Laser diodes power sources providing currents ranging up to 100 amperes for a period of 5 ns to 100 μs are well known. Power Pulses Source is researched and refined in this paper, which gives the possibility for expanding of its application in the field of optical electronics, medicine and welding technologies. The power pulses source is controlled by universal and general elements. The power pulses source possibilities are researched in theory and experiments, with present supply providing currents ranging from 30 to 300 amperes and a period of 100 ns to 10 μs. A multiple variation powering from 24 to 50 volts is expected. The increasing of the pulses power is achieved by key elements placed in parallel. The experimental and simulation results are presented with the help of graphics and tables. The research is done for different loads, which allow the power pulse source to have wide application in different areas.

It has been demonstrated that the Copper Bromide Laser is a promising tool in the micro-machining of several materials (Al, Cu, Brass, Si). These results were achieved with the combination of high average laser power, short pulses, visible radiation, high repetition rate and close to the diffraction-limited beam divergence. The heat-affected zone (HAZ) was relatively small and depends from the cutting speed and number of repetition.

Phase transitions induced by laser irradiation in CdTe wafers have been studied in situ and experimental and computer simulation methods. The samples were irradiated by ruby laser with pulse duration 80 ns in energy density range from 0.02 to 0.5 J/cm². Time-resolved reflectivity (TRR) measurements were carried out at the wavelengths of λ₁=1.064 μm and λ₂=0.532 μm. Dynamics of transmissivity was studied at λ₁. Photoluminescence of CdTe, excited by the ruby laser single pulse, was also investigated. The character of TRR transients changes with the increase of irradiation energy density. The changes are more considerable at λ₁ than at λ₂. The time dependencies of reflectivity are explained by the changes of optical parameters of CdTe in course of laser-induced melting, solidification and evaporation. The experimental data obtained from transmissivity and photoluminescence measurements correlate with those from TRR transients. Laser-induced melting, crystallization and evaporation processes were studied on the basis of the computational solution of a two-phase moving boundary problem with two moving interfaces. The calculated dependency of melt duration on energy density is in a reasonable agreement with experimental data. From our investigation it follows that in the molten state CdTe is characterized by constant or weakly changing reflectivity in the temperature range from T_m to 3000 K.

The opportunity of using intracavity laser spectroscopy for studying the process of formation of fullerenic molecular clusters on carbon and metal-carbon to a basis, synthesized in light erosion to heterogeneous plasma was investigated. As an indicator of formation of fullerenic weights in plasma the effect of condensation of a spectrum radiation tunable the laser served.

Polarization holographic gratings in azopolymers are due to three photoinduced effects: linear anisotropy, circular anisotropy, and surface relief. In our polymers the surface relief grating is with doubled frequency with respect to the volume anisotropic grating. A theoretical analysis is presented and compared with experimental data.

We investigate the photoinduced processes in films of a series of three side-chain azobenzene-containing polymers, which differ only in the length of the spacers attaching the chromophores to the main chain. Two of them are amorphous and one is liquid-crystalline. Illumination of the polymer films with an Ar-laser beam results in changes in their absorption spectra and to the appearance of dichroism. In the polymer with shortest spacers the irradiation gives rise to a considerable photoequilibrium concentration of cis-azobenzenes resulting from the photoinduced reversible trans-cis isomerization. In the polymer with long spacers, which is liquid-crystalline, the main result from the irradiation is the reorientation of the trans-azobenzenes and the photodichroism in this film is much larger. The induced dichroism is stable in this liquid-crystalline film; it disappears with time in the amorphous films.

Refraction index of edible films from polysaccharides (pectin, xanthan, carboxy-methyl-cellulose, polymixan) has been investigated using laser microrefractomeeter, constructed by the authors. Experimental data about the optical density and the thickness of the edible films have been obtained. The results from the investigation can be used in the development of new packing technologies for food products.

In this study stainless steel, silicon and silica glass are used as representatives of metal, semiconductor and isolator with the purpose to create an experimental model for studying the formation of minerals like hydroxyapatite (HA, the bone and teeth mineral part) from aqueous solutions. The samples are Na⁺ implanted and consequently subjected to thermal treatment in air at 873 K. Implantation with Na⁺ is known to lead to formation of hydroxylated surface, i.e. formation of metal- or Si-OH^- groups upon immersion in a liquid, simulating the human blood plasma (simulated body fluid, SBF). The negatively charged hydroxylated surfaces induce HA formation in SBF. The samples are immersed in SBF, irradiated through the solution with a scanning laser beam (CuBr pulsed laser equipped with a scanning system) and subsequently soaked in the solution at 37°C for a shorter time, comparing to the traditional methods for HA growing. The grown HA layers are investigated by Fourier Transform Infrared (FTIR) and Raman Spectroscopies, X-ray Diffraction (XRD), Light Microscopy (LM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) Spectroscopy to evaluate the effect of the surface modification by the thermal treatment following the ion implantation, as well as the effect of the laser irradiation on the process of HA formation.

In this paper the use of stainless steel, silicon and silica glass substrates for the growth of hydroxyapatite (HA, widely used as artificial bone material), induced by a laser-liquid-solid-interaction is reported. The method allows growing of HA layer by using the interaction between a laser beam and a liquid precursor solution, as well as laser irradiation of the substrate during the laser-liquid interaction. The scanned laser beam (pulsed CuBr laser) is directed at the solid substrate, which is immersed in the solution, which resembles the ion composition and concentrations of the human blood plasma (simulated body fluid, SBF). The set-up includes an open deposition system, which allows the introduction of the laser beam led by a scanning system. It is shown that the proposed method enhances the HA formation, in comparison with the traditional methods of prolonged soaking in SBF. The HA layers grown in this manner are investigated by Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) Spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) and Raman Spectroscopy.

