A two-channel double-pass iodine explosively pumped photodissociation laser (EPPL) with an explosively pumped master oscillator (MO) and an SBS mirror is studied. The radiation source, determined by an aperture 6 mm in diameter, through which the radiation from MO enters the turbulent surface air path, is located at a distance of 2.5 km from the amplifier unit input. An SBS mirror with a kinoform raster of microlenses is used to compensate for the amplifier and path optical inhomogeneities and to match the phases in the EPPL channels. The energy and spatial characteristics of the EPPL output radiation are studied experimentally and numerically. Good agreement is obtained between the experimental and calculated distribution of the energy density of the output EPPL radiation in the plane of the MO aperture, which is a pattern of interference between the two channels. The maximum energy density in the aperture plane is by more than 4 times greater than in the case of a single-channel EPPL.

There are two known directions of work on the implementation of inertial thermonuclear fusion using Z-pinches. In the first, to achieve thermonuclear ignition, it is proposed to compress the target by indirect irradiation with Z-pinch X-ray radiation. The other direction is to compress the preheated magnetized plasma with a liner. Preheating reduces compression requirements, while magnetization reduces thermal conductivity losses and provides additional heating by α-particles even at low plasma density. This concept is being developed in the United States at the Z machine (MagLIF project). According to existing concepts, in order to achieve thermonuclear ignition in these schemes, facilities are required that can create a current pulse with an amplitude of ~ 60 MA. The most powerful facilities based on capacitor banks—the Z machine—realizes a current of up to 25 MA. The creation of facilities that are one order of magnitude more powerful than the Z machine is a matter of the future. Along with this, explosive magnetic generators (EMG) today already implement the required energy, although with much longer rise time of current pulse. The paper discusses the possibilities of using the EMG to achieve the ignition, the arising problems and ways to solve them.

Lasing in caesium vapour is obtained at λ ∼ 3 μm (transitions 7P 3/2 → 7S 1/2 and 7P 1/2 → 7S 1/2 ). Longitudinal pumping is performed by the second harmonic of a parametric oscillator pumped by the second harmonic of a Nd 3+ -doped garnet laser. The pump wavelength corresponds to the 6S 1/2 → 7P 3/2 and 6S 1/2 → 7P 1/2 transitions of caesium atoms. The pump radiation has a spectral width of 12 cm −1 , a pulse energy of 10 mJ, and a pulse repetition rate of 10 Hz. The IR laser pulse energy at a vapour cell temperature of 155 °C is 100 μJ. The efficiency of pump energy conversion to the laser radiation energy at λ ∼ 3 μm is ∼1.5%.

The results of imaging system resolution enhancement of the astronomical objects by using a Rayleigh laser guide star (LGS) have been presented. Correction of the distortions of stellar optical image has been performed by the adaptive optical system. The numerical simulation of registration of radiation from the Rayleigh LGS by a Shack-Hartmann wavefront sensor has been carried out. It has been shown that accurate calculation and subtraction of magnitude of the defocus and tip-tilts allows mitigating the reconstruction error concerned with the finite distance to LGS and the angular position of the telescope. It has been demonstrated in the experiment that angular size of the natural star Scheat decreases by 3 times at the use of Rayleigh LGS at range of 5 km.

The results of resolution enhancement of the stellar imaging system by using a Rayleigh laser guide star are presented. The estimation of residual phase error value of adaptive correction is carried out at various position of a laser guide star.

This paper presents the results of the recording of stars under daylight conditions, using video cameras with a silicon photodetector array. It is shown that the SNR increases as the depth of the potential well of a pixel increases. The RT-1000DC video camera, with a potential well of capacity 170 thousand electrons, and the BCA-304 video camera, with frame summation up to an effective potential capacity of 600 thousand electrons, chosen after preliminary testing, made it possible under conditions of typical daylight turbulence of the atmosphere in the northern hemisphere of the sky to observe low-brightness stars (7(m)-8(m)) on level terrain. (c) 2018 Optical Society of America

A seven-channel fibre laser system operated by the master oscillator – multichannel power amplifier scheme is the phase locked using a stochastic parallel gradient algorithm. The phase modulators on lithium niobate crystals are controlled by a multichannel electronic unit with the microcontroller processing signals in real time. The dynamic phase locking of the laser system with the bandwidth of is demonstrated, the time of phasing is .

