Fig. 1. Beam profile degradation due to the gain nonuniformity in the second preamplifier (PA2).

Fig. 2. Principle of the beam shaping with SPs. Each triangle represents one blazed (stepped) grating and, according to the maximum phase modulation , it diffracts a certain amount of energy to the first diffraction order. Diffraction to other orders is neglected for clarity.

Fig. 3. Diffraction order filtering. Only the first diffraction order passes through the spatial filter after the SLM.

Fig. 4. Principle of the wavefront shaping with SPs. Each SP represents one blazed (stepped) grating, and according to the individual constant phase shift, each SP adds a spatially distributed phase delay. The principle is explained on the zeroth diffraction order and diffraction to other orders is neglected for clarity.

Fig. 5. Normalized diffraction efficiency response of the stepped grating as a function of the maximum phase modulation . Measured data are fit with Equation (4).

Fig. 6. Laser system Bivoj model. PA, room temperature preamplifier; MA, main cryo-amplifier; D, diode pumping module; cGC, cryogenic gas cooler. Reprinted with permission from Ref. [27], © Optica.

Fig. 7. Scheme of the front-end beam shaping section of the Bivoj laser system.

Fig. 8. Iterative shaping algorithm schematic. At the beginning of the iteration, the ITF is obtained from the actual and reference beam profiles. Then, the contrast of the ITF is reduced; it is multiplied with the previous ITF, normalized and sent to the SLM.

Fig. 9. Maximum diffraction efficiency as a function of the stepped grating period . The larger the number of pixels in the SP, the more the phase stepped profile converges to the blazed one, which has the maximum diffraction efficiency of 100% in the first diffraction order.

Fig. 10. Output of the second preamplifier PA2 during shaping and the reference beam profile.

Fig. 11. Beam quality coefficients and shaping efficiency during the shaping of the beam at the output of PA2.

Fig. 12. Comparison of outputs from the MA1 amplifier with and without shaping. The circular diffraction patterns in the images are caused by dust particles or defects in the diagnostic optical setup and are not present in the actual beam profile.

Fig. 13. Aberration correction in the front-end of the Bivoj laser system. Wavefronts were measured with a Phasics SID4 wavefront sensor at the output of the second preamplifier PA2 before and after correction.

Fig. 14. Nonordinary beam shapes at the output of the MA1 amplifier (CR, contrast ratio).

Fig. 15. Circular flat-top beam at the output of the MA1 and MA2 amplifiers.