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We report on an analysis of the nonlinear absorption in lithium triborate (LBO) used for second and third harmonic generation of ultrashort laser pulses at average powers in the order of kW and with sub-picosecond pulse duration. Thermographic imaging of the LBO crystals together with a simple analytical model revealed the presence of nonlinear absorption in both harmonic generation processes. Subsequent processing with a numerical model considering the nonlinear mixing, the absorption, and the heat conduction was used to estimate the absorption coefficients. Average powers exceeding 100 W in the ultraviolet and 400 W in the visible spectral range were obtained while maintaining a good beam quality by avoiding excessive nonlinear absorption.

We report on the generation of continuous-wave, intra-cavity frequency-doubled, multi-mode laser radiation in an Yb:LuAG thin-disk laser. Output powers of up to 1 kW at a wavelength of 515 nm were achieved at an unprecedented optical efficiency of 51.6% with respect to the pumping power of the thin-disk laser. The wavelength stabilization and spectral narrowing as well as the polarization selection, which is necessary for a stable and efficient second-harmonic generation, was achieved by the integration of a diffraction grating into the dielectric end mirror of the cavity, which exhibits a diffraction efficiency of 99.8%. At a frequency-doubled output power of 820 W the peak-to-valley power fluctuations measured during 100 minutes of laser operation amounted to only 8.2 W (1.0%). The beam parameter product of the frequency-doubled output was 3.4 mm·mrad (M 2 ≈ 20), which is suitable for standard beam delivery using fibers with a core diameter of 100 µm and a NA of 0.2.

Rubidium titanyl phosphate (RTP) is widely used for electro-optical applications at low switching voltages. RTP is nonhygroscopic and does not induce piezoelectric ringing up to the megahertz range. It has large electro-optic (EO) coefficients and a high damage threshold. We present here the EO coefficient wavelength dispersion measurements in the [550,950] nm spectral range using a method based on spectral interferometry. These data are necessary for, among other things, a quantitative modelization of an EO carrier-envelope phase shifter.

We have developed a diode-pumped Nd:YVO4 cw laser for testing KTiOPO4 crystals designed for intracavity second-harmonic generation at 532 nm. We demonstrate that this source is extremely sensitive to defects inside the crystal, inducing losses at 1064 nm and an index mismatch between fundamental and harmonic waves.