.g. of ns, ps or fs duration, is that heat diffusion into the polymer material is negligible. As a result high precision patterning of the sample, without thermal damage of the surroundings, becomes possible. In this study, laser ablation was performed using commercially available hydrophobic acrylic IOLs, hydrophilic acrylic IOLs, and PMMA IOLs, with various diopters. We investigated the ablation efficiency and the phenomenology of the etched patterns by testing the ablation rate, versus laser energy fluence, at several wavelengths and the surface modification with atomic force microscopy (AFM), or scanning electron microscopy (SEM). The irradiated polymers have different optical properties, at the applied wavelengths, and therefore, present different ablation behaviour and morphology of the laser ablated crater walls and surrounding surfaces. The experimental results, some theoretical assumptions for mathematical modeling of the relevant ablation mechanisms are discussed.

In this invited paper we focus on the discussion of two recent unique applications of the Finite-Difference Time-Domain (FDTD) simulation method to the design and modeling of advanced nano- and bio-photonic problems. We will first discuss the application of a traditional formulation of the FDTD approach to the modeling of sub-wavelength photonics structures. Next, a modified total/scattered field FDTD approach will be applied to the modeling of biophotonics applications including Optical Phase Contrast Microscope (OPCM) imaging of cells containing gold nanoparticles (NPs) as well as its potential application as a modality for in vivo flow cytometry configurations. The discussion of the results shows that the specifics of optical wave phenomena at the nano-scale opens the opportunity for the FDTD approach to address new application areas with a significant research potential.

speed, fibre optic communication or cost per CCD pixel often follow a smooth logarithmic improvement per year. This seems desirable, but progress is frequently only achievable by introduction of new software, different types of storage media or new operating conditions. Consequently technologies become outdated. For transient information this is unimportant, but for long term storage and archiving of information, images, photographs etc, there is an inevitable loss of earlier records. This is not a new phenomenon as even information on stone or clay tablets has decayed or been lost, either by physical decay of storage materials or loss of understanding because of changing language and cultural nuances. Examples emphasise how technological progress has speeded up information decay and loss. Since logarithmic "laws" have been proposed to describe the trends for electronic improvements, one may consider if equivalent trends apply to information loss. It appears that one may propose that the product of three factors is roughly constant. These are the time needed to write the new information; the quantity of information stored, and the average survival time of the information before the storage medium has decayed or is obsolete. The reality of such a "law" is that, whereas we may currently have records and photographs from many earlier generations, our rapidly stored electronic data may be lost within a few years, and certainly will have vanished in a readable form for the next generation.

New methods of control of tooth bleaching stages through simultaneous measurements of a reflected light and a fluorescence signal are proposed. It is shown that the bleaching process leads to significant changes in the intensity of a scattered signal and also in the shape and intensity of the fluorescence spectra. Experimental data illustrate that the bleaching process causes essential changes in the teeth discoloration in short time as 8-10 min from the beginning of the application procedure. The continuation of the treatment is not necessary moreover the probability of the enamel destroy increases considerably. The proposed optical back control of tooth surface is a base for development of a practical set up to control the duration of the bleaching procedure.

A considerable interest, in the recent years, has been allocated in the mid-infrared Er:YAG laser surgery and microsurgery. This interest has been increased after the development of optical fibers and waveguides, for safe and efficient transmission of the ~3.0 μm wavelength beams. On the other hand, a laser delivery system based on common silica glass fibers and caps are not applicable for delivery of the Er:YAG laser light, due to high absorption losses at the mid-infrared wavelengths. Thus, fluoride glass fibers and sealing quartz caps is a promising combination for laser delivery due to their low transmission loss. In this study, we investigated the properties of three sealing quartz caps, suitable for fluoride glass optical fibers, with various distal end geometries, in order to evaluate the attenuation and the spatial and temporal energy distribution of the transmitted laser radiation. Moreover, we evaluated the experimental beam divergence of the sealing caps. As a transmission medium, three fluoride glass optical fibers were used. As a laser source we used a Q-switched Er:YAG laser with a pulse duration of 190 ns and a repetition rate of 1 Hz. The mean value of the energy loss for dome geometry was found (0.73 ± 0.03), for planoconvex geometry was found (0.76 ± 0.03) and for ball geometry was found (0.73 ± 0.05). The beam divergence was found (62.4 ± 0.1) mrad, (156.2 ± 0.3) mrad and (37.5 ± 0.5) mrad for dome, ball and plano-convex geometry, respectively.

