Vacuum ultraviolet (VUV) reflective coatings play an important role in many high-tech fields including cosmic physics, space research, life science and synchrotron radiation. In this research, the emphasis are focused on the aging effect of 135.6nm high reflective coatings. The coatings were deposited by resistive heating method based on Lanthanum fluoride (LaF3) and Aluminum fluoride (AlF3). Optical property, surface morphology and roughness, and composition were characterized in different period after deposited. Due to the porous structure and the worse stability of lanthanum fluoride, the content of C and O element increased in LaF3 thin films during aging process. On one hand, the content of C and O are the hydrocarbon contamination from environment and packing boxes. On the other hand, due to the oxidation of film materials, the fluorides will turn into oxyfluoride, which will increase O content. As a result, there will be an increase of absorption and a decrease of reflectance of the 135.6nm high reflective coating. The surface roughness decreased which led to the reduction of scattering and the rise of reflectivity. There will be LaF3-AlF3 mixed layers between interfaces because of interface diffusion, which will further reduce the film performance.
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.
The multi-object broadband imaging echellette (MOBIE) is the seeing-limited, visible-wavelength imaging multi-object spectrograph (MOS) planned for first-light use on the thirty meter telescope (TMT). The current MOBIE optical design provides two color channels, spanning the 310nm–550nm and 550nm-1000nm passbands. The involved large optics includes an atmospheric dispersion corrector (ADC) prism (1.4m in diameter), a collimator (1.7mx1.0m), a dichroic(680 mm x500 mm x 30 mm), a red folding mirror and two corrector lenses(570mm in diameter) for different channels. In the past two years, Shanghai Institute of Optics and Fine Mechanics (SIOM) has been included in the preliminary study of folding mirror sub-system in MOBIE, especially the study on the large optics manufacture techniques. The research progress of these large optics will be reviewed in this paper. The influence of optical quality of the large optics on the MOBIE is analyzed in order to define the specifications of the large optics. The manufacture methods are designed for different large optics. In order to testify the effectiveness of the manufacture methods, some samples have been processed and the final performance including wavefront error and spectral properties are tested. Finally, the future work including remaining problems and possible solutions are introduced.
The structure properties of random mask of antireflective structure prepared by the thermal dewetting process are investigated. As a low-cost and large-scale technique, the mask obtained in our work has a great prospect in the field of solar cell and high power laser system. Ultrathin films of amorphous Ag are deposited on the fused silica by magnetron sputtering. By fast thermal annealing the structures in Ag film are agglomerated on the substrate and form mask. The influence of different thickness and annealing temperature on the structure properties of random mask are studied. The surface morphologies are characterized by scanning electronic microscopy. The suitable conditions to obtain excellent quality Ag nanomasks with the pebble particles are achieved.
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.
AlF3 thin films were prepared by thermal evaporation at different substrate temperatures and deposition rates. The
relationships between optical properties, mechanical properties and laser-induced damage threshold (LIDT) at 355nm of
AlF3 films were discussed. Both absorption and stress increased with increasing substrate temperatures and deposition
rates, which was a disadvantage to laser-induced damage resistance. Meanwhile, interfacial adhesion and hardness
increased with substrate temperatures and deposition rates, which was an advantage to enhance the LIDT. The LIDT
increased from room temperature to 200°C duo to increasing interfacial adhesion and hardness, and then decreased to
300°C duo to increasing absorption and stress. The LIDT decreased with deposition rates due to increasing absorption
The development of 355 nm high reflection (HR) coatings with high laser-induced damage threshold (LIDT) is one of
the continuing challenges for the high power laser field. To increase the LIDT, many efforts have been done concerning
the coating material, coating design and deposition process. By optimization of the coating design and deposition
parameters, the 355 nm HR coating with LIDT higher than 18J/cm2 has been prepared. The development of the
measuring technique has promoted the investigation of laser damage precursors, enabling a better understanding of laser
The laser-induced damage threshold (LIDT) of optical thin film is influenced by certain preconditioning processes.
HfO2/SiO2 532nm high reflective multi-layers were prepared by electron beam evaporation and were preconditioned by
532nm laser. The 532nm LIDT, surface condition, and damage morphology of the sample were characterized and
compared before and after laser conditioning process. Results are presented that the LIDT of e-beam deposited
multilayer HfO2/SiO2 thin films can be increased after laser conditioning. Possible reasons for such enhancement have been analyzed.
As large amounts of heat need to be dissipated during laser operation, some diode pumped solid state
lasers (DPSSL), especially Yb:YAG laser, operate at cryogenic condition. This work investigated the
laser induced damage of coatings (high-reflective and
anti-reflective coatings) on Yb:YAG crystals at
cryogenic temperature and room temperature. The results show that the damage threshold of coatings at
cryogenic temperature is lower than the one at room temperature. Field-emission scanning electron
microscopy (FESEM), optical profiler, step profiler and Atomic force microscope (AFM) were used to
obtain the damage morphology, size and depth. Taking alteration of physical parameters,
microstructure of coatings and the environmental pollution into consideration, we analyzed the key
factor of lowering the coating damage threshold at cryogenic conditions. The results are important to
understand the mechanisms leading to damage at cryogenic condition.