There is considerable interest in compact pulsed high peak power laser sources emitting at wavelengths near 1.55 micrometers . Rangefinders and other applications with free space propagation could be strongly benefit of such devices. The wavelength of around 1.55 micrometers is in the eyesafe regime where significantly higher pulse energies can be used without damaging human eyes. Erbium and ytterbium doped YAG single crystals were obtained by the Czochralski method. The basis conditions of growth and the results of optical homogeneity measurements of the obtained crystals are presented. Absorption spectra of these Er³⁺- and Yb³⁺-doped YAG crystals were measured in the spectral range 190 divided by 5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectro fluorometer using a diode laser as an excitation source. The measurements of the lifetime of the Er³⁺ ions in the upper laser level of the samples were made by the direct method with pulse excitation.

Liquid phase epitaxy (LPE) is a suitable technique to produce diode laser-pumped solid state lasers with a planar waveguide structure. The thin films of Nd³⁺, Ga³⁺ and Lu³⁺ doped YAG have been grown form a supercooled molten garnet-flux high temperature solution on undoped YAG substrates by the standard LPE dipping technique. The emission spectra and fluorescence lifetimes have been measured for Nd:YAG layers with different concentration of Nd³⁺ ions. Additionally, the films were investigated versus concentration of neodymium, gallium and lutetium using ESR, x-ray diffraction and micro interferometric techniques. According to above measurements it can be concluded that the obtained epitaxial structures are of good quality.

Erbium laser glasses have attracted much attention due to their capability for emission of radiation at the 'eye safe' wavelength of 1.54 microns. The development of erbium glass laser systems has renewed the requirements for additional research into improved laser glass properties and performance. This report describes the effect of variations erbium, ytterbium, chromium ions and glass base compositions on laser efficiency and the improved properties of a new glass base. The spectral properties and laser characteristics were measured for this ne glass. Absorption spectra of these Er³⁺ and Yb³⁺-doped glasses were measured in the spectral range 190 divided by 5000 nm at room temperature. The excitation and luminescence spectra were also recorded at room temperature on a JOBIN-YVON spectrofluorometer using a diode laser as an excitation source. The measurements of the lifetime of the ER³⁺ ions in the upper laser level of the samples were made by the direct method with pulse excitation.

The paper describes growth of neodymium doped borate and tungstate single crystals and their optical and spectroscopic properties. Czochralski and top seeded solution growth techniques were used to crystalize Kgc_1-xNd_x(WO₄)₂ tungstate, and self-frequency doubling YAl₃(BO₃)₄:Nd and Ca₄GdO(BO₃)₃:Nd borates. Single crystals having good optical quality, free from inclusions, bubbles, or cracks were obtained. Transmission and luminescence spectra of investigated crystals were measured. The measurements of Nd³⁺ ions lifetime at the upper laser level for the samples of KGW:Nd, YAB:Nd, and GdCOB:Nd crystals were made by means of direct method with pulse excitation. The obtained results confirm usability of as-grown single crystals for construction of diode-pumped lasers.

We report the first demonstration of Cr⁴⁺ centers generation in YAG:Cr,Mg crystals using CO₂ laser radiation. After crystal growth only a small part of chromium ions is introduced into a crystal structure as Cr⁴⁺ ions in tetrahedral positions, the other ones are at different positions or at mixed valency Cr³⁺ and Cr⁴⁺. Chromium ions of Cr⁴⁺ valency can occur in the desired points of YAG structure as a result of complex reaction sin solid-state phase. Such reactions proceed during multi-stage crystal annealing. The paper presents the result of investigations of YAG:Cr,Mg crystals after CO₂ laser annealing in oxidizing atmosphere at a temperature of 600 divided by 900 degrees C. Investigations of YAG:Cr⁴⁺ spectroscopic properties and measurements of absorption and luminescence bands, allow estimation of chromium ion concentration at particular charging state and positions in YAG crystalline structure, and allow also to determine their mutual relations and influence on non-linear properties of absorber. Basing on ESA and two-level absorber model, the absorption cross section, concentration of active centers, relaxation time, saturation energy, and non-active losses have been estimated.

