Features of nonparaxial propagation of gaussian and bessel beams along the axis of the crystal

Abstract

It is analytically and numerically shown that nonparaxial mode laser beams propagating along the axis of a crystal demonstrate the periodic change of intensity connected with an interference of ordinary and extraordinary beams. For Bessel beams the oscillation period inversely proportional to a square of spatial frequency of a laser beam and a difference of dielectric permittivity. For the linearly-polarized radiation there is a periodic redistribution of energy between two transversal components, and for beams with circular polarization energy is pumped from an initial beam into the vortex beam of the second order and vice-versa. The received dependence allows to select parameters of an incident beam with length of a crystal for full transformation to the vortex beam. For Gaussian beams similar periodic changes have nonlinear character. Laguerre-Gaussian laser modes with high radial order show a behavior close to Bessel beams on small distances. With increase of a distance the length of a period is increasing and the beam is astigmatically deforming.

Experimantal oberving of transformation Bessel beam spreading along axis of crystal during wavelength changes

“…The intensity distribution I(x,y,z) in the propagation of Bessel beam along the axis of the crystal is as follows [9,11,17,18]: I x, y , z   …”

“…It has been shown in the studies [17,18] that during the propagation along the crystal axis neuraxial Bessel beams have other properties than Gaussian beams, namely, experiencing a uniform periodic change of intensity. In this case, the Bessel beam of zero order and second-order are periodically converted from one to another [7-9, 17, 18].…”

“…To improve convergence of the beams in the crystal, it is possible to use telescopic system or to form beams with high numerical aperture. Polarization and mode conversion during propagation along the axis of the crystal were considered for both Bessel and Gaussian beams [7][8][9][10][11][12][13][14][15][16].It has been shown in the studies [17,18] that during the propagation along the crystal axis neuraxial Bessel beams have other properties than Gaussian beams, namely, experiencing a uniform periodic change of intensity. In this case, the Bessel beam of zero order and second-order are periodically converted from one to another [7-9, 17, 18].…”

Formation of probing radiation for investigating a uniaxial x-cut crystal with the help of an aperiodic diffractive axicon

“…Beams of this kind are also useful for investigating optical anisotropy and birefringence. In [14][15][16][17][18][19][20][21][22] it is shown that Bessel beam propagation in birefringent crystals of various cuts is accompanied with the transformation of the beam order or kind. In [23][24][25] the influence of the position and parameters of certain elements of optical scheme (laser wavelength, illuminating beam wavefront curvature, crystal temperature) on the Bessel beam characteristics at the crystal output is analyzed.…”

Modeling of the propagation of Bessel beams in a uniaxial crystal at different positions of the crystal axis

“…Most often, mode and polarization conversions are needed. One tool for such transformations are anisotropic crystals [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. One method of modelling the propagation of electromagnetic waves in anisotropic media is the method of plane waves expansion [21][22][23][24][25][26].…”