Mid-infrared Optical Parametric Oscillator Research Articles

High brightness widely tunable, hundred picosecond mid-IR MgO:PPLN optical parametric oscillator with short cavity

A high brightness hundred picosecond (ps) mid-infrared tunable optical parametric oscillator (OPO) based on MgO doped periodically poled lithium niobate (MgO: PPLN) was demonstrated. The pumping source was provided by a cascade amplified microchip laser at 10 kHz with pulse width of 466 ps. The idler wavelength tuning from 2.8 to 4.3 μm was achieved by the combination of period and temperature tuning. The maximum idler average output power was 262 mW at 2.8 μm with a pulse duration of 252 ps, corresponding to 6.7% conversion efficiency. The average beam quality factor was measured to be M 2 = 2.46, resulting in a brightness value of 0.55 MW sr cm−2. Pulse width of 209 ps at 4.3 μm, which was the shortest pulse width from a short cavity OPO to our best knowledge.

1064 nm laser pumped optical parametric oscillator based on BaGa4Se7 crystal at 1 kHz repetition rate

In this work, a tunable mid-infrared optical parametric oscillator based on type I phase-matching BaGa4Se7 was demonstrated. Using a Nd:YAG master oscillator power amplifier system as pump source, we firstly achieve the 1064 nm pumped BGSe-OPO at 1 kHz repetition rate. With pump double-pass single resonant oscillator configuration, the maximum output power at 4.18 μm was 483 mW and the corresponding conversion efficiency is 8.78 %. Both temperature and angle tuning of BGSe-OPO were studied and widely tunable output in the range of 3.36–5.16 μm was obtained. The average power fluctuation measured within 30 min was 0.98 % root mean square. This study has unveiled the great potential of BGSe crystal in highly stable, widely tunable, high repetition rate mid-infrared pulse generation.

Widely independent tunable dual-color mid-infrared optical parametric oscillator based on BaGa4Se7 crystals

Widely independent tunable dual-color mid-infrared optical parametric oscillator based on BaGa4Se7 crystals

Inter-/intra-pulse dual-wavelength-operated mid-infrared optical parametric oscillator.

We demonstrate a pulsed mid-infrared (MIR) optical parametric oscillator (OPO) with both inter-pulse and intra-pulse dual-wavelength operation capability. A fiber master oscillator power amplifier incorporating an acousto-optic tunable filter (AOTF) was employed as the pump for the OPO. By finely adjusting the drive wave packets for the AOTF, dual-wavelength pump can be realized within each pulse or between two adjacent pulses. These special temporal-spectral behaviors of the pump can be transferred to MIR via an OPO. In the proof-of-principle experiments, two pump wavelengths at ∼1065 and ∼1076 nm were generated and amplified to ∼31.2 W with equivalent spectral intensities for both pulsation modes. At the highest pump power, total idler power of ∼3.5 W was achieved at ∼3.45 and ∼3.55 µm under both pulsation modes. To the best of our knowledge, this is the first demonstration of both inter-pulse and intra-pulse dual-wavelength MIR generation via an OPO with an identical configuration. It is believed that our design may provide a promising solution to many practical applications including differential absorption lidar and tunable terahertz wave generation.

Mid-infrared idler-resonant optical vortex parametric oscillator based on MgO:PPLN

We present a high beam quality, mid-infrared, wavelength tunable, idler-resonant optical vortex parametric oscillator based on a single-grating MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal. The compact, plane-concave cavity used in this work enabled transfer of the orbital angular momentum (OAM) of the pump field to the idler field, to deliver high beam quality, mid-infrared vortex beam emission with measured M2 factors of 2.2 in both orthogonal directions. The wavelengths of the signal (which had a TEM00/Gaussian-like spatial profile) and the idler vortex outputs could be tuned across the ranges 1.505–1.566 µm and 3.318–3.628 µm, respectively, by changing the MgO:PPLN crystal temperature in the range 25 to 200℃. We also investigate the mechanism of OAM transfer within the idler-resonant MgO:PPLN optical parametric oscillator (OPO) by tuning the cavity length. Here, we find that the OAM of the pump beam can be selectively transferred to the signal field by simply extending the cavity length. The maximum measured signal and idler vortex output energies were 3.3 mJ and 1.1 mJ, respectively, and were achieved using both compact and extended cavities at a pump energy of 21 mJ.

