A beam-smoothing method that combines induced spatial incoherence (ISI) and continuous phase plate (CPP) is presented. A method designing special CPPs for ISI is proposed. Then, spatiotemporal character of focal spots with different ISI parameters and different phase plates was numerically analyzed. Using special phase plate consisting of small CPPs designed separately, with 10-nm bandwidth 527-nm light, focal spot nonuniformity at spatial wavelength 10 to 50 μm could be reduced to 2% in 130 ps and was further reduced to 0.5% in 2.3 ns. A two-lens aperture system is added to lower the nonuniformity of the near-field in the light path. Using ISI + CPP, the shape of the focal spot could be controlled perfectly, and the characteristic that the ISI + CPP focal spot changes randomly with time is beneficial to the control of laser and plasma interactions.
Laser beam far-field alignment as well as frequency-doubling and frequency-tripling crystal adjustment is very important for high-power laser facility. Separate systems for beam and crystal alignment are generally used while the proposed approach by off-axial grating sampling share common optics for these two functions, reducing both space and cost requirements. This detection system has been demonstrated on the National Laser Facility of Israel. The experimental results indicate that the average far-field alignment error is <5% of the spatial filter pinhole diameter, average autocollimation angle error of crystals is <10 μrad, and average frequency-tripling conversion efficiency is 69.3%, which meet the alignment system requirements on the beam direction and crystals.
Laser damage performance of large aperture optical components has been study under fourth harmonic of 1053nm Nd:glass laser irradiation (263nm).The threshold of optical components is very low under 263nm laser irradiation ,due to conversion of beam to higher energy photons of the quadrupled frequency (4ω), and is relative to material characteristic. A preliminary test of laser induced damage in fused silica (SiO<sub>2</sub>) and CaF<sub>2</sub>under 263nm laser is reported in this article. Thresholds of these two materials are obtained. Laser damage threshold of SiO<sub>2</sub> is found about 2 J/cm<sup>2</sup> by 1-on-1 method using pulsed 263nm laser, lower than CaF<sub>2</sub> whose threshold.
Because of the limited optical element aperture, damage threshold, gain bandwidth, and so on, the output capability of a
single laser beam is limited seriously. The coherent laser beam combining offers an excellent method to improve the
peak intensity which could be gotten greatly. Aiming at getting the general requirements of the coherent beam combining
for large aperture laser facilities, this work devotes to modeling the influences of the phase factors and spectrum factors
on the combine results. The effects of the phase factors, including the piston error and tip/tilt error, are studied
analytically and numerically. It is found that the expressions of the intensity in the focal plane can be written as three
parts, the scale factor, a point spread function (PSF), and a grid function (GF), for the ideal beam combining and beam
combining with piston error. Every part has its special physical meaning, and decides different characteristics of the
combined focus. For the beam combining with tip/tilt error, though the expression of focal spot intensity can not be
separated like the above situations, every part still has obvious physical meanings. The results show that the beam
configuration can not affect the Strehl ratio of the combined beam, but it influences the FWHM of the main peak and the
ratio of the main peak and the side peak. The piston error affects the grid function greatly, including its maximum value,
transverse translation, and shape. For the two beam combining, a piston error less than 2π/5 rad is suitable. For multibeam
combining, the standard deviation of the piston error should be no more than 2π/10 rad. The tip/tilt error affects the
superposition degree of the focal spots of the combined elements directly. A requirement of 0.5~1μrad for the standard
deviation of the tip/tilt error is adequate. The effects of the spectrum factors, including the longitudinal chromatism, high
order dispersion, and residual chirp, are studied analyzed. Results show that the above spectrum factors have significant
influences on the short pulse coherent beam combining, and must be controlled carefully when the pulse is shorter than