Mercury thiogallate nanosecond optical parametric oscillator continuously tunable from 4.2 to 10.8 μm

Abstract

We demonstrate an optical parametric oscillator based on two HgGa 2 S 4 crystals with an extremely wide tuning range from 4.2 to 10.8 μm. The HgGa 2 S 4 optical parametric oscillator was pumped by a Q-switched nanosecond Nd : YLF laser at 1.053 μm. The absorption spectrum of ammonia was presented to demonstrate the feasibility of the developed optical parametric oscillator system for spectroscopic measurements and gas detection.

Widely tunable (2.6–10.4μm) BaGa4Se7optical parametric oscillator pumped by a Q-switched Nd:YLiF4laser

“…Turning back to figure 4, the maximum idler energy at 8.07 μm (∼14 μJ) was limited by the available Nd:YLF pulse energy. The data could be excellently fitted with a straight line, showing no sign of saturation as expected since the BGSe OPO is pumped even farther from parametric gain saturation as done in [27] that used up to 63 @ ), and which yielded 2 μJ of idler at λ i =7.5 μm (normal incidence) [14], the performance of this BGSe OPO is about 7× superior despite the 4× superior value of HGS effective nonlinear coefficient. Because the OPO mirror cavity reflectivities were almost comparable, this difference in performance may be mainly attributed to the superior optical quality of BaGa 4 Se 7 with respect to HgGa 2 S 4 whose growth in large size, good quality is extremely difficult.…”

“…Low threshold of oscillation (E p,th =0.25 mJ) was achieved by reducing the pump beam diameter to 2w∼1 mm, thus the reported performance corresponds to the operation of the OPO far below parametric gain saturation (and damage threshold). The MIR idler wave tunability extends from 2.6 μm to 10.4 μm, greater than for a mercury thiogallate (HGS) OPO pumped by the same Nd:YLF laser and employing an identical crystal length [14]. Despite the higher χ (2) nonlinearity of HGS (4× that of BGSe), the idler output performance of our present BGSe OPO is 4 to 5 times higher than that of the HGS OPO, delivering a maximum pulse energy of 45 μJ at ∼3.3 μm and 14 μJ at ∼8 μm, whereas the HGS OPO yielded less than 8 μJ over its whole tuning range (4.2-10.8 μm).…”

“…While oxide-based periodically-poled nonlinear compounds belonging to the ferroelectric crystal family (mainly LiNbO 3 , LiTaO 3 and KTiOPO 4 ) are commercially available, their IR transparency does not exceed 5 microns and therefore they cannot be used for deeper MIR applications. For instance the [8][9][10][11][12][13][14] μm range corresponding to one of the atmospheric transparency window is interesting for LIDAR or countermeasure systems while coherent sources in the strongly water-absorbing 6-7 μm range can be used for medical (surgery) applications. More generally tunable coherent MIR laser sources are useful spectroscopic tools to probe rovibrational molecular fingerprints with various applications in trace gas sensing such as environmental monitoring, detection of hazardous species, life science or medical applications such as real-time breath analysis for early disease diagnosis [1][2][3][4][5].…”

“…Since the mid 90's, some novel ternary lithium containing chalcogenides (LiInS 2 , LiInSe 2 , LiGaS 2 , LiGaSe 2 ) produced with large enough single-crystal size have emerged [8,9], leading to various nanosecond OPO demonstrations covering the mid-IR [10][11][12] despite their rather low nonlinearity (d il <10 pm V −1 ) compared to ZGP or the difficult-to-grow mercury thiogallate, HgGa 2 S 4 (HGS) [13,14]. The recently re-discovered II-IV-V 2 chalcopyrite compound CdSiP 2 (CSP) with its high nonlinearity (d 36 =92 pm V −1 [6]) could appear as an alternative to ZGP, however its low bandgap (λ g ∼539 nm) combined with limited MIR transparence (λ6.5 μm) almost restrict its use to the non-critically phase-matched generation of ∼6 μm radiation when pumped at 1064 nm [15].…”

Investigation on phase noise of the signal from a singly resonant optical parametric oscillator

“…Optical parametric oscillators (OPOs) are a mature technol ogy for generating tunable coherent radiation in various spec tral domains from the visible to terahertz [1,2]. In particular, the singly resonant OPO (SRO) possesses several advantages, such as high power, continuous wavelength tuning capability, and good power stability [3,4].…”