ZnO thin layers are promising materials for near UV emission and absorption optical devices, mainly for its relatively wide band gap (3.4 eV at 4.2 K). However, the problems with the optimal growth of the ZnO thin layer depositions are not satisfactory solved. The aim of this study was to compare differences between the layers deposited from the pure Zn target and the target from sintered ZnO. The growth of ZnO thin layers was performed on sapphire substrate under various conditions. The layers were prepared by the pulsed laser deposition using THG Nd:YAG laser at 355 nm. Characteristics of the layers were examined using the methods of atomic force microscopy, scanning electron microscopy and energy dispersive x-ray microanalyses.

The aim of this study was to compare some differences between the growth rate, roughness and surface morphology of Cu and W layers. The growth of metal thin films was performed on silicon substrate. The layers were prepared by the pulsed laser deposition (PLD) using THG Nd:YAG laser at 355 nm. The number of laser pulses (time of deposition) varied from 1000 to 20000. The characteristics of the layers were examined using the methods of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results show that the growth rate of W is higher than Cu.

We present results of the research and development of the CW medium-power fiber lasers emitting in a range of 1-2 μm. Realized light sources are based on the application of rare-earth doped fibers and Raman converters pumped by semiconductor sources. A combination of the fiber lasers emitting at different wavelengths with Raman converters based on germanium or/and phosphorous fibers allows one to build a laser source emitting at any wavelength of near IR range. The reached quality of the fabricated fibers and optimization of reflecting Bragg gratings allowed us to demonstrate fiber lasers with a quantum efficiency closed to 90%. The fabricated lasers were used for a realization of Raman converters emitting at the various wavelengths.

The contribution deals with three investigated problems on Chemical Oxygen-Iodine Laser (COIL) and utilization of the results in advanced COIL development and advanced techniques connected with the COIL. These problems are following i) A gain modulation on the laser transition in iodine atom, I(²P_1/2)-(²P_3/2), by an external magnetic field, and its utilization for the COIL output power stabilization, ii) The evaluation of the Einstein A-coefficient of singlet oxygen, O₂(¹Δ_g), and utilization of this coefficient in the advanced diagnostics for O₂(¹Δ_g) determination in a laser pumping, and iii) A development of the advanced COIL using a chemically driven iodine atom delivery system, and a confrontation of advantages of this system with disadvantages of conventional source of atomic iodine via dissociated molecular iodine. Examples of few recent experimental results are presented.

Deep ultraviolet laser generation is of great interest in connection with both the development of new industrial technologies and applications in medicine, biology, chemistry, etc. The development of metal vapor UV lasers oscillating in the pulsed mode with high pulse repetition frequencies and producing high average output powers is of particular interest for microprocessing of polymers, photolithography and fluorescence applications. At present, metal vapor lasers generate deep-UV radiation on the base of two methods. The first method is non-linear conversion of powerful laser generation from the visible region into the deep ultraviolet region. The second method is direct UV laser action on ion and atomic transitions of different metals.

We demonstrate and investigate (theory, experiment) a peculiar mode of cw Yb³⁺:doped crystal laser operation when two emissions, at two independently tunable wavelengths, are simultaneously produced. Both emissions are generated from a single pumped volume and take place either in a single beam or in spatially separated beams. The laser employs original two-channel cavities that use a Passively Self-Injection Locking (PSIL) control to reduce the intracavity losses or a very simple for practical realization two near collinear channels cavity. A two-wavelength, single, longitudinal mode generation is also obtained. The results reported are based on the example of Yb³⁺:GGG laser and Yb³⁺:YAH laser. The lasers operate in the range 1023-1033 nm and 1030-1040 nm, respectively with a total output power of ~0.4 W.

The technique for measuring wave front distortions in optical elements by the shadow method is developed. Shadow pictures obtained for mutually perpendicular orientations of the Foucault knife-edge are the distributions of components of the gradient of the function describing the wave front relief, so that its shape can be restored by means of integration. An example of measurements of wave front distortions in large-scale optical KDP crystal elements employing the IAB 451 device is given.

An analysis of the maximum average output power and specific average output power achieved in a copper bromide vapor laser is reported. A 100 W CuBr laser MOPA system is presented.

We experimentally generate optical vortices in the output beam of Ti:Sapphire laser emitting 20-fs pulses. Screw phase dislocations are imposed in each spectral component of the short pulses by aligning computer-generated hologram within a 4f-setup.

The spectra of pulsation of signal beam of intracavity four-wave mixing in 1 kW fast-axial-flow CO₂ laser were measured. The information about turbulent parameters of laser-active medium flow was obtained.

It is theoretically shown, that the Brillouin laser of the conjugated wave allows expanding abilities of PC at SBS for excimer lasers broadband radiation. The optical arrangements and nonlinear media for PC at SBS with a feedback of excimer lasers radiation are offered.

It is shown theoretically, that the axial modes of radiation in PC mirrors at four-wave mixing with a feedback without selection in the resonator result to generation of a direct wave and suppress generation of a backward wave with the conjugated wave front. It is established, that due to axial modes in self-starting lasers the holographic feedback is carrying out the function of the output mirror of the resonator forms. The large role of polarization discrimination at Faraday effect in PC mirrors at four-wave mixing with a feedback and in self-adaptive lasers is marked.

The transition from weak to heavy current discharge in the cross-section of radio frequency helium discharge is numerically investigated. It is found the lowest possible voltage, so that this transition takes place. It is established a possible rise of a pre-gap of the discharge on a line, non coinciding with the minimum distance between the electrodes. The obtained results are in good agreement with the existing experimental data. The method is applied and investigations are made for constructive engineering solutions, influenced on the break-through process.

