The characteristics of an Nd:YAG multistage optical amplifier of a laser beam, the spatial parameters of which were corrected by thermal lenses formed in the active elements of each amplifier stage, were studied. Nd:YAG crystals transverse-pumped by laser diode units were used as the amplifier active elements. Removal of lens-compensators was shown to reduce the total optical losses of the amplifier and enhance its compactness. The optical losses of an optical amplifier with five amplification stages and correction of the amplified beam characteristics by thermally induced lenses of active elements were 16

This study considers two types of transversally diode-pumped lasers: a Nd:YAG laser with a Cr4 C VYAG passive Q-switch (lasing wavelength of 1064 nm) and an Yb:Er-glass laser with a Co2C VMgAl2O4 passive Q-switch (1535 nm). The purpose of the study is the experimental and theoretical investigation of the spectral selection properties of the solid-state laser whose monopulses are formed by bleaching filters. Method. The conditions for single-frequency lasing in the laser cavity were defined. Numerical simulations were used to determine the time intervals characterizing the evolution of the monopulses in the laser cavities with the bleaching filters, as well as the number of related radiation trips within the cavities up to the moment of achieving maximum lasing power. Main results. Based on these data, it has been shown that the lasing regime within the cavity of the Yb:Er glass laser with the Co2C VMgAl2O4 passive Q-switch lasts for a longer period compared with that in the Nd:YAG laser with the Cr4C VYAG passive Q-switch. Therefore, the single-mode regime in the Yb:Er-glass laser is realized without introducing an additional frequency-dependent element to the cavity. In contrast, the single-mode regime in the Nd:YAG laser can be achieved by the formation of an interference-polarizing Lyot filter due to thermally induced birefringence of the active element and polarizer. Practical significance. The obtained results have practical applications in the development of compact single-frequency diode-pumped lasers operating within the near-infrared region, including the conditionally safe spectral range. (c) 2024 Optica Publishing Group

The dependence of the initial transmission S0 of a passive Q-switch based on a Cr4:YAG crystal on temperature T has been experimentally investigated. The initial transmission was shown to increase from 16.3 to 24.0

The spatial, temporal, and spectral characteristics of the output radiation of diode-pumped laser systems and optical amplifiers with active elements made of Nd : YAG ceramics are studied. It is shown that the divergence of radiation in the subthreshold regime has the form of concentric nested cones emerging from the active element (AE) faces at angles of 2 – 4 °. A model explaining the experimentally observed phenomenon is proposed based on the mechanism of scattering of the generated beam from the granular structure of the optical ceramics. Analysis of the divergence pattern makes it possible to estimate the grain size and the optical quality of ceramics. The output beam divergence in the lasing regime is determined mainly by the cavity parameters and does not exceed several milliradians. The scattering events in this case serve as sources of additional optical losses. Luminescence enhancement and parasitic oscillations in the AE volume restrict the possibility of using Nd : YAG ceramics for fabricating AEs of high-power optical amplifiers.

We have made a selection of the leading structures among cationic polymethine dyes with different structures of terminal heterocyclic groups and polymethine chains for passive Q-switch of a diodepumped solid-state neodymium laser. Such dyes have a maximum absorption in the region of 1060 nm and a minimum absorption in the region of 810 nm. It was found that the 4-((E)-2-((E)-2-chl oro-3-(2-(2,6-diphenyl-4H-thiopyran-4-ylidene)ethylidene)cyclohex-1-en-1-yl)vinyl)-2,6-diphenylthio pyrylium tetrafluoroborate dye most closely matches these characteristics. The nature of its longwavelength and higher electronic transitions was interpreted based on quantum-chemical calculations by the DFT/B3LYP/6-31G (d, p) method and TDDFT taking into account the polarity of the medium by the PCM method. The use of this dye as a laser Q-switch made it possible for the first time to obtain passive mode locking in diode-pumped neodymium lasers. Copyright (c) 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the EastWest Chemistry Conference 2021.

Operating regimes of an optical system consisting of a compact pulsed master diode-pumped Q-switched Nd:YAG laser and triple-crystal (KTP) ring cell of an optical parametric oscillator have been investigated. It was experimentally shown that the frequency-selective properties of a passive Q-switched unit in natural mode selection are enhanced by creating a Lyot polarization interference filter with the phase plate in the form of a laser active element with thermally induced birefringence and a polarizer. Such Lyot filter appears in the Nd:YAG laser cavity during operation at relatively high energy and repetition rate of radiation pulses (60–100 mJ, 20 Hz). The combined action of the natural mode selection process and the Lyot filter ensures stable operation of a passive Q-switched Ng:YAG laser in single-frequency lasing mode (the lasing bandwidth is <57 MHz). The master single-frequency pulsed Nd:YAG laser (λ = 1.06 μm) allows the energy of pulses applied to the input of the optical parametric oscillator to be reduced by greater than 1.5 times while maintaining the specified energy level of the output pulses (30 mJ, λ = 1.57 μm). An additional increase in the efficiency of the optical parametric oscillator conversion is achieved by introducing a two-lens 1.3× telescope into the master laser cavity.

