Chenghui Jiang

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.

Insights into effects of thermal annealing on optical properties of SiO2 films

Annealing is an important method to alter the properties of thin films. The effects of thermal treatment in air on optical properties of SiO2 thin films were investigated. SiO2 thin films were deposited on Si (110) substrates by an ion beam sputtering (IBS) technique, and then annealed in air under different thermal annealing time of 16 hours, 24 hours, 36 hours, 64 hours and the temperature from 100℃ to 600℃ with 24 hours. Optical properties refractive index and thickness are studied directly after deposition and after thermal treatment, and they are measured by spectroscopic ellipsometry. When the thermal annealing temperature was fixed at 300℃, the refractive index of SiO2 films would reduce with the increase of the thermal annealing time, the optical thickness also reduced but the various quantities are almost the same. The refractive index of SiO2 films changed with the different thermal annealing temperature. As the annealing temperature increased, the refractive index of SiO2 films reduced gradually. When the selected annealing temperature is 500℃, the refractive index of SiO2 films reached minimum. It can be found that the optical properties of SiO2 thin films can be improved by an adapted annealing procedure.

Design and manufacture of high reflective coatings deposited on metal substrate

With increasing of the laser power, higher demand for high reflective thin films in cavity is needed. Higher reflectivity is beneficial to obtaining higher output power and reducing the heat from the cavity. The reflectivity of metal substrate itself is much higher, and much higher reflectivity can be obtained through depositing thin film. Due to good thermal conductivity of metal, the thin film deposition on metal substrate is usually used in high power laser system. Due to existing absorption, we must design proper film system structure and reduce the output heat from the laser cavity. Copper was used as substrate material. Optimizing the film system can reduce the absorption. High reflective coatings were deposited on copper substrate by ion beam sputtering. When the operating angles are from 10 to 35 degrees, the obtained reflectivity reaches over 99.5% at 941nm, and the reflective band is wide.

Accuracy design of ultra-low residual reflection coatings for laser optics*

Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refractive index inhomogeneity to obtain gradient-index coating. In the normal structure of antireflection coatings for center wavelength at 532 nm, the physical thicknesses of layer H and layer L are 22.18 nm and 118.86 nm, respectively. The residual reflectance caused by refractive index inhomogeneity (the degree of inhomogeneous is between −0.2 and 0.2) is about 200 ppm, and the minimum reflectivity wavelength is between 528.2 nm and 535.2 nm. A new numerical method adding the refractive index inhomogeneity to the spectra calculation was proposed to design the laser antireflection coatings, which can achieve the design of antireflection coatings with ppm residual reflection by adjusting physical thickness of the couple layers. When the degree of refractive index inhomogeneity of the layer H and layer L is −0.08 and 0.05 respectively, the residual reflectance increase from zero to 0.0769% at 532 nm. According to the above accuracy numerical method, if layer H physical thickness increases by 1.30 nm and layer L decrease by 4.50 nm, residual reflectance of thin film will achieve to 2.06 ppm. When the degree of refractive index inhomogeneity of the layer H and layer L is 0.08 and −0.05 respectively, the residual reflectance increase from zero to 0.0784% at 532 nm. The residual reflectance of designed thin film can be reduced to 0.8 ppm by decreasing the layer H of 1.55 nm while increasing the layer L of 4.94 nm.

Multiple spectrum analysis and evaluation for optical constants of HfO2 thin films

HfO2 thin films were deposited on ZS1 silica by Ion Beam Sputtering (IBS) technique. Optical constants of HfO2 thin films were obtained by multiple spectrum analysis method, which combined the transmittance spectrum and ellipsometry spectrum of the film. The refractive index and extinction coiefficient of HfO2 thin films were evaluated by etching experiments of the film. The analysis spectral range was between 250nm and 850nm.

Calculate IR optical constants of Si substrate under high temperature condition

A high temperature infrared spectra measuring equipment connected with a FTIR spectrometer (PE) was designed and manufactured. The measuring temperature can range from room-temperature to 500°C and the infrared spectra of substrates and thin films under different temperature can be real-time measured. The Fourier transform infrared transmission spectra of Si substrate under different working temperature were measured in the wavelength region from 2μm to 20μm using high temperature infrared spectra measuring equipment. The measured temperature ranged from room temperature to 500°C with a step of 50°C. Complex dielectric functions of Si substrate under different temperature condition are calculated from FTIR transmittance spectra by WVASE32 software, and the best fitted method was obtained for calculating optical constants of dielectric materials in the high temperature condition. As the increase of working temperature, the refractive index and extinction coefficient of Si substrate increase, when the working temperature reach 300°C, the various quantity of extinction coefficient sharply increase, so Si substrate can be used in the condition below the temperature of 300°C. Thus, through the exact calculated complex dielectric functions under different working temperature condition, we can design and manufacture different thin films using Si as substrate, and applied in in the high temperature condition.

Design and preparation of frequency-doubled laser optical coatings for double wavelength with low waviness in short-wave

Coating for double wavelength is one of the important elements in frequency-doubled solid state laser. In this paper, the normal design and whole numerical optimal design were compared. With the same total number of layers, the waviness of coating for double wavelength is more than 0.4139% based on normal design method, while it will be reduced to 0.0109% by whole numerical design, and also the bandwidth can reach 50nm. In experiments, the HfO2/SiO2 multilayer films were prepared by IBS. The test results of film designed by the second method show that the transmissivity is above 99% at 532nm, waviness is 0.4%, and the reflectivity is above 99.9% at 1064nm.

Aging effect of optical properties on SiO2 films grown on Si substrates by ion beam sputtering

SiO2 is a very important low refractive index material and usually used in combination with high refractive index material to manufacture the coatings with low optical loss. In this paper, SiO2 films were deposited on Si substrates by an ion beam sputtering (IBS) technique and SiO2 target with purity of 99.99% was used as SiO2 thin films forming material. The thickness of SiO2 films grown onto Si substrates are about 900 nm. Aging optical properties of SiO2 films were investigated as a function of time placed in the air. Spectroscopic ellipsometry was used to measure optical constants of SiO2 films. The refractive index of SiO2 films change with the increase of placed time. When the placed time reaches more than 200 days, the value of refractive index tends to be constant and the corresponding variation rate is about 0.5%. As the placed time increases, the physical thickness and optical thickness also drive to be stabilization. It can be seen that optical properties of SiO2 films prepared by IBS technique under some process parameters are very stability.