Femtosecond-laser-written superficial cladding waveguides in Nd:CaF2 crystal

We report on the superficial cladding waveguides fabricated by direct femtosecond laser writing in Nd: CaF2 crystal with three different groups of parameters. The lowest propagation loss of waveguides has been determined to be 0.7 dB/cm at wavelength of 632.8 nm along TE polarization. The near fundamental modal distributions have been imaged through the end-face coupling technique. The guidance of the waveguides is found to possess low sensitivity on polarization of the probe light. By using a confocal microscope system, the micro-photoluminesdence mappings and micro-fluorescence spectra are also obtained, which indicates the photoluminescence features of the Nd3+ ions are well preserved in the waveguide cores after direct femtosecond laser writing.