The results of measurements of optical inhomogeneities in a cesium vapor laser active medium under various conditions are presented. The calculation of phase correction of measured optical inhomogeneities by means of a deformable mirror is carried out. Keywords—alkaline vapour laser; wavefront aberration; optical distortion; Hartmann-Shack sensor; deformable mirror. The present work is devoted to the measurement of optical distortions arising in various operation regimes of the cesium vapor laser [1-3]. The optical inhomogeneities are measured by means of the probing beam of He-Ne laser on passing though the optical path of the cesium vapor laser. The reconstruction of the wavefront of the probing beam is conducted by use of a Hartmann-Shack sensor [4]. The information about the wavefront distortions of the beam is used to calculate the beam intensity in a far field and estimate its divergence. First, the aberrations of the optical scheme, i.e. the aberrations of the probing beam are measured. It is shown that these aberrations correspond to converging wavefront with amplitude of 0.66 μm. The wavefront of the probing beam doesn’t change in the experiment. This makes it possible to subtract the aberrations of the optical scheme form the measured aberrations in all following experiments. Second, the aberrations introduced by the laser medium in a steady state, in circulation of the gaseous medium in various regimes, in heating of the laser medium are measured. It is shown that the medium in a steady state and the flow of the gaseous medium introduces marginal distortions in the wavefront of the probing beam. When the medium is heated up the aberrations rise. The magnitude of aberrations does not exceed 1 μm. The calculated value of the divergence angle of the probing beam approximately equals 0.4 mrad in a steady state, 0.3 mrad in circulation of the laser medium, 0.5 mrad in heating of laser medium. Then, the aberrations of the probing beam in heating of the laser medium by the pumping radiation and in the lasing regime are measured. The wavefront of the probing beam becomes divergent and the magnitude of aberrations rises up to 1.3 μm while pumping. In the lasing regime the form of the wavefront doesn’t considerably change and the magnitude of aberrations fluctuates from 0.8 to 1.6 μm with the frequency of a few hertz. The value of the divergence angle of the probe beam rises up to 0.7 mrad in this case. The estimation of aberration for operating wavelength (0.894 μm) of the cesium vapor laser is carried out assuming that the active medium does not possess dispersion. The calculation shows that the divergence of cesium vapor laser radiation remains at the same level as the divergence of probing beam. Finally, the numerical simulation of phase correction of the probing beam is undertaken. The operation of a closedloop adaptive optics system with a bimorph deformable mirror driven by the stochastic parallel gradient algorithm is simulated. The calculation shows that the divergence of the probing beam can be reduced up to 2 diffraction limits. [1] R. J. Beach, W. F. Krupke V. K. Kanz, S. A. Payne, M. A. Dubinskii, L. D. Merkle, “End-pumped continuous-wave alkali vapour lasers: experiment, model and power scaling,” J. Opt. Soc. Am. B, vol. 21, pp. 2151-2163, 2004. [2] A. V. Bogachev, S. G. Garanin, A.M. Dudov, V. A. Eroshenko, S. M. Kulikov, G.T. Mikaelian , V. A. Panarin, V. O. Pautov, A. V. Rus, S. A. Sukharev, “Diode-pumped caesium vapour laser with closed-cycle laser-active medium circulation,” Quantum Electron., vol. 42, pp. 95–98, 2012. [3] B. Zhdanov, R. J. Knize “Diode pumped 10 W continuous wave cesium laser,” Opt. Lett, vol. 32, pp. 2167-2169, 2007. [4] Fried D., Collected articles on adaptive optics. Under D.Fried's edition, Moscow, 1980.

The phasing of a multichannel laser beam by means of an iterative stochastic parallel gradient (SPG) algorithm has been numerically and experimentally investigated. The operation of the SPG algorithm is simulated, the acceptable range of amplitudes of probe phase shifts is found, and the algorithm parameters at which the desired Strehl number can be obtained with a minimum number of iterations are determined. An experimental bench with phase modulators based on lithium niobate, which are controlled by a multichannel electronic unit with a real-time microcontroller, has been designed. Phasing of laser beams at a system response bandwidth of and phase thermal distortions in a frequency band of about is experimentally demonstrated. The experimental data are in complete agreement with the calculation results.

