Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of annealing on the stress of Ta 2 O 5 films deposited by the IBS method has not been reported in detail. In this study, different thicknesses of Ta 2 O 5 films were deposited by IBS and annealed at different temperatures from 473 to 973 K in air, and the effect of annealing on the stress of Ta 2 O 5 films was investigated. The as-deposited Ta 2 O 5 films deposited by IBS show high compressive stress, which are about 160 MPa. The compressive stress decreases linearly with the increasing temperature, and the wavefront deformation of Ta 2 O 5 films increases linearly with film thickness (within 20 µm) at the same annealing temperature. When the temperature rises to 591 K, Ta 2 O 5 films with zero-stress can be obtained. Ta 2 O 5 films show tensile stress instead of compressive stress with further increasing annealing temperature, and the tensile stress increases with increasing temperature. Meanwhile, with the increasing annealing temperature, the refractive index of Ta 2 O 5 film decreases, indicating the decreasing packing density. The atomic force microscope (AFM) test results show that surface roughness of Ta 2 O 5 films slowly increases with the increasing of annealing temperature. Moreover, X-ray photoelectron spectroscopy (XPS) analysis shows that the Ta in Ta 2 O 5 films can be further oxidized with increasing annealing temperature, namely, the absorption of Ta 2 O 5 film can be reduced. X-ray diffraction (XRD) analysis shows that the annealing temperature should be below 923 K to maintain the amorphous structure of the Ta 2 O 5 film.

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We demonstrated a compact cavity-dumped Q-switched Yb:YAG laser based on a 72-pass pump module. A highly stable nanosecond pulse laser with a duration of 18.38 ns was achieved at a repetition rate of 100 kHz, which is pumped by multimode laser diode stacks at 969 nm. The average output power of more than 150 W is delivered in a good output beam characterized by M2 = 1.53. The result shows that the pulse duration derived from simulation agrees well with the one retrieved from the experimental measurements. To the best of our knowledge, the 43.5% optical-optical efficiency is the highest reported to date from a cavity-dumped Q-switched Yb:YAG TDL (thin-disk laser).

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Multi-layer optical coatings with complex spectrum requirements, such as multi-band pass filters, notch filters, and ultra-broadband antireflection coating, which usually contain very thin layers and sensitive layers, are difficult to be fabricated using a quartz crystal monitoring method or a single wavelength optical monitoring system (SWLOMS). In this paper, a broadband antireflection (AR) coating applied in the wavelength range from 800 nm to 1800 nm was designed and deposited by ion beam sputtering (IBS). Ta 2 O 5 and SiO 2 were chosen as high and low refractive index coating materials, respectively. The optimized coating structure contains 9 non-quarter-wave (QW) layers totally with ultra-thin layers and sensitive layers in this coating stack. In order to obtain high transmittance, it is very important to realize the thickness accurate control on these thin layers and sensitive layers. A broadband optical monitoring mixed with time monitoring strategy was successfully used to control the layer thickness during the deposition process. At last, the measured transmittance of AR coating is quite close to the theoretical value. A 0.6% variation in short wavelength edge across the central 180 mm diameter is demonstrated. A spectrum shift of less than 0.5% for 2 continuous runs is also presented.