High efficiency cascaded third-harmonic generation in a quasi-periodically poled KTiOPO4 crystal

We performed and studied cascaded third-harmonic generation (THG) in a quasiperiodically poled KTP (QPPKTP) crystal allowing simultaneous phase-matching of the two cascading steps omega + omega -> 2 omega and 2 omega + omega -> 3 omega. The phase-matching was achieved at the fundamental wavelength lambda(omega) = 1587 nm when the QPPKTP crystal was heated to 95 degrees C. The energy conversion efficiency reached 40% in the picosecond regime for a fundamental energy of 20 mu J that corresponds to an intensity of 1.5 GW/cm(2). It is the highest value of THG efficiency ever reported to the best of our knowledge. The modeling in the case of the depleted pump regime accurately described the experiments. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement