This PDF file contains the front matter associated with SPIE Proceedings Volume 9447, including the Title Page, Copyright information, Table of Contents, Authors, Introduction (if any), and Conference Committee listing.

We discuss the effect of static and time-dependent longitudinal and transverse magnetic fields on degenerate two-level and three-level systems in Rb atomic vapor. The effect of a transverse magnetic field (TMF) on the absorption spectra of degenerate two-level systems in the D₂ line of ⁸⁷Rb is investigated both analytically and numerically. We compare the effect of the TMF on the absorption of a σ polarized pump in the Hanle configuration with that of a σ⁻ probe in the presence of a σ⁺ pump in the pump-probe configuration, and show that the absorption spectra in both configurations is split in the presence of a TMF and that the splitting is proportional to the magnitude of the TMF. Coherent population trapping (CPT) transients induced by a modulated longitudinal magnetic field (LMF) are investigated theoretically for a realistic three-level Λ system in the D₁ line of ⁸⁷Rb. The contributions to the transient probe absorption from the various subsystems that comprise the realistic atomic system are examined and the absorption of each Λ subsystem is compared to that of a simple Λ system. We also present theoretical results for CPT transients induced by a modulated TMF. The application of a TMF leads to the appearance of new Λ subsystems, the creation of new dark states and the rearrangement of the population among the Zeeman sublevels. We show that transients appear as the system is switched between various steady-state situations and we identify the various components of the total probe absorption.

The pump-probe spectra in a cell of micrometric thickness containing cesium vapor are reported. The line shape and nonlinear features observed in the case of fluorescence in the direction parallel to the cell windows and the transmission spectra observed along the propagation direction of the probe beam show considerable differences in the spectral profiles. We observed Electromagnetically Induced Transparency (EIT) and enhanced Velocity Selective Optical Pumping (VSOP) signals. Atoms moving nearly parallel to the windows and perpendicular to the collinear pump and probe beams will see much lower Doppler shift of incident frequencies and hence will lead to considerable narrowing of the Doppler background in the fluorescence spectra. The coherence decay rate is also low for such atoms as they do not meet with the cell walls. A theoretical model based on five level optical Bloch equations is used to simulate the spectra. The Doppler convolution includes all possible orientation of atomic velocities with respect to the laser beam direction. The simulated curves reproduce the observed sharp EIT peaks and enhanced broad VSOP signals for the closed probe transition in the fluorescence and absorption spectra. The observed effect of the light intensity and temperature change on the non-linear features is reproduced by the simulation.

A simple method for characterization the quality of anti-relaxation coatings of vacuum optical cells filled with alkalimetal vapors is proposed. This method is based on the registration of the temporal dependence of the intensity of the fluorescence from irradiated alkali atoms by pulsed light at resonance. Here it is shown that in order to find quality of coating it is enough to have the value of fluorescence decay speed and the ratio between the intensities of the fluorescence at the beginning and at the end of the laser pulse. The duration of laser pulses considered is of the order of tens of milliseconds - long enough to reach a steady state.

In this short review some essentials concerning creation and testing of nonclassically correlated photons (biphotons) are given. In the introduction we remind the role which the experimentally produced entangled states have been playing for the foundations of the quantum physics, by witnessing against the model of local hidden variables. The well established sources of biphotons are based on spontaneous parametric down conversion in nonlinear crystals. A popular source with two BBO crystals is described, which generates pairs of photons nearly maximally entangled in polarization. Crystalbased sources rely on intrinsically broadband transitions, therefore thus produced biphotons are also broadband. Additional efforts (like applying optical cavities) are needed to reach narrowband biphotons which would comply with the requirements of some implementations in the quantum communication science. The topical issue of our article is a review of another, more recent approaches based on narrowband transitions between levels in cold atoms. Such method provides naturally narrowband biphotons. First, the principles are given of an atomic source of nonclassically paired photons, which is operated in a pulsed write-read mode. Such source is based on two separated in time Raman transitions triggered successively in two Λ-schemes. Next, cw-mode sources based (mainly) on spontaneous four wave mixing process (SFWM) are presented in a generic four-level scheme. Some underlying physics is sketched and profiles of biphoton correlation functions in the time domain are explained. Among other presented SFWM sources, one proves in testing high degree entanglement of generated biphotons, both in time-frequency and polarization (hyperentanglement).

In this study we show the results for parametric non-degenerate four wave mixing (FWM) obtained using double lambda scheme at D1 line in hot potassium vapor. We have investigated the influence of one-photon detuning and two-photon detuning on the FWM gain. The laser frequency is locked at approximately 1GHz from the resonance 4S_1/2 F_g=1 -< 4P_1/2, using external reference cavity. The probe beam passes through acoustooptic modulator that enables controllable detuning around 460 MHz (ground state hyperfine splitting) in respect to the pump beam. The vacuum glass cell containing the potassium vapor was heated by hot air in order to achieve necessary concentration of atoms. The efficiency of FWM process is studied by measuring the gains of the conjugate beam the probe beam, simultaneously. The maximal gain was achieved for nonzero two photon detuning.

A narrowband R-type resonance is formed in a Λ-system, on the D₁ line of Rb atomic vapor using two continuous diode lasers with λ=795 nm. A 8mm- long cell filled with the Rb vapor and 20 Torr neon gas has been used. We have shown that use of an additional (3^rd) laser which is resonant with the Rb D₂ line (λ=780 nm) makes it possible to control the amplitude and sign of the R -type resonance, i.e. to convert a resonance which demonstrates increase in absorption into one which demonstrates reduction in absorption. The good signal/noise ratio of the observed resonance allows us to follow its behavior in an applied magnetic field from several gauss to several hundred gauss. A description in terms of double-Λ systems allows us to explain the experimental results in a simple manner.

In this work we present new features observed in the Saturated Absorption (SA) spectrum on the D₁ line of K. In an uncoated optical glass cell containing pure K atoms, excitation by circularly polarized pump beam produces an enhancement of the amplitude of the crossover resonances due to the hyperfine transitions starting from the ground state F_g = 2. This effect appears to be much more relevant when K atoms are contained in a cell coated with an anti-relaxation film. Here, the crossover resonance in the F_g = 2 set of transition is not observed experimentally with linearly polarized pump light, while in case of circular polarization its amplitude is significantly enlarged. The Light Induced Atomic Desorption (LIAD) effect strongly improves the intensities of the SA resonances observed in coated cell.

