Diode-pumped garnet crystal waveguide structures fabricated by pulsed laser deposition

Abstract

Abstract:We report progress with diode-pumping of garnet crystal waveguide structures fabricated by PLD. Lasing has been achieved in a single-layer Nd:GGG film, and a four-layer structure with a Nd:GSGG core is currently undergoing laser trials.OCIS codes: (140.3530) Lasers, neodymium; (310.1860) Deposition and fabrication Planar waveguide laser structures suitable for diode-pumping present an efficient means of brightness enhancement and wavelength manipulation. The planar waveguide geometry is well suited to diode-pumping, and in particular, side-pumping offers the advantage of performing lasing, pumping and thermal management each on a unique axis. Single-layer devices greater than 50 µm in thickness can be utilised with high power diode-stacks with good coupling efficiency (>80%) [1], however the use of such large thicknesses results in an undesirable highly multimode output. The use of multilayered structures, as have similarly been successfully applied to optical fibres, provides the opportunity to pump with high efficiency into thick cladding layers whilst obtaining single-mode lasing from the smaller inner core [2].Pulsed laser deposition (PLD) is an ideal fabrication technique for making custom designed planar waveguide structures, and the use of thick layers and cladding layers has the secondary advantage of reducing the detrimental effect of particulates [3], which can otherwise be complicated to avoid. The availability of a range of different garnets with slightly different refractive indices makes it possible to produce multilayer waveguides with custom refractive index profiles. Cores based on high index garnets such as GGG or GSGG on a YAG substrate allow the high numerical apertures that are required for efficient diode-pumping to be achieved.A single-layer Nd:GGG film and a four-layer structure consisting of a Nd:GSGG core layer, YGG cladding layers and a YAG capping layer have been fabricated using a PLD system that has been described in more detail in a previous publication [4]. Both structures were deposited on YAG (100) substrates using multiple sequential deposition runs, and in the case of the single-layer film, these were used to build up a thickness greater than 70 µm so that the domed surface profile could be polished back to a more ideal planar structure. In the case of the fourlayer structure, shorter deposition runs were used with different targets to build up the resulting multilayer structure that is shown by an SEM micrograph in Figure 1. The 50 µm thick Nd:GGG film was further processed to make a device and has undergone optical characterisation and laser trials. Polishing of the upper face and ends resulted in a film that was 50 µm in thickness and 7 mm in length. We have observed a significant amount of strain in films over 40 µm in thickness and this strain caused cracking to occur whilst polishing, and prevented all four sides from being adequately polished, leaving only the option of end-pumping. We believe the strain is caused by a Ga deficiency in the film which forces som...

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