High Reflective Optical Coatings Research Articles

Improvement and characterization of high-reflective and anti-reflective nanostructured mirrors by ion beam assisted deposition for 944 nm high power diode laser

Single-layer and multi-layer coatings were applied on the surface of diode laser facets as mirrors. This thin film mirrors were designed, deposited, optimized and characterized. The effects of mirrors on facet passivation and optical properties of InGaAs/AlGaAs/GaAs diode lasers were investigated. High-Reflective (HR) and Anti-Reflective (AR) mirrors comprising of four double-layers of Al2O3/Si and a single layer of Al2O3, respectively, were designed and optimized by Macleod software for 944nm diode lasers. Optimization of Argon flow rate was studied through Alumina thin film deposition by Ion Beam Assisted Deposition (IBAD) for mirror improvement. The nanostructured HR and AR mirrors were deposited on the front and back facet of the laser respectively, by IBAD system under optimum condition. Atomic Force Microscope (AFM), Vis-IR Spectrophotometer, Field Emission Scanning Electron Microscopy (FESEM) and laser characterization Test (P–I) were used to characterize various properties of mirrors and lasers. AFM images show mirror’s root mean square roughness is nearly 1nm. The Spectrophotometer results of the front facet transmission and the back facet reflection are in good agreement with the simulation results. Optical output power (P) versus driving current (I) characteristics, measured before and after coating the facet, revealed a significant output power enhancement due to optimized AR and HR optical coatings on facets.

Tenfold reduction of Brownian noise in high-reflectivity optical coatings

Thermally induced fluctuations impose a fundamental limit on precision measurement. In optical interferometry, the current bounds of stability and sensitivity are dictated by the excess mechanical damping of the high-reflectivity coatings that comprise the cavity end mirrors. Over the last decade, the dissipation of these amorphous multilayer reflectors has at best been reduced by a factor of two. Here, we demonstrate a new paradigm in optical coating technology based on directbonded monocrystalline multilayers, which exhibit both intrinsically low mechanical loss and high optical quality.

Laser-induced damage morphology of high-reflective optical coatings

Two different kinds of 1064nm high-reflective (HR) coatings, with and without SiO2 protective layer, were prepared by electron beam evaporation. Three-dimensional damage morphology, caused by a Nd:YAG pulsed laser, was investigated for these HR coatings. Development of laser-induced damage on HR coatings was revealed by both temperature field calculation and discrete meso-element simulation. Theoretical results met experimental very well.

Curvature compensation in micromirrors with high-reflectivity optical coatings

High-reflectivity coatings on micromirrors are critical to reduce reflection losses and absorptive heating. Unfortunately, coating stress induces an unwanted curvature in micromirrors. This effect is much more serious than in bulk optics because the thin coatings are similar in thickness to the structural material of the mirror. This paper describes a method to apply coatings that simultaneously achieve high reflectivity and optical flatness. The design theory is based on one-dimensional (1-D) static analysis and achieves curvature compensation with only a single additional coating layer The technique is appropriate for any number of coating layers and includes both the elastic and plastic behaviors of the thin film layers. Plastic deformation is modeled using an empirically determined strain versus dielectric thickness curve. Experimental measurements of 200 /spl mu/m/spl times/200 /spl mu/m/spl times/3.5 /spl mu/m polysilicon plates show mirror flatness better than /spl lambda//10.