The dynamics of Light-Induced Atomic Desorption (LIAD) in 6 cells with different coatings (PDMS coated cells prepared with two different concentrations of PDMS in ether, SC-77, PCHS, DCDMS, OTS) is investigated. The rates of desorption and adsorption of the Rb atoms when the illuminating light is switched ON and OFF and their dependence on the illuminating blue-light power are measured. The influence of the homogeneity of illumination for increasing the desorption and adsorption rates is evaluated. The results are interesting for the better understanding of LIAD and its dynamics and for the development of new optoelectronic elements, LIAD-loaded atomic devices and their miniaturization, and new methods for surface and coating diagnostics.

In this work we investigate the magneto-optical resonance on ⁸⁷Rb D₁ line. In two-level degenerated system this resonance is due to the interference between the Zeeman sub-levels, created by interaction of resonance linear polarized laser beam with the atoms. The observed signal is detected by sweeping magnetic field B around its zero value. This phenomenon is also known as a Coherent Population Trapping (CPT) in Hanle-configuration. In a coated vacuum cell the fluorescence signal has a complex form, because the anti-relaxation coating preserves the created coherence, having different relaxation rates. The ground state coherence is transmitted by the laser field to the upper level; thereby polarization moments with different rank contribute to the fluorescence. The manifestation of the different polarization moments in the observed signal depends on the geometry of the experiment – direction of observation, plane of the laser polarization, polarization of the registered light. The resonances obtained in the fluorescence having different polarization are compared in order to clear up what are the contributions to the fluorescent signal from the polarization moments with different rank. The experiment is performed on the D₁ ⁸⁷Rb line, F=2→ F=1 transition in a paraffin-coated cell. The magneto-optical resonances, detected in two orthogonal polarizations are measured. Numerical calculations with parameters, close to the experimental ones are performed by using a program, which is based on the irreducible tensor operator formalism. The results of the modelling are compared with the measured ones at different experimental conditions.

Oxy-fluoride glasses containing strontium carbonate doped with samarium have been prepared. The glasses are sorted with respect to the quantity of strontium carbonate. The fluorescence spectra recorded for different pumping wavelengths are presented. We have investigated the influence of the excitation on the efficiency of the fluorescence, depending on the quantity of strontium carbonate in the samples for a variety of excitation wavelengths. The results of optical pumping in the range 370 - 490 nm show a typical fluorescence spectrum of Sm³⁺. When pumped with wavelengths above 500 nm a new peak that has not been reported appeared in the fluorescence spectrum. From the data analysis the range of appearance of the fluorescence peak was determined and the most efficient source for its excitation was found.

Surface plasmon resonance (SPR) is widely applied for bio/ chemical sensing. The main problem for all sensors is accuracy and sensitivity enhancement. For SPR sensors the accuracy depends on the characteristics of the plasmon resonance. In this work, we study SPR excitation assisted by liquid crystal layer. We consider Kretshmann configuration where a liquid crystal is sandwiched between a prism and glass plate, while the gold layer is evaporated over the glass plate. We show that the Bragg reflection of cholesteric liquid crystals modifies the plasmon resonance in a way increasing the accuracy of its location. Also, features of plasmon resonance excitation are studied for chiral liquid crystals.

Results of spectroscopic investigation of the historical copper and copper alloy objects covered by patina and surface contamination are reported and discussed in this work. For analysis of the surface layers (bulk material, primer/grounding, patina and atmospheric contamination) the Laser Induced Breakdown (LIBS), Raman and X-ray fluorescence (XRF) spectroscopic techniques are used. Useful data on chemical structure and composition are obtained from stratigraphic analysis performed by a stepwise layer penetration with successive laser pulses. The LIBS, XRF and Raman spectra confirm the presence of patina and contamination layers of the compositions influenced by the atmospheric environment. The elemental composition reveals in the case of the original copper substrate the presence of Cu with traces of Ag and Sb, and of impurities Fe and Pb, while objects made of copper alloys (brass) show different Zn/Cu ratios greater than 20% in all cases and admixtures of Sn and Pb. Consistent results are obtained from the elemental and Raman data indicating presence of the antlerite (Cu₃(OH)₄SO₄), carbon and microcrystalline calcite which are ascribed to patina, surface contamination (atmospheric soot) and primer layers, respectively.

The layered nanocomposites of Ag nanoparticles (NPs) and ZnO were laser fabricated and investigated. The double layer (DL) nanostructures of AgNPs/ZnO and the multilayer (ML) nanostructures of AgNPs/ZnO/AgNPs/ZnO on SiO2 substrate were produced. The Ag thin films were decomposed into nanoparticles by laser annealing. The samples were characterized by UV-VIS transmission spectroscopy, Raman spectroscopy and photoluminescence (PL) emission study. A characteristic resonance absorption peak was registered for all the samples at the range of 440 – 530 nm. The Raman spectrum taken for the DL and ML structures significantly differs from the spectrum of bulk ZnO. Usually, the 1LOphonon frequency is between 574 and 591 cm⁻¹. The 1LO peak of ML nanostructure appears at 564 cm⁻¹, which indicates a redshift of more than 10 cm⁻¹. The PL enhancement occurs after annealing and is due to the morphology changes in the nanoscale structures. Room temperature photoluminescence spectrum shows green emission enhancement at 560 nm for the DL structure, while the characteristic ZnO emission enhancement at 380 nm was registered for the ML structure.

Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene thin film for spintronics applications. The use of organic material for spintronics is motivated by the advantages such as long spin diffusion length due to low spin-orbit and hyperfine coupling^1,2, chemical tuning of electronic functionality, easy structural modifications, ability of self-assembly and mechanical flexibility³ etc. However, a major drawback of OS is its low mobility compared to inorganic semiconductors. The PLD growth of rubrene aims on fabricating OS films under more controlled environment to achieve higher crystalline order to improve its mobility and spin coherence length. Among organic materials, rubrene reveals the highest hole mobility - up to 40 cm²/(V∙s) and can be exploited in organic light-emitting diodes (OLEDs) or field-effect transistors (OFETs) ^4. In this work the rubrene thin films are produced from hardened pellets in vacuum using Nd:YAG pulsed laser operated at 1064 nm, 2 Hz and energy fluence around 0.2 J/cm². For the reference rubrene samples on SiO₂ glass the AFM data reveal continuous 5-7 nm thick films. The amorphous structures are confirmed by XRD measurements and also Raman spectra which show signatures of both tetracene and phenyl bands and a broadband at 1373 cm^-1. The obtained results indicate that continuous, defect-free rubrene films can be prepared by means of PLD for investigation of the spin polarization properties of organic-inorganic hybrids. Further studies are on the way to improve crystalline qualities of the rubrene films for less grain boundary related defects and improved mobility and spin diffusion length.