This report presents the development of single-beam barrier laser security system. The system utilizes the near infrared (IR) range λ=(850÷900)nm. The security system consists of several blocks: Transmitter; Receiver; Logical Unit; Indication; Power Supply. There are four individually software programmable security zones Z1 ÷ Z4. The control logic is implemented on a PIC16F84 MCU. The infrared beam is a pulse pack, coded and modulated in the transmitter with frequency of 36 kHz. The receiver demodulates and decodes the beam. The software for the MCU is developed along with the electrical circuits of the security system.

On the basis of thin-film anisotropic thermo converters was developed universal multifunctional compact measuring instrument of characteristics of high intensity laser radiation.

A mirror with a controllable focal length designed for the high power cw CO₂ industrial laser was integrated into the laser beam guiding system in order to verify conditions for the dynamic control of the laser beam focusing properties. The ability of the mirror to correct the thermal distortions in the laser output window was investigated by measuring the beam characteristics versus the mirror shape at different conditions of the laser operation defined by the output power level. The experimental tests prove that the mirror enables dynamic adjustments of the laser beam diameters at the focusing optics and in consequence the control of the focused beam parameters.

In this paper we model the dynamical behavior of a green-emitting upconversion-pumped Er(0.5 at.%):YAG laser, using the rate equations. An important peculiarity of this laser is the reabsorption of laser radiation by the parasitic ⁴I_13/2→²H2_9/2 excited-state absorption process. This process represents a supplementary intensity-dependent loss mechanism that can, in certain conditions, produce self-pulsing behavior of the Er:YAG laser. Stability analysis is used to identify the various regimes of laser emission and the bifurcations leading to them. The results are illustrated by Runge-Kutta integration of the rate equations for values of control parameters corresponding to various laser emission regimes. The model can be applied for the prediction and enhancement of the performances of the green Er³⁺ upconversion lasers.

We present two simple and effective approaches for widening of the tuning range of the two-wavelength generation in two-channel laser cavity. The first is based on the use of combination of interference wedge and linear neutral filter and the second on the use of active mirror. This widening is combined with near equal intensities in both emissions. The use of the active mirror assures a real simultaneous two-wavelength operation. We consider a dye laser.

We have developed and investigated a simple solution of tunable laser with strongly decreased background emission (max pick-to-pick power ratio ≤ 10^-8) by generation at additional wavelengths, except the selected. The cavity scheme permits to obtain easily laser output only at the selected wavelength, using a simple system with interference wedges. The spectral position and the losses at both generations are easily and independently controlled to needed optimal values. The theoretical treatment based on the rate equation system, shows that for the appropriate chosen conditions the technique developed permits to reduce by approximately two orders of magnitude the intensity of the background emission about the selected line (pick power to be less than 10^-8). The investigation is on the example of pulsed dye lasers. The results are applicable for other tunable lasers with homogeneously broadened active medium such as Ti:sapphire, diode, etc. The lasers of considered type (with high spectral purity) are of essential interest for application in biomedical investigations of tissue luminescence spectrum, in Raman spectroscopic investigation, in isotope separation.

An experimental study on a new laser tube construction for the UV Cu⁺ Ne-CuBr laser, conformable to our previous investigation on the reasons leading to a reduction of the tube lifetime, is reported. An optimization of the UV multilane average output power with respect to the discharge condition is presented. Laser tube lifetime up to 180 hours at an average laser power of about 700 mW is also reported.

We present preliminary results on the SHG properties of a number of organic materials in powder form using a Q-switched Nd-YAG laser (7 ns, λ=1064 nm) as the fundamental input. The organic powder was packed into sealed cells, which is set at an angle of 45⁰ to the input beam. The intensity of reflected S.H. light (λ= 532 nm) was measured at an angle of 90° to the input beam. The urea was subjected to the same treatment, and used as a reference. Beside that we have calculated second-order hyperpolarizibilities (β) of the studied materials using PC-GAMESS package.

This paper investigates, theoretically and experimentally, the elements which influence the gain distribute of laser medium. A high power storage laser module has been manufactured. In this module a 6 mm diameter Nd:YAG rod which is 100 mm long is pumped by nine diode-arrays (the peak pump-power is 6500 W). Each array consisted of nine diodes. On account of the uniformity of distribute in whole laser medium, a Nd-doping of 0.6% laser rod is chosen, and in order to eliminate self-oscillation, two ends are made to inclined planes. Numerical calculation has been done to optimize the distance between the diode and Nd:YAG. The experiment result approved that the gain coefficient of this module is 0.3 cm^-1, from it we can infer that the storage power is about 400 mJ per pulse.

Narrowly size distributed PbSe quantum dots were fabricated in phosphate glasses doped with PbO+ZnSe and PbSe by thermal treatment. Absorption spectra in 3 µm range are studied for the first time. Non-linear absorption of the samples near 1.54 μm is studied.

This paper presents the results of works of ILIT RAS on introduction of computer biomodeling and laser stereolithography into medicine practice, and the results of the experiments on 1) rapid manufacture of plastic copies of fragments of the human skeleton; 2) creation of computer models of implants for maxillofacial surgery, fabrication of their plastic copies and moulds for fabrication of implants from biocompatible materials; 3) direct fabrication of biocompatible and bioactive implants for substitution of bone tissue defects.

The hard tissue laser ablation and the relevant laser applications on dental tissues have attracted several investigators, since the ablation efficiency, the lateral thermal and/or mechanical damage and the final surface characteristics must be optimised, in order to fulfil the efficient and safe removal of pathological dental areas in a clinical environment. For example, it was theoretically predicted that the lateral tissue thermal damage might be limited when the laser intensity is high and the interaction time is short. In this case the Q-switched Er:YAG laser operating with a pulse length below the thermal relaxation time of the irradiated tissue, is considered to be very effective. Therefore, the efficacy of the Q-switched Er:YAG laser, versus the free-running operation mode, on dentine ablation was studied, as well as the morphological changes at the irradiated dentine surface. Additionally, the interaction of nanosecond UV laser pulses and IR/visible picosecond laser pulses with hard tissue samples was investigated for comparative evaluation of the different laser ablation mechanisms.

