Nd:Gd_(3)Ga_(5)O_(12) waveguide laser fabricated by pulsed laser deposition method with ceramic target

摘要

Miniature diode-pumped waveguide laser is promising as a compact and high-efficient coherent light source to convert the poor spatial and spectral mode output of the diode laser into a spatially and spectrally pure low noise beam, that is 'coherence converter'. Since waveguide structure leads to highly efficient laser oscillation by the high optical power densities with a short laser length, diode-pumped waveguide laser will be compact and simple coherent light source. In this paper, we report the fabrication of a crystalline 2 at.% neodymium-doped Gd_(3)Ga_(5)O_(12) (Nd:GGG) film grown upon Y_(3)Al_(5)O_(12) (YAG) substrate by pulsed laser deposition (PLD) method with ceramic target. With crystal target, highly efficient Nd:GGG waveguide laser oscillation has already been reported. PLD is attractive in term of its simple experimental setup and fabrication of waveguide with high numerical aperture (NA). For instance, the GGG (refractive index 1.97) on YAG (1.82) waveguide grown in this work has a NA of 0.75. Such a high-NA waveguide is compatible with coupling to highly divergent laser diode. As a target, we used to Nd_(2)O_(3), Gd_(2)O_(3) and Ga_(2)O_(3) sintered targets. Such a ceramic target is suitable for the control of composition ratio and a good cost performance compared to crystal target. Ceramic sintered target was ablated using KrF eximer laser in the chamber at under 10 mTorr oxygen pressure. KrF eximer laser was used with a repetition rate of 20 Hz and an ablation fluence of 0.5 J/cm~(2). As a substrate, a single crystal YAG cleaned with organic catalyst and etched with sulfuric acid was used and heated at 350°C. Deposited films were post-annealed at 1100°C for four hours. Consequently, as shown in Fig. 1, epitaxial films have been grown.