A multilayer antireflection coating based on titanium oxide and silicon oxide has been developed. The dispersions of the refractive index and absorption coefficient of these materials are obtained in a wide spectral region of 500-8000 nm. Taking into account these dispersions, a calculation was made of a four-layer interference coating with ZGP substrate antireflection in the range of 2097 nm and 3500-5000 nm, with residual reflection R≤0.2% and R≤2.1%, respectively. The modes of coating deposition by the method of ion-beam sputtering on the substrate are selected.
The paper shows an increase in the threshold energy density of laser radiation at a wavelength of 2091 nm as the temperature decreases from 0º С to -60º С until the optical breakdown of a ZnGeP2 (ZGP) single crystal sample is reached. With a decrease in temperature from 0º to -60º C, a sharp increase in the threshold energy density is observed from 1.6 to 2.6 J/cm2, with a laser beam diameter of 270 μm, and from 3.2 to 10.2 J/cm2 with a diameter of 100 μm (by 1.5 and 3 times, respectively).
The generation of terahertz (THz) radiation using a ZnGeP2 (ZGP) large-aperture photoconductive antenna (PCA) was demonstrated. The semiconductors were excited above and below the bandgap (400 and 800 nm) by a femtosecond Ti:sapphire laser. The THz pulse waveform generated by the ZGP antenna was measured using a time-domain spectroscopy technique. The antenna’s THz pulse energy dependence on the optical pump energy was measured, and saturation fluence and carrier mobility were estimated. The ZGP and a chemical vapor deposited ZnSe-based PCA were compared.
Volumetric defects in ZnGeP2 single crystal have been visualized by using the digital holography camera. Type, geometrical sizes and positioning of founded defects were determined. Based on this information researching zones were chosen on the test ZnGeP2 plate. Measurements of absorption coefficient and refractive index in THz range were carried out. It is shown that in the frequency range 0,3-1 THz the difference of absorption coefficients reaches the value Δα = 0.2 cm-1 between “clear” zones and zones with volumetric defects. In same time, maximum difference by refractive index is about Δnmax = 0,0015.
Conditions for the formation of THz radiation in ZnGeP2 single crystals when generating a difference frequency are considered. It is shown that effective THz radiation requires two-frequency laser pumping sources with a generation pulse duration of < 1 ns. It is proposed to use IR radiation as such a source dual-wavelength optical parametric oscillator based on the KTP singlecrystal with pumping by Nd:YAG lasers with active Q-switching with simultaneous synchronization mode.
In paper the device – set of hardware and software for non-contact investigation of marine particles is presented. The device is designed on digital holography principles. Hardware features of submersible holocamera (or DHC sensor) are considered. Methods are described for the processing of holograms and retrieve information. Results of approbation of the device are presented.
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