In this work, formation of the Metal Matrix Composite (MMC) surface layers on the titanium-based Ti-6Al-4V and aluminum-based Al 6061 alloys by means of laser dispersing of WC and TiC powder particles is investigated. In the process, the substrate surface is locally melted to the depths up to about several hundreds μm by the slightly defocused high power CO₂ or disk Yb:YAG laser beam. Simultaneously, powder particles of irregular (TiC) or spherical (WC) shape and average size of about 100 microns are injected into the molten material by means of specialized, lateral nozzle. The single traces as well as surface layers consisting of several consecutive traces were produced. The influence of the process parameters, such as: laser beam intensity, scanning speed, powder feed-rate and substrate preheating temperature, on the properties of the composite layer was analyzed and discussed. The optical and SEM inspections of the produced MMC materials revealed the homogeneously distributed powder particles in the best samples obtained.

Different types of ZnO nanostructures were fabricated on metal (Au or Ag) coated silicon substrates by applying the pulsed laser deposition (PLD) method. The samples were prepared at substrate temperatures in the range of 300 – 650 °C, oxygen pressure of 5 Pa, and laser fluence ≤ 1 J.cm^-2– process parameters usually used for thin-film deposition. The metal layer is essential for the preparation of nanostructures. The nanostructures grown at different substrate temperatures showed obvious morphological differences. The substrate temperature increase led to changes in the morphology of the nanostructures from nanowhiskers to nanowalls when a thin Au layer was used. It was also observed that the type and thickness of the metal layer affect the morphology of the nanostructure.

The collagen – elastin biopolymer thin films treated by CPA Ti:Sapphire laser (Femtopower – Compact Pro) at 800nm central wavelength with 30fs and 1kHz repetition rate are investigated. A process of surface modifications and microporous scaffold creation after ultrashort laser irradiation has been observed. The single–shot (N=1) and multi–shot (N<1) ablation threshold values were estimated by studying the linear relationship between the square of the crater diameter D² and the logarithm of the laser fluence F for determination of the threshold fluences for N=1, 2, 5, 10, 15 and 30 number of laser pulses. The incubation analysis by calculation of the incubation coefficient ξ for multi – shot fluence threshold for selected materials by power – law relationship form Fth(N)=Fth(1)N^ξ-1 was also obtained. In this paper, we have also shown another consideration of the multi – shot ablation threshold calculation by logarithmic dependence of the ablation rate d on the laser fluence. The morphological surface changes of the modified regions were characterized by scanning electron microscopy to estimate the generated variations after the laser treatment.

Femtosecond–pulse laser micromachining is based on a laser ablation phenomenon, i.e. total evaporation of material from the target surface during laser irradiation. It is the most precise method of material removal. Moreover it does not require any post processing. Removal of the material occurs only in the laser focus, since the lack of thermal interaction, neither heat affected zone (HAZ) nor debris ocur. Research results have shown that shortening the duration of the laser pulse significantly reduces HAZ, which translates into the high quality of the machined structures. It is the main argument for the use of femtosecond-pulse lasers in the precise micromachining. In this paper, a femtosecond laser system consisting of a solid-state oscillator and the ytterbium-doped pulse fiber amplifier are presented. Average beam power at 343 nm with mode-locking is 4W @25A and pulse length at the oscillator output is 500 fs. Laser micro and nano-machining has found application in different fields. It’s primary use is industrial micromachining of metals, ceramics, polymers, glass, biological material for medical use in eye surgery, and photovoltaic cells.

In this paper we show an experimental procedure for fabrication of metal nanoparticle arrays on metal substrates. The nanostructures are fabricated by laser processing of thin metal films. The films are deposited on the metal substrates by classical PLD technology. The as deposited films are then annealed by nanosecond pulses delivered from a THG Nd:YAG laser system (λ = 355 nm). At certain conditions, the laser treatment leads to a formation of discrete nanoparticle structure on the substrate surface. The optical properties of samples fabricated at different conditions and having different characteristics of the nanostructures are examined by optical spectroscopy measurement. Such analysis shows that the optical spectra of the obtained nanostructures are characterized by plasmon excitation. Finite difference time domain (FDTD) model is used for theoretical description of the near field optical properties of the fabricated nanoparticle arrays. The simulation demonstrates high efficiency of the fabricated structures in enhancement of the near field intensity. The great enhancement observed in the Raman spectra of Rhodamine 6G deposited on the fabricated samples makes such structures very appropriate for applications in Surface Enhanced Raman Spectroscopy (SERS). The produced systems can be also applied in plasmonic solar cells (PSC).

Pulsed laser ablation was used to create Ag nanostructures – nanoparticles and nanowires. Two different type of target motion were used – rotation and computer controlled by using an XY stage. The impact was investigated of the trajectory of the laser beam on the target surface on the characteristics of the ablation process itself and the nanostructures obtained. Two circular trajectories of different diameters generated at the target rotation were utilized. The fundamental (λ = 1064 nm) and the third harmonic (λTHG = 355 nm) wavelengths of a Nd-YAG laser system were used for the fabrication procedure. They were selected in order to study the influence of the two processes accompanying the ablation procedure, namely, scattering and absorption of the incident light by the nanostructures already created (the so-called self-absorption). The two possible nanostructures – nanoparticles and nanowires, were obtained by an appropriate choice of the laser fluence for each of the wavelengths selected. The optical extinction spectra of the fabricated colloids allowed an indirect assessment of the shape and size-distribution of the nanostructures obtained, whose size and morphology were visualized by transmission electron microscopy (TEM). It was established that the most appropriate processing conditions in terms of the efficiency of the ablation and reproducibility of the sample characteristics were achieved using a computer controlled XY stage.

This study presents results on pulsed laser ablation of metallic and bimetallic thin films immersed in liquids. The thin films are deposited by classical on-axis pulsed laser deposition technology by using targets consisted of one or two sections composed of different metals. Using this technique gold, silver and gold/silver thin films are deposited on quartz substrate. By changing the area of the different sections of the target, thin films with different concentrations of the two metals are obtained. The as prepared films are then placed on the bottom of glass vessel filled with double distilled water and irradiated by nanosecond laser pulses delivered by Nd:YAG laser system operated at λ = 1064 nm. This results in fabrication of colloids composed by metallic and bimetallic nanoparticles. The performed TEM analyses revealed spherical and spherical-like shape of the particles produced. The optical extinction spectra of the obtained colloidal nanoparticles show plasmon excitations as the resonance wavelength can be efficiently tuned in a wide range by changing the ratio of the basic metals in the films.

In this paper we present mathematical models for the simulation of polarization mode dispersion and polarization dependent losses based on Mueller matrices. We have simulated the modulation of the spectrum in the communication line as a function of random losses inherent to polarization-dependent components. After statistical treatment of spectra we obtain information about polarization dependent losses (PDL). We have shown that our theoretical results coincide with reported in the literature other simulated data.

Interaction of a CuBr laser, operating at 511 nm wavelength and pulse duration of 30 ns with titanium wafers was studied. It was investigated the efficiency of laser ablation, depending on the laser fluence, on the laser beam scanning speed, and laser pulse frequency. The titanium surface modification was studied by scanning electron microscopy (SEM) and XPS (X-ray Photoelectron Spectroscopy). Nanosecond laser irradiation of Ti led to the formation of high porous granular structures consisting of agglomerated small micro- and sub microparticles.

One year (October 2006 – October 2007) continuous measurements of the aerosol optical depth (AOD) during the development of planetary boundary layer (followed by lidar) were carried out by a sun photometer Microtops II over the city of Sofia, Bulgaria. In order to asses aerosols microphysical properties, the Angstrom coefficients α and β are retrieved from the spectral AOD data using the Volz method. Daily behavior of AOD, Angstrom exponent α and turbidity parameter β as well as their monthly mean variations are presented. Variations in the monthly mean AOD at λ = 500 nm, α and β (computed from the wavelength pair 500/1020 nm) had similar behavior. The mean values of the AOD, α and β for the whole period (October 2006 –October 2007) are found to be 0.28±0.07, 1.21±0.17 and 0.11±0.03, respectively, as highest values of the AOD (0.42±0.21), α (1.62±0.53) and β (0.17±0.10) were obtained in August 2007. The lowest monthly mean AOD, α and β were 0.21±0.09 (in January and February 2007), 1.03±0.42 (in April 2007) and 0.09±0.04 (in January and October 2007), respectively. In addition, Angstrom coefficients α and β are calculated from the wavelength pair 500/675 nm and comparison is done between the results obtained from the two wavelength pairs. The above mentioned values reveal low to moderate turbidity of the atmosphere and dominance of fine-mode aerosols over the city of Sofia associated with heavy vehicular traffic and local anthropogenic pollution sources.

Atmospheric aerosol is known to considerably influence the Earth’s radiative budget and to make an impact on air quality. The influence of aerosols strongly depends on their spatial distribution and optical properties. The aerosol has natural and anthropogenic origin. Aerosol types can be also classified according to their size, sources or geographical origin (desert, continental, marine etc.). Mineral dust is one of the natural aerosols presented in the atmosphere. Its main source is the Sahara desert region. Saharan aerosol layers are frequently observed in Europe by means of active and passive remote sensing devices, especially in the frame of EARLINET and ACTRIS ^{3, 5, 6, 7, 8, 9}. In this paper, observations of vertical distribution of aerosols and assessment of their optical properties will be presented. Two-year (2013-2014) complex measurements were carried out by a ceilometer CHM-15k (Jenoptic) and two lidars in an urban area located in a mountain valley (Sofia, Bulgaria)¹. The ceilometer works 24 hours in automatic mode. Part of the results is compared with results obtained by lidars operating in photon counting modes for specific periods of simultaneous work⁵. Supplementary data from: two meteorological stations; HYSPLIT back trajectory model4; BSCDREAM8b dust model9; and the database of atmospheric radio sounding profiles from Department of Atmospheric Engineering of Wyoming University (USA) are also used in the analysis of the obtained results.

In this work, we present results of two-wavelength lidar observations on Saharan dust layers over Sofia, Bulgaria, in two days of strong dust intrusion events in the fall and winter of the year 2010. Measurements are carried out at two wavelengths (1064 nm and 532 nm) by using two channels of an aerosol lidar based on a frequency-doubled Nd:YAG laser. Optical, dynamical, and microphysical properties of the dust layers are studied and analyzed, distinguishing specifics of coarse and fine aerosol fractions. The spatial-temporal evolution of atmospheric aerosol/dust density fluctuations is shown on height-time coordinate color-map plots for each of the two wavelengths. Time-averaged height profiles of the atmospheric backscattering coefficient at 1064 nm and 532 nm are presented, showing the dust and aerosol density distribution up to about 10 km AGL, with a range/height resolution of 15/8 m. Microphysical properties of dust and aerosol particles are characterized qualitatively by using backscatter-related Ǻngström exponents (BAE). Range-resolved time-averaged height profiles of BAE are shown, particularly for the dust layers, indicating the dominating particle size-modes. Obtained BAE values in the range 0.2-0.5 are typical for desert mineral dust, suggesting coarse particles in the over-micron size range. Frequency-count analysis of the obtained BAE arrays is performed for typical separate dust-containing layers, revealing distributions and changes of particle size modes in terms of BAE, as well as effects of dust mixing with finer urban and industrial aerosols. Some efforts are devoted and focused on characterizing the temporal dynamics of the range distribution and density of dust and aerosols. Peculiarities of spatial distribution, size composition, and temporal evolution of Saharan dust aerosols are revealed, analyzed, and discussed.

Physical analysis and mathematical description are given of the factors conditioning the formation and the fluctuation statistics of the aerosol lidar signals. The considerations are based on the assumption of incoherent scattering from aerosol particles occupying the “scattering laser-pulse volume” having specific cross-section and length. The influence of the atmospheric refractive turbulence is also taken into account. Different types of statistics of the aerosol field and different design parameters of the lidar system are considered as well, as essential factors determining the fluctuation level and distribution. It is shown that the aerosol lidar signal fluctuations can indeed have nearly log-normal distribution, as is frequently assumed, under determinate environment and lidar-design conditions including the probability density distribution and the mean number and variance of the scattering aerosol particles, the temporal and spatial correlation characteristics of the aerosol concentration, the refractive turbulence intensity, the radii of and the distance between the scattering volume and the aperture of the lidar receiving optical system, etc. Thus, the modeling of aerosol lidar signals and the interpretation of aerosol lidar data may be based on the assumption of log-normal statistics of the signal fluctuations whose level is derived on the basis of reasonable physical concepts and determined by the above-indicated conditions and parameters of concern.

The performed analysis reveals interesting and useful features of the distortions of the measured Thomson scattering lidar profile, and the corresponding recovered temperature and density profiles, due to convolution of the lidar response function with the maximum-resolved lidar profile obtainable at a delta-like system response. It is shown that in the case of a symmetric pulse response, far from the pedestal area at the plasma edge, the convolution does not distort the information about the smooth-enough line-of-sight distribution of the electron temperature and density. In the pedestal area such distortions exist. They concern mainly the steep density profiles and depend on the temperature profile steepness. In practice, the temperature profiles are slanting-enough around the pedestal. Then the center-of-mass wavelength and the fitting approaches provide the undistorted temperature profile, and the latter approach provides the density profile convolved with the response function. In the case of an asymmetric system response, distortions of the information about the density distribution exist along the whole line of sight within the plasma torus. They depend on the variability of the electron temperature and density profiles and could be minimal at relatively high temperatures, slanting-enough temperature profiles, and relatively near (the incident wavelength) receiving spectral intervals. Then, both above-mention approaches can be used to obtain the undistorted temperature and convolved density profiles. Under general conditions, deconvolution procedures are necessary for improving the recovery accuracy and resolution. The analytical conclusions deduced in the work are supported by numerical results.

