We investigate the impact of femtosecond laser wavelengths on the properties of inscribed Nd: Y₃Al₅O₁₂ (Nd: YAG) waveguide lasers. The flexibility and adaptability of femtosecond laser inscription have garnered significant interest due to numerous possibilities for 3D micrometric scale modification within dielectric materials. By controlling writing parameters such as pulse energy, translation velocity, and track separation, we can control the laser-matter interaction process and the resulting waveguide properties. However, the impact of the source wavelength on the resulting micro-modifications inside crystalline materials has been relatively unexplored until now.

We conducted a comparative study of double-track Nd: YAG waveguide lasers inscribed with femtosecond laser pulses at 515 and 1030 nm, examining the effects of the source wavelength on micro-modifications. Our results indicate that the modification threshold was around 0.06 µJ for the 515-nm source, while it increased by five times to 0.3 µJ for the 1030-nm source. We also observed differences in track shapes and depths for varying pulse energy. A propagation loss lower than 0.2 dB/cm was achieved for both wavelengths – it is the lowest value reported for similar waveguides inside Nd: YAG crystal. The lasing efficiency is 41 % and 15% for the wavelength of 1030 and 515nm, respectively, at 20 % output coupler; the corresponding pump-power thresholds are 9 and 22 mW. The impacts of scanning speeds and track separations on propagation loss, refractive index change, and lasing performance will be presented.