Refined Sellmeier equations for AgGaS2 down to 0.565 µm.

We revisit the 90° phase-matching conditions for second-harmonic, sum-frequency, and difference-frequency generation in A g G a S 2 thus far reported in the literature. We present refined Sellmeier equations coupled with an updated thermo-optic dispersion formula to correctly reproduce the experimental results for noncritical three-wave interactions obtained in the 0.565-10.5910 µm spectral range.

Mid-infrared electronic wavelength tuning through intracavity difference-frequency mixing in Cr:ZnSe lasers.

Mid-infrared tunable coherent light sources are used in various laser applications, such as trace gas detection, laser processing, and biomedical diagnostics. This study demonstrates mid-infrared generation in the 8.3-11 µm (i.e., 900-1200 cm-1) spectral range by configuring intracavity difference-frequency generation (DFG) using ZnGeP2 (ZGP) in an electronically tuned Cr:ZnSe laser. The broad tunability is achieved with the maximum pulse energies exceeding 100 µJ by combining the electronic wavelength tuning with sligh angle adjustments (Δθ < 0.5°) of ZGP under the spectral noncritical phase-matching condition of the nonlinear material. The proposed DFG method is generalized to give access to a significant fraction of the molecular fingerprint region by utilizing selenide compounds (e.g., AgGaSe2, CdSe) in addition to ZGP, revealing the remarkable potential of ultrabroadband electronic mid-infrared scanning for numerous spectroscopic applications.

Parametric downconversion via vibronic transition.

This Letter presents the first, to the best of our knowledge, demonstration of noncritically birefringent-phase-matched parametric downconversion, which is associated with stimulated emission via vibronic transition in a laser gain medium. The so-called self-difference frequency generation is realized along the a-axis of a Cr:CdSe single crystal pumped by a Tm:YAG laser pulse at 2.013 µm, directly producing an infrared spectrum centered at 9 µm with the maximized effective nonlinearity. The light source, which benefits from the broad vibronic spectroscopic properties together with the wide transparency range of the host material, is expected to generate noncritically phase-matched, mid-infrared spectra beyond 20 µm along with birefringence engineering in the solid solution Cr:CdSxSe1-x.

Efficient generation of few-cycle pulses beyond 10 µm from an optical parametric amplifier pumped by a 1-µm laser system.

Nonlinear vibrational spectroscopy profits from broadband sources emitting in the molecular fingerprint region. Yet, broadband lasers operating at wavelengths above 7 µm have been lacking, while traditional cascaded parametric frequency down-conversion schemes suffer from exceedingly low conversion efficiencies. Here we present efficient, direct frequency down-conversion of femtosecond 100-kHz, 1.03-µm pulses to the mid-infrared from 7.5 to 13.3 µm in a supercontinuum-seeded, tunable, single-stage optical parametric amplifier based on the wide-bandgap material Cd0.65Hg0.35Ga2S4. The amplifier delivers near transform-limited, few-cycle pulses with an average power > 30 mW at center wavelengths between 8.8 and 10.6 µm, at conversion efficiencies far surpassing that of optical parametric amplification followed by difference-frequency generation or intrapulse difference-frequency generation. The pulse duration at 10.6 µm is 101 fs corresponding to 2.9 optical cycles with a spectral coverage of 760-1160 cm-1. CdxHg1-xGa2S4 is an attractive alternative to LiGaS2 and BaGa4S7 in small-scale, Yb-laser-pumped, few-cycle mid-infrared optical parametric amplifiers and offers a much higher nonlinear figure of merit compared to those materials. Leveraging the inherent spatial variation of composition in CdxHg1-xGa2S4, an approach is proposed to give access to a significant fraction of the molecular fingerprint region using a single crystal at a fixed phase matching angle.

Refined Sellmeier equations for BaGa4S7.

This paper reports refined Sellmeier equations for the biaxial nonlinear crystal BaGa4S7 that provide a good reproduction of the phase-matching angles for second-harmonic generation (SHG) and sum-frequency generation (SFG) of the mid-IR outputs of Nd:YAG and Ho:YLF laser-pumped optical parametric oscillators (OPOs) and a frequency-doubled CO2 laser in the 0.7584-8.018 µm range. The theoretical results are found to agree with the recent experimental data for 1-µm-pumped optical parametric processes based on BaGa4S7 beyond 8 µm.

Refined Sellmeier equations for AgGaSe2 up to 18 µm.

