Crystal Planar Waveguides, a Power Scaling Architecture for Low-Gain Transitions

In this paper, we present the underlying advantages that make the crystalline planar waveguide (PW) the key ingredient in power-scaling difficult or “weak” laser transitions, especially those which are extremely challenging to operate in other gain medium configurations. The planar waveguide architecture is shown to enable efficient laser operation of low-gain and/or quasi-four-level transitions that suffer reabsorption losses. Exemplar configurations are reported to make this case, for example, 1.4 W at 1.8 μm from a Nd:YAG double-clad planar waveguide laser (PWL), in addition to 0.5 W at 2.7 μm from a similar highly doped Er:YAG PWL. New laser performance levels from sesquioxide PWs fabricated by pulsed laser deposition are also presented for the first time, with >1 W obtained from a Yb:Y₂O₃ PWL. Current performance and future prospects are discussed for this laser architecture.