Mid-infrared coherent sources and applications: introduction

Peer ReviewedPostprint (published version

Fiber-laser-based, high-repetition-rate, picosecond ultraviolet source tunable across 329-348 nm

We report a compact, fiber-laser-based, high-repetition-rate picosecond source for the ultraviolet (UV), providing multi-tens of milliwatt of average power across 329-348 nm. The source is based on internal sum-frequency-generation (SFG) in a singly-resonant optical parametric oscillator (OPO), synchronously pumped at 532 nm by the second harmonic of a picosecond Yb-fiber laser at 80 MHz repetition rate. Using a 30-mm-long single-grating MgO:sPPLT crystal for the OPO and a 5-mm-long BiB3O6 crystal for intracavity SFG, we have generated up to 115 mW of average UV power at 339.9 nm, with >50 mW over 73% of the tuning range for 1.6 W of input pump power. The UV output exhibits passive rms power stability of ~2.9% rms over 1 min and 6.5% rms over 2 hours, in high beam quality. Angular acceptance bandwidth and cavity length detuning with pump power and crystal temperature have also been studied.Peer ReviewedPostprint (author's final draft

Continuous-wave, multimilliwatt, mid-infrared source tunable across 6.4–7.5 μm based on orientation-patterned GaAs

We report a continuous-wave (cw) source of tunable mid-infrared radiation providing tens of milliwatt of output power in the 6460–7517 nm spectral range. The source is based on difference-frequency generation (DFG) in orientation-patterned (OP)-GaAs pumped by a Tm-fiber laser at 2010 nm and a 1064 nm-Yb-fiber-pumped cw optical parametric oscillator. Using a 25.7-mm-long OP-GaAs crystal, we have generated up to 51.1 mW of output power at 6790 nm, with >40 mW and >20 mW across 32% and 80% of the mid-infrared tuning range, respectively, which is to the best of our knowledge the highest tunable cw power generated in OP-GaAs in this spectral range. The DFG output at maximum power exhibits passive power stability better than 2.3% rms over more than 1 h and a frequency stability of 1.8 GHz over more than 1 min, in high spatial beam quality. The system and crystal performance at high pump powers have been studiedPostprint (published version

Room-temperature, rapidly tunable, green-pumped continuous-wave optical parametric oscillator

We report the first realization of a stable, room-temperature, green-pumped cw OPO using fan-out-grating MgO:sPPLT, providing rapid, continuous and wide-tuning across 734-1929nm, 2.2W of output-power, frequency-stability of 518MHz (2mins.) and linewidth of 6.9MHz, in good-beam-quality.Peer ReviewedPostprint (author's final draft

Stable, High-Average-Power, Degenerate Optical Parametric Oscillator at 2.1 μm

We describe a degenerate 1.064-μm-pumped pulsed optical parametric oscillator based on MgO:PPLN in compact Littrow-grating cavity configuration, providing 2.7W of average power at 2.1μm with high spectral and power stability in good spatial beam quality.Peer ReviewedPostprint (author's final draft

Continuous-wave, single-pass, single-frequency second-harmonic-generation at 266 nm based on birefringent-multicrystal scheme

We report the implementation of a compact cascaded multicrystal scheme based on birefringent crystals in critical phase-matching, for the generation of continuous-wave (cw) radiation in the deep ultraviolet (UV). The approach comprises a cascade of 4 single-pass second-harmonic-generation (SHG) stages in β-BaB2O4 (BBO) pumped by a single-frequency cw green source at 532 nm. A deep-UV cw output power of 37.7 mW at 266 nm has been obtained with a high passive power stability of 0.12% rms over more than 4 hours. Characterization and optimization of the system in each stage has been systematically performed. Angular phase-matching acceptance bandwidth under tight focusing in BBO, and spectral properties of the deep-UV radiation, have been studied. Theoretical calculations for SHG in the cascaded scheme based on birefringent phase-matching have been performed, and enhancement in UV power compared to single-stage single-pass scheme are studied. Theoretical comparison of BBO with other potential crystals for deep-UV generation in cascaded multicrystal scheme is also presented.Peer ReviewedPostprint (published version

