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This paper presents the results of experimental studies of active mode-locking in an external-cavity semiconductor laser. Two methods of obtaining active mode-locking regimes have been studied: by modulation from an external generator with a frequency close to the intermode frequency of the external laser cavity and by laser current modulation at the frequency of intermode beats of the external laser cavity through an amplification feedback loop. In the first case, a stability of intermode beats of 10 ^-14 is experimentally achieved, and in the second case, it is shown that semiconductor laser current modulation by an amplified intermode beat signal from the output of a photodetector provides a stable mode-locking regime also with mode frequency tuning, i.e., a mode-locking regime involving intermode frequency tuning with optical cavity tuning. The effects that accompany mode locking, in particular, the pulling effect and the stability of the mode-locking regime, and possibility of obtaining highly stable intermode beats by suppressing the amplitude noise component in the modulating signal have been studied. A phenomenological study of the pulling and phase locking of the intermode frequency is attempted.

The shape of the diffractive structure of a deflecting kinoform element designed for focusing high-power laser beams with a wavelength of 10.6 μm is studied. Formulas are derived for calculating light losses induced by tilting of the incident beam, diffraction, and technological blurring of the steep slope of the structure. It is demonstrated that the height of the structure varies from the minimum to the maximum value depending on the azimuthal angle. It is found that light loss induced by shadowing due to oblique incidence of the beam is rather low (0.6-1.3%), and that caused by diffraction is smaller by an order of magnitude and can be neglected. The light losses induced by technological blurring of the slope and by deviation of the structure height from the design value (in the case of violation of the azimuthal dependence) can exceed 10%.

This paper presents the results of modeling the propagation of multichannel radiation under free diffraction conditions and discusses features inherent in this type of beams under these conditions. In addition, the effect of distortions arising in a turbulent atmosphere on radiation quality is considered, and the efficiency of adaptive compensation of atmospheric turbulence is analyzed.

Natural oscillations of a spherical interface between a gas and a liquid in a bubble are registered. A possibility of measuring the geometric parameters of stationary and moving particles of the disperse phase by a laser Doppler anemometer is demonstrated. A method for simultaneous determination of the size and velocity of a bubble or a droplet in a two-phase flow is developed. The mean sizes of a group of bubbles settled on a ruler are compared: the results are obtained by two independent methods, i.e., by analyzing the image and by processing the Doppler signal containing information about the natural oscillations of the spherical interface between the media. A possibility of using a laser Doppler anemometer for simultaneous measurements of the velocity and size of bubbles or droplets in a two-phase flow is confirmed.

Theoretical results on the energy evolution in ring and linear cavities of dissipative soliton fiber lasers are analyzed. The correctness of the theoretical results is confirmed by mathematical modeling.

A rapid method is proposed to evaluate the efficiency of excitation energy transfer between ytterbium and erbium ions from measured relative luminescence intensity in different spectral regions in an active fiber preform, taking into account the concentration of active ions and their spectroscopic constants.

This paper presents a method for calculating the cross-wind speed at the entrance aperture of an adaptive system from the coordinates of the energy centers of gravity of the focal spots measured by a Shack-Hartmann wavefront sensor. The range of applicability of the method are determined for data obtained in an experiment on an atmospheric path depending on the intensity of turbulent distortions and the optical parameters of the sensor.

The process of interactive modeling of geometric shapes defined by mathematical functions is studied. A method of interactive modeling of functionally defined objects without preliminary triangulation is proposed. This allows more accurate definition of three-dimensional shapes and simplifies the modeling system. A method adapted for graphic processing units is used for rapid visualization of objects.

The current status of the list of elements of uncooled infrared (IR) imaging arrays based on thermal insulation of their sensors and on accumulation of heat in the element volume during the time necessary for taking one frame is considered. Specific features of operation and the structure of resistive microbolometers and pyroelectric elements are described, as well as typical parameters of these elements. Prospects of improving the parameters of thermally insulated sensors of megapixel arrays are considered. It is noted that the main factor limiting further improvement of the parameters of pixels in IR imaging arrays and increasing the size of the latter is the value of the thermal resistance between the sensor and the substrate. At the modern level of technology development, the thermal resistance has actually reached the limiting value. Another physical principle of operation of IR detectors is required for a further increase in the sensitivity of sensors, a decrease in their response time, and an increase in the size of uncooled megapixel IR arrays; this principle should not include the necessity of thermal insulation of IR detectors. The operation principle based on using pyrotechnical effects will be considered in the second part of the paper.

An experimental method of fabrication of a sensor based on a metal-dielectric structure (Al + ZnS) and optimization of its characteristics is described. The coefficient of light reflection ( p -polarization) from the aluminum layer is studied as a function of the layer thickness for different angles of incidence at the wavelength of 532 nm. Based on calculations, which are qualitatively consistent with experimental results, a structure consisting of matched layers of aluminum and zinc sulfide is fabricated; this structure has a higher angular resolution than the aluminum film with no dielectric coating. The detection limit of angular measurements by the sensor based on this structure is estimated as 2.6 · 10 ^-5 RIU (refraction index units).