High peak-power mid-infrared ZnGeP_2 optical parametric oscillator pumped by a Tm:fiber master oscillator power amplifier system

Abstract

We report on the utilization of a novel Tm:fiber laser source for mid-IR ZnGeP2 (ZGP) optical parametric oscillator (OPO) pumping. The pump laser is built in a master oscillator power-amplifier configuration delivering up to 3.36 W of polarized, diffraction limited output power with 7 ns pulse duration and 4 kHz repetition rate. This corresponds to a peak power of ∼121 kW and a pulse energy of ∼0.84 mJ. With this source, we generated 27.9 kW of total mid-IR peak power in a doubly resonant oscillator (DRO) configuration. This is, to the best of our knowledge, the highest ever demonstrated mid-IR peak power from a directly Tm:fiber laser pumped ZGP OPO. Moreover, a DRO output with about 284 μJ of total mid-IR pulse energy was demonstrated using 100 ns pump pulses. The wavelength tuning of the idler was extended to 6 μm with lower output power in another OPO experiment.

Ultrashort pulse generation in the mid-IR

“…A variety of OPO systems has been demonstrated with ZGP [144,145,193,194,195,196,197], yielding up to 15 kW peak power pulses at 3.7 µm [80]. This very year 200 mJ pulses (signal and idler) were obtained in the 3 to 5 µm with 585 high beam quality (M 2 ) using ZGP pumped by a Ho:YLF laser [198].…”

“…These sources are discussed in the first section of this review. Traditional solid-state laser based-solutions relying on Chromium ion (Cr 2+ )-doped bulk to transfer optical energy from the visible or near-IR into the 2-5 µm range along with Thulium (Tm) and Holmium (Ho) doped materials 80 are then discussed in Sec 2 of this review. The particular relevance of Tm and Ho doped solid-state lasers as pump for nonlinear parametric down-converters allows us to transition to the third section of this review in which differencefrequency generation, optical parametric amplification and optical parametric oscillation-based solutions are discussed as sources of mid-IR ultrashort pulses.…”

“…Tm-doped laser system have also been successfully Q-switched to drive nonlinear parametric down-converters [78,79,80]. In addition to being highly relevant for high power CW operation and 255 suited for Q-switched operation, Tm-doped fiber lasers -contrary to Tm-doped crystals [81] -exhibit a broad and smooth emission spectrum [82] making those lasers highly suitable for mode-locked operation in the picosecond [83] and few hundreds of femtosecond regimes [84,85].…”

Thulium fiber laser and application development

“…While Ho:fiber lasers have several potential advantages over Tm:fiber lasers, such as output beyond 2.1 μm and ~90% theoretical efficiency when pumped with Tm:fiber lasers, the development of these sources is still in initial stages. As Tm:fiber lasers have matured, they have proven extremely attractive in terms of defense and sensing applications, particularly as pumps for mid-IR optical parametric [22][23][24] and supercontinuum 25 generation.…”

“…Despite the relatively low efficiency of flexible and rod-type PCF, the ultra large-mode area and low NA enables scaling to high peak powers without suffering nonlinear degradation while maintaining nearly diffraction-limited beam quality. The combination of high beam quality and high peak power have proven extremely useful for OPO pumping as summarized in figure 3 24 . Based on results to date, it is clear that the mode field area of Tm:PCFs can be further scaled to provide peak powers beyond 1 MW; however low efficiency limits such amplifiers to low duty cycle.…”