Results of phase transition investigations of Nd:YVO₄ single crystal to Nd:YVO₄ single crystal in hydrogen at 1200 degrees C for 1h were presented. The refined lattice parameters obtained for the latter case, a₀ equals 5.2858(1) angstrom, b₀ equals 5.5956(2) angstrom and c₀ equals 7.5854(2) angstrom, are slightly larger only than those of YVO₃. Valency change was also investigated of Cr ions due to transition in Cr⁴⁺:Y₃Al₅O₁₂ and Cr³⁺:SrLaGa₃O₇ Ho and Pr ions in LiTaO₃ and Co³⁺ due to transition in LaGaO₃ single crystals under influence of annealing in reducing and oxidizing atmospheres and gamma and proton irradiations.

Results of absorption and radio luminescence measurements of YalO₃, Y₃Al₅O₁₂, LiTaO₃, LiNbO₃, YVO₄ single crystals and Li₂B₄O₇ single crystals and glasses doped with rare-earth and transition metal ions and LiF crystal were presented. Analysis of excitation energy transfer of x-rays from lattice sites to active ions was performed. Changes in absorption spectra were also analyzed due to (gamma) -quanta irradiation of Nd³⁺ doped LiYF₄ single crystal with a dose of 10⁵ Gy.

Condensed gas mixtures are considered as laser active materials basing on the correlation between values of the classical oscillator strength and the energy flux of pumping radiation at laser threshold. For the emission lines of active centers Rb²⁺F^-, Cs²⁺F^-, Cs²⁺Cl^-, Xe⁺F^-, ¹³C¹⁸O, CO-Hg, NO and ¹³CO₂ doped into Ne, Ar, Kr and N₂ condensed phase hosts and observed in a wide spectral region from VUV to far IR the calculated values agree with experimental results. The strongest transitions of CO/N₂ in the IR region and the excimer one of XeF/Ar(B yields X) in VIS require the lowest pumping of the range of 10^-4 J/cm² while the ionic excimers are characterized by a much larger values. This is confirmed by the oscillator strength which for the XeF/Ar (B yields X) case amounts 0.22.

Luminescence and absorption spectra of the silica samples prepared by a sol-gel technique and originally doped with Cu solutions in the range of 500/1-3000/1 are recorded. For alternatively applied CuCl₂ or Cu(AA)₂ dopants the same spectral profiles of dry solids are observed. A slightly structured emission band centered at 330 nm and ascribed to the 3d⁹4s¹ yields 3d¹⁰ transition of the Cu⁺ ion is recorded for excitation around 300 nm of samples previously dried and annealed below 455 K. The band shows a red shift for annealing at higher temperatures, and vanishes completely at 1173 K. Instead of broad emission band of more than double half width and of about 25 times higher intensity in the line center at 560 nm occurs most probably due to temperature dependent structural transition accompanied by the Cu⁺-Cu²⁺ change of the dopant valence.

The paper presents the results of investigations on spectroscopic properties of new non-linear absorbers used for diode-pumped laser systems: yttrium-aluminium garnet doped with trivalent vanadium ions and Te doped GaAs semiconductor absorber. In this work we present the result son YAG:V³⁺ single crystal growth and examination of Q-switching of laser resonator in near IR band. YAG single crystals doped with V³⁺ ions of different concentrations were obtained by the Czochralski method. The absorption and emission spectra measurements on those crystals are presented. The as grown crystals have not non- linear absorption bands of V³⁺ ions in tetrahedral positions. After crystals annealing in reducing atmosphere absorption bands in NIR region arise. The investigations of changes in transmission properties of YAG crystals with different concentrations of V³⁺ ions have been carried out as a function of power density of transmitted radiation at 822 nm, 1064 nm, and 1318 nm. Dependence of transmission changes of the GaAs:Te on power density of diagnostic radiation of 1064 nm have been determined. The following parameters of non-linear absorbers were estimated: non-active losses, absorption cross-section, saturation energy, concentration of active centers, relaxation time, and energy losses caused by absorber bleaching. Generation characteristics of YAG:Nd³⁺ laser with GaAs:Te and YAG:V³⁺ modulators have been investigated.

The paper presents initial results of examination of glasses doped with uranium ions. In such material an effect of non- linear adsorption is possible within a spectral range of 1.5 micrometers . A synthesis of silicate glasses, silicate-borate and phosphate glasses doped with uranium ions was performed. Substantial thermal parameters as well as optical and spectroscopic properties of the obtained glasses were examined. It was stated that wide absorption band in a spectral region of 1.4 divided by 1.6 micrometers , originated from U²⁺ ions, appears only in phosphate glasses. U²⁺ doped phosphate glass shows non-linear absorption effect in this region. Absorber transmission varying with increase in energy density of the transmitted radiation of 1.535 micrometers was determined. A giant-pulse erbium glass laser, generation the pulses of energy of 8 mJ and duration 25 ns, was applied for these investigations. Energy density of a diagnostic pulse was changed within a range of 0.001 divided by 30 J/cm³. Non-active losses, absorption cross section, saturation energy, concentration of active media, relaxation time, and energy losses for absorber bleaching were determined.

