Design and optimization of an adaptive optics system for a high-average-power multi-slab laser (HiLASE)

Abstract

We report numerical and experimental results obtained with an optical setup that simulates the heating and cooling processes expected in a multi-slab high-average-power laser head. We have tested the performance of an adaptive optics system consisting of a photo-controlled deformable mirror (PCDM) and a Shack-Hartmann wavefront sensor for the effective correction of the generated wavefront aberrations. The performance of the adaptive optics system is characterized for different layouts of the actuator array and for different configurations of the heating mechanisms. The numerical results are benchmarked using a PCDM, which allowed us to experimentally compare the performances of different deformable mirrors.

Design of deformable mirrors for high power lasers

“…As an example of preliminary test, Figure 6 reports the acquisition of the far-field images obtained by setting as a target aberration of the closed loop the aberration calculated with the thermo-optical simulation of the HiLASE amplifier as reported in Refs. [3][4][5]. Figure 6(b) shows the spot image when the DM has realized the amplifier aberration with an error smaller of 0.08 waves r.m.s.…”

“…The important parameters to be estimated are: maximum required DM deformation (stroke), spatial frequency and temporal evolution of the aberrations. The aberrations can be calculated with simulations [3][4][5] using numerical models or estimated by previous experiments on similar systems [6,7] .…”

“…In the case of multi-slab amplifier [4][5][6] , the laser beam is amplified in composite slabs of active media and absorptive cladding which is present for reduction of parasitic oscillations. For example, in the case of the HiLASE laser [8] four numerical models have been developed in order to estimate the thermal effects within the gain media, optical aberrations introduced by the main multi-slab amplifier (see Figure 1) and the wavefront correction.…”

“…By using the optical path difference (OPD) estimate from the output of the Miró model, the performance of the DM has been estimated by the fourth numerical model [5] .…”

“…Usual frame rate of these types of wavefront sensors is in the order 15-100 Hz on a laptop without the use of specific hardware such as a digital signal processor [24] or a field programmable gate array. In most of the cases, the laser aberrations are generated by heat accumulation and have a much slower time variation [5] and therefore a fast time control is not necessary.…”