Mid-IR lasers are already used successfully in numerous surgical operations. The Er:YAG and the HF laser, are the main laser sources emitting in the 3.0 μm range of the spectrum, and as this wavelength coincides with the peak of the water and other main soft and hard tissue components absorption curves, it is clear that these lasers would be very useful in numerous medical fields as dentistry, dermatology, angioplasty, ophthalmology etc. Recently, the development of flexible, low loss, able to deliver high power and safe to enter the human body waveguides and fibers for pulsed mid-infrared laser radiation initiated the efforts of the extension of laser surgery in the area of the minimally invasive endoscopy. The laser-induced fluorescence (LIF) is proposed for diagnosis in several pathologies, as in arterial atherosclerosis, in malignancy or for early dental caries detection. LIF is also investigated as a suitable method for monitoring the on line laser surgery interventions.

A laser-spectroscopy complex was developed for fluorescent diagnostics and photodynamic therapy of age related macula degeneration using the Russian photosensitizer Photosense. The complex is based on slit lamp which was additionally equipped with an optical adapter, and the video adapter allows to combine the procedure of photodynamic therapy and the control of its carrying in the frame work of one procedure. The sensitivity and spatial resolution of the complex were investigated using a special test object. The availability of the developed complex and Photosense itself was examined on experimental animals.

In this study we evaluate the cytotoxicity of 5,10,15,20- tetra (4-sulfophenyl) porphyrins on a tumor cell line LSCC-SF-Mc29, obtained from a transplantable chicken hepatoma induced by the myelocytomatosis virus Mc29, a timor line LSR-SF-SR, obtained from a transplantable sarcoma in rat induced by Rous sarcoma virus strain Schmidt-Ruppin and for normal mouse cell line (BALB/c-3T3-A31) and bovine kidney cell line (MDBK). The cells were exposed to irradiation from a pulsed CuBr vapor laser system at 510.6 nm and 578.2 nm at fluence rate 50 mW/cm² and pulse frequency rate 20 kHz. The viability of cells was determined by the neutral red uptake cytotoxicity assay. The light dose-response curves and light exposures that ensure viability drop to 50 % were obtained for each cell line. The cytotoxic effect of TS₄PP is most distinguished for LSCC-SF-Mc29. The bovine cell line is more vulnerable than the mouse line, especially at 510.6 nm. The 2-4 times higher viability of the normal cell lines in comparison with the tumor lines has been obtained.

The goal of this study is fluorescence investigations in the process of caries growth in presence of bacteria metabolism products. Spectra of teeth, illuminated with 337 nm nitrogen laser were measured during in vitro caries formation. Spectra, obtained from sound tooth consist of one intensive peak at 480-500 nm and one secondary peak at 430-450 nm. In the process of the caries formation of the teeth we observed increase in intensity at 430-450 nm and appearance of two peaks in the red spectral region at 590-650 nm. A general decrease in the intensity of the fluorescence signal is observed, but changes in spectral shape are more significant. We observe that the peak increase at 430-450 nm is related to the tooth demineralization. Bacteria presence and their metabolism products induce fluorescence signal in the red region. These results allow consideration of caries in terms of two different processes, which lead to its formation: demineralization and metabolism products increase, which are caused by bacteria activities, and could be used to obtain a more complete picture of caries formation.

The present investigations are directed at a more detailed studying of methods for colour determination aimed at estimation of human teeth whiteness degree, sufficiently handy for common use in clinical practice. In order to be obtained unbiased results of the whitening, specific techniques for the degree of whiteness (coloration) determination had been developed on the basis of common colorimetric and spectral methods and apparatus, including a standard computer processing and accorded to the three-dimensional colour scheme Vita 3D. Comparative experimental investigations with two lasers (Ar+, CuBr) and three experimental whitening compositions for treatment of 6 different groups of samples were carried out. The results of the applied spectral and colorimetric techniques are in a good agreement with those of the standard computer processing of the corresponding digital photographs and comply with the visually estimated degree of the teeth whiteness judged according to the standard reference scale commonly used in the aesthetic dentistry.

The study is devoted to investigation of fluorescent and photodynamic properties of near-infrared photosensitizer bacteriochlorophyllide-serine. The peculiarities of its fluorescence under different laser excitation conditions, dynamics of concentration and selectivity of accumulation were investigated. Photodynamic therapy of mice and investigation of tissue deoxygenation during tumor irradiation were performed. It was shown that bacteriochlorophyllide-serine is an effective photosensitizer for PDT and fluorescent diagnostics of tumors.

Kinetics of water diffusion in laser-irradiated cartilage and cornea was studied. Optical polarization analysis was applied for visualizing of aqueous solution diffused through laser-irradiated biological tissues. Diffusion coefficients of different physiological solutions in cartilage and cornea were measured.

Methods of optical diagnostics and methods of photodynamic therapy are actively used in medico-biological researches. The system for delivery of optical radiation is one of the key methods in these researches. Usually these systems use flexible optical fibers with diameters from 200 to 1000 micron. Two types of systems for delivery are subdivided, first for diagnostic researches, second for therapeutic procedures. Existing diagnostic catheters, which have most widely applied in medicine, have bifurcated with diameter of the tip equal 1.8 mm. These devices, which are called fiber-optical catheters, satisfy the majority endoscopes researches. However, till now the problem of optical-diagnostics inside tissue is not soled. Especially it is important at diagnostics of a mammary gland, livers, thyroid glands tumor, tumor of a brain and some other studies connected with punctures. In these cases, it is necessary that diameter of fiber-optical catheters be less than one millimeter. This work is devoted to the development of these catheters. Also in clinical procedures such as photodynamic therapy (PDT) and interstitial laser photocoagulation (ILP), cylindrical light diffusing tips are rapidly becoming a popular device for the administration of the desired light dose for the illumination of hollow organs, such as bronchus, trachea and oesophagus. This work is devoted to the development of these catheters.

Using scattering of light in Teflon as a scattering element, a new method for measuring power of light radiation of face and cylindrical fibers and photodiodes has been developed. A compact device for measurement has been built, suitable for mass production.

The paper presents the analysis of the requirements to the laser systems used to cure the ischemic disease of the heart by the method of transmyocardial laser revascularization (TMLR). Among the medical laser systems under discussion (solid-state Nd:YAG, Er:YAG, Ho:YAG, excimer lasers, etc.) the high-power CO₂ laser with pulse energy to 40 J is most suited to produce channels in the heart muscle. The paper provides the description and the technical characteristics of medical laser systems of “Perfocor” series, based on high-power waveguide CO₂ lasers with pulse energy to 60 J, developed at ILIT RAS. The methods to determine the time of laser radiation penetration through the myocardium/blood boundary have been briefly discussed. The application of the “Perfocor” system in other laser operations on blood-filled organs has also been discussed.

In this paper we propose a simple method for eliminating the population losses of MC resonances by involving all atoms of the Na ground state in the formation of the narrow coherent resonances observed in the fluorescence when scanning around zero value the applied magnetic field. As a result, dark resonances with a contrast up to 100% have been observed. Results are obtained in two different experimental configurations: using laser excitation of linear and circular polarization, leading to different population redistribution among Zeeman and hf levels. Theoretical analysis of the results is also presented. It is shown that at certain conditions complete optical pumping of atoms to levels F_g=2, m_Fg=2 or m_Fg=-2 can be achieved, which means complete orientation of the atoms.

We report advances towards the development of frequency standards based on narrow two-photon transitions in the silver atom at 576 and 661 nm from the ground 4d¹⁰5s²S_1/2 state to the ²D_3/2,5/2 levels of the configuration 4d⁹5s². We describe detection schemes for metastable atoms, localisation of the position of the metastable ²D_5/2 level and diode-pumped Nd:YLF lasers around 1.3 μm destined to replace dye lasers for both cooling and spectroscopy of the clock transition. Our result for the position of the ²D_5/2 level is more than a factor of two improvement over previous vales.

Techniques for coating hollow glass fibers with layers of silver and cyclic olefin polymer have been developed for low-loss delivery of infrared laser light as well as a visible pilot beam. They have yielded losses of only 0.2 dB/m for Er:YAG and CO₂ laser light and only 0.7 dB/m for red LD laser light. Debris is kept from entering the hollow output end of a fiber by hermitically sealing it with a quartz cap, and various focusing effects in both air and water have been obtained by controlling distal-end geometry of the caps during fabrication. Controlled focus patterns of Er:YAG laser light with an output energy of more than 400 mJ and a 10-Hz repetition rate have been delivered in saline through the fibers with sealing caps. Calculi were fragmented in vitro by using a hollow fiber with a sealing cap. It has been shown that Er:YAG laser combined with an effective delivery system could be used for minimally invasive calculi fragmentation.

Investigation on coherent population trapping and electromagnetic induced absorption effects has been made in Cs vapors. A detailed analysis of degenerate and non-degenerate cases is reported. Possible application to precise magnetic field measurements is discussed and preliminary results described.

The advent of the Dense Wavelength Division Multiplexing (DWDM) technology in Optical Fiber Networks (OFNs) has resulted in the necessity of developing advanced Optical Add/Drop Multiplexers (OADMs) on the basis of submicron Bragg gratings. The OADMs for dense multichannel OFNs with bit rates 10-40 Gbits/s per channel and channel spacing 200, 100 and 50 GHz must possess rectangular-shaped reflection/transmission spectra and linear phase characteristic within the stop/passband. These features can not be achieved using uniform Bragg gratings and therefore nonuniform gratings with space-modulated coupling coefficient and/or phase shifts π should be used. We present the recent advances in the design and fabrication of narrowband wavelength-selective filters for DWDM applications using submicron nonuniform Bragg gratings. The peculiarities of propagation, interaction and diffraction of electromagnetic waves in nonuniform grating structures are considered. Narrowband reflection filters using single-mode quartz fibers with side-polishing and relief gratings on dielectric and polymeric materials are designed and fabricated. The filters have nearly rectangular shape of the stopband with 0.4-1.6 nm width and peak reflectivity R > 99% in the 1.55 μm wavelength region. The architecture of multichannel OADMs for high-speed OFNs using planar polymer Integrated Photonic Circuits (IPCs) with biharmonic Bragg gratings, possessing phase shifts π, is discussed.

We present a further development of the proposed by us an injection-locking technique for all-optical and high gain (~10³-10⁶) amplification of a periodically modulated (PM) intensity, low power (~μW), laser radiation. The problem that limits the use of standard injection locking optical amplifier is to obtain a linear response to the PM injection. We have solved this problem by introducing a competitive CW injection in appropriate ring and linear schemes and have carried out previously the detailed consideration for the sinus low modulated radiation. Here we report the application of our original technique for amplification of information sequences of rectangular pulses. The amplifier operation is modeled with the rate differential equations system. We have shown the applicability of the proposed technique for amplification of pulses with repetition rate more than 40 MHz and in special conditions-to approximately 128 MHz without loss of the information capability. The pumping is with 100-250 MHz mode locked Nd:YAG laser (0.53 μm harmonic). The consideration is on the example of Rhodamin 6G dye laser. The pulses with peak power of 0.1μ W to 200 μW are amplified by factor of 10⁹-10⁶ (to more than 2000 W).