Researchers and specialists of the Institute of Nuclear Problems of the Belarusian State University, Belarusian State University of Informatics and Radio Electronics, Physical-Technical Institute, and the Research and Production Center for Material Science of the National Academy of Sciences of Belarus in collaboration with JINR physicists have developed, produced, and tested at the liquid helium temperature of 4.2 K, three pilot elliptical superconducting niobium cavities at a frequency of 1.3 GHz for accelerators of electrons and positrons. The cavities are constructed in the framework of the International Linear Collider (ILC) project. For the first time in Belarus, the cavities operated in superconducting mode, and the maximum value of the loaded Q-factor of the resonator equal to 2.8101 × 109 was obtained with the absolute matching of the cavity and the RF path at the standing wave ratio of 1.0000.

Исследованы нелинейно-оптические характеристики Cr4+:YAG кристалла методикой Zсканирования по схеме с открытой апертурой. В качестве пробного источника использовано излучение непрерывного лазера на длине волны 1030 нм мощностью до 400 мВт. При этом наблюдалось нелинейное поглощение лазерного излучения, которое связано снасыщением возбужденного состояния кристалла. Определена интенсивность насыщения и проведена оценка сечений поглощения в основном и возбужденном состоянияхCr4+:YAG кристалла.

We investigated the conditions for forming the single-frequency monopulse operation mode of the transversally diode pumped Yb,Er-phosphate glass laser with a passive Q-switch based on the Co 2 + :MgAl 2 O 4 crystal. It was shown experimentally that the spectral selectivity that ensures the stable single-frequency operation for the Yb,Er-laser is achieved in the intracavity Fabry–Perot interferometer in the form of the totally reflecting mirror and nearest end surface of an active element with plane-parallel faces, as well as the polarization interference filter (PIF, Lyot filter). Meanwhile, the PIF created by an active element with thermally induced anisotropy and a polarizer in the form of a passive Q-switch plate, oriented at Brewster’s angle to the resonator axis, acts as a preliminary spectral selector. The maximum energy of the formed output laser pulses was 6 mJ with a duration of 20.2 ns, a repetition rate of 1 Hz, and a singlefrequency lasing spectrum width of 41 MHz.

It was found that the long-wavelength absorption band of the laser dye IR 1061 and its analogue with an unsubstituted polymethine chain is strongly broadened and decreases in intensity in polar solvents, while the fluorescence band remains narrow and practically does not change in a wide range of solvent polarities. Based on the quantum-chemical calculations of these dyes by the ab initio DFT/B3LYP/6-31G (d,p) and TDDFT methods, taking into account the polarity of the medium by the PCM method, it is shown that the reason for this difference is the weakening of solvation in the fluorescent state as compared to the ground state due to the greater equalization of the charge in the first than in the latter. An increase in the alternation of bond orders in the polymethine chain in the fluorescent state was found, which causes an increase of vibronic interactions in the radiative transition as compared to the absorptive one. Spectral effects caused by a change in the angle of rotation of phenyl groups in the thiopyrylium cycle upon excitation have been analyzed.

Polymethine dye-based optical compounds characterized by low absorption at the pump radiation wavelength 808 nm and at the same time by high absorption at the lasing wavelength 1064 nm have been developed for the diode pumped Nd:YAG laser systems. It has been theoretically shown that the thiopyrylotricarbocyanines with saturated bridging groups in the polymethine chains are the most effective medium for such applications. The passive Q-switch unit as well as the saturable absorber mirror fabricated using the developed polymethine dye-compounds were examined experimentally. It has been shown that these dye-based optical components can provide the efficient lasing in the modes of the Q-switching and formation of the picosecond pulse train.

We found that the long-wavelength absorption band of the laser dye IR 1061 and its analogue with an unsubstituted polymethine chain is strongly broadened and decreases in intensity in polar solvents, while the fluorescence band remains narrow and does not change in a wide range of solvent polarities. Based on the quantum-chemical calculations performed for these dyes by the ab initio DFT/B3LYP/6-31G(d,p) method and TDDFT and taking into account the polarity of the medium, we demonstrated by the PCM method that the reason for this difference is the weakening of solvation in the fluorescent state as compared to the ground state due to the greater equalization of the charge in the former dye than in the latter one. An increase in the alternation of bond orders in the polymethine chain in the fluorescent state was found, which causes an increase in vibronic interactions in the radiative transition compared to the absorptive one. Spectral effects caused by changes in the angle of rotation of phenyl groups in the thiopyrylium cycle upon excitation have been analyzed.

