Education of the republic of uzbekistan tashkent state technical university named after islam karimov

 
Keywords: 
optical parametric amplification, dispersion, femtosecond pulses, cubic 
susceptibility, LiNbO
3
, crystals with a regular domain structure.
 
 
INTRODUCTION. 
In nonlinear optics, laser radiation frequencies can be converted 
using various nonlinear optical media. Despite the whitewash of the frequency conversion 
processes, the process of optical parametric amplification (OPA) of laser radiation in quadratic 
crystals plays a unique role. There are several reasons for this. Most importantly, this process 
can convert coherent sources from the visible spectrum to the infrared. In addition, using it is 
possible, to convert the laser wavelength not discretely, but "smoothly". 
A shot history of the OPA as follows. The nonlinear optical OPA process was first 
predicted theoretically in 1962 by Kroll [1], Akhmanov and Khokhlov [2], Kingston [3] and 
others. This was later demonstrated in practice by Wang and Reisett [4], Akhmanov [5], 
Jordmain and Miller [6] and others in 1965. 
It has been proven that this nonlinear optical process is based on the influence of a 
medium with nonlinear optical properties (for example, KDP or LiNbO
3
crystals). In this case, 
a very low energy signal radiation, which is planned to be amplified by a high energy light 
wave, called the fundamental (or pump) wave, is incident on the nonlinear optical medium 
simultaneously. Then, under certain conditions of the phase mismatching, the nonlinear optical 
medium emits coherent radiation with three different frequencies, which are called pump, 
signal and idler waves. Here the main wave, i.e., the pump wave gives own energy to the 
remaining two waves. In this case, the rule of superposition of oscillations is not fulfilled. 
In recent years, the implementation of the OPA process in nonlinear photonic crystals 
has become widespread [6-9]. One of the main reasons for this is that these crystals can be 
oriented to any OPA process. Since a wave number of the nonlinear photonic crystal 
compensates a wave mismatch of chosen OPA.

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