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.

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.

Досліджено характеристики мініатюрних компактних лазерів на Nd:YAG та Nd:YVO4 з діодною накачкою у режимі пасивної модуляції добротності. З використанням полімерного лазерного затвора на основі поліуретану, забарвленого барвником біс-4-діметиламінодітіобензил нікелю, реалізована генерація на довжині хвилі 1,064 мкм з частотою слідування імпульсів до 25 кГц, тривалістю 2–5 нс та потужністю до 130 мВт при накачці до 3,5 Вт. Твердотільні мінілазери з діодною накачкою і пасивною модуляцією добротності затворами сендвічевого типу є ефективними компактними джерелами коротких потужних імпульсів з високою оптичною якістю пучка.

It has been experimentally shown that incorporation of the λ/4 phase plate into a cavity of the solid-state laser with the ring Q-switch modulator leads to an enhancement of the maximum achievable energy Emax of the output lasing pulses over a wide interval of the pulse repetition rate f. This is achieved by an improvement of the spatial phase distribution for two orthogonal polarization components formed in the laser cavity by the ring Q-switch modulator. These components transform into each other during every round trip of the laser cavity, thus forming the polarization ring cavity without appreciable hole burning effects. For the transversally diode pumped Nd:YAG laser source with the ring Q-switch modulator and λ/4 phase plate the output pulses with Emax ≈ 584–600 mJ were obtained in the range of f ~ 30–100 Hz at the excitation energy of 2.0–2.2 J.

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.

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 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.

A model system of two differential rate equations is proposed to describe the temporal characteristics of the radiation of a solid-state laser with high-energy pumping. Using a laser head with a YAG:Nd active element and a side-pumped laser diode array unit as an example, a method is discussed of determining the excitation levels of the active elements at which the amplified luminescence and the nonaxial (stray) lasing modes begin to manifest themselves in the output radiation dynamics all the way to the limitation of the maximum pulse energy generated by a solid-state laser in the Q-switched regime. The proposed approach to analyzing the role of the processes associated with the formation and evolution of amplified luminescence fluxes and nonaxial (stray) lasing modes in the active media can also be applied to other types of laser radiators.

An automated low-background NaI(Tl) gamma-ray spectrometer for in situ underwater measurements consisting of a submersible unit with a radiation detector and of a surface microcomputer unit is developed and described. Along with an ultra low-background NaI(Tl) radiation sensor, the submersible unit contains a specially designed FPGA-based electronics with low energy consumption and with abilities both for remote data acquisition by a 1200 m conducting cable and for an autonomous operation mode. The unit is enclosed in a waterproof polyacetal housing withstanding a pressure of 4 MPa at a depth of 400 meters. The surface microcomputer unit contains an all-in-box software for acquisition, storage, and processing of data from the detector unit, for real-time monitoring of activities of dissolved radionuclides, for their identification and quantification. The software functions are accessed remotely by a web-interface using Wi-Fi or Ethernet. Several techniques for gain control (including an auto-adjustment of the gain by setting a selected photopeak in a prescribed channel) together with the corresponding approaches to the energy-scale calibration are implemented and examined over a wide temperature range −10÷+50°C in a thermo-chamber calibration experiment with 152Eu point gamma-ray sources. Calibrating the energy resolution of the detector is performed from line-width measurements of reference gamma-ray sources. The detection-efficiency calibration is carried out using Monte Carlo simulations based on the GEANT4 code taking into account the materials and geometry of the detector as well as the water environment. In addition, the efficiency of the detector immersed in a 8m3 water tank with dissolved gamma-ray sources of 139Ce, 137Cs and 40K of known activities is determined experimentally and compared with the theoretical findings. Finally, a trial deployment of the gamma-spectrometer in the Yellow Sea together with test measurements of the activity concentrations of dissolved radionuclides is fulfilled. The Minimum Detectable Activity concentrations (MDA) for 137Cs in fresh and sea water are calculated from the water tank experiment and from the test deployment experiment correspondingly.

The feasibility of using light-emitting devices, the radiation spectrum of which has maxima at wavelengths of 1.7, 1.9, and 2.2 μm for determining the water concentration in oil and oil products (gasoline, kerosene, diesel fuel) has been demonstrated. It has been found that the measurement error can be lowered if (i) the temperature of the light-emitting diode is maintained accurate to 0.5–1.0°C, (ii) by using a cell through which a permanently stirred analyte is pumped, and (iii) by selecting the repetition rate of radiation pulses from the light-emitting diodes according to the averaging time. A meter of water content in oil and oil products has been developed that is built around IR light-emitting device–photodiode optrons. This device provides water content on-line monitoring accurate to 1.5%.