Abstract: Dr. Petrov will review his recent research on spectral narrowing the signal and idler outputs of non-resonant optical parametric oscillators (NRO), the spectra of which do not exhibit mode structure. Volume Bragg Gratings (VBGs) for the signal wave are used as a cavity mirror to narrow the signal bandwidth and consequently the idler bandwidth. In a PPLN based 1064 nm pumped NRO a spectral narrowing by more than an order of magnitude is achieved, to less than 2 nm, by sacrificing about 10% of the conversion efficiency which exceeded 49% at a maximum output power of 9.84 W (5.32 W signal at 1880 nm and 4.52 W idler at 2450 nm) for a repetition rate of 30 kHz and a pulse duration of the order of 10 ns. Using two chirped VBGs, tunability from 1860 to 1900 nm for the signal and from 2420 to 2486 nm for the idler is achieved. Broader tunability seems possible by seeding the NRO at the signal wavelength instead of using a VBG which is potentially interesting also for single frequency operation. Initial results using a Tm fiber laser with a < 0.1 nm linewidth show that the effect can be transferred to the idler wave with similar signal / idler bandwidths up to a certain average pump power (of the order of 4 W). Further average power scaling would require the use of thicker (> 1 mm) PPLN crystals or further increasing the repetition rate. While such high average power NROs generate relatively low (< 0.2 mJ) single pulse energies, operating at lower repetition rates can provide much higher energy levels: with a similar NRO based on a 5-mm thick PPKTP crystal, the signal plus idler output energy reached almost 5 mJ at a repetition rate of 100 Hz corresponding to a conversion efficiency of ⁓26% with both signal and idler being narrowband (0.5 nm at 1942 nm and 0.76 nm at 2355 nm). To demonstrate the importance of the spectral narrowing results for efficient frequency conversion to the mid-IR part of the spectrum beyond 5 µm, intracavity mixing the signal and idler pulses of a narrowband nanosecond singly resonant OPO based on PPLN is presented using orientation-patterned GaAs (OPGaAs). The maximum average difference-frequency generation (DFG) output power reached 215 mW at 8150 nm for a repetition rate of 35 kHz. The temperature tuning range spanned over 8026–8710 nm with a maximum overall conversion efficiency from 1 µm of ⁓1.3%.
Speaker Bio: Valentin Petrov received his master's degree in nuclear physics in 1983, and Ph.D. in optical physics, for work on mode-locked dye lasers, from the Friedrich-Schiller-University, Jena, Germany, in 1988. He worked as an Assistant Professor at the Quantum Electronics Department, Faculty of Physics, University of Sofia, Bulgaria, from 1988 to 1991. After a one year Post. Doc. research visit to the University of Regensburg, Germany, he joined the Max-Born-Institute for Nonlinear Optics and Ultrafast Spectroscopy (MBI) in Berlin, Germany, in 1992. Further research stays abroad include a JRDC STA fellowship at RIKEN (Japan) in 1996-1997 and a visiting professorship to the Université Joseph Fourier (Grenoble, France) in 2014. From 2018 to 2021 he was also a Distinguished Professor with the Tianjin University of Technology, China. His research interests include ultrashort light pulses, laser physics, nonlinear optics, and optical materials. He has co-authored about 600 papers in peer-reviewed scientific journals and about 700 conference presentations. His h-index is 66 with >17500 total citations (Google Scholar). Among the international projects coordinated, he has led two EU consortia within the 6th and 7th Framework Programmes, www.dt-crys.net and www.mirsurg.eu.
Dr. Petrov is a member of the Optical Society of America. He served on the committees of few major international conferences, incl. CLEO, CLEO Europe, ASSL-ASSP, MICS, Europhoton, Photon. West, and Ultrafast Optics, and as a topical editor (Lasers) in Optics Letters.
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