Coherent population trapping (CPT) resonances on the degenerate two-level system of the (F_g=2→F_e=1) transition of the ⁸⁷Rb D₁ line were investigated in an uncoated vacuum cell by means of level-crossing type experiments-sweeping a magnetic field around zero value and using a single laser beam. The two-photon resonance manifests itself as fluorescence canceling when the system of levels is degenerate (at zero point of magnetic field). The influence of weak transverse magnetic fields on the amplitude and width of the resonance was investigated. The CPT resonances were observed with linear, circular and elliptical polarized laser light. Transverse magnetic field widens the resonances obtained by linear and circular polarization but splits the resonance created by slightly elliptically polarized laser light. The dependence of this splitting on the elliptical ratio and experimental geometry were investigated. Due to its narrow width and sensitivity to low magnetic fields (< 1 G) this resonance is very promising for small magnetic field measurement.

In this paper we present a detailed description of a method for reduction of the light shift in laser-pumped gas-cell atomic clocks. The method consists in using a multi-frequency optical pumping obtained through frequency modulation of the laser spectrum with precisely controllable parameters. Experimental evidence of a strong reduction of the frequency dependence of the LS in an optical pumping Rb gas-cell clock is demonstrated in a large frequency interval, which is in a very good agreement with the numerical estimations reported.

The quenching process of He (2¹S, 2¹P) states by collisions with nitrogen molecules in a He+N₂ mixture at low pressure is experimentally investigated by a time-resolved spectroscopy method combined with pulse electron excitation. The influence of nitrogen atoms in quenching process is taken into account. The rate constants and corresponding cross sections for quenching ⁴He(2¹S), ⁴He(2¹P), ³He(2¹S) and ³He(2¹P) states by collisions with ground state N₂ molecules at T_g=600 K are: k[⁴He(2¹S)] = (2.7±0.1)x10^-10 cm³s^-1, k[⁴He(2¹P)] = (1.9±0.3)x10^-9 cm³s^-1, k[³He(2¹S)] = (2.8±0.1)x10^-10 cm³s^-1, and k[³He(2¹P)] = (3.2±0.6)x10^-9 cm³s^-1 and σ[⁴He(2¹S)] = (14.2±0.5)x10^-16 cm², σ[⁴He(2¹P)] = (100±16)x10^-16 cm², σ[⁴He(2¹S)] = (12.7±0.5)x10^-16 cm², and σ[⁴He(2¹P)] = (145±27)x10^-16 cm².

In Multi-Spot Diffusing (MSD) configuration, the communication channel can be considered virtually ideal at data rates of hundreds of Mbps. Thus, the main concern is power efficiency. We propose transceiver optical designs that allow for a reconfigurable transmitter output and independent communication channels. Transmitter employs multiple light sources that can be turned on and off independently. This way, optical signal is provided only where it is needed, which optimizes power usage. Receiver utilizes an imaging optical system and segmented photodetector, thus performing direction diversity reception. We show that when maximum ratio combining is employed for the electric signals processing and power efficient modulation schemes like L-PPM are used significant power savings can be obtained.

Radiative lifetimes of 1 1 levels in Cd I belonging to the 5s5p ¹p^o₁ and 5snd ³D_1,2(n=6-9) and 5sns ³S₁ (n=7,8) series, and of 5 levels of Cd II belonging to the 4d¹⁰5p ²p^o_1/2,3/2, 4d¹⁰6s ²S_1/2, and 4d¹⁰5d ²D_3/2,5/2 configurations were measured using the time-resolved laser-induced fluorescence technique. Free neutral and singly ionized cadmium were generated by laser ablation. Single- or two-step excitation processes were used to populate the levels under study. Transition probabilities and oscillator strengths for Cd I and Cd II transitions were also deduced by combining the experimental lifetimes and theoretical branching fractions obtained in multiconfigurational relativistic Hartree-Fock calculations, taking core-polarisation effects into account.

Experimental transition probabilities arising from 4d⁸ 5s², 4d⁹ 6s and 4d⁹ 5d levels of Ag II and 3d⁸ 4s² level of Cu II were measured. A time-resolved system with a Nd-YAG laser that produced free neutral and ionized silver and copper plasma by ablation was used. Transition probabilities were deduced by measured branching ratio and experimental and theoretical data for radiative lifetimes. A comparison between our values and the theoretical ones is made where available.

Observation of ultra-fast relaxation processes with time-constants below 1 ps in a wide spectral range can be made using a low-coherent light source, which is equivalent to a very short pulse in the non-linear correlation spectroscopy. The same approach can be used for very accurate and practically in real time determination of spectra of coherent and non-coherent light sources by recording and processing of their correlation functions. To check the proposed approach, we made a prototype of a correlation Fourier spectrometer based on a Michaelson interferometer and we developed a method for processing of the recorded interferograms which had been proved by a Monte-Carlo simulation. Different semiconductor light sources (LD, LED and high-power LED) were tested. The good quality of the obtained spectra was confirmed by comparison with OSA measurements (resolution 0.28 nm). The time required for data recording and spectrum restoration is within few seconds. This permits current tuning of the investigated sources, which extends their possible applications in spectroscopy, optical communications, computer technologies, etc.

Theoretical model describing the influence of a parasitic magnetic field on CPT-resonance in Hanle configuration in a strong laser field was proposed. The exact solution of the system of equations has been obtained for the transition between a ground state with J_φ=1 and an excited state with J_f=0 and/or 1. The solutions for the tensor components f ^k₀, describing the population and longitudinal alignment of the upper level f, are obtained, and the dependences of the resonances on the different parameters and parasitic fields were analyzed. The results are in qualitative agreement with resent experimental investigations.

Diode laser system with frequency modulation in the GHz region has been built. The two first sidebands of the frequency modulated laser spectrum are used for preparation of CPT resonances in ⁸⁷Rb. The CPT resonance splitting in magnetic field is examined by registering the fluorescence or its first derivative in dependence on the modulation frequency. Measuring the frequency difference between the CPT resonances, the value of the magnetic field is determined.