We present refined Sellmeier equations for AgGaSe2 that provide good reproduction of the phase-matching angles for frequency upconversion of CO2 laser radiation in the 1.7652-10.5910 µm range and for frequency downconversion in the 1.85-18 µm range thus far reported in the literature.

Effective nonlinearity of the new quaternary chalcogenide crystal BaGa2GeSe6.

The unknown magnitude and relative signs of the trigonal crystal ${\rm BaGa}_{2}{\rm GeSe}_{6}$BaGa2GeSe6 nonlinear coefficients have hindered defining an optimum orientation for maximum frequency conversion efficiency. This issue is resolved in the present work, obtaining ${d_{11}}= + {23.6}$d11=+23.6, ${d_{22}}= - {18.5}$d22=-18.5, and ${d_{31}}= + {18.3}\;{\rm pm/V}$d31=+18.3pm/V for frequency doubling of the 10.591 µm radiation.

Thermo-optic dispersion formula for BaGa2GeSe6.

A thermo-optic dispersion formula for ${{\rm BaGa}_2}{{\rm GeSe}_6}$BaGa2GeSe6 nonlinear crystal is reported. The experimentally determined temperature-dependent phase-matching conditions for second-harmonic and sum-frequency generation of Nd:YAG laser-pumped ${{\rm KTiOPO}_4}$KTiOPO4 (KTP) and ${{\rm RbTiOAsO}_4}$RbTiOAsO4 (RTA) optical parametric oscillators as well as a ${{\rm CO}_2}$CO2 laser and its harmonics in the 0.805-10.5910 µm range are precisely reproduced by the formula when combined with the Sellmeier equations previously reported by the present authors [Appl. Opt.57, 7440 (2018)APOPAI0003-693510.1364/AO.57.007440].

Programmable deep-UV laser platform for inspection and metrology.

This Letter reports on a high-power, narrow-linewidth deep-UV laser platform built upon a frequency-quintupled, Yb-fiber master-oscillator and power-amplifier system. The source, emitting at a pulse repetition rate of 120 MHz with a linewidth of 90 GHz and beam quality of MX/Y2∼2.1/1.5, has been stably maintained over two weeks by successively changing positions and temperatures of nonlinear crystals in parallel, while outputting a 0.5-W average power at 213 nm.

Thermo-optic dispersion formula for LiGaS2.

This paper reports on new experimental results on the temperature-dependent phase-matching properties of LiGaS2 for second-harmonic generation and sum-frequency generation in the 0.820-10.5910 µm spectral range. In addition, we present a thermo-optic dispersion formula that provides a good reproduction of the present experimental results when combined with the Sellmeier equations presented in our previous paper, Kato et al. [Opt. Lett.42, 4363 (2017)OPLEDP0146-959210.1364/OL.42.004363].

Phase-matching properties of BaGa2GeSe6 for three-wave interactions in the 0.778-10.5910 µm spectral range.

We present new experimental results for the phase-matching properties of the recently discovered BaGa2GeSe6 crystal for harmonic generation of a Nd:YAG laser-pumped KTP OPO and a CO2 laser in the 0.778-10.5910 µm spectral range. In addition, we present new Sellmeier equations that provide a good reproduction of the present experimental results as well as the published data points for SHG of a CO2 laser at 10.5910 µm and a 1.85 µm-pumped OPO in the 2.156-3.220 µm and 4.348-13.035 µm spectral ranges.

Thermo-optic dispersion formula for BaGa4Se7.

This paper reports on the thermo-optic dispersion formula for BaGa4Se7 that provides a good reproduction of the temperature-dependent phase-matching conditions for type-1 and type-2 second-harmonic generation of a Nd:YAG laser-pumped AgGaS2 optical parametric oscillator (OPO) and a CO2 laser in the 0.901-10.5910 µm spectral range, as well as the published data points for a Nd:YAG laser-pumped OPO at λi=3.9040 µm when combined with the Sellmeier equations of the present authors [Appl. Opt.56, 2978 (2017)APOPAI0003-693510.1364/AO.56.002978].

Phase-matching properties of LiGaS2 in the 1.025-10.5910 µm spectral range.

This Letter reports on the new experimental results for second-harmonic generation and sum-frequency generation in LiGaS2 in the 1.025-10.5910 µm range, together with the new Sellmeier equations, which provide a good reproduction of the present experimental results, as well as the published data points for a Ti:Al2O3 laser (λ=0.8200 µm)-pumped optical parametric amplifier in the 3.7434-11.0079 µm range and a Nd:YAG laser-pumped optical parametric oscillator at ∼5.457 µm.

