Yiqin Ji

Influence of cleaning process on the laser-induced damage threshold of substrates

The cleaning process of optical substrates plays an important role during the manufacture of high-power laser coatings. Two kinds of substrates, fused silica and BK7 glass, and two cleaning processes, called process 1 and process 2 having different surfactant solutions and different ultrasonic cleaning parameters, are adopted to compare the influence of the ultrasonic cleaning technique on the substrates. The evaluation standards of the cleaning results include contaminant-removal efficiency, weak absorption, and laser-induced damage threshold of the substrates. For both fused silica and BK7, process 2 is more efficient than process 1. Because acid and alkaline solutions can increase the roughness of BK7, process 2 is unsuitable for BK7 glass cleaning. The parameters of the cleaning protocol should be changed depending on the material of the optical components and the type of contamination.

Optical and interfacial layer properties of SiO2 films deposited on different substrates.

SiO2 films were deposited on fused silica, silicon, glass, germanium, and sapphire substrates by an ion beam sputtering technique. The optical properties of SiO2 films on different substrates and interfacial layer properties between SiO2 films and different substrates were researched by the spectroscopic ellipsometry technique. The refractive indices of SiO2 films deposited on different substrates are about 1.477 at the wavelength of 632.8 nm. The optical anisotropy property of SiO2 films on fused silica substrate is the best. The impact of thermal treatment on surface roughness and interfacial layer properties between SiO2 films and Si substrates were also investigated. When the annealing temperature is 550°C, the least surface thickness and thinnest interface layer thickness between v films and silicon substrate can be achieved. The results indicate that the surface and interface layer properties between SiO2 films and silicon substrate can be greatly improved when the optimum annealing temperature is selected.

Evaluation and analysis of polished fused silica subsurface quality by the nanoindenter technique

We evaluate the subsurface quality of polished fused silica samples using the nanoindenter technique. Two kinds of samples, consisting of hundreds of nanometers and micrometers of subsurface damage layers, are fabricated by controlling the grinding and polishing processes, and the subsurface quality has been verified by the chemical etching method. Then several nanoindentation experiments are performed using the Berkovich tip to investigate the subsurface quality. Some differences are found by relative measurements in terms of the relationship between the total penetration and the peak load on the surfaces, the modulus calculated over the defined depths and from unload, and the indented morphology at a constant load near the surface collapse threshold. Finally, the capabilities of such a mechanical method for detecting subsurface flaws are discussed and analyzed.

Correlation between properties of HfO 2 films and preparing parameters by ion beam sputtering deposition

Ion beam sputtering is one of the most important technologies for preparing hafnium dioxide thin films. In this paper, the correlation between properties of hafnium dioxide thin films and preparing parameters was systematically researched by using the orthogonal experiment design method. The properties of hafnium oxide films (refractive index, extinction coefficient, deposition rate, stress, and inhomogeneity of refractive index) were studied. The refractive index, extinction coefficient, physical thickness, and inhomogeneity of refractive index were obtained by the multiple wavelength curve-fitting method from the reflectance and transmittance of single layers. The stress of thin film was measured by elastic deformation of the thin film-substrate system. An orthogonal experimental strategy was designed using substrate temperature, ion beam voltage, ion beam current, and oxygen flow rate as the variables. The experimental results indicated that the temperature of the substrate is the key influencing parameter on the properties of hafnium oxide films, while other preparing parameters are also correlated with specific properties. The experimental results are significant for selecting proper parameters for preparing hafnium oxide films with different applications.

LIDT of HfO2/SiO2 HR films by different test modes at 1064nm and 532nm

In order to evaluate the laser induced damage threshold (LIDT) of our HfO2/SiO2 high reflectance films prepared by reactive electron beam evaporation process at 1064nm and 532nm, the four popular test methods are performed according to the ISO 11254 and other relevant standards. The improvement of laser conditioning effect and influence of cumulative effect have been studied and estimated during the tests by comparing the deviations of the thresholds along the damage probability curves and relationship between the thresholds and the pulses number. Moreover, the details are carefully inspected during raster scan especially at 1064nm with all the >2μm nodules and damage sites marking and recording, then the ejection probability and growth rate of nodules are given. Note that attention should be paid to the submicron absorbing particulates at 532nm which are probable to trigger the damage.

A global sub-aperture stitching algorithm and its precision evaluation

Sub-aperture stitching interferometry is a method to test the surface of the large optics, which can effectively extend the lateral range of the standard interferometer and can also enhance its lateral resolution. The stitching algorithm based on the overlapping area plays a very important role in sub-aperture stitching interferometry. Due to the misalignment in the sub-aperture test cycle, relatively tilt and shift are calibrated. And the global stitching method is applied to minimize the differences of phase distributions in the overlapping areas. The inspection of stitching quality of the overlapping area is also necessary after the interferograms which have been stitched. This paper uses the statistical principle to evaluate the quality of the overlapping area.

Study interfacial layer properties of SiO2 films deposited on different substrates

Interfacial effect, mainly caused by matching of substrate and SiO2 film materials, had greatly influenced application of SiO2 films. Interfacial layer properties of SiO2 films and substrates, effects of thermal treatment are investigated.

Effect of wet chemical treatment on BK-7 substrate

Surface cleanness and roughness to BK-7 substrates are important factors affecting the performance of laser optics. The conventional RCA cleaning method is widely used in removing particles from substrate surface, with high removal efficiency but rough surface. Therefore, more precise control of the chemical cleaning performance of BK-7 substrate is required than what is available today. In this study, four groups of BK-7 samples were dealt with different cleaning treatments to explore the effects of chemical solutions. The influences of chemical solutions on removal efficiency, etching depth and surface roughness were studied. An optimal cleaning method of BK-7 substrates was proposed, which could remove contaminations completely and gets smoother surface.

Influence of Cleaning Process on the Laser Induced Damage Threshold of Substrates

Two kinds of substrates, fused silica and BK-7 glass, are treated with ultrasonic cleaning protocol to determine the influence of cleaning process on LIDT. The contaminant-removal efficiency, weak absorption and LIDT are measured and analyzed.