We present a systematic quantitative comparison of the performance parameters of two Extended Cavity Diode Lasers (ECDL), stabilized to Doppler and sub-Doppler profiles. The experimental study is carried out on Rb atomic vapour cells. The frequency shift of the resonance under investigation with respect to a reference resonance is measured and analyzed, in dependence on the modulation amplitude, cell temperature, laser power, applied magnetic field and misalignment of the pump-probe beams angle. The Allan variance is measured for both locking methods. It shows that the stabilization to the Doppler profile results in about one order of magnitude lower stability than the one to SA resonances for the short-term measurement. However, the stability achieved using both methods is sufficient for many applications and for some of them the simplicity of the Doppler locking method can be advantageous.

In the present communication we report on the investigation of the effect of elliptically polarized laser light exciting the F_g=3 Cs D₂ absorption line. Coherent resonances in Cs have been studied, obtained in Hanle configuration by scanning of magnetic field parallel to the light propagation direction. The resonances were investigated depending on the polarization of the irradiating light field. It has been observed that for linear polarization dark resonances in the fluorescence are registered, while for circularly polarized light, bright resonances are obtained, probably due to stray orthogonal magnetic field. For elliptical polarization a narrow peak appears superimposed on a broader dip. Theoretical description has been made, which shows that at elliptical polarization and orthogonal magnetic field in the case of weak light fields, a single peak in the excited state population is observed, while strong fields lead to the splitting of this peak into two peaks. The presence of both weak and strong light fields, probably due to reflection of the light beam on the cell walls, could lead to the experimentally observed fluorescence behaviour.

A novel approach to photonic crystal fabrication is proposed. It is based on the use of computer-generated holograms (CGHs) for photonic crystal structure definition. CGH allows for defining arbitrary structures, perfect or with any type of defect in a single lithographic step. CGH lithography is applicable to both 2D and 3D structures. Furthermore, a CGH can be made reconfigurable if a liquid crystal is used as a hologram medium. Hence, a single device can be used for fabrication of any photonic structure.

With proper system design, infrared multi-spot diffusing (MSD) communication links promise an order of magnitude higher bit rates compared to existing radio links. Because of the uniform distribution of the secondary sources (diffusing spots) the channel characteristics and system performance practically do not depend on the particular receiver position with respect to transmitter. However, the amount of received optical signal and noise power depends strongly on the receiver position and orientation with respect to the diffusing spots grid and the ambient light sources. The only way to properly describe such a link is to use a statistical approach. Using this approach, the impact of the optical subsystems on the channel characteristics is investigated and the results prove undoubtedly the great potential of MSD configuration.

First research in laser technology had been initiated at the beginning of 60th of the last century. Since then great achievements had been gained in different laser types development, understanding of laser beams interaction with matter, simulation of the processes, development of wide range of operations of material processing and different devices to monitor the working conditions. In spite of unique results obtained in very short historic period this dynamic technology has still a lot of problems to be solved. Lasers itself had to be more efficient transformers of energy, the range of wavelength had to be broaden both in far infrared region and to near ultra violet and X-ray fields. Laser systems must be more compact and versatile, equipped with the whole variety of control and monitoring devices for the processing. Still needs the solution the problem of development the fast and precise techniques for non-destruction testing of processing results. As nearest and further prospects in laser technology it is possible already to expect the advent of more sophisticated type of laser with possibilities to change in wide range both wavelength of radiation and duration of the pulses. It will be simpler to get very short and ultra short pulses and to use them for the realization of different processes based on material ablation. High power CW highly efficient laser will be developed and implemented into industry. Many new hybrid laser processing may appear with wide integration of information technologies. The main goal in further laser processing development will be the achievement of higher quality of the product at possibly lower cost, improvement in maintaining of the laser systems and increasing their reliability.

The results are presented of an experimental research and estimating modeling of kW-level CW CO₂ laser focused beam penetration into liquid and sustaining keyhole (KH). The conditions of evaporative and turbulent convective heat losses from the KH surface to the bulk of the liquid were varied. A drastic dependence of KH depth upon heat exchange conditions was stated.

The laser cladding technique was applied to obtain Co-based stellite SF6 coatings on the chromium steel base. The coatings were prepared by means of a direct cladding of metal powder using a 1.2 kW cw CO₂ laser stand with a controlled preheating of the substrate material. Results of the metallographic tests revealed a fine-grained, dendritic microstructure and proper metallic bonding between substrate and coating. A nearly constant concentration of mian elements at different areas of the coating cross-section indicated on homogeneous chemical composition of the laser-cladded SF6 alloy samples. A significant decrease of the micro-crack number with increasing temperature of the base preheating was observed. This was accompanied by a drop of the wear and corrosion resistance.

The paper presents research results of the welding of cobalt-iron-based amorphous alloy with Nd:YAG laser. The aim of the research was the production of a high quality welding joint, by preserving the amorphous structure. Amorphous alloy VAC 6025 [(CoFe)₇₀(MoSiB)₃₀] in the shape of foils with different thickness (0.025 and 0.030 mm) were overlapingspot welded. The quality fo the foils surface, by measuring of the roughness, measuring of the reflection from the surface of the foils and estimation of the absorption grade, were investigated as basic characteristics of the laser beam welding of amorphous alloy foils. The quality of the welded joints was tested by microstructure analysis with optical microscope and SEM and the micro hardness of the welded joints.

The choice of proper configuration of laser technological equipment is one of the main stages of the development of technological process. The rational choice of movements that laser beam and work piece perform greatly improves the efficiency of laser processing and significantly reduces costs of the operation being developed. For this purpose all possible ways of laser beam delivery and workpiece manipulation were analyzed. There were used different coordinate systems and responsible movements along each axis. An algorithm was developed to generate all possible connections between modules of laser system. On a basis of this algorithm we have developed a software that optimizes the process of the selection of laser equipment by implementing the requirements to it. A software could be extended by using additional economical and constructional factors that may influence on the required laser equipment configuration. For each coordinate system there were made schemes of laser equipment with responsible movements indicated.

