SU724035A1 - Method and device for inversing depolarized laser beam wave front - Google Patents

Description

(54) METHOD OF APPEALING A WAVE FRONT OF A DIPOLARIZED LASER BEAM AND A DEVICE FOR ITS IMPLEMENTATION

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The invention relates to laser technology and can be used in adaptive optics and in laser nuclear synthesis. ;

The known phenomenon of wavefront reversal upon stimulated scattering of light l. The case of the full-polarized beams is considered. In practice, cases with spatially inhomogeneous polarization are more widely represented. So, for example, powerful amplifiers on: neodymium glass bring into the beam not only phase changes with ny, but also a spatially new water polarization change due to induced birefringence. For laser thermo-nuclear synthesis, the principle of Hia homing can be used, based on a 6-wave wavefront (rVFB). But in this process, at the stage of scattering from the target, the initial weak radiation is strongly depolarized. .

A known method and apparatus for reversing the wavefront of a depolarized laser beam 2.

In this method, a laser beam is passed through a phase plate and, i

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enter it into a nonlinear medium. The disadvantage of the method is that the light beams with a spatially inhomogeneous polarization distribution transform into the reversed wave partially: there is a background in the reflected back wave. For a fully depolarized pumping, the background is one third of the total energy of the backscattered wave. All the energy cannot go to the reversed wave, since the volume of chaotic polarizations created by the unbalanced device is presented in the caustic volume of the lens focusing the light beam into a nonlinear medium. The negative consequence of this is the loss of contrast in the angular distribution of the pulse: as the amplifier stages pass through, the background, which has worse divergence characteristics, is amplified faster than the pulse itself.

The purpose of the invention is to eliminate this drawback and increase the efficiency of the wavefront reversal.

Claims (2)

This is achieved by separating the laser beam that has passed the phase plate into two beams with mutually orthogonal polarizations, in one of which the polarizations are rotated 90 and directing these beams to the general area of the nonlinear medium. Due to this, any primordially taken pump beam with Any random polarization distribution falls inside the waveguide with a single, namely, linear polarization.: At the same time, the efficiency of converting the pump beam into exactly reversed wave is maximum. The proposed method can be implemented using a device, containing a housing, a diaphragm, a phase plate, a lens of an optical fiber with a nonlinear medium, an element is placed successively along the line of the two rays along the path of the two plates along the code of the phase plate. The phase shifter and compressor are placed; in this case, the case of the devices is made by the possibility of rotation along the longitudinal axis passing through the center of the diaphragm. The drawing shows a diagram of the races ni3ji6 eHHH. optical elements of the device implementing this method. The circuit contains a laser beam 1 with a transversely inhomogeneous polarization of a rectangular diaphragm 2, a phase plate 3, an element 4 which spreads the beams of the orthogonal polarization at the final angle (in this example, a birefringent wedge}, phase shifter 5, compensator 6 , focusing element 7 (converging lens), rectangular waveguide 8, common body 9, beams 10 and 11 with mutually perpendicular floor polarization; (;;..:.: - -. i.- .. The laser beam .1, the passage of the diaphragm 2, the phase plate 3, split it with a beam of a DUI-th ellum luminescent class .4 into beams 1 0 and 11 according to the perpendicular polarization orts. The elements 2,3, and 4 are located at a distance (3) from each other, where d is the smallest side of the diaphragm, X is the length of the full reversal radiation. 5, the polarization of the beam 10 is rotated 90 dO to coincide with the voltage of the polarization of the other beam 11. A transparent plate b is needed to complete the positive path difference gained by the beam 11 after passing the phase shifter 5, i.e. The beam 11 has the same additional optical path as the beam 10. The focusing element - lens 7 directs both into the waveguide 8. The lens displays the rectangular aperture 2 at a similar rectangular input of the waveguide 8 All of these elements are rigidly fixed In unit housing 9, which, after installation in the working space, the head can be rotated around the device's parent axis, passing through the center of the diaphragm. Due to the fact that the randomly polarized beam turns into two with coinciding linear fields, and then these two beams are reduced to a single region of nonlinear waveguide, a complete wavefront reversal takes place. Thus, backward from the circuit on the way back from the waveguide to the diaphragm, and then exactly along the path of beam 1 (towards it), a spatially polarized reversed wave with improved energy, brightness and contrast characteristics will go. Equalization of intensities in the optical arms 10 and 11 is achieved by rotating the device as a whole around the axis of rotation. The proposed device when used in. High-power laser systems can significantly improve the angular characteristics of the beams, which will lead to simpler obtaining of high peak intensities, and as a result, to cheaper laser systems and increased productivity in scientific research. , Claim 1. A method for converting a wave front of a depolarized laser beam, comprising passing the beam through a phase plate and introducing it into a nonlinear medium, characterized in that, with the aim of increasing the conversion efficiency, the laser beam passing the phase plate is divided into two beams with mutually orthogonal polarizations, in one of which the polarization is rotated by 90 and directs these beams to the general area of the nonlinear medium. 2. An apparatus for carrying out the method of Claim 1, comprising a housing, a diaphragm, a phase plate, a lens, a light guide with a nonlinear medium, characterized in that along the beam behind the phase plate an element is placed successively polarizing, the paths of these two rays are placed on the phase shifter and compensator. In this case, the device body is designed to rotate around a longitudinal axis passing through the center of the diaphragm. Sources of information taken into account in the examination 1.Zeldovich B.Ya. JETP Letters, 1972, 15, p. 160 2.Blaschuk V.N. and others. Forced scattering of depolarized beams theory and experiment. Deposited by the Institute of Applied Physics of the Academy of Sciences of the USSR, 1978, p. 1-15.