Phase-matching properties of LiGaSe2 for SHG and SFG in the 1.026-10.5910 µm range.

This paper reports on the new experimental results for second-harmonic generation and sum-frequency generation in LiGaSe2 in the 1.026-10.5910 µm range, and the improved Sellmeier equations that provide a good reproduction of the present experimental results, as well as the published data points for a Ti:Al2O3 laser (λ=0.8200 µm)-pumped optical parametric amplifier and a Nd:YAG laser-pumped optical parametric oscillator in the mid-IR.

Phase-matching properties of BaGa4Se7 for SHG and SFG in the 0.901-10.5910 µm range.

We report new experimental results on the phase-matching properties of a BaGa4Se7 crystal for harmonic generation of a Nd:YAG laser-pumped AgGaS2 optical parametric oscillator (OPO) and a CO2 laser in the 0.901-10.5910 µm range. In addition, we present new Sellmeier equations that provide a good reproduction of the present experimental results as well as the published data points for a Nd:YAG laser-pumped OPO and an optical parametric amplifier (OPA) in the 3.10-15.22 µm range and a Ho:YAG laser-pumped OPA in the 3.49-5.18 µm range.

High-efficiency single-crystal third-harmonic generation in BiB3O6.

Third-harmonic generation of high-intensity, sub-100-fs idler pulses from a Ti:sapphire-laser-pumped optical parametric amplifier is demonstrated by using a single nonlinear crystal of BiB3O6 (BIBO). Maximum internal energy conversion as high as 11% from the fundamental to the third harmonic is achieved by phase- and group-velocity matching for the direct cubic nonlinear process together with the velocity-mismatched cascading quadratic processes.

Picosecond mid-infrared optical parametric amplifier based on the wide-bandgap GaS(0.4)Se(0.6) pumped by a Nd:YAG laser system at 1064 nm.

Operation of a GaS(0.4)Se(0.6) optical parametric amplifier is demonstrated with a 5-11 µm idler tuning range, maximum energies of ∼10 µJ for sub-30-ps pulse durations, and performance ∼3 times better than with pure GaSe.

Simultaneously phase-matched blue and red light generation using BIBO.

BiB3O6 has been found to be simultaneously phase matchable for sum-frequency generation at 0.4627 and 0.6260 microm by mixing the outputs of a 0.5321 microm pumped parametric oscillator with the fundamental source at 1.0642 microm. The simultaneous blue and red light generation is achieved under the temperature-insensitive phase-matching condition, and the relative strength of blue and red light can be controlled by changing the effective nonlinear constants through the azimuth angle. In addition, wide wavelength tuning of the simultaneous phase matching is obtained by the use of a noncollinear geometry, enabling a compact red-green-blue laser system based on the powerful solid-state laser.

Phase-matched pure chi((3)) third-harmonic generation in noncentrosymmetric BiB3O6.

Third-harmonic generation (THG) has been investigated in the monoclinic BiB(3)O(6). The symmetry and birefringence analysis revealed that there are phase-matching conditions for the direct third-order nonlinear process, where the cascading second-order processes are precluded by the zero effective nonlinearity. The first phase-matched pure chi((3)) THG in a noncentrosymmetric crystal is presented together with the improved Sellmeier and thermo-optic dispersion formulas.

Comparison of photopic negative responses elicited by red and white xenon flashes in monkeys.

PURPOSE: The photopic negative response (PhNR) is a negative component of the photopic electroretinogram (ERG), and is believed to originate mainly from the retinal ganglion cells. The PhNR is commonly elicited by red light-emitting diodes. The purpose of this study was to compare the amplitude of the PhNR elicited in monkeys by red stimuli and white stimuli obtained from a xenon light source. METHODS: The PhNRs were elicited from six rhesus monkeys by photopically matched red and white xenon flashes (peak output, 600 nm) on a rod-saturating blue background. The amplitudes of the PhNR elicited by white flashes were compared with those elicited by the red flashes before and after the intravitreal injection of tetrodotoxin (TTX). RESULTS: The differences in PhNR amplitudes between the red and white stimuli, and the changes in the PhNR amplitudes after the injection of TTX, were not statistically significant. CONCLUSION: These results suggest that red and white xenon flashes are of approximately equal value for assessing inner retinal function using the PhNR under our recording conditions.