The creation of a caesium vapour laser with closed-cycle circulation of the laser-active medium is first reported. The power of the laser radiation amounted to similar to 1 kW with the 'light-to-light' conversion efficiency of similar to 48 %. Quasi-two-dimensional computational model of the laser operation that provides adequate description of experimental results is considered. Calculated and experimental dependences of the laser radiation power on the temperature of the cuvette walls, laser medium pressure and pump power are presented.

We investigated the phasing of pulsed two- and fourchannel laser beams due to phase conjugation upon transient stimulated Brillouin scattering (SBS) in a double-pass amplification scheme. A high quality of beam phasing was experimentally demonstrated with the use of a microlens raster and an angular selector in the SBS-mirror scheme. The data obtained in the numerical simulation of transient SBS are in good agreement with experimental ones.

A new scheme of a cascaded converter of the first harmonic of broadband cw laser radiation into the second harmonic (SH) with compensation for the group walk-off in cascades is proposed and investigated. The conditions under which high conversion coefficients of broadband (∼33 cm-1) single-mode fibre laser radiation with low peak power (∼300 W) into the SH are determined for frequency doublers based on the most promising LBO crystal. Conversion of cw radiation with an average power of 300 W and efficiency η = 4.5 % into the SH is obtained in a single LBO crystal. Effect of coherent addition of SH radiation excited in different cascades is demonstrated for two- and three-stage schemes. The expected conversion efficiencies, calculated disregarding loss but taking into account real aberrations of elements, are 18 % and 38 %, respectively. The effect of pumping depletion begins to manifest itself in the third cascade of a three-stage converter; it may reduce the latter value to ∼30 %.

The results of experimental investigations of wide-aperture (100 × 100 mm) plasma-electrode Pockels are presented. Time characteristics, contrast, transmission factor, and optical uniformity of the cell are measured. It has been found that the half-wave effective voltage of the cell is 10 kV, the duration of the transmission window can vary from 250 to 550 ns, its leading and trailing edges are 40–50 and 70–100 ns in duration, respectively, and the time of the cell plasma electrode formation is 40 ± 5 ns.

We study experimentally stimulated Brilluoin scattering (SBS) of vortex laser beams, namely, the LG(1)(1) and LG(0)(1) Laguerre-Gaussian modes. The wave front transformation is experimentally demonstrated in the case of SBS of the LG(1)(1) laser mode, directly focused into the SBS cell, when the fundamental Gaussian mode LG(0)(0) rather than the conjugate mode is selected from the Stokes beam. It is shown that optical vortices become phase conjugate by destroying the laser mode structure in the SBS cell. Phase conjugation (PC) of the LG(0)(1) and LG(1)(1) modes is obtained in the SBS mirror using a regular aberrator (microlens raster) in the system of laser beam focusing into the SBS cell.

The sensing of phase front of the vortex laser beams has been carried out with the help of a Hartmann-Shack sensor. The vortex beam is generated in the form of a Laguerre-Gaussian beam (LG(0)(1) mode) with the help of the special helicoidal phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmannogram are compared with the calculated shifts. From the measured wave front tilts the reconstruction of singular phase surface has been performed with using the novel reconstruction technique. The phase surface reconstruction is demonstrated in the case of distorted vortices as well. The correction of an optical vortex is undertaken in the close-loop adaptive system including the bimorph deformable piezoceramics-based mirror.

In the clinical trials it was shown, that characteristics of optical scattering and absorption are sensitive to the tissue type and state. System for optical biopsy was tested in the Regional Oncology Center of Nizhny Novgorod, Russia. During a year more than 160 patients with breast tumors were investigated using this system. White light from a xenon lamp was delivered into the breast tissue using special probe with fibers. The radiation scattered from the breast tissue was collected by another fibers and its spectrum was measured. Obtained optical data was analyzed to find general optical characteristics of scattered radiation in different types of tissue and revealing the major peculiarities in the spectral scattering coefficients of malignant tumors and their distinctions from benign tumors and healthy tissue. Using different mathematical algorithm the typical template of scattering spectrum was found for benign and malignant type of breast tumor. Then the algorithm of automatic detection of malignant spectra in the data flow was developed. Using this algorithm the datasets of all patients were processed and analyzed and the diagnoses were obtained. The automatic diagnoses were compared with those given by physicians. As a result the indexes of sensitivity and specificity for the optical biopsy diagnostic method were found equal to 91% and 90% correspondingly.