Low-threshold mid-infrared ZGP optical parametric oscillator pumped by wavelength-selectable Tm:YLF laser at 1.93 μm

Low-threshold mid-infrared ZGP optical parametric oscillator pumped by wavelength-selectable Tm:YLF laser at 1.93 μm

High-Resolution Laser in Widely Tunable Range (4.16–7.13 µm) Based on Mid-Infrared BaGa4Se7 Optical Parametric Oscillator Pumped at 1064 nm

A widely tunable 4.16–7.31 μm high-resolution mid-infrared optical parametric oscillator with a type-I BaGa4Se7 (BGSe) crystal pumped by a 1064 nm laser was demonstrated for the first time. We have achieved a wavelength tuning accuracy of less than 5 nm through simultaneously performing temperature tuning and angular tuning on the BGSe (46°, 0°) Optical Parametric Oscillation (OPO). The wavelength resolution will be less than 1 nm when using commercial temperature control equipment.

Quartz-Enhanced Photoacoustic Spectroscopy Assisted by Partial Least-Squares Regression for Multi-Gas Measurements.

We report on the use of quartz-enhanced photoacoustic spectroscopy (QEPAS) for multi-gas detection. Photoacoustic (PA) spectra of mixtures of water (H2O), ammonia (NH3), and methane (CH4) were measured in the mid-infrared (MIR) wavelength range using a mid-infrared (MIR) optical parametric oscillator (OPO) light source. Highly overlapping absorption spectra are a common challenge for gas spectroscopy. To mitigate this, we used a partial least-squares regression (PLS) method to estimate the mixing ratio and concentrations of the individual gasses. The concentration range explored in the analysis varies from a few parts per million (ppm) to thousands of ppm. Spectra obtained from HITRAN and experimental single-molecule reference spectra of each of the molecular species were acquired and used as training data sets. These spectra were used to generate simulated spectra of the gas mixtures (linear combinations of the reference spectra). Here, in this proof-of-concept experiment, we demonstrate that after an absolute calibration of the QEPAS cell, the PLS analyses could be used to determine concentrations of single molecular species with a relative accuracy within a few % for mixtures of H2O, NH3, and CH4 and with an absolute sensitivity of approximately 300 (±50) ppm/V, 50 (±5) ppm/V, and 5 (±2) ppm/V for water, ammonia, and methane, respectively. This demonstrates that QEPAS assisted by PLS is a powerful approach to estimate concentrations of individual gas components with considerable spectral overlap, which is a typical scenario for real-life adoptions and applications.

High power widely tunable mid-IR (5–7.2 μm) ZnGeP2 optical parametric oscillator pumped by a 2.09 μm laser

A high-power widely tunable nanosecond (ns) mid-infrared (mid-IR) optical parametric oscillator (OPO) in a ZnGeP2 crystal has been demonstrated. The OPO is pumped by a Q-switched 2.09 μm Ho: YAG laser with 10 kHz repetition frequency. Based on optimizing the parameters of ZGP-OPO system, a maximum idler power as high as 5.47 W is achieved at 5.05 μm with photon conversion efficiency of up to 46.4 %. By rotating the angle of the ZGP crystal, the idler tuning region across from 5 to 7.2 μm is realized, with >1 W of idler power over almost the entire tuning region. The idler operation displays high pulse stability with peak to peak amplitude fluctuation less than ±2.8 % in near-Gaussian spatial mode.