The distribution of aerosol load in the atmosphere due to two forest fires near Sofia (the capital city of Bulgaria) was studied using two aerosol lidars which operated at 510.6 nm and 1064 nm. Experimental data is presented as 2D-heatmaps of the evolution of attenuated backscatter coefficient profiles and mean profile of the aerosol backscatter coefficient, calculated for each lidar observation. Backscatter related Angstrom exponent was used as a criterion in particle size estimation of detected smoke layers. Calculated minimal values at altitudes where the aerosol layer was observed corresponded to predominant fraction of coarse aerosol. Dust-transport forecast maps and calculations of backward trajectories were employed to make conclusions about aerosol’s origin. They confirmed the local transport of smoke aerosol over the city and lidar station. DREAM forecast maps predicted neither cloud cover, nor Saharan load in the air above Sofia on the days of measurements. The results of lidar observations are discussed in conjunction with meteorological situation, aiming to better explain the reason for the observed aerosol stratification. The data of regular radio sounding of the atmosphere showed a characteristic behavior with small differences of the values between the air temperature and dew-point temperature profiles at aerosol smoke layer altitude. So the resulting stratification revealed the existence of atmospheric layers with aerosol trapping properties.

The field of optical trapping has dramatically grown due to implementation in various arenas including physics, biology, medicine and nanotechnology. Certainly, optical tweezers are an invaluable tool to manipulate a variation of particles, such as small dielectric spheres, cells, bacteria, chromosomes and even genes, by highly focused laser beams through microscope. As the main disadvantage of the conventional optical trapping systems is the diffraction limit of the incident light, plasmon assisted nanotrapping is reported as a suitable technique for trapping sub-wavelength metallic or dielectric particles. In this work, firstly, we report briefly on the basic theory of plasmon excitation, focusing on the interaction of nanoscale metallic structures with laser light. Secondly, experimental and numerical simulation results are also presented, demonstrating enhancement of the trapping efficiency of glass or SiO2 substrates, coated with Au and Ag nanostructures, with or without nanoparticles. The optical forces were calculated by measuring the particle’s escape velocity calibration method. Finally, representative applications of plasmon assisted optical trapping are reviewed, from cancer therapeutics to fundamental biology and cell nanosurgery.

The light exposure on a daily basis has been well accepted as a competitive method for decontamination of wastewater. The catalytic properties of TiO₂ offer a great potential to reduce the transmission of pathogens in the environment. Although the titanium dioxide shows high activity against pathogens, its general usage in water cleaning is limited due to the insufficient excitation natural light (about 3% of the solar spectrum). A hydrophobic dodecylpyridyloxy Zn(II)-phthalocyanine with four peripheral hydrocarbon chains of C12 (ZnPcDo) was immobilized on a photocatalyst TiO2 anatase (P25). The resulted greenish colored nanoparticles of phthalocyanine were characterized by the means of absorption, fluorescence and infrared spectroscopy. The laser scanning confocal fluorescence microscopy was used to visualize the phthalocyanine dye by the red fluorescence emission (650 – 740 nm). The intensive Q-band in the far red visible spectral region (~ 690 nm) suggested a monomeric state of phthalocyanine on TiO2 nanoparticles. Two pathogenic bacterial strains (methicillin-resistant Staphylococcus aureus - MRSA and Salmonella enteritidis) associated with wastewater were photoinactivated with the suspension of the particles. The effective photoinactivation was observed with 1 g.L^-1 TiO₂ anatase at irradiation with UVA 364 nm as with UVA 364 nm and LED 643 nm. The gram-negative Salmonella enteritidis was fully photoinactivated with ZnPcDo-TiO₂ and TiO₂ alone at UVA 346 nm and at irradiation with two light sources (364 nm + 643 nm). The proposed conjugate appears as an useful composite material for antibacterial disinfection.

In this report we will present our recent investigations of the fluorescence properties of lower part gastrointestinal tissues using excitation-emission matrix and synchronous fluorescence spectroscopy measurement modalities. The spectral peculiarities observed will be discussed and the endogenous sources of the fluorescence signal will be addressed. For these fluorescence spectroscopy measurements the FluoroLog 3 system (HORIBA Jobin Yvon, France) was used. It consists of a Xe lamp (300 W, 200-650 nm), a double mono-chromators, and a PMT detector with a work region at 220- 850 nm. Autofluorescence signals were detected in the form of excitation-emission matrices for the samples of normal mucosa, dysphasia and colon carcinoma and specific spectral features for each tissue were found. Autofluorescence signals from the same samples are observed through synchronous fluorescence spectroscopy, which is a novel promising modality for fluorescence spectroscopy measurements of bio-samples. It is one of the most powerful techniques for multicomponent analysis, because of its sensitivity. In the SFS regime, the fluorescence signal is recorded while both excitation λexc and emission wavelengths λem are simultaneously scanned. A constant wavelength interval is maintained between the λexc and λem wavelengths throughout the spectrum. The resulted fluorescence spectrum shows narrower peak widths, in comparison with EEMs, which are easier for identification and minimizes the chance for false determinations or pretermission of specific spectral feature. This modality is also faster, than EEMs, a much smaller number of data points are required.¹ In our measurements we use constant wavelength interval Δλ in the region of 10-200 nm. Measurements are carried out in the terms of finding Δλ, which results in a spectrum with most specific spectral features for comparison with spectral characteristics observed in EEMs. Implementing synchronous fluorescence spectroscopy in optical methods for analyzing biological tissues could result in a better differentiation between normal and dysplastic tissue. Thus could establish fluorescence imaging as a diagnostic modality among optical techniques applied in clinical practice.

