Karel Nejezchleb

1444-nm Q-switched pulse generator based on Nd:YAG/V:YAG microchip laser

Q-switched microchip laser emitting radiation at eye-safe wavelength 1444 nm was designed and realized. This laser was based on composite crystal which consists of 4 mm long Nd:YAG active medium diffusion bonded with 1 mm long V:YAG saturable absorber. The diameter of the composite crystal was 5 mm. The initial transmission of the V:YAG part was T0 = 94% @ 1440 nm. The microchip resonator consists of dielectric mirrors, directly deposited onto the composite crystal surfaces. These mirrors were specially designed to ensure desired emission at 1444 nm and to prevent parasitic lasing at other Nd3+ transmissions. The output coupler with reflectivity 94% for the generated wavelength 1444 nm was placed on the V3+-doped part. The laser was operating under pulsed pumping for the duty-cycle up to 50%. With increasing value of mean pumping power a strong decrease of generated pulse length was observed. The shortest generated pulses were 4.2 ns long (FWHM). Stable pulses with energy 34 μJ were generated with repetition rate up to 1.5 kHz. Corresponding pulse peak power was 8.2 kW. The wavelength of linearly polarized TEM00 laser mode was fixed to 1444 nm.

Luminescence spectroscopy of excitons and antisite defects in Lu3Al5O12 single crystals and single-crystal films

The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu3Al5O12 (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of LuAl antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and LuAl antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb2+ ions. The structure of the luminescence centers, related to the background emission of impurity Pb2+ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides (Al2O3, Y2O3) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O− ions and electrons localized at excited levels of Lu3+ cations.

Continuous-wave blue generation of intracavity frequency-doubled Pr:YAP laser

We report the cw blue generation of Pr:YAP laser emission at room temperature, which has been achieved by intracavity frequency doubling of the near-IR-emitting Pr:YAP laser operating at a fundamental wavelength of 747 nm. For active medium pumping, a GaN laser diode providing up to 1 W of output power at approximately 448 nm was used. With beta barium borate crystal employed as a nonlinear medium, 12.3 mW of output power at 373.5 nm has been obtained.

Pr:YAlO 3 microchip laser

A cw Pr:YAlO(3) microchip-laser operation in the near-IR spectral region is reported. A microchip resonator was formed by dielectric mirrors directly deposited on the Pr:YAlO(3) crystal surfaces. For active medium pumping, a GaN laser diode providing up to 1W of output power at approximately 448 nm was used. 139mW of laser radiation at 747nm wavelength has been extracted from the microchip-laser system. Slope efficiency related to the incident pumping power was approximately 25%.

1.6 μm Er:YAP and Er:YAG Lasers Resonantly Pumped by Er:Glass Laser

Abstract1623 nm Er:YAP and 1648 nm Er:YAG lasers resonantly pumped by a solid state Er:glass laser operating at 1535 nm were investigated. Laser generation was reached for Er:YAP and two Er:YAG crystals with different Er ion concentration. The maximal output energies were 20 and 45 mJ for Er:YAP and Er:YAG laser systems, respectively.

Luminescence and ESR Study of Irregular Ce

Luminescence of new irregular Ce³⁺-related centers: the unperturbed and perturbed Ce³⁺ ions located in Al³⁺ sites and the Ce³⁺ _Lu ions perturbed by Lu³⁺ _Al ions was found. The systematic study of these centers by means of the ESR and luminescence methods and their influence on scintillation characteristics was performed. The structure and symmetry of the irregular Ce³⁺ centers was established and their spectral characteristics were explained.

^{3+}

Thinking about the pumping and generated power of the longitudinally diode-pumped solid-state laser enhancement, the question of an active material cooling should be solved. One of the possible solutions is the active material cooling surface enlargement. Besides the cylindrical surface of the crystal, the laser rod front surfaces could be cooled through undoped ends. The temperature gradient effect in three various samples was investigated in a computer experiment, and the differences in generated output power were measured experimentally. The samples were three Nd:YAG rods - one conventional, one with one undoped end, and one with two undoped ends. The crystal samples were placed in sequence into a resonator 6 cm long and longitudinally diode-pumped. The dependencies of the generated power on the absorbed pump power have shown that with the two undoped ends the output power is more than twice as high as against the conventional Nd:YAG sample. The results were explained by a computer experiment based on the heat transfer equation solution where the changes of the temperature gradient were least for the Nd:YAG rod with two undoped ends.