During the last several years research activities have been conducted to study PDT availability in stomatology for pathogenic microflora suppression, which presence causes different kinds of oral cavity inflammatory disease. Studies indicate that PDT can be alternative to traditional antibiotic therapy. We carried out research in order to determine the optimal method of tooth irradiation to provide necessary therapeutic radiation dose for affected parodontium tissue in case of inflammatory disease. These data can be used for fiber-optic catheter positioning for further influence on oral cavity nidus of inflammation during PDT and PD. 20 teeth ex vivo were examined. Teeth were irradiated with diode laser (680 nm). In different teeth regions laser radiation intensity was measured by LESA-01-Biospec spectrometer. Optimal radiation method for PDT and PD was found.

We made our aim to investigate the effect of the low intensive laser with λ=630 nm in the visible red spectrum of light at Herpes simplex treatment. For this purpose we carried out a clinical research upon 62 persons with Herpes simplex lesions which have been divided into two groups of 31 persons. At the first group the effect of laser with power density 100 mW/cm² ± 5 mW/cm² and time of exposure 3 min. on field was traced out. At the second group the low intensive laser with the same characteristics has been used but in combination with the patent medicine Granofurin H as a photosensibilizer. The clinical approbations of this method showed high therapeutical effectiveness. The obtained results showed that at both groups there is an expressed anaesthetic, anti-inflammatory and regeneration stimulating effect and at the second group with the use of Granofurin H the reconvalescent period is shorter.

Upper airway obstruction due to bilateral vocal cord paralysis presents a serious challenge to the Otolaryngologist. Various surgical techniques have been advocated for the management of patients with vocal cord patients with vocal cord paralysis. Among these techniques, the individual use of laser CO₂ arytenoidectomy and posterior cordotomy has gained wide acceptance. In this report, we describe our experience in the management of bilateral vocal cord paralysis by combining posterior partial cordotomy as described by Dennis and Kashima with total arytenoidectomy as described by Ossoff. We report the long term results in the management of 24 patients with bilateral vocal cord paralysis treated in our Department during the last 9 years.

The new low level laser therapy (LLLT) is widely applied for treatment of diseases of the oral mucosa and parodont. Depending on indication, different optical tips and light-guides are used to create beams with a required shape. However, to the best of our knowledge, the developed irradiation geometries are usually proposed assuming validity of Bouger-Lambert law. This hardly corresponds to the real situation because of the dominating multiple scattering within 600-1200 nm range that destroys correlation between the emitted laser beam and the spatial distribution of the absorbed dose inside the tissue. The aim of this work is to base the dosimetry of the LLLT procedures of periodontal tissues on radiation transfer theory using a flexible Monte-Carlo code. We studied quantitatively the influence of tissue optical parameters (absorption and scattering coefficients, tissue refraction index, anisotropy factor) on decreasing of correlation between the emitted beam and the energy deposition for converging or diverging beams. We evaluated energy deposition for the developed by us LLLT system in a 3-D model of periodontal tissues created using a cross-sectional image of this region with internal structural information on the gingival and the tooth. The laser source is a CW diode laser emitting elliptical beam within 650-675 nm at output power 5-30 mW. To determine the geometry of the irradiating beam we used CCD camera Spiricon LBA 300.

We have made an investigation on three-wall and four-wall osseous defects on which a surgical treatment was conducted with application of Bio-Oss ( Geistlich ) and laser therapy. After conducting of clinical oral hygiene to the patients and curettage with flap, a Bio-Oss Spongiosa of Geistlich is applied. We have conducted the laser therapy pre- and postoperative scanning with power density of 100 mW/cm² on scheme. The patients were traced out within 1 year. The obtained results showed that the application of laser therapy gives anaesthetic, anti-inflammatory and regeneration stimulating effect.

Objectives: To assess outcome, in adult individuals undergone Laser Assisted Tympanostomy (LAT) without ventilation tube placement. Method: LAT was performed on a total of 95 ears (72 individuals). Indications included serous otitis media with effusion (44 ears/31 patients), eustachian tube dysfunction (32 ears/24 patients), acute otitis media (13 ears/11 patients), and endoscopic visualization of the middle ear (6 ears/6 patients). Results: Middle ear disease was resolved after the closure of tympanostomy in 48% of patients with serous otitis media with effusion. In 78% of patients with Eustachian tube dysfunction symptoms were diminished. All patients with acute otitis media had a satisfactory outcome. LAT was found quite effective in patients undergoing middle ear endoscopy. Conclusion: LAT without ventilation tubes provides a safe alternative surgical option in adult patients in certain cases. The selection criteria for this procedure are addressed in detail.

Although the low-level laser therapy (LLLT) is accepted in the clinical practice, its efficiency is still questionable because of the unclear mechanisms of LLLT action. This work presents the results of LLLT applied to volunteers who need recovery from trauma or suffer from rheumatic diseases, inflammatory disorders, etc. The control group we used for comparison consisted of patients being treated by conventional therapy that included massage and acupuncture needles. The effectiveness of the LLLT was graded under four categories. Short-term and long-term side effects as well as conditions responding only to LLLT were recorded. The successful treatments were up to 70%, which coincided with the result of the control group. The LLLT was performed with a GaAs laser system SIX LASER IR - Bulgaria provided with additional set of six light CW emitting diodes to scan a larger area of a tissue surface. To evaluate the light delivery inside the tissue, the spatial maps of the light spot at the laser output in different operating regimes were measured. On their basis, the absorbed dose was calculated both in the boundary layer under the tissue surface and in depth using a reduced variance Monte-Carlo code.