Wang Yan-Zhi

An improved transmitting multi-layer thin-film filter

The angular resolutions of the phase-shifted Rugate thin-film filters, the ultra-narrow bandpass filters, and a cutoff filter-combination device are discussed, and the electric field distributions of the filters are compared. The results show that the three transmitting multi-layer thin-film filters can realize the same angular resolution, but the electric field in the cutoff filter-combination device is the lowest. Because a lower electric-field distribution corresponds to a higher laser-induced damage threshold of the thin films, the cutoff filter-combination device may replace the traditional spatial filters in high power laser systems.

Laser Resistance of Ta2O5/SiO2 and ZrO2/SiO2 Optical Coatings under 2 μm Femtosecond Pulsed Irradiation

Ta2 O5/SiO2 and ZrO2/SiO2 high reflecting (HR) coatings are prepared by ion beam sputtering and electron beam evaporation, respectively. The laser-induced damage thresholds (LIDTs) of these samples are investigated with 2 ?m femtosecond pulse lasers (80 fs, 1 kHz). It is found that the Ta1O5/SiO2 HR coating has a higher capability of laser damage resistance than the ZrO2/SiO2 HR coating in the 2 ?m femtosecond regime. The scanning electron microscope results show that the damage sites of the ZrO2/SiO2 HR coating have a relatively porous structure, the loose structure of coatings will provide more sites for water molecules, and the LIDTs of HR coatings will be reduced as a result of the strong water absorption at the wavelength of 2?m.

Analysis of the spatial filter of a dielectric multilayer film reflective cutoff filter-combination device

The experiment setup of a reflecting combination device, which has more advantages than a transmitting combination device, is designed in this study. To achieve angular spectrum selectivity, only one type of reflective component is needed, so difficulties of design and preparation are reduced. A dielectric multilayer film is applied to the reflective component, and the long wave-pass coating stacks of the structure are designed. To achieve high stopband transmittance and reduce electric field intensity at a wavelength of 1053 nm, an objective function is proposed for designing an optimized coating. The final optimized coating has good spectral characteristics and a high laser-induced damage threshold. A dielectric multilayer film with high reflectance plays an important role in preparing and applying a dielectric multilayer film reflecting cutoff filter-combination device.

Design and Fabrication of Chirped Mirror

Chirped mirrors (CMs) are designed and manufactured. The optimized CM provides a group delay dispersion (GDD) of around –60 fs2 and average reflectivity of 99.4% with bandwidth 200 nm at a central wavelength of 800 nm. The CM structure consists of 52 layers of alternating high refractive index Ta2O5 and low refractive index SiO2. Measurement results show that the control of CM manufacturing accuracy can meet our requirement through time control with ion beam sputtering. Because the GDD of CMs is highly sensitive to small discrepancies between the layer thickness of calculated design and those of the manufactured mirror, we analyze the error sources which result in thickness errors and refractive index inhomogeneities in film manufacture.

Design and manufacture of high dispersion mirror

The designed and manufactured high dispersion mirror combines the characteristics of chirped mirror and Gires-Tournois interferometer(GTI) mirror and provides high dispersion compensation with about -800fs 2 GDD in a wavelength range of 780-830 nm and about -2500fs 2 GDD in a wavelength range 1030-1050 nm, respectively. The dispersion mirror is manufactured by ion beam sputtering. The performance of the mirror has reached the designed values and can compensate the normal dispersion from ultrafst laser system effectively.