Inhibition of the phase conjugation of orbital angular momentum superpositions in cylindrical vector beams during stimulated Brillouin scattering

Abstract

Phase conjugation with stimulated Brillouin scattering can be used to correct wavefront aberrations in high-power laser systems. Here, we consider such process with cylindrical vector lasers beams. By using a vectorial approach and a modal decomposition, we obtain a differential matrix equation that enables the calculation of the structure of Stokes vector eigenmodes and their Brillouin gain. The emphasis is put on the mode with the largest gain, which contributes the most to the Stokes beam. We show that the phase conjugation of orbital angular momentum in cylindrical vector beams is prevented from happening almost everywhere on the higher-order Poincaré sphere. This phenomenon is traced to the tendency of the Stokes beam to acquire a polarization structure similar to the incident pump beam, which constraints the possible combinations of topological charges of the two orbital angular momentum modes making up the Stokes cylindrical vector beams. However, near the poles of the higher-order Poincaré sphere, the Stokes mode with the largest gain acquires an additional helical phase factor that produces the conjugated topological charge for the stronger circularly polarized component without affecting the polarization structure.Experimental results are found to agree with our theoretical predictions.

Wavefront‐Reversal, Low‐Threshold, and Enhanced Stimulated Brillouin Scattering for Arbitrary Structured Light

“…The noise-initiated focused SBS geometry is also known as a phase-conjugation mirror (PCM), in which the wavefront of the incident pump wave can be conjugated whereas the polarization state cannot. [1][2][3] Hence, this DOI: 10.1002/lpor.202301080 PCM can realize only scalar phase conjugation, or rather, wavefront reversal of the incident wave. The SBS configuration has been used in high-power laser systems to compress pulses and correct distorted wavefronts caused by thermal effects or a turbulent atmosphere.…”