| Abstract [eng] |
Optical parametric systems pumped by passively Q-switched sub-nanosecond microlasers operating at kHz repetition rates enable the generation of high-energy (µJ - mJ) pulses in compact, cost-effective and stable configurations [2–4]. In recent years, sub-nanosecond parametric systems based on periodically poled nonlinear crystals with quasi-phase matching (QPM) structures, such as multi-grating or fan-out geometries, have been demonstrated [23,24]. These systems are actively investigated due to their potential for applications requiring widely tunable sources in both the infrared and visible spectral regions [5–13,15,16]. However, the realization of tunable sources in the sub-nanosecond visible spectral range remains challenging due to lower LIDT, limitations of QPM structures and absorption as well as noncollinear QPM effects in periodically poled crystals [19,64]. Considering the practical importance of tunable radiation in the visible spectral region, technological limitations and relatively low level of development in this field, the aim of this work was to develop an efficient sub-nanosecond optical parametric amplification (OPA) system with continuous tunability in the visible range. In this study, the seed source was optical parametric generation (OPG) radiation produced in multi-grating MgO:PPLN crystal pumped by 532 nm. The OPA was stage was realized in two subsequently arranged LBO crystals pumped by 355 nm, enabling the generation of shorter-wavelength signal radiation. By tuning the grating period and the temperature of MgO:PPLN crystal, continuous tuning of the signal and idler waves in the 690 – 2300 nm range was achieved, with a conversion efficiency of 57 – 65 %. Using this OPG radiation as a seed in the subsequent OPA stage, continuous tuning in the 419 – 690 nm range was realized. Due to the high-energy seed, efficient OPA interaction was achieved, with a conversion efficiency of 15 – 34 %, or 9 – 23 % when optimizing the system for better beam quality. The generated OPA pulse durations were in the sub-nanosecond regime, ranging from 356 to 345 ps, while the spectral bandwidth across the entire tuning range did not exceed 1 nm (FWHM). The obtained results demonstrate that microlaser-pumped multi-stage parametric systems enable the realization of compact, high-energy and widely tunable light sources, which are important for applications in spectroscopy, biomedicine, nonlinear optics etc. |