The propagation is investigated of a continuous laser beam through homogeneous tissue-like turbid media such as diluted emulsions of Intralipid or milk having presumably sharply forward directed Henyey-Greenstein or Gaussian indicatrices. The cross sectional radial distributions of the detected forward-propagating light power at different depths along the beam axis in each medium of interest are experimentally determined. The detected-power spatial distribution, for both the types of indicatrices, is also described analytically by a solution of the radiative transfer equation in the so-called small-angle approximation. The experimental results are consistent with the analytical expressions obtained that are shown to allow one to estimate the extinction ( αt), reduced-scattering (αrs) and absorption (αa) coefficients and the gfactor of the investigated media. The values obtained of α quite reasonable and behave, depending on the dilution turbidity, in a way observed formerly in other similar experiments. The comparative analysis of the estimated characteristics of the dilutions shows that in the case of Henyey-Greenstein indicatrix we have a smaller value of the g-factor and larger value of αrs with respect to the case of Gaussian indicatrix. At equal g-factors, in the former case we shall have a narrower forward-propagating scattered-light beam with higher on-axis intensity as compared with the latter case.

This investigation is carried out on two groups of patients with corpus alienum corneae. In every group are included 40 patients (40 eyes). For the first group standard treatment is applied after extraction of the corpus alienum corneae using antibiotic drugs (Oftaquix®) and epithelizing gel (Corneregel). First group is used as a control. For the second group of patients immediately after extraction of the corpus alienum corneae, eyes are irradiated for 3 minutes with He-Ne laser (Mediray 04, Optella Ltd., Sofia, Bulgaria) at emission wavelength at 632 nm and power density 0.1 mW/cm2. Second group of eyes is treated with the same drugs as the control group. We observed epithelisation of the damaged cornea in the first group - after 24 hours, and in the laser-irradiated group of eyes significant epithelisation is pronounced the 10th hour after irradiation. Epithelization is proved by fluorescein reaction to detect the eye cornea recovery. The patient eyes of the both groups were investigated under bio-microscope in cobalt-blue illumination. For irradiated eyes by LLLT, we have found that the healing period is shortened significantly by 42 % (p<0,001). Our results revealed that LLLT application is appropriate and perspective for recovery therapy after corpus alienum corneae extraction.

Phthalocyanines of gallium(III) and indium(III) (GaPc1 and InPc1) bearing four methylpyridyloxy groups on the periphery of the phthalocyanine ring were synthesized. The both phthalocyanines were obtained with a good solubility in water solutions, which make them suitable for application in the Photodynamic therapy (PDT). The absorbance in the Uv-vis region of the complexes is typical for MPc with a highly intensive maximum in the far red spectra (681 nm - 697 nm for GaPc1 and for InPc1, both in DMSO). The fluorescence maxima are red shifted (691 nm/716 nm). The fluorescence quantum yields of the both complexes are lower than that for the unsubstituted MPcs with values of 0.25 for GaPc1 and much lower for InPc1 (0.012), which suggested a quenching from the substituents. The photochemical properties of singlet oxygen generation show quenching curves of "Furane" test with a ¹O₂ formation that increase significantly in the presence of the heavy atoms such as Ga(III) and especially In(III). Photodynamic efficacy against C. albicans in planktonic media was evaluated with a high photodynamic effect for GaPc1 at low concentrations (0.5 μM, - 3 μM) at mild irradiation parameters (30-60 J cm^-2 and 50 mW cm^-2). The inactivation of the fungus cells with InPc1 was insignificant even at strong treatment conditions (6.8 μM; 60 J cm^-2). The water-soluble phthalocyanine complexes of Ga(III) and In (III) were compared to the recently studied by us water-soluble Zn(II)-phthalocyanine, which was shown to have a high potential for photodynamic inactivation of variety pathogenic bacterial strains.

We review the photo-driven directed charge, spin and acoustic phonon transport in dielectrics and semiconductors, in bulk and hetero-structures, lacking spatial inversion symmetry. We express these photo-galvanic effects in terms of photo-induced driving forces bilinear in the coherent light field amplitude mediated through the spatial asymmetry of the medium. We discuss their interrelations with nonlinear optical analogues and also nonlinear optical time resolved techniques for their study. These issues are of certain relevance in optoelectronics and photonics and in the emerging fields of phononics and photo-spintronics as they introduce new unidirectional and nonreciprocal photonic functionalities. They are manifestations of photo-driven ratchet and pawl processes.

