We report a two-stage two-pass compact amplifier based on SrF2 crystal with gains of over 106. The shape of the crystal is irregular, so that the gain length is increased and parasitic oscillation is suppressed. The amplified spontaneous emission (ASE) and spectral characteristic of amplifier are analyzed. The results show that ASE increases with the pump power, and the simultaneous use of different crystals types can increase the output bandwidth. This work has a potential application in high-power / high-energy laser devices.
Tabletop high-energy repetition-rate picosecond lasers can be utilized to drive secondary radiation sources such as infrared lasers, facilitating more convenient and efficient research into attosecond pulses and high-energy density physics. Compared to Nd3+, Yb3+ have advantages including a small quantum defect (~9%), a longer fluorescence lifetime, high saturation fluence, high thermal conductivity of matrix crystal, and a wide range of doping concentration. The LD-pumped Yb3+-doped repetition-rate lasers possess a unique combination of pulse duration and energy, which confer an intrinsic advantage in the field of high-energy picosecond lasers. In this paper, we proposed a hybrid Yb3+-doped crystal as the gain medium, employing a multi-pass amplification configuration to achieve sub-picosecond laser output with a peak power exceeding 1 TW in 2 m3. This scheme can provide a new technical route for tens of TW high-energy picosecond lasers.
We will present our proposal for a low-coherence laser facility - 'kunwu' - based on neodymium glass amplification of super-luminescent light pulse(SLP) with ~3.5 THz (13nm) bandwidth, and the beam has been converted to second harmonics before focusing on the target. We are validating the output capability of the laser (>10J/cm2@1ω) and improving the beam quality to achieve a more smoothing focal spot. We believe that this is a very ideal driving laser for laser inertial confinement fusion, and the scheme is very likely to be the best choice for the development of high-power laser drivers.
Regenerative amplifiers containing multiple diverse laser heads have the ability of scaling up output power as well as broadening spectral bandwidth. However, the thermal lensing effect will be more complicated. A method using a 4f system to simplify the thermal lensing effect in a multidisk condition is proposed. Two kinds of Yb-dropped sesquioxide materials are chosen as an example. On the basis of calculating the thermal lensing parameters of the thin-disk laser heads, a feasible cavity design that can minimize the fluctuation of beam size when changing the pump power is given out. The 4f system consisting of concave mirrors will introduce astigmatism in the cavity. The influence of astigmatism and the compensation method are discussed. Astigmatism can be compensated by adding extra convex mirrors and controlling the angle of incidence at each mirror.
KEYWORDS: Crystals, Laser crystals, High power lasers, Pulsed laser operation, Laser systems engineering, Laser energy, Laser induced damage, Frequency conversion, Crystal optics, Fusion energy
In high power laser system, the 3ω laser fluence can up to 6J/cm2 with triple frequency conversion efficiency up to 75%. Two high fluence laser experiments have been done for proving high efficiency output and damage resistance of KDP crystal. The KDP crystals have different performance in these two experiments due to their characteristics nuances. For the third harmonic crystal in first experiments, centimeter damage occurred on this crystal after about 50 number laser shots, and more than ten thousands micrometer damage points occurred on this crystal. For the second KDP crystal after about 60 number laser shots, most damage size are micrometer, including bulk damage and damage on back surface, micrometer damage doesn’t exist because of its good quality. We classify these damages of crystals to different kinds, observe characteristics of these damages. Observation of laser damage on third-harmonic converter crystals have been done in this paper.
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 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 (SiO2) and CaF2under 263nm laser is reported in this article. Thresholds of these two materials are obtained. Laser damage threshold of SiO2 is found about 2 J/cm2 by 1-on-1 method using pulsed 263nm laser, lower than CaF2 whose threshold.
The crucial problem of DKDP crystal for third harmonic generation (THG) is its low laser-induced damage threshold with respect to KDP, which greatly limits energy fluence of the output laser and crystals' useful life. In order to study the relation between wavelength and laser-induced damage of DKDP, we carried out some related experiments in present work. DKDP crystal was conventionally grown from 80%-deuterated solution of high pure materials and the crystal was cut to tripler sample of type II. Laser-induced damage threshold of DKDP crystal for THG was measured under different wavelengths and the effect of laser annealing was also investigated. The experiment shows that laser annealing could obviously improve laser-induced damage threshold of DKDP crystal. The threshold is improved to 1.4, 1.9 or 2.7 times that before annealing for fundamental, second or third harmonic, respectively. Thus laser annealing is an effective approach to enhance laser-induced damage resistance of DKDP crystal.
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