Proc. SPIE. 10899, Components and Packaging for Laser Systems V
KEYWORDS: Fiber amplifiers, Optical components, Energy efficiency, Optical amplifiers, Laser energy, High power lasers, Laser beam propagation, National Ignition Facility, Laser systems engineering, Fusion energy
High-energy, high-power laser system for inertial confinement fusion (ICF), such as National Ignition Facility (NIF), is large in size and expensive in construction. The multi-pass amplifier (MA) with the large aperture amplifiers is widely used in high-power laser systems, such as ICF drivers. The systems with MA usually have four features: square beam, single aperture, single pulse and unidirectional propagation, and the expensive preamplifier systems are required to compensate for the limited gain of the main amplifiers. The gain and the extraction efficiency are limited in part by the number of passes that the beam can make through the amplifiers. Besides, the laser system in the multi-pass amplifier should operate at much higher fluence to achieve high extraction efficiency, which results in a technical challenge in the damage of optical components under high-power lasers irradiation.
To efficiently extract the stored energy with low injection energy at low laser fluence operation and make the system compact and reliable, a bidirectional ring amplifier (BRA) with twin pulses is proposed and discussed. The structure of the bidirectional ring amplifier is described. The characteristics of the bidirectional ring amplifier on extraction efficiency and output energy capability are simulated and discussed. The simulation results show that an extraction efficiency of 62.3% and the output energy of 13.4 kJ per pulse at the B integral limit can be obtained at low average fluence of 10.3 J/cm2 and the low injection energy of 3.9 mJ in the bidirectional ring amplifier. Compared with the multi-pass amplifier, the bidirectional ring amplifier is more compact and the extraction efficiency is much higher at low laser fluence operation, which is beneficial to reduce the effects of nonlinear phase shift. Furthermore, the preamplifier system for the bidirectional ring amplifier is simple, only a fiber oscillator and a regenerative amplifier can work.
Paint removal based thermal stress with high repetition pulse is considered in this paper. The temperature distribution of aluminum substrate and paint under laser irradiation is simulated and the thermal stress generated by thermal expansion is calculated. The adhesion force between the paint and the substrate was calculated according to adhesion formula. The conditions for the paint removal can be obtained by comparing the force of thermal stress and adhesion. At the scan speed of 5000 mm/s, the fiber laser with wavelength of 1064 nm, pulse width of 240 ns and frequency of 100 kHz is used to strip red paint from aluminum without any damage. And the stripping effect at the different output power is also taken into account.
In this paper, the laser cleaning soil rust layer on the surface of ceramic artifacts by the way of ablation and thermal stress with infrared high-repetition pulse laser is carried out. A cleaning effect can be achieved with laser scanning 10 times at the speed of 480 mm/s and fluence of 795.7747 J/m<sup>2</sup> near the ablation threshold. However, the external force is required to make the soil rust layer fallen off. In contrast, a better cleaning effect that the soil rust layer is directly peeled off under the effect of thermal stress without ablation at the contact surface and external force can be observed with the fluence of 1591.5494 J/m<sup>2</sup> and laser scanning at 1 time. Furthermore, a two-layer structure model is built to analyze the mechanism of cleaning by thermal stress based on the heat conduction and thermal stress equation. The maximum peeling thermal stress at the contact surface is 2.854×10<sup>7</sup> N/m<sup>2</sup>, which is greater than the adhesion stress of 2.050×10<sup>7</sup> N/m<sup>2</sup>. This is in agreement with experiments.
The slit spatial filter can be used in high-power laser system. The performance of two-lens slit spatial filter is described and discussed. The laser intensity at the slit edge and the peak intensity of the focal line with different F-numbers and the cut-off frequencies are compared with that of the traditional spatial filter. Simulation results show that the laser intensity at the slit edge and the peak intensity of the focal line are less two orders of magnitude than that of the traditional spatial filter. Besides, the vacuum degree required in the slit spatial filters is about 10<sup>-1</sup> <i>Torr</i>, which is less two orders of magnitude than that of the traditional spatial filter.