Mathematical similarities and parallels between two different physical objects, optical solitons and matter-wave solitons, both described by similar mathematical models: the nonlinear Schrodinger equation (NLSE) and the Gross-Pitaevskii equation (GPE) model, open the possibility to study both systems in parallel and because of the obvious complexity of experiments with matter-wave solitons, offer outstanding possibilities in studies of BEC system by performing experiments in the nonlinear optical system and vise versa. In this report we briefly overview recent theoretical studies of the existence and stability of 3D solitons. With contributions from major groups who have pioneered research in this field, the report describes the historical development of the subject, provides a background to the associated nonlinear optical processes, the generation mechanisms of soliton bullets. The main features of nonautonomous matter-wave solitons near the Feshbach resonance with continuously tuned scattering length are investigated. We focus on the most physically important situations where the applied magnetic field is varying in time linearly and periodically. In nonlinear optical applications, this kind of periodic graded-index nonlinear structure with alternating waveguiding and antiwaveguiding segments can be used to simulate different and complicated processes in the total scenario of matterwave soliton bullets generation.

Experimental and numerical results on the interaction of the Raman-soliton continuum and dispersive waves through inelastic collisions mediated by four wave mixing are presented. In particular the spectral broadening of the continuum to longer wavelengths beyond a second zero dispersion point through four wave mixing of the dispersive wave produced by soliton self-frequency shift cancelation and other solitons in the continuum is considered.

Nonlinear photonic crystals are materials in which the second order susceptibility is modulated. These structures are often used in nonlinear optics applications for compensating the phase mismatch between interacting waves. The progress in techniques of modulating the nonlinearity enables to explore new applications, based on all-optical control of the phase, amplitude and polarization of the nonlinearly generated waves. This enables the realization of functional nonlinear optical devices, such as nonlinear lenses, switches, polarization rotators, deflectors and beam shapers. Here we will discuss in detail two applications that are enabled by specially designed nonlinear photonic crystals: All optical polarization switching, and the generation, nonlinear mixing and manipulation of accelerating Airy beams.

Edge-pumping is very advantageous for pumping disk lasers because it provides a long absorption path for the pump compared with end-pumped one. In the current work, we report an edge-pumped Yb:YAG disk laser pumped from four sides with diode laser stacks. For delivering the pump light into the gain medium, asymmetric hollow ducts have been employed. For any type of disk laser system, the key criterion is a uniform deposition of absorbed pump power and in turn a uniform temperature distribution throughout the disk. We try to meet this restriction by designing an appropriate asymmetric hollow duct. In order to obtain laser output power, a self-consistent numerical model has been developed for simulating lasing properties of our configuration. A Monte Carlo ray tracing based code and two-dimensional finite element analysis have been utilized to calculate the absorption power and temperature distribution inside the crystal, respectively. The model is used to investigate the influence of the effective parameters on the operational efficiency of the disk laser.

In real thin disk laser systems, a fraction of absorbed pump power is dissipated as heat. Consequently, the thin disk lasers experience a temperature gradient in the axial direction of the disk which produces inhomogeneous stress and strain distributions. In this paper, we present the numerical calculation of Von Mises stress and the thermal lensing due to temperature gradient, stress gradient and deformation. Based on the results of our numerical study, it was proved that the most dominant parameters, which cause optical path difference and therefore thermal lensing, are temperature-dependent refractive index and deformation of the disk. Moreover, these are both directly related to absolute temperature values within the crystal.

The thermally induced stress in pulsed pump solid state lasers with super-Gaussian profile has been investigated. An analytical expression for the thermal stress is introduced. We consider the heat deposited in the crystal due to the pump. The temperature distribution in the crystal has been calculated by solving the non-steady state heat conduction equation. A Ti: Sapphire crystal is assumed pumped by a pulse laser. All the stress components have been obtained and discussed in details. The results show that the non-homogenous temperature distribution is induced by the thermal stress in the crystal.