We investigated the conditions for forming the single-frequency monopulse operation mode of the transversally diode pumped Yb,Er-phosphate glass laser with a passive Q-switch based on the Co 2+ :MgAl 2 O 4 crystal. It was shown experimentally that the spectral selectivity that ensures the stable single-frequency operation for the Yb,Er-laser is achieved in the intracavity Fabry–Perot interferometer in the form of the totally reflecting mirror and nearest end surface of an active element with plane-parallel faces, as well as the polarization interference filter (PIF, Lyot filter). Meanwhile, the PIF created by an active element with thermally induced anisotropy and a polarizer in the form of a passive Q-switch plate, oriented at Brewster’s angle to the resonator axis, acts as a preliminary spectral selector. The maximum energy of the formed output laser pulses was 6 mJ with a duration of 20.2 ns, a repetition rate of 1 Hz, and a single-frequency lasing spectrum width of 41 MHz.

We studied the thermo-optic properties of diode-pumped high-power pulsed ceramic- and crystalline-activeelement Nd:YAG lasers with neodymium ion concentrations of 2.0 and 1.1 at. %, respectively. We showed that under comparable excitation conditions, the mean heat generation from the ceramic Nd:YAG active element is 30%-35% higher than that from the crystalline Nd:YAG active element. The difference in thermal power is apparent from the energy of the polarized output laser pulses as a function of frequency. A quarter-wave plate partially compensates for thermally induced birefringence. This technique was found to be effective up to maximum frequencies of 50 and 70 Hz, for the ceramic and crystalline active elements, respectively. (C) 2020 Optical Society of America

The optical losses introduced into the cavity of transversally diode pumped Nd:YAG lasers operating in the linearly polarized Q-switched mode by the induced birefringence were evaluated. The relationship between the loss values and the state of the side surface of laser active elements was established. It has been shown that the active elements with adhesive light-scattering layers on their side surfaces make it possible to create the laser sources not only with a high degree of uniformity of the distribution of radiation within the output beam cross-section, but also with a low level of the optical depolarization losses.

The temporal dynamics of diode-side-pumped Yb-Er laser, with a passive Co2+:MgAl(2)O(4)Q switch illuminated by a light beam (total fluence of 0.15-0.16 J cm(-2)) from a semiconductor pulsed module, is investigated. It is shown that, using this external illumination, one can change the lasing onset delay and the time jitter Delta T-gi . The dependence of Delta T-gi on the interval between the instant of switching the illumination module on and the lasing peak position t(i) has a minimum at vertical bar t(i)vertical bar approximate to 10 mu s. The decrease in Delta T-gi with a change in vertical bar t(i)vertical bar from 91 to 10 mu s indicates that instant of lasing peak occurrence for the Yb-Er laser is partially controlled by the pulse from the highly stable semiconductor module. If vertical bar t(i)vertical bar < 10 mu s, the enhanced luminescence fluence in the cavity of Yb-Er laser exceeds 0.16 J cm(-2); the light beam from the module does not affect much the lasing process in the ytterbium-erbium laser; and, as a consequence, the time jitter recovers the initial value.

The formation features of the single-frequency unidirectional monopulse lasing mode of a Nd:YAG laser with a triple-mirror ring cavity and a side diode-pump with injection of external narrow-band optical radiation into the cavity are studied. The asymmetric layout of the intracavity elements relative to the output mirror and depolarization effects in them cause the energy and polarization of the monopulse Nd:YAG ring laser to differ depending on the input direction (clockwise or counterclockwise) of the injected radiation. The difference in the output characteristics of the single-frequency unidirectional monopulse Nd:YAG ring laser is most evident for a change from active to passive Q-switching.

The formation features of the regime of single-frequency unidirectional monopulse lasing of Nd:YAG laser with a triple-mirror ring cavity and a side diode-pump under the condition of injection of external narrow-band optical radiation into the resonator are studied. It is experimentally shown that the asymmetrical layout of the intracavity elements relative to the laser output mirror and the depolarization effects in these elements lead to a difference in the energy and polarization of the monopulse Nd:YAG ring laser depending on the direction (clockwise or anticlockwise) of the input of the injected radiation. The difference in the output characteristics of the single-frequency unidirectional monopulse Nd:YAG ring laser is the most evident in the case of transition from the active to the passive Q-switching.

A laser source for bleaching passive -switches of erbium-ytterbium lasers is developed and studied. The developed and studied compact pulsed module (peak power exceeding 10 W in a pulse with a duration of 1 mu s at a wavelength around 1551) nm) is made on the basis of a semiconductor lasers with an ultra-narrow waveguide integrated with a pulsed pump card. To optimise the output laser characteristics, a series resistance was used in the laser pump circuit. The powers of the free-space and fibre-coupled modules at a temperature of 25 degrees C arc 15 and 12 W, respectively, at a pulse shape close to rectangular.