Two approaches have been proposed for distinction objects by third generation thermal imagers are discussed in the report. The first approach is based on recalculation of the original Johnson’s criteria and the second one is based on the dependences of the minimum resolvable temperature difference and temperature contrast on spatial frequency. In this paper, the most sensitive parameters are determined for optimization the numerical objects distinction by third generation thermal imagers.
On the base of density functional theory (DFT) calculations, it was ascertained that the GaN/AlN heterointerfaces without Al and Ga contacting layers intermixing and with the total substitution of the contacting layers are energetically more probable than the heterointerfaces with another amount of intermixing. The displacement of nitrogen atom from its site to second coordinate sphere between Ga and Al contacting layers is more probable than the displacement to the Al part of the cluster. The presence of nitrogen atom vacancy in the heterointerface does not influence the Al and Ga contacting layers intermixing, but complex defect nitrogen vacancy + interstitial N atom in the second coordinate sphere can be stable in contrast to the case of Al vacancy + interstitial Al atom in the second coordinate sphere. On the base of comparison of calculated and experimental data, it was ascertained that the most probable location of nitrogen vacancy in the vicinity of GaN/AlN interface is the location in the first Ga layer in respect to the GaN/AlN interface.
The results of calculation of nitrogen vacancy geometry in GaN/AlN heterointerface and its comparison with experimental data are discussed in the paper. The methods of calculation of point defects geometry in the GaN/AlN interface within the frameworks of self-consistent field and density functional theory are compared.
The present paper is aimed to development of the powerful illumination module based on powerful AlGaAs/GaAs laser diode matrix with short laser pulses, high repetition rate, given radiation divergence characteristics and stabilized parameters. Developed modification of the powerful illumination module gives the chance to realize powerful pulse laser radiation on the wavelength of 846 nm with the effective form of the laser pulse, wide range of duration from tens to hundreds of nanoseconds and the frequency of repetition rate of pulses up to 10 kHz in the set space angle of radiation 27° × 8°.
The results of the influence of point defects (vacancy with interstitial atom) on the GaN/AlN heterointerface is presented. It was ascertained that presence of Al atom vacancy in the heterointerface leads to the contacting layer atoms rearrangement. The presence of N atom vacancy does not influence on the contacting Ga and Al layers intermixing.
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 M2 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.
Power, special and temporal characteristics of high–performance advanced LD–pumped solid–state laser systems
emitting in the spectral ranges of 1064, 1535 and 1570 (fundamental modes) as well as 266, 355 and 532 nm (fourth,
third and second harmonics) are discussed. The ways for further improvement of those laser systems are proposed. In
addition, the problem of optimization of the pump unit based on the powerful laser diode arrays (LDAs) is analyzed. The effect of the LDA internal optical loss on the amplified spontaneous emission flux value developed within the LDA
active layer is considered in detail.