Optical parametric generation in orientation-patterned gallium phosphide

Abstract

We report the first optical parametric generator (OPG) based on the new nonlinear material, orientationpatterned gallium phosphide (OP-GaP). Pumped by a Qswitched 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, we have generated a total average output power of up to ~18 mW, with ~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 hour, at a crystal temperature of 120 ºC, 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 50ºC to 19.4% at 160ºC. © 2015 Optical Society of America OCIS codes : (190.4360) Nonlinear optics, devices; (190.4400) Nonlinear optics, materials; (190.4410 Mid-infrared (mid-IR) coherent sources based on optical parametric down-conversion are of great significance for a variety of applications such as spectroscopy [1], up-conversion imaging [2] and as pump source for other nonlinear processes [3]. Oxide-based nonlinear crystals, and especially their quasi-phase matched (QPM) counterparts such as MgO-doped periodically-poled LiNbO3 (MgO:PPLN), stoichiometric LiTaO3 (MgO:sPPLT) and KTiOPO4 (PPKTP), have enabled broadband mid-IR coverage up to ~4 μm, in all time-scales from continuous-wave (CW) to femtosecond domain [4][5][6][7]. However, the onset of multiphonon absorption in these nonlinear crystals has been a fundamental barrier to reach spectral regions into the deep mid-IR. Non-oxide-based nonlinear materials with extended transparency in the mid-IR, such as ZnGeP2 (ZGP) and orientation-patterned GaAs (OP-GaAs), offer potential for the development of parametric sources beyond 4 μm. However, their low bandgap requires pumping beyond 2 μm to avoid two-photon absorption. The more recently developed nonlinear crystal, CdSiP2 (CSP), is an important new addition to the family of birefringent nonlinear materials for parametric downconversion into the deep mid-IR. The high optical nonlinearity, noncritical phase-matching (NCPM) capability, and a wide transparency range extending down to below ~1 μm, enable the deployment of the widely available Nd-based solid-state or Ybbased fiber lasers as pump source for deep mid-IR wavelength generation up to ~7 μm [8,9]. On the other hand, the new semiconductor nonlinear material, orientation-patterned GaP (OPGaP) can be considered as the QPM analog of CSP, and a promising alternative for deep mid-IR generation. As a QPM material, OP-GaP offers unique flexibility for tunable wavelength generation into the deep mid-IR using grating engineering under NCPM with no spatial walk-off. Moreover, unlike ZGP and OP-GaAs, it has sig...

Performance characterization of mid-infrared difference-frequency-generation in orientation-patterned gallium phosphide

“…Since the OP-GaP crystal end-faces are AR-coated for high transmission (R<1%) at 1064 nm and 1500-1900 nm, with >80% transmission over 2500-2800 nm, the major contribution to the drop in the transmission at the interacting wavelengths is associated with the absorption and propagation losses in the bulk crystal. We also observed that the transmission of the crystal was dependent on the operating temperature, as reported previously [17,21]. The low crystal quality, operating at a pump wavelength close to the band edge and the temperature dependence of the absorption could be attributed to the Urbach tail or free-carrier absorption in OP-GaP.…”

“…Recently, we also demonstrated a tunable DFG source based on OP-GaP operating across 2548-2781 nm by mixing the input pulses from a Q-switched nanosecond Nd:YAG pump laser at 1.064 μm with the tunable signal from a MgO:PPLN pulsed OPO in a 40-mm-long crystal, providing up to ~14 mW of average output power at 80 kHz repetition rate [16]. In another report, we demonstrated an optical parametric generator (OPG) based on OP-GaP pumped directly by a Q-switched Nd:YAG laser at 1.064 μm [17]. The OPG was temperature-tuned across 1721-1850 nm in the signal and 2504-2787 nm in the idler, providing up to ~18 mW of the total average output power at 25 kHz repetition rate, with ~5 mW of the idler output power.…”

Singly-resonant pulsed optical parametric oscillator based on orientation-patterned gallium phosphide

“…However, the signal wavelengths for the pump power of 4.2 W are 8-12 nm shorter than those for the pump power of 1.2 W at each temperature across the tuning range. Given the signal tuning rate of 0.7 nm/ºC, this means that the internal temperature of the OP-GaP crystal pumped at 4.2 W is about 11-17 ºC higher than when pumped at 1.2 W, indicative of significant thermal effects in the OP-GaP crystal, which is attributed to strong pump absorption, as also observed previously [17]. In addition, due to reduced thermal effects, signal and idler wavelengths obtained with 1.2 W pump power are closer to the theoretical tuning curves calculated from the relevant Sellmeier equations [15], represented by the solid lines in Fig.…”

“…We also reported a pulsed nanosecond mid-IR source based on difference-frequency-generation (DFG) in OP-GaP, providing tunable output across 2548-2781 nm, with highest average power of 14 mW at 2719 nm at 80 kHz repetition rate [16]. We further demonstrated optical parametric generation (OPG) in OP-GaP pumped by a nanosecond Nd:YAG laser at 25 kHz, resulting in a highest total power of ~18 mW and a temperature tuning range of 1721-1850 nm for signal and 2504-2787 nm for idler [17]. In this letter, we describe what we believe to be the first nanosecond pulsed OPO in singly-resonant oscillator (SRO) configuration based on OP-GaP.…”

Long-wave infrared generation from femtosecond and picosecond optical parametric oscillators based on orientation-patterned gallium phosphide

“…DFG and optical parametric generation (OPG) have been demonstrated with nanosecond and picosecond pulse 1-µm lasers [28][29][30], but the mid-IR wavelengths generated were around 3 µm, which fails to take advantage of OPGaP's transparency range up to 12 µm. DFG between continuous-wave lasers was used to generate 3.40 µm [31] and 5.85 µm [32] in OPGaP.…”