Research and Development of High Energy 2 - Micron Lasers Based on TM: Doped Ceramic Laser Gain Media and TM: Doped Optical Fibers

Abstract : Our research and development of 2-micro(m) femtosecond lasers over the past few years include development of mode-locked Tm:fiber lasers, super-continuum generation starting at 2 micro(m), and efficiently converting the femtosecond pulses of well-developed 1-micro(m) mode-locked lasers to 2 micro(m) and 4 micro(m). In this report we briefly overview our past work through this contract on the development of an all-fiber Tm mode-locked laser and super-continuum generation, and early work on half-harmonic generation of 2 micro(m) and 4 micro(m) femtosecond pulses and present our recent work on high-power half-harmonic generation at 2 micro(m), GaP-based half-harmonic generation at 4 micro(m), and theoretical studies of simulton formation in half-harmonic generation. We have achieved more than 65% of conversion efficiency for the half-harmonic generation, and more than 1.7 W of approximately 30-fs pulses at 2-micro(m). We have also achieved approximately 43% conversion efficiency in the second stage of half-harmonic generation using orientation-patterned GaP (OP-GaP) resulting in approximately 220 mW of approximately three-optical-cycle pulses at 4 micro(m). Since the initial 1-micro(m) laser was a frequency comb source, we could measure the absolute frequencies of the resulting comb at 2 micro(m) and 4 micro(m) and show that cascaded half-harmonic generation of frequency combs was an intrinsically frequency-locked down-conversion process. Using a split-step Fourier numerical tool, we discovered a new operation regime of half-harmonic optical parametric oscillators (OPOs), where self-consistent pulses are formed in the resonators, enabling extremely high slope efficiencies. Experimental observations match the theoretical prediction, and they pave the way to further enhancement of the conversion efficiency and spectral coverage of half-harmonic generation.