The laser-induced damage of fused silica optics significantly restricts the output ability of large laser systems. Hydrofluoric (HF)-based etching is an effective processing to eliminate impurities and mitigate subsurface defects. Traditional polished fused silica samples were etched for different time in a HF-based etchant (2.3% HF and 11.4% NH<sub>4</sub>F) assisted by a 1.3 MHz megacoustic field. The laser-induced damage thresholds (LIDT) were measured by R-on-1 method, and fourier transform infrared absorption spectras of the samples were obtained. The results of the LIDT demonstrated that the LIDTs of the fused silica samples increased after megacoustic field assisted etching. The more surface materials were removed, the higher LIDT was obtained. The analysis of the infrared spectra illustrated that structural densification materials were removed during the etching, and thus the LIDT can be improved.
Fluent jet polishing is a new precision optical surface machining method. To improve the removal efficiency of jet machining, a rectangular-nozzle has been designed to take the place of the traditional round nozzle. According to the principles of fluid dynamics, the flow field characteristic of rectangular-nozzle structure was analyzed theoretically. The flow field distribution of different models is calculated. The shape of the rectangular nozzle has an important influence on the jet flow field distribution. So an analysis model is established to discuss the fluid field characteristics of different rectangular-nozzle structure. The impact process of several typical rectangular-nozzle is simulated by FLUENT, and the flow jet pressure and velocity distribution on the workpiece have been obtained. Then the influence on the dynamic characteristics of different impact angle is analyzed, and the corresponding rectangular-nozzle flow field distribution features are calculated by changing the impact angle.
To realize the smoothing character of continuous phase plate the tolerance capability of this kind element is analyzed in
this paper. A series of wavefront with different aberrant parameters are simulated and the far-field distributions of these
wavefront are calculated. The results show that with the varying of the distortion depth of the aberrant wavefront, the
distribution of the far-field faculas are calculated. To analyze the tolerance of continuous phase plate, the rms values of
the far-field faculas about the aberrant wavefront are calculated.
The test of wavefront of large aperture continuous phase plate(CPP) is difficult to obtain by whole aperture once because
of CPP’s characteristic such as large phase depth and large phase gradient,so sub-aperture stitching technique is often
used to test the CPP’s wavefront in whole aperture.We analysed some problems in the traditional sub-aperture stitching
test and put forward a new stitching model mathematically in order to improve the precision in CPP’s sub-aperture
stitching test.We have found that this new model is available by a serial experiments.
Laser-induced plasma can expedite the deposition of incident laser energy and the laser-induced damage in optical glass is considerably affected by the magnitude and distribution of the plasma shock wave. The spatial distribution of energy deposition and expansion pressure of the laser plasma shock wave is analyzed based on the moving breakdown model. Furthermore, damage morphologies are discussed in light of the spatial distribution of pressure and glass properties. It was found that with the increase of laser pulse energy, the shock wave expands rapidly in the direction opposite to the incident laser, resulting in that the damage morphologies transform from sphere to spindle gradually. The laser energy deposits mostly in a narrow plasma channel. The diffusion of the plasma with high temperature and pressure leads to the shock wave; the intensity of which decreases sharply with the axial distance from the centerline. As a consequence, the glass near the centerline fractures and melts, and the refractive index also changes near the end of cracks.
Large size of YCa<sub>4</sub>O(BO<sub>3</sub>)<sub>3</sub>(YCOB) crystals were grown both by Czochralski and Bridgman methods. Large size elements as large as 60 mm clear aperture were cut and polished with surface flatness of 1/5 wavelength. Optical
homogeneity of YCOB crystal was found in the order of 10<sup>-6</sup>. Laser damage thresholds of several YCOB crystal
elements were tested using different laser facilities with different pulse widths or wavelengths, with thresholds varied
from 0.8 GW/cm<sup>2</sup> to more than 1 TW/cm<sup>2</sup>. One SHG and two optical parametric chirped-pulse amplification (OPCPA)
experiments were executed to characterize the nonlinear optical properties of YCOB crystals and the quality of the
crystals. The results shown that YCOB had good performance in OPCPA application, especially with low content of
parameter florescence. Combined with good NLO performance and possibility to grow large size crystals, YCOB crystal
was a good choice for high power OPCPA applications.
Silicon is a key material to electro-photonic detectors, which makes the studies of laser induced damage of
silicon significantly important in laser detecting and military applications. The damage characters of silicon under
high-intensity nanosecond laser pulses have been investigated in this paper. The results show that the synergy of thermal,
shock and spectral radiation effects of laser plasma determines the damage characters in silicon. Due to thermal and
shock effects of laser plasma, the material is melt, vaporized, ionized and pushed out in laser irradiated area. This way,
pits are formed and the cool ejected effluents are distributed radially. The interference between scattered and incident
laser can form a periodic structure because of the periodic distribution of thermal stress in particular area. N, O and Si
characteristic spectrum in laser plasma suggests that colored film is the mixture of SiO<sub>x</sub>:SiN<sub>y</sub> from laser plasma under repetitive laser pulses.
The automatic inspection of surface imperfections of precise elements is a durable problem expected to be solved. These goals require the use of objective methods to automatic inspection of surface imperfections. Based on the defects image which are light in dark background in scattering imaging system, a complete digital evaluation system of surface imperfections, is presented in this paper. Using the XY- scanning system to detect sub-aperture, digital image could be stitched based on isometric serial images. Implementing binary image segmentation and marginal test, feature extraction by using erosion and dilation algorithm was studied. In this system, the lateral resolution is approximately 1μm. The results provide theoretical and practical evidence to establish the precise surface imperfections evaluation system.
In this paper the defects' harm is pointed out and previously used inspection techniques are reviewed <sup>1, 3, 5,</sup> and then a new measurement of defects--microscopic scattering imaging system suitable for digital image processing is put forward, which can detect defects in random distribution and random shape on the surface of optical component with large aperture. The imaging system is a 0.7×~4.5×zoom microscope. Multi-beam fiber optic illuminators are evenly distributed in annularity, and illuminate the detected surface with a special angle α; in the image are bright defects in black background, what is suitable for digital image processing; match defects to a set of standard defects and assess the dimensions of defects accurately. In the new system, the lateral resolution is approximately 1μm or even smaller, and the image and experimental results are very good. The experiment result has been proved by Scanning Electron Microscope (SEM).