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Operating regimes of an optical system consisted of compact pulsed master diode-pumped Q-switched Nd:YAG laser and triple-crystal (KTP) ring cell of the optical parametric oscillator have been investigated. It has been experimentally shown that frequency-selective properties of a passive Q-switched unit in the “natural mode selection” are enhanced by creating a polarization interference filter Lyot with the phase plate in the form of a laser active element with the thermally induced birefringence and a polarizer. Such filter Lyot 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 the stable operation of a passive Q-switched Nd:YAG laser in the single frequency lasing mode (the lasing bandwidth is less than 57 MHz). The master single frequency pulsed Nd:YAG laser (λ = 1.06 μm) allows reducing the energy of pulses applied to the input of the optical parametric oscillator by more 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 1.3x telescope into the master laser cavity.

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 Co2+:MgAl2O4 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.

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.

Temperature effects on photoluminescence and absorption spectra of the active medium (LGS-DE erbium phosphate glass) and passive Q-switch (MgAl2O4:Co2+ crystal) of a diode-side pumped Yb,Er-laser are studied. The obtained data are applied to an analysis of the spectral and energetic characteristics of compact erbium emitters. It is established that the dominant generation channel in the temperature range 233–328 K is the optical transition between lower Stark sublevels of Er3+ states 4I13/2 and 4I15/2 (λ = 1532.0–1533.9 nm). A rate-equation system taking into account thermal population of Stark sublevels of states 4I13/2 and 4I15/2 is proposed to describe the experimental temperature dependence of the threshold absorbed power of the pumping radiation. This system and the lasing threshold enable modeling of Yb,Er-emitter output energetic and temporal characteristics.

An optical scheme of an optical parametric oscillator with a master laser based on an Nd : KGW active element excited by two orthogonally oriented diode side pump modules is proposed to form radiation pulses with energies above 30 mJ and a repetition rate of 1 – 20 Hz in the eye-safe spectral range of 1.5 – 1.6 μm. The two-module excitation of the active medium makes the distribution of the master laser radiation intensity in the output beam cross section more uniform and provides a reliable operation of the optical parametric oscillator.

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.

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%.

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.

We studied the thermo-optic properties of diode-pumped high-power pulsed ceramic- and crystalline-active-element 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.

A system of balance equations is used to calculate the time (t) dependence of the intensity (I) of the output of a Nd:YAG laser rod from the time a pump pulse is applied for different levels of excitation of the rod by arrays of laser diodes (transverse pump configuration). Comparison of the calculations with experimental data shows that an analysis of the I(t) curves can be used to determine the contributions of amplified luminescence and parasitic lasing modes, which do not leave the volume of the active medium, to the overall loss of pump radiation energy. The model approach developed here can be used to evaluate the quality of the active media in diode-pumped solid-state lasers.

The spectral characteristics of light emitting diodes based on a InAs/InAsSb/InAsSbP heterostructure, which emit in a wavelength range of 3.5–4.5 µm, are investigated experimentally. It is shown that the temperature shift of the maximum emission wavelength of a light emitting diode in the temperature range 80–313 K is 1.8 nm/K. The temperature dependence of the band gap of the InAs0.88Sb0.12 active layer is described by the Varshni formula with the characteristic parameters: Eg0 = 0.326 eV, a = 2.917 × 10–4 eV/K, and s = 168.83 K. The results of our measurements of the concentrations of carbon dioxide (CO2) using the studied light emitting diodes show the possibility of the reliable detection of CO2 in the concentration range 300–100000 ppm.

The power and output beam spatial properties of the transversally diode-pumped Q-switched Nd:YAG laser with the active element surrounded by the low-absorption light-scattering layer have been investigated. The layer consisted of the bonding agent in which the solid particles, like aluminum oxide or magnesium oxide, effectively scattering the light was uniformly distributed. The particle diameter was mainly in the range of 2 – 5 μ m . It has been shown that application of such layer to the diode-pumped Q-switched Nd:YAG laser head allows suppressing the amplified spontaneous emission and/or internally circulating parasitic lasing modes. At the optimized concentration of the light-scattering solid particles the output lasing pulses with the energy of 188–210 mJ (the wavelength of 1064 nm, the pulse repetition rate of 30 Hz) and improved spatial characteristics were obtained using the pump unit based on three laser diode matrixes.