This paper presents new analytical solution of equation describing, so called 'fast' non-linear absorbers, relaxation time of which is shorter than the time of interaction with giant-pulse laser. A special LambertW function was used for description of dynamics of non-linear absorber bleaching, i.e., the changes in transmission, given as a function of intensity of incident laser radiation. The result of performed analyses were compared with theoretical models for 'thin' and 'thick' 'fast' absorber as well as with experimental results obtained for non-linear YAG:V³⁺ and YAG:Co²⁺ absorbers.

The use of the downhill Simplex algorithm in reconstruction of optical parameters of planar silica waveguides is described. The original Nelder-Mead approach has been modified to include physical constraints of the waveguide system. Numerical results are provided to illustrate the behavior of the modified algorithm.

In this paper, we present an analysis of relaxations oscillations in planar circular grating DFB and DBR lasers. In our theoretical model, we take into account the transverse and longitudinal field distribution. That model allows to study the influence of the real structures parameters on the relaxation oscillations.

The effect of the mode non-orthogonality on the laser linewidth as well as the coherence of light is analyzed taking saturation effects fully into account. A stochastic approach based on the solution of the time-dependent Fokker- Planck equation is used. Our theoretical model allows to define the influence of the real structures parameters on the laser linewidth.

In this paper threshold analysis for circular grating DBR/DFB with (lambda) /4 phase-shift lasers is presented. In particular, the influence of the phase-shift position in grating on the spectrum of the laser modes and gain is analyzed. It is shown that for central perturbation of the grating the mode selection is enhanced remarkably with comparison to laser structure with uniform grating, when the ratio of active medium length to the grating length is small.

In this paper optimization of the quality of the output beam as a function of the Gaussian mirror position and Gaussian mirror parameter in hollow-waveguide SLAB lasers is presented. It is shown that using of the Gaussian mirror in such kind of resonators makes possible remarkably decease number of lateral stripes in far field distribution.

In this paper transverse mode selectivity in hollow- waveguide SLAB lasers with Gaussian output mirror is presented. It is shown that using of the Gaussian mirror as transmission one in SLAB resonators makes possible to obtain fundamental transverse mode laser action.

There are presented special laser mirrors exhibiting high reflectivity and negative group delay dispersion over broad frequency range. These dielectric laser mirrors are enabled to compression of the generated radiation and offer a general solution for broadband feedback and dispersion control in femtosecond laser systems. Such mirrors would been used to OPO systems, to chirped pulse amplification systems and pulse compressors.

In the present paper, a possibility of a manufacturing nitride VCSELs is discussed. It is evident from the analysis, that the VCSEL configurations of nitride lasers need more advanced technology then their edge-emitting counterparts. In particular, extremely high-reflective low- loss resonator mirrors and extraordinarily high quality, uniform structure layers are necessary to reach in nitride VCSELs a laser action at room temperature. Besides, until now there has not been found efficient technological process to define precisely current paths for lateral injection. Nevertheless, a rapid progress in nitride technology is still observed which may finally enable us to manufacture reliable and efficient nitride VCSELs earlier than it is generally expected.

To meet the requirements for the narrow emission line of ht laser diode pumping system exactly at 808 nm wavelength, an optimization of the laser (AlGa)As heterostructure because of the composition and thickness of the constituent layers is necessary. In the paper the design principles, the characteristics of the manufactured laser diodes based on this design and intrinsic limitations of the possibility of 'tuning' the lasers to desired wavelength in the MOVPE growth process are presented.

SIMS depth profiles of Al, Ga and Be were investigated in the GaAs/AlGaAs GRIN SCH SQW laser diode structures grown by MBE at various substrate temperature. Additionally, SIMS distribution of Si and O in MMQW laser structures grown at constant temperature with the active region doped with Si and undoped intentionally are also shown. Because the diffusion coefficient of Be is significantly larger than that of Si an effect of the p-n junction displacement towards the n-AlGaAs cladding layer is observed in structures with undoped active region and grown in high temperature. Our results confirmed results obtained by other authors which indicate that the movement of Be atoms is stopped when the active region is doped with Si. Simultaneously, it was also observed that amount of O accumulated at the GaAs/AlGaAs heterointerface was reduced. It was discussed that decreasing the amount of O together with the control of the Si doping profile are of the significant importance from the point of view of laser performance.