High-efficiency broad-linewidth widely-tunable mid-infrared OPO based on fan-out PPLT

We reported a high-efficiency, broad-linewidth, wide-tuning-range singly-resonated optical parametric oscillator (OPO) based on a fan-out PPLT crystal. When the PPLT crystal was operated at 120 °C and pumped by Q-switched 1064 nm laser at 14.17 W with a circular pump profile, the overall output power of OPO was 7.22 W (η = 50.4%) for both the signal and idler waves. The central wavelength and linewidth of the mid-infrared (MIR) laser were 3770 nm and ∼40 nm. A wavelength tuning range of 3538–3941 nm was accomplished by adjusting the crystal period through simple mechanical movement. Due to the larger coverage of gratings with an elliptical pump profile, the output linewidth of the MIR laser was further broadened to ∼100 nm, which is ten times more than other non-fan-out PPLT OPOs. Both pumping methods with different profiles were operated at 30 kHz, 49.2 ns for the 1064 nm laser, the power fluctuation of the obtained MIR laser was within 3.5%.

15-µJ picosecond hollow-core-fiber-feedback optical parametric oscillator.

We report a high-energy, picosecond, mid-infrared (MIR) optical parametric oscillator (OPO), in which a length of hollow-core-fiber (HCF) is employed to enable operation at 1-MHz repetition rate in a compact cavity format. The OPO is synchronously pumped by an ytterbium-doped-fiber (YDF) master-oscillator-power-amplifier (MOPA) system, seeded by a 1040-nm gain-switched laser diode (GSLD). Using periodically poled lithium niobate (PPLN) as the nonlinear crystal, the OPO generates signal and idler beams with tunable wavelengths in the range of 1329-1641 nm and 2841-4790 nm, respectively. The OPO provides 137-ps pulses with a maximum signal energy of 10.05 µJ at 1600 nm and a maximum idler energy of 5.13 µJ at 2967 nm. This, to the best of our knowledge, represents the highest energy MIR pulses, as well as the highest total converted pulse energy (15.18 µJ), ever achieved from a fiber laser pumped picosecond OPO.

Generation of tunable, non-integer OAM states from an optical parametric oscillator

We report on the generation of an off-axis vortex with tunable non-integer orbital angular momentum (OAM), generated using an idler-resonant mid-infrared optical parametric oscillator (OPO) based on KTiOAsO4. The design of the OPO enables the OAM of the signal and idler outputs to be varied from 0 to 1 through precise adjustment of cavity length. The maximum vortex output energies at 1.5 and 3.5 μm were 1.95 and 1.1 mJ, respectively, and were obtained at a maximum pump energy of 20 mJ. The means by which the OAM was shared between the signal and idler fields was theoretically examined by modeling the spatial coupling among the pump, signal, and idler fields within the cavity. This work offers a unique means by which exotic vortex laser beams with tunable non-integer OAM can be generated and tuned simply through cavity length adjustments.

High-power mid-infrared ZGP optical parametric oscillator directly pumped by pulsed Tm:YLF laser at 1908 nm

This paper presents the first demonstration of a mid-infrared optical parametric oscillator (MIR OPO) based on ZGP crystal which was directly pumped by an acousto-optical Q-switched Tm:YLF laser at 1.908 μm. Profited from the improved quality of ZGP crystal with low absorption coefficient (<0.04 cm−1) and high laser-induced damage threshold (>3 J/cm2) at 1.908 μm, output power of 17.8 W for both the 3.53 μm signal and 4.15 μm idler lasers was achieved when the double-pump-pass, doubly-resonated ZGP OPO was pumped at 28.6 W. To the best of our knowledge, this is the highest output power and efficiency for any kind of Tm-laser directly-pumped OPOs.