Phase-Modulation-Mode-Locked Continuous-Wave MgO:PPLN Optical Parametric Oscillator

We report phase-modulation mode-locking of a continuous-wave (cw) singlyresonant optical parametric oscillator (OPO) in the near- and mid-infrared based on MgO-doped periodically poled LiNbO3 (MgO:PPLN) and pumped by an Yb-fiber laser at 1064 nm. By investigating the spectral output and pulse formation characteristics of the OPO, we observe a clear transition from an unstable spectrum in cw operation to a stable and smooth profile under phase modulation, confirming mode-locked operation. Pulse generation and spectral characteristics under different operating conditions are studied, including the effects of the location of the intracavity phase modulator and the number of oscillating modes on mode-locked output pulse duration.Peer ReviewedPostprint (published version

Fiber-laser-based, green-pumped, picosecond optical parametric oscillator using fan-out grating PPKTP

We report a stable, Yb-fiber-laser-based, green-pumped, picosecond optical parametric oscillator (OPO) for the near-infrared based on periodically poled potassium titanyl phosphate (PPKTP) nonlinear crystal, using fan-out grating design and operating near room temperature. The OPO is continuously tunable across 726–955 nm in the signal and 1201–1998 nm in the idler, resulting in a total signal plus idler wavelength coverage of 1026 nm by grating tuning at a fixed temperature. The device generates up to 580 mW of average power in the signal at 765 nm and 300 mW in the idler at 1338 nm, with an overall extraction efficiency of up to 52% and a pump depletion >76%>76%. The extracted signal at 765 nm and idler at 1746 nm exhibit excellent passive power stability better than 0.5% and 0.8% rms, respectively, over 1 h with good beam quality in TEM00TEM00 mode profile. The output signal pulses have a Gaussian temporal duration of 13.2 ps, with a FWHM spectral bandwidth of 3.4 nm at 79.5 MHz repetition rate. Power scaling limitations of the OPO due to the material properties of PPKTP are studied.Peer ReviewedPostprint (author's final draft

Continuous-wave green-pumped optical parametric oscillator based on fanout MgO:PPLN

We report a green-pumped continuous-wave OPO using a fanout-grating MgO:PPLN, tunable across 813-1032 nm (signal) and 1098-1539 nm (idler) with >30% extraction efficiency in excellent beam-quality and power stability better than 3% rms over 1 hour.Peer ReviewedPostprint (published version

Green-pumped continuous-wave parametric oscillator based on fanout–grating MgO:PPLN

We report the first green-pumped continuous-wave (cw) optical parametric oscillator (OPO) based on MgO:PPLN in a fanout grating design. Pumped by a single-frequency cw laser at 532 nm, the OPO provides tunable radiation across 813–1032 nm in the signal and 1098–1539 nm in the idler by simple mechanical translation at a fixed temperature of 55°C. By deploying a 25-mm-long crystal to minimize thermal effects and using output coupling for the signal wave, we generate a total output power of up to 714 mW at 30% extraction efficiency in excellent Gaussian beam quality with ¿2<1.1 and high output stability. Simultaneous measurements of signal and idler power result in passive stability of 2.8% and 1.8% rms, respectively, over 1 h. Strong thermal effects contribute to the high stability and excellent beam quality, while linear and green-induced infrared absorption limit the power scaling capabilities of the OPO. The output signal is single-mode with an instantaneous linewidth of ~3MHz and frequency stability of ~84MHz over 72 s.Ministerio de Ciencia, Innovación y Universidades (nuOPO, TEC2015-68234-R); Generalitat de Catalunya (CERCA Programme); Severo Ochoa Programme for Centres of Excellence in RD (SEV- 2015-0522-16-1); Fundación CellexPostprint (published version