Typical scheme of cw laser diode driver proposed by Toshiba has been studied. A response of the driver to a strong impulse interference has been determined.

This paper presents an electronic circuit which can be used as a very fast electronic 'fuse' in laser diode drivers. The main causes of damage of laser diodes are either unexpected electrical transients or catastrophic facet damage occurring at optical power density exceeding 10⁶ W/cm². Both can be induced by electromagnetic interference in typical drivers with automatic power control. Presented scheme has a reaction time about 2 microsecond(s) , which reduces the possibility of over driving the laser diode.

Laser diode parameters are highly dependent on temperature. Therefore the problem of maintenance of semiconductor laser emission parameters at certain degree is a very relevant question. This paper present a laser diode controller prepared and constructed. It presents also an algorithm which enables to provide the values of operating current intensity in a certain temperature, in order to maintain a demanded value of output power. The experiments were conducted for various types of laser diode.

The paper presents optimization of energy and peak power of the pulse oaf laser with a slow passive Q-switch. The excited states absorption (ESA) in absorber is included in an optimization process. The described laser's model provides determination of the optimal values of unsaturated absorber transmission and reflectivity of the output mirror as a function of the normalized initial gain coefficient z and a, characterizing the ratio of the absorption cross- section of the nonlinear absorber to the emission cross- section of the laser medium. In addition, the a parameter has been modified with its value dependent on the magnification M, determining the ratio of the cross-section of the laser beam in the laser medium to the cross-section of the laser beam in the nonlinear absorber. To optimize the passively Q-switched laser the charts and simple analytical formulas, presented in the paper, can be applied. The paper presents also analytical formulas determining the values of laser pulse generation, i.e., pulse duration, its energy, and peak power. As an example, optimization of energy and peak power of the pulse of Nd:YAG laser, with Cr⁴⁺:YAG crystal as passive Q-switch, pumped by 100 W matrix of laser diodes was presented. It was shown that for laser energy optimization, ESA slightly changes the value of optimal unsaturated absorber transmission and optimal reflectivity of the output mirror of the laser.

The analysis of pump geometry presented in this work allowed to determine optimal conditions of excitations of diode pumped solid state lasers for oscillation of quasi-Gaussian TEM₀₀ mode. There appears the existence of weak transverse mode structure. The heterodyne analysis for two kinds of laser: Nd:YAG and Nd:YVO₄ was performed. We found the strong mode competition effect decreasing long- term frequency stability of the lasers. The offset frequency stability between two Nd:YVO₄ lasers for short averaging time is 10^-10. Using offset frequency feedback loop, stability of the level of 300kHz has been obtained.

Selectivity diode pumping of rare earth-doped solid state lasers show important differences between broad-band frequency lamp pumping and monochromatic diode pumping. In such a process all effects of up-conversion and excited state absorption should be taken into account. Experiments at room temperature were carried out to study the higher order processes that produced the orange, yellow, green and blue fluorescence in diode pumped solid state lasers and micro lasers with the high pump power density up to 30 kW/cm². These higher order processes were energy transfer up-conversion and excited state absorption of both pump and laser radiation. Such type of a process may be an important loss mechanism for monochromatic pumping of laser. Energy transfer up conversion reduces the population of the upper laser level, effectively shortened its lifetime. Additional heat deposition increases strongly under non lasing conditions. Attributed to up-conversion and ESA there is a significant different in thermal lens power between lasing and non-lasing conditions. Generation of heat in the laser medium is a fundamental problem which ultimately sets limits on the maximum operating power.

The analytical model of intracavity frequency doubled end pumped laser has been worked out and applied to optimize the major components of such laser. The experiments of cw and passively Q-switched intracavity doubled Nd lasers were carried out. About 1 W of averaged green power, with pulse energy of 150 (mu) J, pulse duration of 40 ns were achieved for 10 W fiber coupled pumping diode. The directions of optimization of such lasers were formulated.