The energy levels of gallium and arsenic vacancies as well as silicon impurities in the band gap of InxGa1 − x As have been found as functions of the indium content. The effect of defects on the lasing output power and on the optimal reflection coefficient of output mirrors of laser diode arrays (LDAs) based on the In0.11Ga0.89As/AlGaAs heterostructures has been estimated. It has been shown that the lasing output power of LDAs whose active level contains defects with deep energy levels in the band gap is substantially lower (with other conditions being the same) than that of LDAs with shallow level defects in their active layers.

The optimal value of the output mirror reflection coefficient providing the maximum output power under a constant level of electrical power consumption and the maximum external (slope) lasing efficiency for powerful InGaAs/AlGaAs laser diode arrays (LDA) has been estimated experimentally and theoretically. The LDA active layer overheating and amplified spontaneous emission have been taken into account. For advanced LDAs with the thermal resistance of 0.2 K/W and the internal optical loss of 0.5 cm −1 the optimal output mirror reflection coefficient is equal to 20%. This value is shifted to the high output mirror reflection coefficient side with a decrease of the LDA excitation level, the LDA thermal resistivity and the internal optical loss. It has been shown that the right selection of the output mirror reflection coefficient optimal value provides the LDA operation with 20% excess of the lasing output power and 10% excess of the external lasing efficiency.

Compact eye-safe pulsed optical parametrical oscillator based on Nd:KGW laser with two orthogonal diode pump modules has been developed. The oscillator is characterized by output energy at 1.57 μm in excess of 30 mJ and the pulse repetition rate up to 20 Hz.

A model taking into account the up-conversion processes involving the upper laser level and the presence of the unpumped regions within the active element along with the lasing transitions has been developed for the passive Q-switched ytterbium–erbium glass laser which was transversally pumped by the laser diode arrays. The results of the simulation allow determining the working point providing the stable and long-term operation of the laser. The correctness of the proposed optimized model was experimentally proved by means of a comparative investigation of the utmost permissible output lasing characteristics. The maximum output lasing pulse energy up to 16.5 mJ with the pulse duration of 11.5–16.0 ns at the wavelength of 1.535 μm has been achieved with the rectangular active element for the length of 32 mm.

A relationship between the laser diode array (LDA) near field fill factor, the power of the amplified spontaneous emission fluxes developed within the LDA active layer and the operation efficiency of the ytterbium–erbium glass laser transversally pumped by the laser diode arrays has been studied taking into account the electric and optical processes in the LDA heterostructure layers. It has been found that there is a critical value of the fill factor (0.65–0.85) below of which an abrupt rise of the ytterbium–erbium laser threshold as well as the decrease of the laser operation efficiency is observed. It has been shown that the increase in the InGaAs/AlGaAs LDA fill factor leads to the increase in the LDA threshold current related with the increase of the ASE flux power. For a suppression of the ASE flux power value it has been proposed to etch the LDA heterostructure emitter layer between the stripe contacts.

The development of amplified luminescence fluxes in powerful InGaAs/AlGaAs laser diode arrays (lasing wavelength 940–960 nm) has been studied experimentally and theoretically at pump levels above the threshold value. Flux density values for amplified luminescence propagation along (1.88⋅109 W/m2) and across (1.21⋅109 W/m2) the laser diode array cavity axis have been evaluated for the threshold pump level at room temperature (293 K). The contribution of the recombination rate induced by the amplified luminescence to the threshold current generation of the laser diode array reaches 7%. It has been shown that the amplified luminescence flux density is increased by 49% as the pump level rises from one to three threshold values.

The influence of the amplified luminescence (AL) and spreading of nonequilibrium charge carriers on the threshold, dynamic, and power characteristics of high-power InGaAs/AlGaAs laser diode arrays (LDAs) is studied. It is found that, depending on the near-field fill factor, the contribution of AL-induced recombination to the lasing threshold of LDAs may reach 11%. It is shown that the losses of the LDA pump energy, associated with the AL, increase with the injection current growth above its threshold value because of the increase in the intensity of radiation, propagating normally to the LDA cavity axis.

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.

