Search

Based on the fundamental theory of heat transmission,the transient thermal and stress distributions of laser gain medium in a laser diode end-pumped Nd doped glass disk amplifier are studied by means of finite element analysis. The cooling characteristics of glass disk on different boundary conditions in repetition mode are also discussed. Furthermore,three kinds of different thermal management schemes are proposed with the progress and their thermal effect characteristics are compared. The simulation results show that the cooling configuration with transparent sapphire plate adjacent to the pumping surface which is mounted with TEC-cooled copper housing outside is much attractive. The peak temperature about 120℃ occurs in the centre of non-pumping surface. Although its cooling ability is not much effective as that of direct water cooling but it can avoid some problems brought out by the latter. The simulation analysis also proves that the heat within glass disk is difficult to be taken away radially because of its large heat resistance. In practice,the thermal management system should be designed to cool glass disk along axis direction.

In a conventional laser-driven inertial confinement fusion (ICF), Nd-doped phosphate glass is used as a gain medium. However, the repetition frequency operation of such a laser system is restricted by the low thermal conductivity of the phosphate glass. To attain a high ICF performance, the laser driver must be able to operate at a repetition frequency of no less than 10 Hz. Typically, an Nd-doped laser glass operates at a repetition frequency well below 10 Hz. In this paper, an Nd, Y:CaF2 crystal is taken as a gain medium for the laser amplifier, and experiments are carried out to demonstrate the capability of Nd, Y:CaF2 crystal to act as a gain medium for ICF laser driver. A laser-diode plane-array five-direction horizontal-side-pumped Nd, Y:CaF2 laser amplifier 5 mm70 mm is developed and an experimental study is carried out. The absorption spectrum and emission spectrum of Nd, Y:CaF2 crystal and the fluorescence distribution of the amplifier are measured. The Nd:CaF2 co-doped with Y3+ ions results in a broad absorption band, which makes the laser diode pumping more efficient. The strongest excitation band peak is centered around 796 nm. The small signal gains of Nd, Y:CaF2 and Nd:Glass working respectively at repetition frequencies of 10 and 1 Hz under the same pump power are measured. The small signal gain of Nd, Y:CaF2 amplifier reaches 6.12 under a pump power of 9.63 kW, which is 1.5 times that of Nd:Glass amplifier. The measurements of the spectrum of the seed beam and the spectrum from Nd, Y:CaF2 amplifier show that the signals have no change before and after being amplified. Most likely the Nd, Y:CaF2 crystal is a promising laser material for repetitive ICF laser drivers.

A joule-level Nd: YAG nanosecond laser of high repetition frequency and high beam quality is developed for Thomson scattering diagnosis. The laser is designed as a master oscillator power-amplifier system mainly including single longitudinal mode seed, pre-amplifier unit and energy extraction unit. The single-longitudinal-mode Q-switched laser of a high stability is taken as the seed laser of output pulse at J level. The pre-amplifier unit amplifies the J-level pulse laser beam into hundreds of mJ level. In order to obtain the high-quality laser beam output, phase conjugation is adopted to compensate for the laser beam distortion. The ultra-filtered FC-770 is taken as an SBS gain medium of 0.0011 cm-1 absorption coefficient, 197.9 GW/cm2 optical breakdown threshold and 3.5 cm/GW gain coefficient. The double-pass amplification of SBS phase conjugation could realize a real-time repair towards the non-uniformity, deformation and wavefront aberration caused by thermal distortion of the optical components and the laser amplifier to achieve the uniform amplified beam output of high quality close to the diffraction limit. In the energy extraction unit, the amplifier of large-diameter slab is used for energy amplification. The size of the slab is 7 mm 35 mm138.2 mm of 56 cutting angle and 0.6% Nd3+ doping concentration. The slab is plated by a layer of SiO2 against light leak. Horizontal pumping mode is adopted. And the slow axis of the laser diode is almost the same as the length of the slat and the direction of laser transmission. The single-plane array is composed of 8 groups of vertical stacks and each group consists of 12 laser diode bars of power 200 W. At 200 Hz repetition frequency, 250 s pump pulse width and 140 A pump current, the up to 2.3 J stored energy can be achieved The energy extraction unit achieves high gain amplification and finally outputs high-quality laser beam. Under the condition of 200 Hz high repetition frequency and 8.23 J single pulse energy injected by the single longitudinal mode seed, 1.85 J output energy is gained. The energy extract efficiency of the laser system is 52.46%. The output laser possesses a pulse width of 5.36 ns, a far field beam spot 1.72 times the diffraction-limited value, and 1.3% energy stability (RMS).