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

Optical parametric generator based on orientation-patterned gallium phosphide

We report the first pulsed optical parametric generator based on Orientation-patterned Gallium Phosphide. The output is tunable from 1721-1850 nm (signal) and 2504-2787 nm (idler), providing a total output power of 18 mW.Peer ReviewedPostprint (author's final draft

Grating tunable 4-14 mu m GaAs optical parametric oscillator pumped at 3 mu m

We demonstrate a broadly and continuously tunable optical parametric oscillator (OPO) based on orientation-patterned GaAs (OP-GaAs) operating at 2 kHz repetition rate. With the choice of the pump wavelength near lambda = 3 mu m, we were able to achieve tunable output in the whole range of 4-14.2 mu m with a linewidth between 2 and 6 cm(-1), using a single OP-GaAs structure with a domain reversal period of 150 mu m. The OPO output was tuned using (i) an intracavity diffraction grating, and (ii) fine adjustment of the pump wavelength near 3 mu m. In certain portions of the spectrum this system potentially allows fast (sub-millisecond scale) wavelength tuning over \u3e 2500 nm by fast steering the diffraction grating at a fixed pump wavelength

Critically phase-matched Ti:sapphire-laserpumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2

We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on type-I critical phase-matching in CdSiP2 (CSP), pumped directly by a Ti:sapphire laser. Using angle-tuning in the CSP crystal, the OPO can be continuously tuned across 7306–8329 nm (1201–1369  cm−1) in the deep-IR. It delivers up to 18 mW of idler average power at 7306 nm and >7  mW beyond 8000 nm at 80.5 MHz repetition rate, with the spectra exhibiting bandwidths of >150  nm across the tuning range. Moreover, the signal is tunable across 1128–1150 nm in the near-infrared, providing up to 35 mW of average power in ∼266  fs pulses at 1150 nm. Both beams exhibit single-peak Gaussian distribution in TEM00 spatial profile. With an equivalent spectral brightness of ∼5.6×1020photons s−1 mm−2 sr−10.1% BW−1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics.Peer ReviewedPostprint (author's final draft

Multimilliwatt, tunable, continuous‐wave, mid‐infrared generation across 4.6‐4.7 m based on orientation‐patterned gallium phosphide

We report the generation of tunable continuous-wave (cw) mid-infrared (mid-IR) radiation across 4608–4694 nm using the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). By exploiting difference-frequency mixing between a cw Tm-fiber laser and a home-built cw optical parametric oscillator in a 40-mm-long crystal, we have generated up to 43 mW of cw output power, with >30  mW across >95% of the mid-IR tuning range. The output at 4608 nm exhibits high beam quality with a passive power stability of 2.5% rms over 1.5 min. The temperature acceptance bandwidth of the OP-GaP crystal has been measured and compared with theory. The performance of the mid-IR source at high pump powers and polarization-dependent transmission in OP-GaP has been investigated.Peer ReviewedPostprint (author's final draft

High power and spectral purity continuous-wave photonic THz source tunable from 1 to 4.5 THz for nonlinear molecular spectroscopy

We report a diffraction-limited photonic terahertz (THz) source with linewidth \u3c 10 MHz that can be used for nonlinear THz studies in the continuous wave (CW) regime with uninterrupted tunability in a broad range of THz frequencies. THz output is produced in orientation-patterned (OP) gallium arsenide (GaAs) via intracavity frequency mixing between the two closely spaced resonating signal and idler waves of an optical parametric oscillator (OPO) operating near lambda = 2 mu m. The doubly resonant type II OPO is based on a periodically poled lithium niobate (PPLN) pumped by a single-frequency Yb:YAG disc laser at 1030 nm. We take advantage of the enhancement of both optical fields inside a high-finesse OPO cavity: with 10 W of 1030 nm pump, 100 W of intracavity power near 2 mu m was attained with GaAs inside cavity. This allows dramatic improvement in terms of generated THz power, as compared to the state-of-the art CW methods. We achieved \u3e 25 mu W of single-frequency tunable CW THz output power scalable to \u3e 1 mW with proper choice of pump laser wavelength

Broadband Dual-Comb Spectroscopy in the Spectral Fingerprint Region

Infrared spectroscopy in the spectral fingerprint region from 6-12 um accesses the largest molecular absorption cross-sections, permitting sensitive, quantitative and species-specific measurements. Here, we show how dual-comb spectroscopy--a form of high-speed Fourier-transform spectroscopy involving no moving parts and capable of very high resolutions--can be extended to the 6-8um wavelength band using femtosecond optical parametric oscillators (OPOs). By acquiring dual-comb interferograms faster than the mutual decoherence time of the OPO combs we implement line-shape-preserving averaging to obtain low-noise, high-fidelity spectra of H2O and CH4 at approximately 0.3 cm-1 resolutions from 1285-1585 cm-1

Optical parametric generation in orientation-patterned gallium phosphide

We report an optical parametric generator (OPG) based on the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched nanosecond Nd:YAG laser at 1064 nm with 25 kHz pulse repetition rate, the OPG can be tuned across 1721–1850 nm in the signal and 2504–2787 nm in the idler. Using a 40-mm-long crystal in single-pass configuration, we have generated a total average output power of up to ∼18  mW∼18  mW, with ∼5  mW∼5  mW of idler power at 2670 nm, for 2 W of input pump power. The OPG exhibits a passive stability in total output power better than 0.87% rms over 1 h, at a crystal temperature of 120°C, compared to 0.14% rms for the input pump. The output signal pulses, recorded at 1769 nm, have duration of 5.9 ns for input pump pulses of 9 ns. Temperature-dependent loss measurements for the pump polarization along the [100] axis in the OP-GaP crystal have also been performed, for the first time, indicating a drop in transmission from 28.8% at 50°C to 19.4% at 160°C.Peer ReviewedPostprint (author's final draft

Singly-Resonant Optical Parametric Oscillator Based on Orientation-Patterned Gallium Phosphide

We report a pulsed singly-resonant optical parametric oscillator based on orientation-patterned gallium phosphide pumped by a Q-switched Nd:YAG laser. The mid-IR idler can be tuned across 2.8-3.1 μm with an average power of 20 mW.Peer ReviewedPostprint (author's final draft