Adaptive wavefront correction on a 100-TW/10-Hz chirped pulse amplification laser and effect of residual wavefront on beam propagation

100 TW ultra-intense femtosecond laser systems

“…The wavefront before correction exhibits mainly astigmatism with distortions of 0.7µm Peak to Valley (PV) that gives a Strehl ratio of 35%. After the correction the distortions are reduced to 0.22 µm PV (43 nm rms) and the Strehl ratio is higher than 90% [69] ( figure 12). The Strehl ratio is the ratio between the experimental peak intensity and the calculated peak intensity of the experimental distribution associated to a flat wavefront.…”

“…Figure 12: Corrected wavefront of a 100 TW laser system. [69] The correction is very efficient in the far field but nevertheless some drawback of that technique appear in the midfield. The remaining phase distortions exhibit the frame of the actuators of the mirror even if the mirror is not segmented.…”

“…This is due to each influence function of each actuator. These very low distortions have a relatively high spatial frequency that leads to a deterioration of the energy distribution during the beam propagation [69]. Figure 13 shows the evolution of the calculated energy distribution for different propagation lengths (Z).…”

Fresnel phase retrieval method using an annular lens array on an SLM

“…However, wavefront aberrations originated by imperfections, misalignments and stress of the opticals mounts in the chains inside femtosecond amplifier systems enlarge the spatial dimensions of the focal spot. It is now well established that the measurement and the correction of wavefront aberrations of the laser pulse is crucial for high-quality stable focusing [1][2][3]. An adaptive optics system, which consists of a wavefront sensing device and a compensating unit, measures and corrects the wavefront aberrations of a laser pulse, and eventually delivers a nearly diffraction-limited focal spot to a target.…”

“…Several phase-measurement methods have already been proposed and demonstrated. The most popular is the ShackHartmann wavefront sensor (SHWS) where the measurement of the local phase slopes of the wavefront provides the entire beam phase [1][2][3][4][5][6][7]. This technique requires a microlens array that divides the pulsed beam into a number of beamlets and has been implemented, for instance, to test the temporal stability of pulsed laser beams [8].…”