Mid-infrared BaGa4Se7 optical parametric oscillator with high conversion efficiency (invited)

Mid-infrared BaGa4Se7 optical parametric oscillator with high conversion efficiency (invited)

Highly efficient, widely tunable fan-out MgO: PPLN mid-infrared optical parametric oscillator

Highly efficient, widely tunable fan-out MgO: PPLN mid-infrared optical parametric oscillator

High Energy，High Beam Quality Idler-resonant mid-infrared Optical Parametric Oscillator Based on KTiOAsO4

High Energy，High Beam Quality Idler-resonant mid-infrared Optical Parametric Oscillator Based on KTiOAsO4

A Passively Wavelength-Stabilized Mid-Infrared Optical Parametric Oscillator

High-power and widely tunable continuous-wave optical parametric oscillators (cw OPOs), as mature radiation sources in the mid-infrared range, are limited by their frequency fluctuation. We built a cw OPO working at the near- and mid-infrared ranges and discuss the extent to which its frequency stability is affected by the mechanical temperature and the air pressure of the cavity. In addition, we artificially provoked mode hops by changing the above two factors to analyze the thermal-induced refractive index variation of the crystal. An inequality between the spacing of the hops and the free spectrum range (FSR) was observed. The wavelength stability of the cw OPO was guaranteed passively, and the longest mode-hopping-free time exceeded 13 h through sealing the cavity and thermal control. Further analysis of factors affecting frequency drift is critically essential for the reliability of cw OPO, particularly in environments outside the laboratory, and may provide a new method for high-precision tuning wavelengths.

Pump tuning of a mid-infrared whispering gallery optical parametric oscillator.

Optical parametric oscillators (OPOs) constitute an important coherent, narrow-linewidth and widely tunable light source with applications in spectroscopy and many other fields. Their realizations based on whispering gallery resonators (WGRs) provide a small footprint and ultra-low thresholds, with demonstrations of tunability typically done via temperature variation. In this work, we show the pump tuning capabilities of a mm-sized WGR mid-infrared OPO made of CdSiP2. By tuning a telecom wavelength diode laser by 16 nm, we generate tunable light from 2708 to 3575 nm. Furthermore, we show controlled tuning in steps of 1 free spectral range (FSR) and the possibility of 12 GHz of continuous tuning. All these features are in good agreement with the theoretical predictions. We conclude that tuning from 2.4 to 4.9 µm is even possible, while still using commercially available near-infrared diode lasers. This work highlights the advantages of pump tuning of WGR OPOs and provides valuable insights for their precise control.

43 W, 7 ns constant pulse duration, high-repetition-rate langasite cavity-dumped Ho:YAG laser and its appilcation in mid-infrared ZGP OPOs

In this paper, we demonstrate a langasite (LGS) electro-optic Ho:YAG cavity-dumped laser that suppresses the gain dependence of pulse duration in Q-switched lasers. A constant pulse duration of 7.2 ns was achieved at a repetition rate of 100 kHz. Benefiting from the LGS crystal has no significant reverse piezoelectric ring effect and thermally induced depolarization, a stable pulse train was achieved at an output power of 43 W. For the first time, the application of cavity-dumped laser in mid-infrared (mid-IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO) has been realized, providing a reliable way to achieve high repetition rates and short nanosecond pulse times for high-power mid-infrared ZGP OPOs. The average output power was 15 W, corresponding to a pulse duration of 4.9 ns and a repetition rate of 100 kHz.

High Repetition Rate, Tunable Mid-Infrared BaGa4Se7 Optical Parametric Oscillator Pumped by a 1 μm Nd:YAG Laser

A tunable and compact mid-infrared optical parametric oscillator (OPO) based on BaGa4Se7 (BGSe) crystal with a repetition rate up to 250 Hz was demonstrated. A high energy and more approachable side-pumped Q-switched Nd:YAG laser was employed as the pump for the BGSe OPO. Due to the pump double-pass single-resonant oscillator (DP-SRO) configuration, the maximum average power of 250 mW and the maximum pulse energy of 1.28 mJ at 4.06 μm was achieved with the repetition rate of 250 Hz and 100 Hz, respectively. The tunable mid-infrared output from 3.42–4.73 μm was obtained. The influence of repetition rate and cavity length was studied and the thermal effect was analyzed.