Non melanoma skin cancer is one of the most frequent malignant tumors among humans. A non-invasive technique, with high sensitivity and high specificity, would be the most suitable method for basal cell carcinoma (BCC) or other malignancies diagnostics, instead of the well established biopsy and histopathology examination. In the last decades, a non-invasive, spectroscopic diagnostic method was introduced, the laser induced fluorescence (LIF), which could generate an image contrast between different states of skin tissue. The noninvasiveness consists in that this biophotonic method do not require tissue sample excision, what is necessary in histopathology characterization and biochemical analysis of the skin tissue samples, which is worldwide used as an evaluation gold standard. The object of this study is to establish the possibilities of a relatively portable system for laser induced skin autofluorescence to differentiate malignant from nonmalignant skin lesions. Unstained human skin samples, excised from humans undergoing biopsy examination, were irradiated with a Nd:YAG-3ω laser (λ=355 nm, 6 ns), used as an excitation source for the autofluorescence measurements. A portable fiber-based spectrometer was used to record fluorescence spectra of the sites of interest. The ex vivo results, obtained with this spectroscopic technique, were correlated with the histopathology results. After the analysis of the fluorescence spectra of almost 60 skin tissue areas, we developed an algorithm to distinguish different types of malignant lesions, including inflammatory areas. Optimization of the data analysis and potential use of LIF spectroscopy with 355 nm Nd:YAG laser excitation of tissue autofluorescence for clinical applications are discussed.

Wine and brandies are multicomponent systems and conventional fluorescence techniques, relying on recording of single emission or excitation spectra, are often insufficient. In such cases synchronous fluorescence spectra can be used for revealing the potential of the fluorescence techniques. The technique is based on simultaneously scanning of the excitation and emission wavelength with constant difference (Δλ) maintained between them. In this study the measurements were made using FluoroLog3 spectrofluorimeter (HORIBA Jobin Yvon, France) and collected for excitation and emission in the wavelength region 220 - 700 nm using wavelength interval Δλ from 10 to 100 nm in 10 nm steps. This research includes the results obtained for brandy and red wine samples. Fluorescence analysis takes advantage in the presence of natural fluorophores in wines and brandies, such as gallic, vanillic, p-coumaric, syringic, ferulic acid, umbelliferone, scopoletin and etc. Applying of synchronous fluorescence spectroscopy for analysis of these types of alcohols allows us to estimate the quality of wines and also to detect adulteration of brandies like adding of a caramel to wine distillates for imitating the quality of the original product aged in oak casks.

The experimental investigations on different aspects of optical tomography require the knowledge of the optical parameters of tissues and tissue-like phantoms in order to unambiguously interpret the experimental data and specify characteristic inhomogeneities in tissue diagnostics. The main optical parameters of interest are the absorption coefficient, the scattering, backscattering, and reduced-scattering coefficients, the total attenuation (extinction) coefficient and the anisotropy factor. In this work, we extend our investigations of the optical properties of tissuemimicking phantoms, such as Intralipid-20% fat emulsion, using an approach we have developed recently based on the peculiarities of laser radiation beams propagating through semi-infinite turbid media. The dependence of the total attenuation coefficient on the Intralipid concentration, for laser radiation wavelengths λ=405, 672, 850, and 1314 nm, is studied, by using a set of phantoms consisting of different dilutions of Intralipid in distilled water. The experimental results for the extinction are in agreement with our previous results and with empiric formulae found by other authors concerning the wavelength dependence of the scattering coefficient of Intralipid -10% and Intralipid - 20%. They are also in agreement with known data of the water absorptance. As a whole, the results obtained in this work confirm the consideration of the experimental phantoms as semi-infinite media. They also confirm and extend theoretical and experimental results obtained previously, and reveal advantages of using longer wavelengths for deeper diagnostics of tissues and mimic turbid media.

Autofluorescence has been proven to be a very sensitive, accurate, noninvasive method for detection of early pathological changes in tissues. This optical method has the potential to provide a real-time diagnosis of different benign, dysplastic and malignant tissue pathologies. We obtain tissue samples after surgical excision of preliminary clinically diagnosed tumours. Ethical approval for our investigations is received from Ethical Committee of University Hospital “Queen Jiovanna-ISUL” – Sofia, where the samples will be obtained as well. The investigations presented in this report are based on ex vivo measurements of excitation-emission matrices (EEM) for normal and neoplastic human tissue samples with various cutaneous malignant and dysplastic lesions, as well for gastrointestinal tract (GIT) normal mucosa, polyps and carcinoma. The origins of the endogenous fluorescence are found and the differences observed are discussed from the point of view of their diagnostic value and correlation with the morphological and biochemical changes occurred during the tumour development.

Three samples taken from two paintings partly burned by fire are investigated for cleaning with lasers. The paintings belong to the collection of the National Gallery of Athens and were made by the great Greek artist Konstantinos Parthenis. To remove the damaged surface and achieve an acceptable restoration result, the optimum combination of fluence and wavelength are sought. Seven different wavelengths with a set of fluences where used, i.e., the five harmonics of a Nd:YAG laser (1064, 532, 355, 266, and 213 nm), a TEA 10.6 μm CO₂ and a free running laser Er:YAG 2.94 μm. Characterization was performed prior and after the cleaning process by optical and electron microscopy and analysis (SEM/BSE EDS), as well as X-Ray Diffraction (XRD). The results of this work indicate that the wavelength in the visible spectrum (532 nm) with fluences between 0.1–0.4J/cm² show the optimum cleaning. The optical microscopy observation shows that with these laser parameters the burnt layer was preferentially removed, exposing the original colors that Parthenis had used in these paintings. Electron microscopy imaging and chemical analysis revealed that the original texture and materials of these samples are preserved after irradiation. Since the damage varies along the surface of the painting, more experiments should be performed in order to find and optimize the full cleaning and characterization process for the homogeneous cleaning of the whole surface of the painting.

The efficiency of the laser radiation effect on the oxyhemoglobin in blood vessels and its dependence on the wavelength of the irradiation are investigated. In vivo experimental measurements of the quantum yield of the laser-induced photodissociation of oxyhemoglobin in cutaneous blood vessels in the visible spectral range are presented. The spectral effectiveness of the photodissociation approximately correlates with their absorption spectrum and the transmission spectrum of skin tissue. Different aspects of biomedical application of this phenomenon are discussed. Non-invasive three-wavelength technique for determination of oxyhemoglobin concentrations in blood is also developed.

Liposomes are the most attractive lipid vesicles for targeted drug delivery in nanomedicine, behaving also as cell models in biophotonics research. The characterization of the micro-mechanical properties of drug carriers is an important issue and many analytical techniques are employed, as, for example, optical tweezers and atomic force microscopy. In this work, polyol hyperbranched polymers (HBPs) have been employed along with liposomes for the preparation of new chimeric advanced drug delivery nanosystems (Chi-aDDnSs). Aliphatic polyester HBPs with three different pseudogenerations G2, G3 and G4 with 16, 32, and 64 peripheral hydroxyl groups, respectively, have been incorporated in liposomal formulation. The atomic force microscopy (AFM) technique was used for the comparative study of the morphology and the mechanical properties of Chi-aDDnSs and conventional DDnS. The effects of both the HBPs architecture and the polyesters pseudogeneration number in the stability and the stiffness of chi-aDDnSs were examined. From the force-distance curves of AFM spectroscopy, the Young’s modulus was calculated.

