Under-Seawater Immersion β-GaO Solar-Blind Ultraviolet Imaging Photodetector with High Photo-to-Dark Current Ratio and Fast Response.

This work displays a photovoltaic solar-blind UV photodetector based on a β-GaO photoelectrode/simulated seawater (NaCl). The photodetector exhibits extremely high photocurrent (6.70 μA); the responsivity can reach 23.

Anisotropic luminescence and third-order electric susceptibility of Mg-doped gallium oxide under the half-bandgap edge.

Strong anisotropy of photoluminescence of a (100)-cut β-GaO and a Mg-doped β-GaO single crystals was found in UV and visible spectral range, the bands of which were attributed to different types of transitions in the samples. Green photoluminescence in the Mg-doped sample was enhanced approximately twice. A remarkable enhancement of two-photon absorption and self-focusing in β-GaO after doping was revealed by 340-fs laser Z-scanning at 515 nm.

Thermochromic and Femtosecond-Laser-Induced Damage Performance of Tungsten-Doped Vanadium Dioxide Films Prepared Using an Alloy Target.

Thermochromic tungsten-doped VO₂ thin films were successfully fabricated using a W-V alloy target. X-ray diffraction analyses showed that the W-doped VO₂ film had a preferred orientation of (011), and that the doping did not degrade the film crystallinity compared with that of the pure film. X-ray photoelectron spectroscopy and energy-dispersive spectroscopy showed that the doped 0.

Enhanced visible transmittance and reduced transition temperature for VO thin films modulated by index-tunable SiO anti-reflection coatings.

The low visible transmission is one of the bottleneck problems for the application of vanadium dioxide films since the high refractive index (RI) of VO films results in strong reflection in the visible wavelength. To address this problem, in this paper, high-purity VO films were deposited on fused silica by DC reactive magnetron sputtering at low temperature of 320 °C. Silica sol-gel coatings with tunable refractive index (RI) coated onto VO films have been fabricated to enhance visible transmittance with the potential application in the field of smart windows.

High dispersive mirrors for erbium-doped fiber chirped pulse amplification system.

We report on the development of near-infrared high dispersive mirrors (HDM) with a group delay dispersion (GDD) of -2000 fs. A HDM pair based on one optimized result at two reference wavelengths (1550 nm and 1560 nm) can reduce the total oscillation of the GDD effectively in the wavelength range of 1530-1575 nm. This HDM pair is designed and fabricated in a single coating run by means of the nonuniformity in film deposition.

Suppression of nano-absorbing precursors and damage mechanism in optical coatings for 3ω mirrors.

Damage precursors in the 3ω (351 nm) mirror for a high-power laser system are investigated as well as the relevant damage mechanisms. The precursors are classified into two ensembles according to the different laser resistance and damage features. The former is nano-absorbing precursors, which are sensitive to the standing wave electric field and vulnerable to the laser irradiation.

Intrafilm separation of solgel film under nanosecond irradiation.

We have observed large-scale intrafilm separation after the irradiation of solgel film with a single Nd:YAG pulse (1064 nm, 12 ns) in air. The irradiated but undamaged surface or the surface after intrafilm separation is densified. These damage features are distinctly different from the scalding surface of the electron beam evaporation coating or the ripple structures on the rear surface of fused silica, which indicates the extreme pressure gradients at the free surface-film interface.

Scattering analysis for random antireflective structures on fused silica in the ultraviolet.

Random antireflective structures are fabricated on fused silica by the thermal dewetting process and reactive ion etching, which shows a broadband antireflective effect over the whole visible wavelength. However, the transmittance in the ultraviolet is limited by the scattering from the etched structures. A graded refractive index model ignoring the scattering in the visible range is applied to extract the etched profile.

Beam modulation caused by the plasma scalds in the multilayer dielectric films.

The near-field phase modulation (NFPM) caused by the plasma scalds is investigated with a newly proposed mixed overcoat layer model. Based on the NFPM, the far-field intensity modulation (FFIM) is calculated and discussed with the scalar diffraction theory. The results indicate that both the NFPM and FFIM are sensitive to the scalding depth.

Near-field enhancement of the nanostructure on the fused silica with rigorous method.

A rigorous electromagnetic method is developed to analyze the resonance effect of near field caused by nanoscale subsurface defects, which play a key role in describing absorption enhancement during laser-matter interaction for transparent dielectric materials. The total electric field calculated with this new method is consistent with the result of finite-difference time-domain simulation. The concept of mode amplitude density spectrum is developed to analyze the specific modes of the total field.

Defect analysis of UV high-reflective coatings used in the high power laser system.

By considering the rapid change of standing-wave electric-field and assuming the interface defect distribution, an improved model is developed to analyze the defect density distribution and assess the damage performance of high-reflective coatings. Two kinds of high-reflective coatings deposited by e-beam evaporation (EBE) and ion beam sputtering (IBS) techniques are analyzed with this method. The lower overall damage threshold is the major feature for the coatings deposited by IBS method according to the defect parameters extracted from the model.

Optical limiting properties of a nonlinear multilayer Fabry-Perot resonator containing niobium pentoxide as nonlinear medium.

The optical limiting effect was numerically simulated and experimentally observed for a 25-layer thin-film Fabry-Perot microresonator by 7 ns laser pulses at 532 nm. The sample, made by vacuum evaporation and consisting of alternating Nb2O5 and SiO2 layers, has an ultranarrow line of transparency at near 532 nm within a wide spectral band of reflection. By adjusting simulated results in accordance with experimental dependencies of transmittance, reflectance, and absorbance on incident light intensity, the coefficient of optical nonlinearity of Nb2O5 was estimated at (6+1i)·10(-12)  cm2/W.

Nanosecond laser pulse induced concentric surface structures on SiO2 layer.

We report the periodic concentric surface structures on SiO2 layer induced by a single shot nanosecond laser pulse at 1.06 μm. The fringe period of the structures ranges from 7.

Damage threshold influenced by the high absorption defect at the film-substrate interface under ultraviolet laser irradiation.

The laser-induced damage threshold (LIDT) of a single-layer coating at the nanosecond (ns) regime is obviously lower than an uncoated substrate or a high reflectivity coating coated by the same material. To elucidate this phenomenon, we demonstrate the LIDT of three types of samples at 355 nm with 8 ns. High absorption defects are found at the film-substrate interface by comparing their LIDTs and damage morphologies.

Optical properties and microstructure of Ta2O5 biaxial film.

This study investigates the optical properties and microstructure of Ta(2)O(5) film deposited with the glancing angle deposition technique. The tilted nanocolumn microstructure, examined with scanning electron microscopy, induces the optical anisotropy of thin film. The optical properties of thin film are characterized with an inverse synthesis method.

Nonpolarizing and polarizing filter design.

We describe a nonpolarizing filter design at oblique incidence and a polarizing filter design at normal incidence that use a uniaxially anisotropic layer. The phase thicknesses and the optical admittances of the layers are compensated for by the birefringent properties of a thin film at oblique incidence. This concept can be applied to the design of nonpolarizing bandpass and edge filters at oblique incidence and of polarizing beam splitters at normal incidence.