Femtosecond laser assisted selective etching of microchannels in lithium niobate.

Here, we report on the fabrication of cm-long microchannels in LiNbO3 by selective etching of femtosecond laser inscribed tracks using hydrofluoric acid. We achieved a 1 cm long microchannel after 300 h of etching a single track inscribed into the volume along the optical axis of LiNbO3. Furthermore, we investigated the dependence of the etching behavior on various writing parameters. Highly selective etching with a selectivity up to 104 was achieved and a functional relationship between the etched depth and time was found. Thus, our results set the first milestone for future fabrication of 3D-hollow microstructures in the volume of LiNbO3 combining its outstanding physical properties such as the strong nonlinearity as well as the acousto- and electrooptic properties with both microfluidic and photonic structures in a monolithic setup.

µJ-level multi-cycle terahertz generation in a periodically poled Rb:KTP crystal.

We demonstrate multi-cycle terahertz (MC-THz) generation in a 15.5 mm long periodically poled rubidium (Rb)-doped potassium titanyl phosphate (Rb:PPKTP) crystal with a poling period of 300 µm. By cryogenically cooling the crystal to 77 K, up to 0.72 µJ terahertz energy is obtained at a frequency of 0.5 THz with a 3 GHz bandwidth. A maximum internal optical-to-terahertz conversion efficiency of 0.16% is achieved, which is comparable with results achieved using periodically poled lithium niobate crystal. Neither photorefractive effects nor damage was observed with up to 900mJ/cm2, showing the great potential of Rb:PPKTP for multi-millijoule-level MC-THz generation.

MHz-repetition rate fs-laser-inscribed crystalline waveguide lasers inscribed at 100 mm/s: erratum.

We present an erratum concerning the repetition rate of the fs-laser system used for the inscription of the waveguides stated in our paper [Opt. Express 28, 12011-12019 (2020)]. The Fidelity HP High Energy laser supplied by Coherent Inc. features a repetition rate of 10 MHz instead of the value of 1 MHz stated in the paper.

MHz-repetition rate fs-laser-inscribed crystalline waveguide lasers inscribed at 100†mm/s.

We report on fast direct laser inscription of waveguide laser structures in a crystal. For the first time, a 1 MHz-repetition rate fs-laser was utilized for this purpose. We inscribed and characterized more than 100 tracks with different inscription parameters in Yb:CALGO crystals. Waveguide lasing with slope efficiencies of up to 57% at a maximum output power of 3.4 W and more than 55% of optical efficiency was obtained under pumping with an optically pumped semiconductor laser (OPSL), even in waveguides fabricated at record-high inscription velocities of 100 mm/s. Such laser performance is similar to previously reported waveguide lasers inscribed at 1 kHz repetition rate and paves the way toward an industrial fabrication of such waveguides.

Highly efficient Q-switched Yb:YAG channel waveguide laser with 5.6 W of average output power.

In this Letter, we present high-power continuous wave (CW) and Q-switched femtosecond laser-written Yb:YAG channel waveguide lasers. In Q-switched operation, obtained by a semiconductor saturable absorber mirror (SESAM), as well as in CW operation, the laser generates average output powers of more than 5.6 W and reaches slope efficiencies above 74%. The Q-switched laser operated at a maximum repetition rate of 5.4 MHz with a minimum pulse duration of 11 ns, and with a maximum pulse energy of 1 µJ. This laser has almost an order of magnitude higher average output power than previously reported Q-switched channel waveguide lasers.

Efficient Yb³âº:CaGdAlO4 bulk and femtosecond-laser-written waveguide lasers.

We report on, to the best of our knowledge, the first fs-laser-written waveguide laser in Yb3+:CaGdAlO4 (Yb:CALGO). With Yb:CALGO crystals grown in our labs, we obtained a slope efficiency of 69% and up to 2.4 W of continuous wave (cw) output power in a waveguide-laser configuration. Moreover, bulk laser experiments with Yb:CALGO were performed, and slope efficiencies up to 73%, optical-to-optical efficiencies of 65%, and maximum cw output powers of 3.3 W were reached. These are the highest efficiencies in the laser configuration with Yb:CALGO.