The paper presents experimental results of flashlamp pumped Nd:YAG laser operated at wavelength (lambda) equals 1.1318 micrometers , (lambda) equals 1.338 micrometers , (lambda) equals 1.356 micrometers , (lambda) equals 1.414 micrometers and (lambda) equals 1.444 micrometers . Thresholds and resonator losses at these lines have been determined. The laser was also operated at line 1.318 micrometers in the Q-switched mode both active and passive. In active Q- switching, output pulses up to 29 mJ energy and pulsewidth of 41 ns have been obtained. In passive Q-switching with V²⁺:YAG crystalline saturable absorber, on the other hand, output pulses up to 4.5 mJ energy and 35 ns duration have been generated. Moreover, an intracavity Raman laser producing 1.53 micrometers radiation when pumped by Nd:YAG laser operated at 1.318 micrometers is presented. Output Raman pulses up to 10 mJ energy have been obtained. Raman beam cleanup and 36 percent energy conversion efficiency have been observed.

Main directions of investigations and possible applications of laser systems generating radiation within 'eye safe' range are presented. The results of examinations of spectroscopic properties and generation parameters of new active media, i.e., Er³⁺ and Yb³⁺ doped glasses and Er³⁺, Cr⁴⁺, Ho³⁺, Tb³⁺, and Tm³⁺ ions doped crystal are given. Substantial optical and structural characteristics of new materials used for radiation conversion systems, including shift of generated wavelength to 'eye safe' range with application of molecular crystalline Raman shifter and OPO generators have been determined. We present also the results of investigations on spectroscopic properties and non-linear absorption effect in new absorbers used for the systems generating radiation at 1.5 micrometers such as YAG:V³⁺, U²⁺ doped difluoride alkaline earth metals and glasses, Er³⁺ doped crystals, and Co²⁺ ions doped media. Literature data was compared with the results obtained for investigations carried out at the Institute of Optoelectronics and relate to materials engineering, spectroscopy, structural analysis, and generation characteristics of various laser systems generating radiation within a spectral range of 1.5 divided by 2 micrometers .

A positive effect of application of permanent magnets field in argon ion laser has been observed. Some ring magnets producing quasi-homogeneous field increases several times the output power. This influence is stronger with respect to magnet coil application. The reason of this phenomenon is caused by electron temperature increasing in radial magnetic field areas. Application of permanent magnets field should substantially enhance the output power of air cooled argon lasers.

In this paper we repot efficient laser oscillation on the IR 840.4 nm Ag II transition in a He-Ag laser with high voltage 3 mm I.D. and 20 cm long helical hollow cathode. Small- signal gain coefficient of about 60 percent/m for that line was measured at the discharge current 2 A. A similar gain was reported in a conventional HCD at about 10 times higher linear discharge current density. The Ag II 840.4 nm laser transition was found to be homogeneously broadened.

The influence of ³He isotope on laser performance of a sputtered segmented hollow cathode discharge He-Cu ion laser oscillating on 780.8 nm transition is presented. At low currents the laser power and small-signal gain are higher for ³He than for ⁴He. At higher discharge currents the laser parameters are similar both isotopes. However, due to lower discharge voltage for ³He, the same laser output power is obtained at small electrical input power.

Influence of the discharge current oscillations, mechanical vibrations of the laser construction as well as the on- uniformity of the active medium properties on the output beam characteristics were studied experimentally for a high power, transverse flow, cs CO₂ industrial laser. The factors influencing the laser output power stability were investigated together with the temporal behavior of the spatial beam profiles.

A measuring device based on a rotating pinhole method was designed and developed at IF-FM for recording the spatial structure of high power cs CO₂ laser beams in the near and far field region. The main performance parameters of the device are presented together with the measurement results concerning the beam propagation characteristics of the 1.2 kW technological laser.

Some results of plasma-chemical modeling of CO₂ laser discharges are presented in this paper. The influence of various mixture components and products of chemical processes on the CO₂ laser operation-parameters is discussed. The crucial role of electronic excited species was proved. The calculated values of N₂O concentration in different laser mixtures were close to the ones measured by a FTIR spectroscope.

Results of investigations of RF excited CO₂ waveguide lasers in pulse regime are described. The shapes of the output pulses monitored and simulated for the different operation conditions are shown. The characteristics of the power levels are presented. Some aspects of spectral properties of the laser output radiation in pulse regime are given.

The control systems of laser frequency stabilization use a few mechanisms of tuning: thermal, piezoelectric and electro optic. Thermal tuning is a very slow process but it enables to tune the resonator laser even over few tens of microns. Piezoelectric tuning is usually limited to a few of microns and in the frequency band of tens of Hz. The electro optic phase modulator inserted inside a laser resonator gives the fastest tuning in the band of few tens of kHz.