The influence of amplified spontaneous emission (ASE) on the dynamic characteristics of transversely diode pumped erbium-ytterbium glass laser with Co:spinel Q-switch has been investigated. ASE cavity loss coefficient for passively Q-switched laser has been determined. The dependences of ASE cavity loss coefficient on the active element length, output mirror reflection coefficient, and initial transmission of the passive Q-switch have been defined. Laser dynamics has been modelled on the basis of the rate equation set for ion population densities and photon numbers, taking into account the amplified spontaneous emission. It has been shown that ASE accounting does not influence significantly the energy and duration of the output laser pulse. Variations of the laser turn-on time and pulse repetition rate of about 5‐10% have been revealed in the case of ASE taken into consideration.

Judd–Ofelt parameters (Ω2 = 5.09∙10–20, Ω4 = 0.92∙10–20, and Ω6 = 0.63∙10–20 cm2) and oscillator strengths of fundamental optical transitions involved in lasing at wavelength 1.54 μm have been calculated for borosilicophosphate glass co-activated with Er3+ and Tb3+ ions based on experimental luminescence and absorption spectra and refractive indices. The results were used to determine the emission (6∙10–23 cm2) and absorption (5∙10–21 cm2) cross sections for λ = 1.54 μm and the gain cross section as a function of inverse population levels.

The rates of radiative recombination (including transitions induced by enhanced luminescence) and nonradiative recombination, internal quantum yield of luminescence, and the matrix element for band-to-band optical transitions were determined for the first time for InAsSb/InAsSbP diode lasers oscillating at wavelengths of 3.1–3.2 μm. It is established that the contribution of nonradiative recombination to the lasing threshold can be as large as 97%. The internal quantum yield of luminescence for the InAs0.97Sb0.03 compound is no higher than 3%. Most likely, the nonradiative channel is formed with involvement of Auger recombination with the constant C = 4.2 × 10−38 m6s−1 (T = 77 K). The studied samples of lasers feature relatively low optical losses ρ = 900 m−1 and internal quantum efficiency of emission at the level of 0.6. The spontaneous lifetime of nonequilibrium charge carriers as determined from the radiative-recombination rate is equal to 6 × 10−8 s, which is consistent with known published data.

It has been shown that the cavity trapped amplified luminescence (CTAL) flux formed within the active region of a powerful 1.02 μm InGaAs/AlGaAs DQW laser diode (LD) with a ridged waveguide structure, can cause the bleaching of passive areas leading to abrupt hysteresis-type changes in the light–current and spectral characteristics. The post-threshold rise of the CTAL flux within the non-lasing parts of the active region is most likely to play significant role in the nonlinear optical phenomena observed in investigated LDs. The frequency-integrated CTAL flux density at which bleaching takes place is equal to 6.5×108 W/m2. The hysteresis-type loop can be removed through the LD “run-in” procedure or high-temperature annealing of the LD chip in an hydrogen atmosphere.

Based on analysis of the laser emission spectra of borosilicophosphate glass, coactivated by Er3+ and Yb3+ ions, we have determined the structure of the Stark splitting of the luminescence band for the erbium ion in the 1.5 µm region (the transition 4I13/2 → 4I15/2). In the wavelength interval 1532–1547 nm, we identified 12 sets of lines belonging to different types of optical centers of predominantly cubic symmetry.

We have achieved intracavity parametric conversion of the radiation from a laser based on Nd:YVO4 with high-power diode pumping. An LiF2- crystal was used as the passive Q-switch for the Nd:YVO4 laser. We have shown that by using an active element in the master laser with a passive region, we can form pulsed laser beams at a wavelength of 1.57 μm with peak power 3.2 kW and repetition rates up to 80 kHz, with beam quality parameter 1.4–1.8.

The work is devoted to the development and creation of the powerful all solid–state air–cooled multiwave Nd:YAG laser integrated with the output telescope system and to the development of the LD-pumped solid–state source with the extremely narrow lasing linewidth. The laser sources are meant for operation with the multiwave aerosol LIDAR (atmosphere probing altitude is up to 40 km). Keywords—LD-pumped Nd:YAG laser; LIDAR; multiwave laser source

The power and spatial characteristics of a longitudinally diode-pumped laser based on a composite YVO4/Nd:YVO4 crystal are studied. It is shown that the use of a composite crystal allows one to increase the external slope quantum efficiency from 36% to 41% and decrease the quality factor M2 of the output beam from 2 to 1.5 compared to these parameters for a Nd:YVO4 crystal.