Ions in LuAG:Ce Single Crystals

Intrinsic emission of undoped and Ce3+ doped single crystal (SC) and single crystalline films (SCF) of YALO3 (YAP) was studied using the time-resolved luminescence spectroscopy under excitation by pulsed X-ray and synchrotron radiation. In contrast to YAP SCF, the YAP bulk SC are characterized by the presence of Y-in-Al-positions antisite defects (AD) and large concentration of vacancy-type defects (VD) of different types, which contribute to the intrinsic emission of YAP SC. Such type defects are centers of the luminescence in the UV (6.0-4.75 eV) and near UV (4.75-2.2 eV) ranges, overlapping with the Ce absorption and emission bands. Furthermore, they can give rise to shallow trapping centers as well. For this reason the AD and VD can strongly influence the scintillation properties of YAP:Ce SC. Specifically, the decay kinetics of the Ce emission in YAP:Ce SC, besides the fast component (23.3 plusmn 3.5 ns) related to radiative 5d-4f transition of Ce ions, contains also two slow components in the hundred ns and mus ranges, which are due to the AD and VD-related traps. The advantages of scintillators based on YAP:Ce SCF, namely faster scintillation decay and lower contribution of slow components in the total light yield, can be achieved due to the absence of above mentioned bulk crystal defects.

Comparison of different composite Nd:YAG rods thermal properties under diode pumping

V:YAG saturable absorber was used for efficient Q-switching and mode-locking of Nd:YAG and Nd:YAP flash-lamp or diode pumped lasers operating in 1.3 mm region. Crystals of Yttrium-Aluminum Garnet (YAG) doped with three-valence vanadium V3+ in tetrahedral position (V:YAG) were grown using of Czochralski method in reducing protective atmosphere. High purity oxides were used for crystal growth (Y2O3 (5N), Al2O3 (5N), V2O5 (4N)). Concentration of V2O5 in the melt reached up to 1 wt. %. Discs of the diameter 5 or 10 mm and of various thickness were machined from grown V:YAG crystals. The discs were both sides polished and AR coated so that minimum reflectivity at 1.08 and 1.34 microns was reached. The initial transmission of the saturable absorber was dependent on the samples thickness and its annealing process. We report stability improvement of passively mode-locked (by these V:YAG crystals) Nd:YAP flash-lamp pumped lasers. The maximum output energy 53 mJ at wavelength 1340 nm was obtained for Nd:YAP flash-lamp pumped laser operating at repetition rate 5 Hz. Mode-locked train envelope width was measured to be 22 ns (FWHM). Individual pulses inside the train were shorter than 1 ns. Also results with composite Nd:YAG rod Q-switched by V:YAG crystal and with Nd:YAG/V:YAG monolith rod under CW longitudinal diode pumping was obtained and compared. These laser systems represent new powerfull sources in the near infrared region.

Intrinsic and

A preliminary investigation of the passively Q-switched resonantly pumped Er:YAG laser system operating at wavelength 1645 nm has been performed. The output characteristics of the designed and constructed laser, i.e., the output energy, temporal profile, and spatial beam structure were registered. The Er:YAG laser crystals longitudinally pulse-pumped by Erbium glass laser radiation (repetition rate 0.5 Hz, wavelength 1535 nm) were investigated. The passive Q-switch was a Co:MALO (Co2+:MgAl2O4) crystal. To optimize the system, three Er:YAG crystals with various in Erbium/Yttrium concentration and length were studied in the free-running regime. The curved pumping mirror of linear hemispherical oscillator had a high transmittance at the pumping wavelength and maximal reflectance at the generating wavelength around 1645 nm. The output flat dielectric coupler reflectance was 90 % at 1645 nm. Out of the three Er:YAG active laser crystals, the best output characteristics in free running regime were reached for the medium with Er3+ concentration 0.2 at.% Er/Y and length 25 mm. For the Q-switching, three saturable absorbers Co:MALO with various length, that is various transmission, were investigated. These crystals had no anti-reflection layer and were placed between the active crystal and output mirror. The laser resonator length was 162 mm. For an incident pump energy of 131 mJ, the 1.6 mJ Q-switched single pulse energy with 58 ns pulse duration (FWHM) was obtained. The corresponding peak power was 28 kW. The spatial beam structure was close to the fundamental profile.