Dermatological diseases, such as neurofibroma (Recklinghausen disease) or hemangiomas can be efficiently treated using photothermolysis from laser irradiation. We have utilized a developed 975 nm fiber diode laser as a low-cost alternative over common Nd:YAG lasers. This paper describes the investigations of interaction of 975 nm diode laser radiation-pulses with optical skin phantoms which were designed and manufactured in our laboratory. Such phantoms match the scattering and absorption coefficients of real human skin. Spatial and temporal temperature evolutions during laser irradiation with various laser settings (pulsed and CW mode), were recorded by an IR camera. Subsequent analysis yielded optimum choice of parameters for laser therapy of coetaneous lesions.

We report the results of our study of the spectral shifts caused by surrounding refractive index changes (SRI) in bent fibre tapers. Fused and etched fibre tapers were fabricated using a gas burner and HF acid. Spectral shifts as high as 200 nm have been observed for SRI variations from 1.33 to 1.44 and sensitivity as high as 830 nm/r.i.u. around water RI values. We present results for refractometric measurements of cow milk of varying fat content and compare results with those obtained with conventional Abbe refractometers and high sensitivity double resonance LPGs.

The filamentation of focused beams at wavelength of 800 and 248 nm in air is studied experimentally and numerically. The results indicate that relatively tight focusing can lead to the coalescence of individual regions of high fluence and high plasma density that result from multiple refocusing, whereas in the case of weak focusing such regions are separated in the pulse propagation direction. The lower multiphoton ionization order in the case of UV radiation leads to a stronger effect of geometric focusing on filament formation. We show the possibility to control the parameters of femtosecond laser plasma filaments by introducing astigmatism in laser beam wavefront. Strong astigmatism can lead to the splitting of the channel into two separate regions. We demonstrate that the self-phase modulation in the thin passthrough dielectric plate decreases the distance to the filament start in air and increases the length of plasma channel.

The interpenetration of the main ideas and methods being used in different fields of science and technology has become one of the decisive factors in the progress of science as a whole. Mathematical analogies between different physical systems can be extremely fruitful in understanding the novel physical concepts. Accordingly to the new theory of bio-energy transport along protein molecules in living systems and modified Davydov molecular soliton theory, we propose a nonautonomous model that can be considered as a candidate of the bio-energy transport mechanism in protein molecules. Based on the generalized nonlinear Schrödinger equation model with varying-intime harmonic oscillator potential, we show that conditions of its exact integrability in one-dimensional case indicate conclusively the way for solitonlike pulse generation in polypeptide molecular systems. The most important properties of this soliton transport of bio-energy are related with periodically changed energy-release conditions and the influences of structure nonuniformity in protein molecules. By analogy with the corresponding optical phenomena in inhomogeneous optical fibers with varying properties along the length, we study the main features of modified Davydov soliton on the basis of the unified nonautonomous nonlinear Schrodinger model in the parameters region of the exact integrability of the model under consideration.

Using the results for the time- and spatially-averaged electron temperature, which were previously obtained by the lineratio method of optical emission spectroscopy for several metal halide vapor lasers excited in nanosecond pulsed longitudinal discharge and analytically solving steady-state heat conduction equation for electrons as well, radial distribution of time-averaged electron temperature, i.e. spatially-resolved electron temperature, is obtained. 2D (r, t) numerical solution of nonstationary heat conduction equation for electrons is also found out.

It is known that the Nonlinear Schrödinger equation (NLSE) very well describes the evolution of nanosecond and picosecond pulses in isotropic nonlinear dispersive medium. For exploration the propagation of femtosecond and attosecond light pulses it is necessary to be used the more general nonlinear amplitude equation. Therefore it is important to clarify the difference between the solutions of these two equations. In the present paper are investigated the one-dimensional soliton solutions of the NLSE and the nonlinear amplitude equation describing the evolution of optical pulses in a single-mode fiber with negative dispersion of the group velocity. It is shown that for a fundamental soliton the main difference between the two solutions is in the phases of the pulses. It is also seen that the soliton obtained in our work is with the same width as this of the NLSE but with an amplitude √2 times greater.

We present the algorithm based on the Lax pair generalization to reveal some properties of nonautonomous KdV solitons. Starting from the general method of solution for the nonisospectral IST problem, we demonstrate how the varying-coefficient KdV equation can arise in nonuniformed and inhomogeneous media. We write down the one- and two-soliton solution of the nonautonomous varying-coefficient KdV with the time-dependent spectral parameter and consider some special cases of the isospectral solutions of the KdV equation with varying dispersion, nonlinearity, and gain. Finally, we compare these solutions with the nonautonomous solitons of the NLSE emphasizing their common features.

The nonlinear Schrödinger equation (NLSE) model with an external harmonic potential is one of the most important in modern science. This model makes it possible to analyze a variety of nonlinear phenomena, in nonlinear optics and laser physics, biophysics and in the theory of Bose-Einstein condensation of atoms. It is shown that the main specific feature of the dynamics of dark GP matter wave solitons in a parabolic trap is the formation of solitons with dynamically changing form-factors producing the periodic variation in the modulation depth (the degree of “blackness”) of dark solitons. In general, the period of dark soliton oscillations in trapping potential depends on the specific conditions of the experiment and does not coincide with the oscillation period of a linear quantum-mechanical oscillator. In the case of an immobile pedestal in the trap, the oscillation period of the black soliton considerably increases because of the periodic transformation of the black soliton to the gray one and vice versa. Surprisingly, that if the dark soliton is superimposed on the base pedestal oscillating in the trap and displaced from the trap center, the oscillation period of the dark soliton coincides with the period of oscillations of the linear harmonic oscillator, while the dynamics of the dark soliton is similar to that of a classical particle obeying the Newton mechanics laws.

The famous principle of wave-particle duality in quantum physics holds that matter and light exhibit the behaviors of both waves and particles, depending on the experiment being performed. Is there a similar analogy for the soliton? What other analogies have not been established so far? The key conceptual result of our work consists in the demonstration of a deep analogy between the Schrödinger soliton tunneling through the classically forbidden potential barrier and the Gamow scenario of quantum mechanical tunneling effect and alpha-particle decay. Guided by this constructive (but obviously only formal) analogy, we reveal a hidden role of the soliton self-interaction ("binding") energy and its dramatic impact on the wave-particle duality of scattered solitons. The solitonic analog of the de Broglie wavelength, "shooting out" of high-energy de Broglie video-solitons from arbitrary N-soliton superposition and phenomena similar to the Ramsauer-Taunsend effect and the Geiger--Nuttall law ought to be expected for solitons.

