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Metal multi-layer dielectric gratings (MMDG) for pulse compressors in high-energy laser systems should provide broad bandwidth as well as high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDG is an important factor that limits damage resistant capabilities. MMDG for pulse compressors operating at 800 nm with a corrugated SiO layer are designed by using a genetic algorithm and the Fourier mode method. The diffraction efficiency, bandwidth, and near-field distribution of the MMDG are theoretically investigated. For the single dielectric match layer grating, the bandwidth is 140 nm, if the thickness and refractive index of the match layer are changed, the maximum electric field in the grating ridge, match layer, and metal layer of the grating increases with the decrease in grating diffraction efficiency. For the multi-dielectric match layer grating, the bandwidth and the maximum electric field in the metal layer decrease with the increase in high- and low-index material pairs, and the maximum electric field in the grating ridge and match layer initially decreases and then increases. Over a wide wavelength range, the maximum electric field in the grating ridge, match layer, and metal layer is minimal near the central wavelength. Moreover, MMDG should be used at larger incident angles while keeping enough bandwidth to reduce the electric field in the grating. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A broadband, polarization-independent, and wide angle metamaterial absorber (MA) with tapered cylinder structures is investigated with finite difference time domain simulations. The titanium nitride (TiN) and indium tin oxide (ITO) thin film are introduced as the tapered cylinder structures. The unit cell structure is mainly composed of two pairs of TiN/ITO layers and one TiN base layer. The absorption is higher than 99% between the wavelength 700 nm and 1000 nm. The broadband, polarization independent average absorption remains above 95% between 400 nm and 1200 nm with a wide range of incident angles from 0° to 40°. The electrical field intensity distributions are studied to disclose the broadband absorption mechanism. This designed broadband absorber appears to be very promising applications in the plasmonic sensing and photovoltaic devices. [ABSTRACT FROM AUTHOR]

Plate laser beam splitter (PLBS) coatings for intensity-splitting in high-power laser applications face increasing requirements, where the challenge is to simultaneously satisfy a given transmittance (T)/reflectivity (R) intensity-splitting ratio with a certain bandwidth, and a high laser damage threshold (LIDT). Traditionally, a given T/R ratio is achieved by using a non-quarter-wave design. We propose a quarter-wave design strategy for arbitrary T/R ratios by using mixture layers with tunable refractive index (n) and optical bandgap as high- n layers. Two quarter-wave PLBS coatings based on HfO 2 –Al 2 O 3 mixture with a designed T/R ratio of 50:50 are experimentally demonstrated and compared with the traditional PLBS coating. The mixture-based PLBS coating shows good spectral performance, low surface roughness, and high LIDT. For an s -polarized 8 ns pulse laser at a wavelength of 1064 nm, a mixture-based PLBS coating design can improve LIDT by a factor of ∼ 2 with a slightly wider bandwidth. This tunable mixture-based PLBS coating design strategy provides support for the increasingly high output power of high-power laser systems. [ABSTRACT FROM AUTHOR]

Abstract: Multiple laser irradiations induce a critical issue as regards the lifetime of optical components. HfO2/SiO2 AR coatings for 1064nm were prepared by conventional electron beam deposition. The evolution of laser-induced damage threshold (LIDT) and 100% damage probability threshold with shot numbers were investigated to illustrate the incubation mechanism of defect-induced damages and the intrinsic material modifications of coatings. It was found that the multi-shot LIDTs were lower than that of single-shot because of “fatigue effect”. The 100% damage probability threshold also decreased with increasing shot numbers. This incubation phenomenon implied laser-induced modifications to the coating material that weaken it to subsequent pulse exposures. LID probability curves simulated with a statistical model assuming Gaussian distribution of defect threshold were used to highlight information on defects. Simulation results showed that the thresholds of different kinds of defects decreased with the increase of shot numbers. Optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profiler were employed in mapping damage morphology features and damage depth to discuss the initiators and mechanism of damage initiation. Additionally, damage regions were accessed by X-ray photoelectron spectroscopy (XPS) to indicate the changes in elemental content and valence of the materials with increasing pulse numbers. [Copyright &y& Elsevier]

Abstract: Thin film beam splitters with high reflectivity at 532nm and high transmittance at 1064nm were deposited via reactive electron-beam evaporation with optimized parameters. The damage performance of the samples was investigated under irradiations of 532nm laser only, 1064nm laser only, and various combined laser fluences. The damages induced by the 1064nm laser were primarily attributed to the initiators at the interface between the coatings and substrate. Under 532nm laser irradiation only, two distinctive damage pits initiated by the submicron absorptive defects located at different coating depths and correlated to interfaces were observed. The damage effect under simultaneous irradiation in multilayer films was also investigated. The respective sensitive defects of the two lasers remained the precursors for causing damage. However, the dominant damage factors in simultaneous irradiation changed with the 1064nm laser fluence, which also determined the coupling effect between the two lasers in terms of causing damage. Finally, correlative analysis methods were used to discuss the different coupling effects. [Copyright &y& Elsevier]