Applications of sub-wavelength grating mirrors in high-power lasers

Abstract

A grating waveguide mirror (GWM) results from the combination of a waveguide and a sub-wavelength grating which lead, for given incidence conditions, to polarization and or wavelength filtering. In the present paper, we report on the application of such elements for the selection of the polarization (linear, radial, or azimuthal) as well as the narrowing, stabilizing and tuning of the emission spectrum of high-power lasers. Using a leaky-mode circular GWM, beams with radial and azimuthal polarization with output powers of up to 275 W and 145 W, respectively, could be extracted from a Yb:YAG thin-disk with optical efficiencies of 52.5 % and 43 % , respectively. In both cases, the GWM was composed of a highly reflective (HR) mirror and a sub-wavelength grating as the end-mirror of the resonator. Using a leakymode linear GWM operating under Littrow condition, beams with linear polarization and a narrow spectral bandwidth were obtained from a Yb:YAG thin-disk laser. In multimode operation, an output power of 325 W was achieved at an optical efficiency of 53.5 % . In near-fundamental mode operation, 110 W was extracted at an optical efficiency of 36.2 % . In this latter case, the spectral bandwidth was measured to be around 25 pm. Moreover, continuous wavelength tuning from 1007 to 1053 nm was demonstrated with our device.

Sc2O3 on sapphire all-crystalline grating–waveguide resonant reflectors

“…The methodology to develop the all-dielectric all-crystalline grating-waveguide resonant reflector (CGWRR) follows a three-part approach: the design, fabrication, and characterisation. The design phase was based upon previous works [2] employing rigorous coupled-wave analysis of the structure [8,9]. In fabrication, as the grating structures must be sub-wavelength, nanofabrication processes needed to be developed and implemented.…”

“…Resonant grating-waveguide structures (GWS) [1] are the combination of a planar waveguide and a sub-wavelength grating that can be used as a polarisation-selective, highly dispersive, and high-efficiency reflector. Our motivation is to capitalise on the characteristics of GWS but using all-dielectric materials that are suitable for high-power laser cavity components, as demonstrated in [2]. GWS have been utilised for intracavity wavelength selection and spectral stabilisation using resonant diffraction [3] and resonant reflection [3,4].…”

“…However, the intrinsic absorption in semiconductor materials at the wavelengths of interest for high-power lasers would limit their utility. Instead, alldielectric crystalline materials as employed here have an order-of-magnitude higher thermal conductivity than silica, the typical mirror substrate used [2][3][4][5]. Potentially, these devices offer better thermal resilience in high-power operation assuming that the intrinsic absorption is comparable with standard dielectric GWS.…”

Sub-picosecond 1030 nm laser-induced damage threshold evaluation of pulsed-laser deposited sesquioxide thin films

“…36 The latter elements offer the possibility to control the temporal, 37 spectral, 38 or spatial profile of light within or from high-power laser systems. 39 This study intends to explore the sesquioxides as potentially interesting materials for use in high-power ultrashort-pulse laser systems. Moreover, the uniqueness of this study lies in the testing of non-traditional sesquioxide materials in their crystalline form.…”

Sub-ps 1030 nm laser-induced damage threshold evaluation of pulsed-laser deposited sesquioxides and magnetron-sputtered metal oxide optical coatings

“…27 The later optical components allow control of the temporal, 28 spectral 29 and spatial profiles of light within or from high-power laser systems. 30 In this work, sesquioxides in their crystalline form and amorphous metal oxides are being investigated as prospective materials for use in ultrashort-pulse laser systems.…”