The effect of thermal lensing is a critical factor for resonator design and must be considered to improve the beam quality. The absorption of the pump radiation by laser material and surface cooling leads to a nonuniform temperature distribution in the rod. In this letter the temperature distribution in a cylindrical Nd:YAG rod under repetitive flash lamp pulses is numerically simulated, when pumped by flash lamp with 150 μs pulse width and 10 Hz repetition rate . We consider Gaussian pump pulse shape in time and redial absorption in laser rod. Our calculations show that the temperature converges to a finite value and doses evolve in time noticeably. Also by computing the changes of refraction index, we obtain the focal length of the heat dispersion.

Propagation of short laser pulses governing by a vector type 3D+1 non-linear Schrödinger equation in Kerr-type medium with anomalous dispersion and spatial dependence of the nonlinear refractive index is investigated. Finite energy analytical soliton solutions in spherical coordinates are found. Conditions for experimental observation are discussed.

In this paper, a careful analysis is provided of the nonlinear propagation of three-dimensional pulses with large spectral bandwidth in isotropic media. After applying the small parameter method to nonlinear amplitude equation, approximate analytical solutions up to first order are obtained.

Optimization of the Petzval objective with various evolution strategies and the damped least squares is presented. All algorithms are shortly described and their advantages and shortcomings are discussed. Application of evolution strategies to the optimization of optical systems is outlined. Analysis of the Petzval objective optimizations is given.

We study theoretically the non-phase-matched degenerate four-wave mixing of type ω_s = 2ω₁ ωω₂ , involving beams carrying two-dimensional spatial phase dislocations in the form of singly-charged optical vortices (OVs). Accompanying third-order nonlinear processes in the non-resonant nonlinear medium (NLM), which are accounted for, are self- and cross-phase modulation. In the case of pump OV beams with identical topological charges the model predicts the generation of signal beams carrying OVs of the same charge. If the pump beams carry OVs with opposite charges, the generated signals are predicted to carry triply charged vortices which, in the case of a nonnegligible initial free-space propagation from the plane of vortex generation to the NLM, decay inside the NLM into three singly-charged vortices with highly overlapping cores.

Passive Q-switching of a diode pumped Nd:YVO4 laser with Cr⁺⁴:YAG saturable absorber was studied experimentally. At 3Wof incident pump power, the laser pulses of duration 37 ns and energy 5.2 μJ with peak power of 140 W and repetition rate of 100 kHz were obtained.

Based on the generalized nonlinear Schrödinger equation model with sign-reversal varying-in-time harmonic oscillator potential, we show that conditions of its exact integrability in one-dimensional case (1D) indicate conclusively the way for solitonlike bullets generation in 3D nonautonomous nonlinear and dispersive systems. It turns out that generation of matter-wave soliton bullets can be realized if periodic variations of nonlinearity and confining potential are opposite in phases so that peaks of nonlinearity inside the atomic cloud coincide in time with repulsive character of trapping potential. In nonlinear optical applications, periodic graded-index nonlinear structures with alternating wave-guiding and anti-wave-guiding segments open remarkable opportunities in studies of BEC systems by performing experiments in nonlinear optical systems.

A detailed study of axicon-based Bessel-Gauss resonator for the thin disk laser has been carried out. A paraxial ray analysis is performed to find the self-consistency condition to have stable periodic ray trajectory after one or two round trips. By using the Fox-Li method, it is possible to find the lowest mode shape and associated optical loss for an arbitrary optical resonator. Nevertheless, the mentioned routine is very time-consuming and therefore, we make use of a technique in order to convert the Huygens-Fresnel integral self-consistency equation into a matrix one and then find the eigenvalues and the eigenfields of the resonator. Here, special attention is paid to investigate the dependence of the transverse profile and the loss on the cavity length.

We present two novel applications of optical properties of the interference wedge (compact realization of the Fizeau Interferometer) for the case of illumination with a small diameter laser beam. The first one is a new and competitive wavelength division multiplexing structure. The main advantages of the device are the possibility for separate frequency tuning of each input-output channel as well as its compactness. The made computer simulation proves that the structure can work with very short laser pulse duration (~ 0.1 ns), which corresponds to pulse repetition rate of order of ten GHz and more, thus fulfilling the requirements of modern digital communication systems. The theoretical analysis and the experimental check with laboratory model of a free-optical communication system show a sufficient resonant narrowline transmission up to 75% with the linewidth of emission from 0.05 nm to few nm. The second proposal is a device which allows for distant laser measurement of small linear translation of a rigid object for distances from a few meters up to hundred meters.

