  This paper reports on the quasi-three-level continuous wave laser operation
based on waveguide structures in neodymium doped calcium niobium gallium garnet
disordered crystal. Laser wavelength selection through the waveguide cross
section was observed. Waveguide structures with different cross sections were
fabricated by the ultrafast laser inscription, which have propagation losses
around 1 dB/cm. With suitable pumping conditions, laser emissions were observed
at the low-wavelengths of ~930 nm and ~890 nm. The lasing threshold for the
low-wavelength emission was around 50 mW, which is far below the threshold of
several watts reported in the bulk laser system. In addition, it was found the
laser generation at the wavelength of ~890 nm has direct relationship with the
volume of the waveguide structure. The results suggest advantages of the
waveguide platforms over the bulk systems on the low-wavelength laser emission.
