Femtosecond laser written Nd:YAG channel waveguide laser with a PLD grown Cr4+:YAG thin film absorber

The Pulsed Laser Deposition (PLD) technique has several advantages such as the possibility to produce thin films of any compound with a stoichiometric material transfer from the target to the substrate. Also the high energy of the ablated material is a benefit, leading to crystalline film growth due to the high mobility of the atoms on the substrate surface. In combination with a recently demonstrated efficient Nd:YAG waveguide laser, the PLD technique is suitable for producing passively Q-switched waveguide lasers by depositing thin films of highly doped Cr⁴⁺:YAG on one endface of the waveguides. This paper reports on the fabrication of waveguides using a chirped pulse amplification femtosecond laser system providing laser pulses at a wavelength of 775 nm, a pulse duration of 140 fs, pulse energies up to 1 mJ, and a repetition rate of 1 kHz. For producing the Cr⁴⁺:YAG saturable absorber, the target consisting of each 10 at% chromium oxide and magnesium oxide and as well as the host oxides, was sintered at 1700degC for 80 h. Magnesium is necessary for charge compensation and to obtain tetravalent chromium in the thin film.