We investigate the damage characteristics and mechanism of neutral density filters consisting of metal film on K9 glass substrate by 1064-nm pulsed laser. The damage morphologies present marked differences with different laser pulse energies. Specifically, with the increase of laser fluence, the damage pits density increase as well, and at the same time, the cracks appear around the pits and interconnect, which lead to the abscission of film. The damage mechanism has been studied from the viewpoint of embedded impurities in the film. The theoretical results show that the difference between the thermodynamic properties of impurities and film can lead to thermos-elastic stress, which plays important roles in deformation of film, nucleation and propagation of cracks. Last, methods have been proposed to improve the laser damage resistance by controlling the size distribution of impurity particles and increasing the film tensile strength.
This paper first studies the structure effect law in order to design a reasonable option in theory for the Final Optics Assembly(FOA)’ harmonic converter module, involved in the design of the fluid theory, including the basic equations of fluid motion, the form of fluid motion and fluid movement in the small hole. Optimizing the structure need to be applied to the simulation software, which requires the Fluent simulation principle. Then, combined with theoretical knowledge to design the overall structure of the multiplier module, It will apply the simulation software to optimize structural parameters of the board and use control system to realize it for verifying the law obtained by simulation under various conditions whether consistent with the law in actual work of the sweeping system.
The Integration Test Bed (ITB) is a large-aperture single-beam Nd:glass laser system, built to demonstrate the
key technology and performance of the laser drivers. It uses two multipass slab amplifiers. There are four
passes through the main amplifier and three passes through the booster amplifier. The output beam size is
360mm by 360mm, at the level of 1% of the top fluence. The designed output energy of ITB at 1053nm is
15kJ in a 5ns flat-in-time (FIT) pulse, the third harmonic conversion efficiency is higher than 70%. The first
phase of the ITB has been completed in July 2013. A series of experiments demonstrated that laser
performance meets or exceeds original design requirements. It has achieved maximum energies at 1053nm of
19.6kJ at 5ns and 21.5kJ at 10ns. Based on a pair of split third harmonic generation KDP crystals, the third
harmonic conversion efficiency of about 70% and 3ω mean fluences as high as 8.4 J/cm<sup>2</sup> have been obtained
with 5ns FIT pulse.
The influence of laser beam size on laser-induced damage performance, especially damage probability
and laser-induced damage threshold (LIDT) is investigated. It is found that damage probability is beam
size dependent when various damage precursors with different potential behaviors are involved. This
causes damage probability and LIDT are different between tested under large-aperture beam and under
small-aperture beam. Moreover, fluence fluctuations of large-aperture laser beam bring about hot spots
moving randomly across the beam from shot to shot. Thus it leads to the most probable maximum
fluence after many shots at any location across components is several times the average beam fluence.
These two effects result in difference of damage performance of components in large-aperture lasers
and in small-aperture lasers.
Laser induced damage experiment was carried out on a large aperture laser facility. Severe damage has
been observed on a large-aperture fused silica grating which presented dense craters on the front
surface and six cracks alternatively located at the front and the rear surface. The bizarre fact about the
damage on the grating is that, unlike other optics, the damage craters are almost on the front surface.
According to observation, damage phenomenon is due to the Stimulated Brillouin Scattering (SBS)
effect happened in the grating.
Laser-induced damage is a key lifetime limiter for optics in large laser facilities. After tested on a
large-aperture high-power laser facility, a damaged fused silica component is disassembled and
conditioned to receive damage test on a small-aperture laser. The damage threshold and growth
behavior show the corners on the component are less damage resistant. The acid etch on corner has not
effectively increased the damage threshold but lowered the damage growth coefficient. A
statistic-based model is presented to extrapolate the threshold data in small-aperture test to predict the
damage threshold under functional conditions.
We report a novel frequency tripler for efficient conversion of broadband high power laser pulses at 1 μ;m. The tripler is
composed of several segmented partially deuterated KDP with discrete values of deuteration. Deuteration level can be
used as a degree of freedom to alter the phase-matching wavelength of a partially deuterated KDP crystal. The
segmented partially deuterated KDP crystal is made by thermal bonding method. It has been shown that this new tripler
is capable of enhancing the acceptance bandwidth of frequency tripling. A two-segment design is presented, which is
applicable to the efficient frequency tripling of chirped pulses with a bandwidth of ~1.2-nm.