The damage resistance of 355nm laser can be improved for fluoride mirrors with an SiO2 overcoat layer. Three kinds of samples are deposited with the overcoat layer of different thicknesses. Calculated with Stoney equation, the residual stress of the film can be altered to the compressive stress with the increase of the overcoat layer. Through the investigation of the damage pits, we find the damages are the thermal-mechanical coupled and induced by the nodules buried in the fluoride multilayers. The surface morphologies around the damage pits are analyzed from the two respects: Cracks and surface ablation. The two characters of the damage morphologies can be suppressed with the addition of the SiO2 overcoat layer.
Hafnia-silica (HfO2/SiO2) mixed thin films with a wide range of different compositions have been deposited on fused silica substrate by E-beam co-evaporation. The change in composition is achieved by changing the deposition rates of individual materials. The transmittance spectra are measured by the spectrometer, and then the refractive indexes are calculated with Essential Macleod. The vertical uniformity and grain structure of the films are analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The experimental results demonstrate that the coatings have good uniformity, and all the films are amorphous except the pure HfO2 film. In addition, the mixed coating with about 16.85% SiO2 content has a higher refractive index than the pure HfO2 coating.
Al2O3 monolayer films were deposited on fused silica substrate and K9 glass substrate by electron-beam deposition. Annealing as a general post-treatment was used to enhance the quality of the Al2O3 coatings. The optical properties of the films were analyzed from the transmission spectra of the samples. The composition of the samples before and after annealing were measured by X-ray photoelectron spectroscopy (XPS). According to the analysis of the results, it can be found that the oxidation degree of the coatings increases after annealing in O2 inside coating chamber. The laser-induced damage thresholds of the Al2O3 films can be increased after the annealing process. Finally, the damage morphologies of the Al2O3 coatings were analyzed.
In this paper, metallic pulse compression gratings (MPCG) with three kinds of grating structures are manufactured. The diffraction efficiency and bandwidth of samples are measured and it can be found that the different grating structure has different diffraction efficiency and bandwidth. Laser damage tests of samples are implemented by an 800±30 nm laser at pulse duration of 31 fs and it can be also found that the different grating structure has different laser-induced damage threshold. Experimental measurements illustrate that the grating structure has a great influence on bandwidth, diffraction efficiency and damage threshold. The typical damage morphologies of MPCG reveal that the damage is induced by absorption and thermal stress.
Typical damage features of the silica films, prepared by the sol-gel and e-beam deposition methods, are investigated and compared under the irradiation of the single nanosecond pulse. The laser induced damage threshold of the sol-gel silica film is higher than that of e-beam deposited silica coating. The concentric surface structures are observed in all damage pits. Furthermore, the large scale mechanical delamination that is not from the film-substrate interface but from the inner of the film is interesting for the sol-gel silica coating, which is distinct from the explosive boiling that observed on the surface of the coating deposited by the e-beam deposition method.
The laser damage resistance of coatings for high power laser systems depends greatly on the surface quality of substrate.
In this work, experimental approaches with theoretical simulation were employed to understand the coupling effect of
subsurface defect and coating on the laser resistance of coating. 1064 nm anti-reflection coating was deposited by
E-beam deposition on fused silica. Substrate with and without micro-scale pits were fabricated precisely by femtosecond
laser processing. Experimental results indicate that impurities induced in the finishing process shifted to the substrate
surface and aggregated during the heating process. Theoretical simulation result shows that the coupling effect of the
aggregated impurities and coating are mainly responsible for the low LIDT of E-beam deposition coating.
This paper presents two optical systems of descent cameras. These two lens systems have the same parameter whose effective focal length is 14 mm, F-number is F/8, field of view is 72 degree and the working wavelength rang is 0.5-0.8μm. Two different optical structures were used respectively in these two systems. This paper analyses and compares their capacity respectively. Only two kinds of glass material were used in these two optical systems, the difference from the usual imaging system is that this system is required to be fit for the demand of spaceflight environment. It should be small and light enough on the one hand, and the imaging quality should be high on the other hand.
The detector whose image element size is 14 um, its Nyquist cut-off frequency is 35.711p/mm, its diffraction limit MTF is 0.76. Program 1's 1.0 field MTF≥0.58 at the Nyquist cut-off frequency. The biggest relative distortion of this system is+0.2%, Image irradiance at the edge of the field was found to be 50% of the central value. In the design of program 2, MTF approach diffraction limit, the biggest relative distortion in 1.0 field is 0.7%. Because of the structure of telecentric beam path design, the relative illumination in 72° view field is comparatively average.
Subpixel imaging is one of the effective ways to increase spatial resolutions of optical imagers by reducing frequency aliasing caused by the sampling process of discrete sensor grid. This paper presents a novel subpixel imaging system with linear CCD sensors. The system is consisted of a specially designed focal-plane-assembly(FPA) with two 2048 pixel linear CCD, a CPLD(Complex-Programmable-Logic-Device)-based controller, analog signal chain, and related image processing software. Firstly, analysis of the relationship between MTF and subpixel displacement is conducted, with quantum results presented, and the design of the FPA are analyzed. Secondly, we reviewed related image deconvolution algorithms, and discussed the precision image registration and improved Wiener filtering algorithm for this system, potentials of wavelet-based image restoration are also invoked. Preliminary pushbroom tests of a prototype subpixel imaging system show that the resolution of the subpixel system is 1.5~1.6 times greater than that of conventional system at Nyquist frequency, considerable resolution improvment has been obtained.