Optical spectroscopy in channel waveguides made in Nd:YAG crystals by femtosecond laser writing

In this work, we present an optical characterization of channel waveguides fabricated by means of femtosecond laser writing on Nd:YAG substrates. These guiding structures show a refractive index increment of about 1×10^?3 which allows TE propagation. By pumping with a CW solid-state laser at 532 nm reaching the ²G_9/2 and ⁴G_7/2 manifolds of Nd³⁺ ions, we have explored the emission band corresponding to ⁴F_3/2→⁴I_9/2 optical transitions (peaked at 890 nm). From data, we have found that emission showed similar characteristics for waveguide and bulk. On the other hand, the lifetime corresponding to the ⁴F_3/2 metaestable level was determined to be 240 μs for bulk and waveguide. Summarizing, we have made suitable channel waveguides in Nd:YAG crystals, by fs interaction, with similar spectroscopic properties to those of the bulk, a fact that boosters the photonics application of these devices. For the first time to our knowledge, a direct index increment waveguide made by interaction with ultra-short intense pulses in YAG crystals has been performed. This fabrication procedure can be an efficient tool to make several optical circuits in active materials by means of the one-step, fast and low-cost processing.