Self-focusing suppression in a system of two nonlinear media and a spatial filter

Abstract

Recently, it was shown that certain 'smart' self-avoiding trails have end-to-end distances R 2 N ∼ N in three dimensions. Also, the corrections to scaling of R 2 N /N and the specific heat are qualitatively very similar to those for polymers exactly at the θ point. The question was thus posed whether they are in the same universality class as linear polymers at the θ temperature. We show that this is not the case since these trails show a first-order transition, instead of the second-order transition at the usual θ point. We argue that this is due to the fact that the 'smartness' of these trails implies that the renormalized n-body interactions vanish identically for any finite n 3. We conjecture that the qualitative similarity with recent simulations of θ polymers indicates that for n-body interactions the renormalized three-body interaction is small in real polymers.

The study of second harmonic generation of the femtosecond laser pulses with a 950nm central wavelength

“…This conversion efficiency was quite low, as the energy of the laser beam with a wavelength of 475 nm was 22 μJ. a b For theoretical calculations of the model experiment the condition of calculations were specified, namely: phase was calculated using FRESNEL [17]. Previously models used the zero phase of beam, which in practice to achieve pretty hard.…”

Self-filtering of beam fluence fluctuations at free space propagation

“…An approximate equation similar to (18) was proposed in [8] based on numerical simulation in case of CW beam and amplitude noise (S Im = 0) only.…”

“…In practice, the most dangerous consequence of spatial noise is the so-called hot spots where the local maximum of beam fluence w max considerably exceeds w 0 . Detailed analysis of w max distribution is beyond scope of this paper, but useful estimation was proposed in [8], which assuming RMS ≪ w 0 results in:…”

“…Even if the intensity of the far-field noise spectrum is known, the beam fluence fluctuations, which are ultimately responsible for the optical breakdown, remain to be determined. In this context, it is worth mentioning the work [8], in which an empirical formula relating the fluence fluctuation root-mean-square (RMS) to the integral noise power was obtained by numerical simulation, but only for the case of a monochromatic wave.…”

Band-stop angular filtering with hump volume Bragg gratings

“…Previous research showed that the SSSF effect could be suppressed by minimizing the accumulated nonlinear phase as well as by reducing spatial noise [7] . In the latter case, a traditional pinhole spatial filter is usually employed to suppress the SSSF effect by filtering most medium and high frequencies in the laser beam [8, 9] , although it is limited by the huge size, high cost for the vacuum environment and the pinhole-closure effect induced by the high focal intensity [10] . To solve these problems, angular filters based on volume Bragg gratings (VBGs) with excellent Bragg selectivity, high diffraction efficiency and high damage threshold have been proposed in recent years [11–13] .…”