The nonlinear optical responses of perovskite films CsPbI2Br, MAPbI3 + 1% PVC, MA0.15FA0.75Cs0.1PbI2.85Br0.15, and MA0.15FA0.75Cs0.1PbI3, irradiated by femtosecond laser pulses with wavelengths of 1064 and 532 nm, are investigated using z-scan measurements. Nonlinear absorption is found to occur in perovskite films irradiated at a wavelength of 1064 nm; the nonlinear absorption coefficient in thin films (45 – 65 nm) greatly exceeds that in thick ones (120 – 350 nm): 524 – 928 and 38 – 50 cm GW−1, respectively. It is shown that the nonlinear absorption saturation intensity for perovskite films depends on the pump pulse duration and increases with pulse shortening. It is also established that the nonlinear absorption coefficient of organometallic perovskite films exceeds that of a film of inorganic perovskite CsPbI2Br. Bleaching of film samples during z-scanning at a wavelength of 532 nm is related to the irreversible photochemical degradation of films exposed to intense light. The kinetics of photochemical bleaching of the films is detected at a wavelength of 532 nm.

The application of a fiber with W-type refractive index profile as a stretcher of ultrashort laser pulses for chirped pulse amplification is shown. As a result, pulses were obtained with energy of 3 mu J and duration of 270 fs, with high pulse contrast due to dispersion compatibility of the fiber stretcher and compressor on diffraction gratings. A comparative analysis of several types of fibers for use as a stretcher for amplification of chirped pulses is given in terms of their compatibility with the compressor. (C) 2019 Optical Society of America

The use of a heavily doped germanosilicate fibre with a W-profile refractive index and small core diameter in stretchers of ultrashort laser pulses with their subsequent amplification and compression in all-fibre laser systems is considered. The application of fibres of this type makes it possible to stretch, amplify, and then compress a laser pulse with minimum distortions of its initial shape and width. Due to the dispersion properties of these fibres, which allow the pulse duration to be increased significantly at a small fibre length and the third-order positive dispersion of the diffraction-grating-based output compressor to be compensated for, amplified pulses with an energy of 2 mu J and width of 250 fs, free of a picosecond pedestal, are obtained. Several types of fibres intended for the use in stretchers of ultrashort laser pulses are comparatively analysed from the point of view of their dispersion compatibility with a diffraction-grating-based output compressor.

The application of a fiber with W-type refractive index profile as a stretcher of ultrashort laser pulses for chirped pulse amplification is shown. As a result, pulses were obtained with energy of 3 µJ and duration of 270 fs, with high pulse contrast due to dispersion compatibility of the fiber stretcher and compressor on diffraction gratings. A comparative analysis of several types of fibers for use as a stretcher for amplification of chirped pulses is given in terms of their compatibility with the compressor.

Efficient operation of diode-pumped solid-state lasers with both high average power and good beam quality is generally limited by thermal effects in the laser gain medium. The effects of these distortions can be mitigated by application different pumping and extraction architecture. Zigzag slab lasers (see, for example, [1,2]) have demonstrated near-diffraction-limited output power at above 1 kW, because zigzag propagation by means of total internal reflections (TIR) eliminates thermally induced optical path differences over the entire beam area [3]. In experiment we have used the composite active slab made of three parts by a method of diffusion bonding. The central 40mm length of the slab is 0.8 % Nd:YAG, with 11-mm-long diffusion-bonded undoped YAG end caps that reduce end effects. End faces of the slab have been cut under 45 0 , for use of a longitudinal pumping. Special polymer has been put on TIR planes to reduce losses at total internal reflection of a laser beam. The pumping was symmetrically organized from both faces with two set of laser diode modules. Temperature distribution along the optical axis of the slab was studied by the interferometric technique. The steady state interference pattern allows to observe temperature distribution along the slab corresponding to the some pumping rate. While using the interferometric investigation it is possible to calculate the real temperatures along the slab at different absorption coefficients (fig.1). This temperature profile does not effect the lasing efficiency and beam quality in the case of homogeneous pumping distribution in a slab cross-section. But high values of the temperature gradient along slab can lead to the slab fracture. Thermooptical distortions of the HeNe probe beam were experimentally estimated at different absorbed pump power distribution in slab cross-section. We used two methods to estimate value of the thermal lens: method of multiple narrow probe beams and interferometric method. It was shown that high nonuniform absorption pump power distribution in slab results in focusing even in zigzag direction. Using more uniform distribution (Fig. 2a) with 3-lens pump focusing system allowed to reduce thermooptical distortions to less than 1 wavelength (λ=632.8 nm, Fig. 2b) in zigzag direction and in several times in non-zigzag plane (at absorbed pump power 380 W). Experimental investigation of losses in slab with zigzag beam path was done. It was shown that the main factor is the loss in the protective layer deposited on the TIR of the active element. Using SIEL type polymer as a protective coating on the TIR was proposed. Measurements of the small signal gain in zigzag slab amplifier were made at different pumping conditions. At effective pump absorption coefficient 0.7 cm -1 gain was g0l = 0.7 at 350 W pumping. Four-pass slab amplifier was realized with g0l = 2.3 in continuous wave. The main factor limited gain in multiple-pass amplifier was influence of the thermal lens and cutting of the beam at the slab aperture. In the case of inhomogeneous pumping in the slab the 3-D thermal lens was arrived. Its appearance and influence is clearly seen when using the pulsed pumping instead of CW. In plane cavity there was no lasing at pump power more than 200 W in CW because of high value of thermal lens optical power. Using more uniform absorbed pump power distribution in slab cross-section (Fig. 2a) we observed lasing with output power more than 100 W with 34 % slope efficiency at absorbed pump power around 400 W and there was no thermal lens influence on output characteristics (Fig. 3).

A diode-pumped Nd:YAG oscillator with an end-pumped zigzag slab architecture and polymer coating of total internal reflection (TIR) surfaces is developed. An output power of 105 W with a slope efficiency of 34% and an optical conversion efficiency of 25% is achieved from the plane-plane resonator, which emits the maximum power at 400-W pump power. The influence of evanescent wave losses on the lasing efficiency is demonstrated.

Efficient operation of diode-pumped solid-state lasers with both high average power and good beam quality is generally limited by thermal effects in the laser gain medium. The effects of these distortions can be mitigated by application different pumping and extraction architecture. We investigate experimentally the degree of absorbed pumping inhomogeneity which could influence the beam quality.

Generation characteristics of the neodymium laser with disk active element and diodepumped active medium were studied. It was shown that lasing occurs at a cavity length significantly exceeding the focal length of the thermal lens induced in the active element. Bending radii of the active disk surface were determined depending on the absorbed pump power. The cavity calculation performed taking into account the active disk surface bending showed that the negative lens formed by such bending of the surface and a laser mirror deposited on it efficiently compensates for the positive thermal lens, thus expanding the stability region of the disk laser cavity.