Physical and fabrication peculiarities which provide the high output energy and beam quality for the diode pumped erbium glass and Nd:YAG lasers are considered. Developed design approach allow to make passively Q-switched erbium glass eye-safe portable laser sources with output energy 8 − 12 mJ (output pulse duration is less than 25 ns, pulse repetition rate up to 5 Hz) and beam quality M 2 less than 1.3. To reach these values the erbium laser pump unit parameters were optimized also. Namely, for the powerful laser diode arrays the optimal near-field fill-factor, output mirror reflectivity and heterostructure properties were determined. Construction of advanced diode and solid–state lasers as well as the optical properties of the active element and the pump unit make possible the lasing within a rather wide temperature interval (e.g. from minus forty till plus sixty Celsius degree) without application of water–based chillers. The transversally pumped Nd:YAG laser output beam uniformity was investigated depending on the active element (AE) pump conditions. In particular, to enhance the pump uniformity within AE volume, a special layer which practically doesn’t absorb the pump radiation but effectively scatters the pump and lasing beams, was used. Application of such layer results in amplified spontaneous emission suppression and improvement of the laser output beam uniformity. The carried out investigations allow us to fabricate the solid-state Nd:YAG lasers (1064 nm) with the output energy up to 420 mJ at the pulse repetition rate up to 30 Hz and the output energy up to 100 mJ at the pulse repetition rate of of 100 Hz. Also the laser sources with following characteristics: 35 mJ, 30 Hz (266 nm); 60 mJ, 30 Hz (355 nm); 100 mJ, 30 Hz (532 nm) were manufactured on the base of the developed Nd:YAG quantrons.

New methods for precise control of main parameters of LD-pumped solid-state lasers assigned for spectroscopic applications have been developed. Tunable lasing in wide range has been achieved. Active elements on the base of crystals (Nd 3+ :YAG, Nd 3+ :YVO 4 ) and glasses (Er,Yb doped boro-silico-phosphate glass) were used. The active crystals with uniform and non-uniform distribution of the activator ions were studied. Output beams with high quality and polarization degree have bean realized.

A method of modelling the conditions for side pumping a passively Q-switched erbium laser with linear laser-diode arrays is proposed that makes it possible to determine the most efficient geometry for the placement of the linear arrays relative to the active element, taking into account the characteristics of not only the diode arrays and the active element, but also of the optical cavity that is used. The results of the modelling make it possible to choose the distance between the linear arrays and the active element and the allowable shift of the linear arrays relative to each other, and this optimizes the matching of the excitation and lasing conditions. The proposed optimization method takes into account the divergence and polarization of the radiation of the diode arrays, the geometrical and optical properties of the active element, and the configuration of the lasing mode. The theoretical results of the modelling are compared with the experimental data.

An all-solid-state multiwave laser radiator (lasing wavelengths 1064, 532, and 355 nm), integrated in a single implement with a telescope, has been developed for use in aerosol lidars. The main radiator is the master laser and an amplifier based on a YAG:Nd crystal, excited by laser diode arrays using a transverse pumping layout. In the Q-switched regime, the energy of the output pulses of the YAG:Nd laser radiator reaches 400 mJ (1064 nm). With simultaneous lasing at three wavelengths, the radiator forms radiation pulses at 1064, 532, and 355 nm, with energies of 170, 150, and 80 mJ, respectively. The pulse width is 8–11 ns at a repetition rate of 10 Hz. The developed multiwave laser radiator is effective for use as a component of aerosol lidars with an atmospheric probing range of up to 40 km.

The propagation parameter M2 of the beam of an ytterbium-erbium glass laser with transverse diode pumping has been experimentally investigated for various cavity configurations. The polarization characteristics of the laser radiation are presented for cases in which the active medium is excited by two and four linear laser-diode arrays.

A slab laser based on borosilicate phosphate glass doped with erbium and ytterbium with transverse diode pumping has been developed and investigated. In the passive Q-switching regime, using a shutter based on a glass-crystalline material with nanosize spinel doped with divalent cobalt ions, the energy of the output radiation was 1.3mJ with a pulse width of 19ns. With active Q switching, the energy of the developed laser was 2.3mJ. The internal optical losses are estimated, and the parameters of the passive shutter are determined.