By the method of magnetron sputtering the nanocrystalline films LiNbO₃ on the surfaces of (001)Si, (111)Si and of Si- SiO2 heterostructure have been synthesized. The elemental and phase composition, structure and surface morphology, the electrical-physical parameters of the heterostructures (001)Si-LiNbO₃ and (111)Si-SiO₂-LiNbO₃ have been studied.

In this work we study the influence of the additional second- and third-order dispersion introduced in a femtosecond laser cavity by varying the beam's penetration into a prism of the double-pass intracavity prism compressor on the output pulse duration, as well as on the emission spectral bandwidth and its central wavelength. The theoretically calculated pulse durations are found to be in a good agreement with the respective experimental data from frequency-resolved optical gating and interferometric autocorrelation measurements.

The discovery of stimulated Raman self-scattering (SRSS) effect of femtosecond optical solitons is acknowledged to be among the most notable achievements of nonlinear fiber optics. This effect is also often called intrapulse stimulated Raman scattering (ISRS), or soliton self-frequency shift (SSFS), thereby emphasizing the unusual regime of stimulated Raman scattering, when the spectrum of a high-power ultrashort laser pulse proves to be so broad that it covers the band of Raman resonances of the medium. The soliton-like wave packets with continuously shifted spectrum traveling not only in the ordinary space and time, but also in the spectral space, are known as colored femtosecond solitons. Colored solitons play an important role in the soliton supercontinuum generation. The most interesting features of colored optical solitons are connected with the possibility of their tunneling in the spectral domain through a potential barrier-like spectral inhomogeneity of group velocity dispersion (GVD), including the forbidden band of positive GVD. This effect is known as soliton spectral tunneling effect (SST). In this Report, we consider the influence of the soliton binding energy on dynamics of the SST effect assuming that the amplitude and duration of the tunneling soliton vary in time when the soliton spectrum approaches a forbidden GVD barrier. We show that soliton self-compressing effect has dramatic impact on the SST through forbidden spectral region of positive GVD.

An active volume scaling in bore and length of He-SrBr₂ laser excited in nanosecond pulsed longitudinal discharge is carried out. The optimal temperature regime is found for laser oscillation at several different Sr atom and ion lines. Optimal discharge conditions, such as active zone diameter, vapor pressure, buffer-gas pressure, electrical excitation scheme parameters, average input power, pulse repetition frequency, are found. At multiline operation a record average output power of 4.30 W for the Sr atom lasers is obtained, more than 90 % of which is concentrated on the 6.45-μm Sr atom line. A new discharge tube with furtherly increased active volume in bore is developed. The effect of neon additive to the helium buffer gas on the gas and electron temperatures is investigated.

Recent studies have thrown doubt on the ideal treatment of soliton tunneling. The most important enigmas in this field can be formulated in the following way: As to whether nonlinear soliton tunneling effect will resemble more the point like classical particle case or the quantum mechanical behavior in which the particle itself has an internal structure? How "hidden" degrees of freedom can show up in the process of soliton tunneling? What happens if the amplitude and duration of the input soliton vary in time when the soliton approaches a classically forbidden barrier? In particular, what happens in the case of the nonlinear tunneling of self-compressing soliton when its binding energy is increased? As to whether this case will resemble more the classical particle case or the quantum mechanical behavior? These questions are taken up in this Report.

Linear regime of propagation of short optical laser pulses in isotropic dispersive medium with attenuation in the frame 3D+1 non-paraxial model is investigated. The corresponding amplitude equation is solved in ( k_x, k_y, k_z, t ) space and fundamental solution is found. In case of weak attenuation we found, that the loss term in the equation do not influence the phase, and change considerably the real amplitude only.

In this work we study the evolution of dark beams of finite length carrying edge-screw phase dislocations in selffocusing Kerr nonlinear media aiming to find appropriate conditions to control the process of filamentation of the background beam. In the case of a single fractional vortex dipole, geometry-controlled conditions for changing the intensity ratio of the peaks and their offset are found. Depending on their orientation, two parallel or two in-line mixed phase dislocations carried by a common background beam are predicted to perturb it and to initiate filamentation of different number of peaks with different spatial distributions.