In this work we report experimental measurement of an intentionally introduced pulse front tilt on femtosecond laser pulses by using an inverted field correlator/interferometer. The results obtained with a low-dispersion diffraction grating are in good qualitative agreement with the data from a previously developed analytical model and with these from an independent interferometric measurement.

In this paper we present numerical investigation of the influence of intrapulse Raman scattering (IRS) on the stable stationary pulses. Our basic equation, namely cubic-quintic Ginzburg-Landau equation describes the propagation of ultra-short optical pulses under the effect of IRS in the presence of linear and nonlinear gain as well as spectral filtering. Our aim is to examine numerically the influence of IRS, on the stable stationary pulses in the presence of constant linear and nonlinear gain as well as spectral filtering. Numerical solution of our basic equation is performed by means of the “fourth-order Runge-Kutta method in the interaction picture method” method. We found that the small change of the value of the parameter which describes IRS leads to qualitatively different behavior of the evolution of pulse amplitudes. In order to study the observed strong dependence on the IRS, the perturbation method of conserved quantities of the nonlinear Schrodinger equation is applied. The numerical analysis of the derived nonlinear system of ordinary differential equations has shown that our numerical findings are related to the existence of the Poincare-Andronov-Hopf bifurcation.

We study the soliton time shift in the presence of linear and nonlinear gain, saturation of the nonlinear refractive index, spectral filtering, third-order of dispersion and self-steepening effect. The applied model generalizes the complex cubicquintic Ginzburg-Landau equation (CCQGLE) with the basic higher-order effects in fibers: the intrapulse Raman scattering (IRS), third-order of dispersion (TOD) and self-steepening effect. Soliton perturbation theory (SPT) is derived with which the influence of the saturation of the nonlinear refraction index, self-steepening and TOD on the appearance of the Poincare-Andronov-Hopf bifurcation is analyzed. It has been shown that TOD and self-steepening effect can lead to reduction in the time shift of the pulse. This prediction has been verified by numerical solution of generalized CCQGLE.

The phenomenon of dynamic speckle is used for non-invasive whole-field detection and visualization of physical or biological activity in various objects through statistical description of laser speckle dynamics. Usage of 2D optical sensors to capture sequences of correlated 2D speckle patterns allows for building a pointwise estimate of a given statistical measure which should give a quantitative high contrast detailed 2D map of the spatial distribution of activity across the object surface. The aim of the present paper is to find out an effective way to enhance visualization of the activity map obtained by the normalized correlation-based algorithms. Similar to all processing algorithms, the built estimates exhibit strong fluctuations from point to point due to speckle nature of the acquired patterns. The fluctuations decrease the contrast of the built 2D activity map and worsen sensitivity and resolution of the dynamic speckle method. As a first task, we studied the distributions of the built estimates by processing of synthetic speckle patterns. As a second task, we applied smoothing to the activity map to achieve enhanced visualization. As a third task we considered building a map of a parameter related to the correlation radius of the temporal correlation function of the processes undergoing within the sample. The results are verified both by simulation and experiment.

In this article we present a study of the photoinduced birefringence (Δn) in films of a water soluble azopolymer: poly[1- [4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). Varying the concentration of the azopolymer in the solution, films with wide range of thicknesses are obtained – from 50 to 2500 nm. The film thickness is determined with a Talystep precision profilometer. Birefringence is measured using a polarimetric setup with a recording laser at 473 nm and probe He-Ne laser at 633 nm. As shown experimentally, the maximal photoinduced birefringence (Δn_max) does not depend on the thickness and is of the order of 0.07 for all of the investigated samples. The recording time however considerably increases for films thicker than 500 nm.

Successful application of optical materials in lens design is based on the knowledge of their refractive and dispersive properties in the considered spectral region. We have obtained precise refractometric data of various optical polymers in the visible and near-infrared area. Different refractive index measuring techniques have been used. On base of the detailed study of refractive, dispersive, thermal and other important material characteristics of polymers, optical design of all-plastic systems for laser applications is proposed: a laser expander for 532 nm emission wavelength and a focusing microlens intended for reading/recording laser heads of DVD discs at 650 nm. Geometric and wave aberrations are computed and minimised.

The cations of 3d metals in water and alcohol create aqueous complexes, with the creation and stability of the aqua cations are of particular importance. The number of water molecules connected with the metal by direct metal-oxygen bonds determines the properties of the complex. The traditional measurements of, for example, ions mobility, ostensible radii of the hydration ions and the entropy of hydration, do not yield detailed information for the aqua ions, which is why studies of their spectral properties becomes necessary. These properties depend on the composition and the symmetry of the surrounding medium. In this work, the absorption of the complexes [Co(H₂O)6]²⁺ and [Co+Ni(H₂O)6]²⁺ were measured in the spectral region 395 – 600 nm. The energies of the electron transitions in Co²⁺ were calculated and the role of the spin-orbit coupling was evaluated. The calculated and experimental Lorentz profiles of the complexes investigated are also presented.

Modulated 532 nm laser pulses were generated by a Nd:YVO₄ microchip laser and a KTP crystal end-pumped by a 808 nm laser diode. The interest in such works arise from the efficiency of this type of laser in several applications. To obtain the desired type of the modulated laser pulses, the electrical circuit of the laser diode was designed so as to enable varying their driving signal and current values. Different modulated signals were used, such as square wave, sine wave, and burst mode pulses. Varying the peak drive current, the duty cycle, and the number of pulses allowed us to adjust the laser energy. For the burst mode experiment, the pulse energy obtained was about 1.2 μJ.

Recent developments in laser materials, such as Nd/Cr:YAG ceramic with a broad absorption spectrum in the visible, have been applied to achieve highly-efficient and low-cost optical pumping by conventional sources. Our simulator based on the implementation of a mathematical model under Matlab Simulink allowed us to show the correlation between the characteristics of the laser mode of operation (such as Relaxation, Quasi-continuous wave (QCW), Continuous wave, Burst, Q-switched) and the various physical parameters of the oscillator. This model was applied to the Nd:YAG crystal, Nd/Cr:GSGG crystal and Nd/Cr:YAG ceramic. The simulation results demonstrated that Nd/Cr:YAG ceramic is an excellent candidate for solar and quasi-solar pumping, as its pumping efficiency exceeds by a factor of four that of the Nd:YAG crystal medium, and by a factor of two that of Nd/Cr:GSGG crystal. A pumping by a light guide was considered in this simulation.