Yu. A. Shakir

Submillimeter-wave generation with ZnGeP2 crystals

This paper describes detailed analysis of optical and dielectric properties of ZnGeP2 crystals in middle IR and FIR spectral ranges, and also first experimental results on 1 W level 102 - 110 micrometers emission generation by means of difference frequency generation of CO2 laser line pairs. It is shown that MW level is achievable now, and AgIn0.35Ga0.65Se2 crystal can be used for efficient generation of FIR emission.

Far-infrared generation by CO2 lasers frequencies subtraction in a ZnGeP2 crystal

A pulsed radiation power of approximately 1 W was reached for the first time, with the aid of a ZnGeP2 crystal, at the difference frequency of CO2 lasers radiation in the submillimeter spectral range.

Mechanisms of loss formation in nonlinear optical crystals ZnGeP2 in the terahertz frequency range

Physical mechanisms of formation of radiation losses in the terahertz range in ZnGeP2 crystals have been experimentally studied in the wave number range of 5–350 cm−1 at temperatures of 10–300 K. The dominant contribution of two-phonon difference processes to the loss formation in the given frequency range has been shown.

Far infrared generation by CO2 lasers frequencies subtraction in a ZnGeP2 crystal

Abstracta pulsed radiation power of the order of 1W in the submillimeter range (102–110 µm) was reached for the first time, with the aid of a ZnGeP2 crystal, at the difference frequency of CO2 laser radiations.

Efficiency of difference frequency generation with ZnGeP2

Using experiment data of laser damage threshold for ZnGeP2 surface we have made calculations of dependence of different frequency generation efficiency from nonlinear crystal length for different values of sum laser intensity (up to 10 GW/cm2) corresponding to definite CO2 laser types. Computation results showed that more 1-MW submillimeter power values are possible if to use sufficiently short powerful pump. These pulses are of considerable interest for many applications in matter investigations. Also we suggest to generate powerful laser half-cycle pulse at submillimeter wave region by means of difference frequency generation with ZnGeP2 and by converted radiation reflection and absorption switch on semiconductor wafers.

Simulation of parametric oscillation in the submillimeter range at pumping of the ZnGeP2 crystal by a train of 100-ps high-power pulses

Analysis is given for a possibility of singly resonant parametric oscillation in the submillimeter range at synchronous pumping of the ZnGeP2 crystal by a train of 100-ps second-harmonic pulses from the CO2 laser with the radiation energy 1.0 J. The calculation shows that using the ZnGeP2 crystal and the second harmonic of the CO2 laser with the energy density 1.8 J cm−2, one can get the peak submillimeter radiation power from 3.6 to 12 MW in the range from 95 to 300 µm (1.0–3.3 THz). The expected peak power values are larger than the experimental ones obtained by other nonlinear optics methods.

Parametric oscillation of high-power 3-THz pulse by synchronously pumped ZnGeP2 crystal: Computer simulation

Possible parametric oscillation of 3-THz pulse at synchronous pumping of the ZnGeP2 crystal by a train of short second-harmonic pulses from the CO2 laser has been analyzed. Calculation shows that at changing laser pulse duration τ between 4 and 500 ps and correspondingly pumping energy density (0.5–3.5 J cm−2) THz pulse peak power varies from 3 to 70MW with maximum at τ =9 ps.

Nonstationary mixing in AgGaSe2 crystal

For the first time three-wave interaction of picosecond pulses was investigated as difference frequency generation with Ag- GaSe2 crystal. Group velocities and radiation absorption were taken into account during spectral analysis realization. Calculations were executed for CO2 laser parameters: 100 divided by 5 ps, 15 divided by 150 GW/cm2. Spectral characteristics and pulse power versus crystal length are represented for difference wavelength 800.5 micrometer.

High-power CO2 laser radiation conversion by means of AgGaSe2 and AgGa(1-x)In(x)Se2 crystals

In 7.7 divided by 39.6 cm1 range investigated for the first time refraction and absorption spectra of AgGaSe2 and AgGa1- xInxSe2 crystals allowed to compute a phase matching characteristic and efficiency values of difference frequency generation with total laser intensity from 60 MW/cm2 up to 15 GW/cm2. The maximum efficiency values were close to 1*10-3. Powerful half-cycle pulse generation is proposed with the investigated crystals.

Probe investigations of close-to-surface plasma, produced by CO2 laser nanosecond pulse train

Investigations of currents in close-to surface plasma, produced by CO2-laser radiation of different temporal structure have been carried out. The character of evolution of registered currents temporal structure at growing energy density was different when the target was irradiated in air and in vacuum by the train of short (τ = 2.5 ns) pulses. Experiments in vacuum have revealed that the transit from smooth single mode pulse to the nanosecond pulse train of the same total energy was followed by a considerable decrease in plasma formation energy thresholds and by the increase of amplitudes of currents induced by plasma. The current pulses from the target were registered after finishing the laser irradiation; their appearance was probably connected with cumulation effects, caused by the ring form of the irradiated area.