Pulsed Optical Parametric Oscillator Research Articles

High-average-power single-frequency pulse optical parametric oscillator based on pulse-integrated seed-injection automatic locking.

Near-infrared nanosecond (ns) single-longitudinal-mode (SLM) pulse light generated from an optical parametric oscillator (OPO) is an important source in nonlinear optics and high-precision spectral analysis. In this Letter, a stable SLM near-infrared ns pulse light source generated from the OPO is presented, which is achieved by developing a seed-injection automatic locking technique based on a pulse-integrated photodetector (PIPD). Depending on the PIPD, the peak power of the pulse light detected by the photodiode is converted to the average power by integrating several pulses. As a result, the detector saturation is thoroughly eliminated, and the interference signal including the resonance point between seed and pulse lights can easily be attained by scanning the resonator length. On this basis, a microcontroller unit (MCU) is employed to realize automatic locking by looking for the minimum value of the interference signal. Finally, a SLM 824 nm pulse light source with an output power of 20.5 W and a linewidth of 51.42 MHz is obtained. The presented method can pave the way to implement a low-cost and compact high-average-power SLM pulse OPO.

Near to Mid-Infrared (1.3–5 μm) Widely Tunable, High Power Picosecond Pulsed Laser

We present a high-power, widely tunable, synchronously pumped picosecond pulsed optical parametric oscillator (OPO) generating emissions in the near to mid-infrared wavelength ranges. The OPO is pumped using a Nd:YVO4 picosecond pulsed laser and utilizes a fan-shaped, multi-grating MgO doped PPLN crystal (MgO:PPLN). The system generates near to mid-infrared output across the wavelength range 1.3–5 µm, with a high overall conversion efficiency of 75.15%.

A versatile and narrow linewidth infrared radiation source for ro-vibration state-selected preparation of molecules in molecular beams.

We describe the design and characterization of a versatile pulsed (5ns, 10Hz repetition rate) optical parametric oscillator and amplifier system capable of generating single longitudinal mode, narrow linewidth (0.01 cm-1) radiations in the wavelength range of 680-870nm and 1380-4650nm. Using a combination of power-normalized photoacoustic signal and a Fizeau interferometer-based wavemeter, we are able to actively stabilize the output wavenumber to within 0.005 cm-1 (3σ) over a timescale longer than 1000s. We demonstrate an application of this system by performing ro-vibration state-selected preparation of CO in the v = 2 state, via direct overtone excitation (v = 0 → 2 at 2346nm) and subsequent state-selected detection in an internally cold molecular beam.

Thermometry of liquid water through slow light imaging spectroscopy.

This work presents the first, to the best of our knowledge, experimental demonstration of slow light imaging spectroscopy for thermometry of liquid water. This novel technique for measuring temperature relies on detecting the spectral shift of Brillouin peaks in water using the temporal delay through a cell containing an atomic vapor. Stand-off sensing capabilities are achieved by time-domain measurements of Brillouin scattering tuned to be near a rubidium atomic resonance and passed through a cell filled with rubidium vapor. An injection seeded optical parametric oscillator (OPO) is demonstrated to be a versatile light source for slow light imaging spectroscopy applications. The narrow OPO pulse spectrum allows for a precise profiling of slow light features of rubidium and accurate tracking of the temperature dependence of Brillouin scattering spectral shift. A comparison between the experimental data and numerical simulation over a temperature range of 20 to 99 degrees Celsius shows a good agreement for both qualitative and quantitative results.

The He-H3 + complex. II. Infrared predissociation spectrum and energy term diagram.

The rotationally resolved infrared (IR) spectrum of the He-H3 + complex has been measured in a cryogenic ion trap experiment at a nominal temperature of 4K. Predissociation of the stored complex has been invoked by excitation of the degenerate ν2 mode of the H3 + sub-unit using a pulsed optical parametric oscillator system. An assignment of the experimental spectrum became possible through one-to-one correlations with bands of the spectrum theoretically predicted in Paper I [Harding et al., J. Chem. Phys. 156, 144307 (2022)]. 19 bands have been assigned and analyzed, and the energy term diagram of the lower states of this floppy molecular complex has been derived from combination differences (CDs) in the experimental spectrum. Ground state combination differences (GSCDs) reveal a large part of the energy term diagram for the He-H3 + complex in its vibrational ground state, v = 0. Experimental and theoretical term energies agree within experimental accuracy for the rotational fine structure associated with the total angular momentum quantum number J and the parity e/f as well as for the coarse spacing of the lowest K states of the complex. This favorable comparison shows that the potential energy surface (PES) calculated in Paper I is accurate. The barriers between the three equivalent global minima in this PES are relatively low and the He-H3 + complex is extremely floppy, with nearly unhindered internal rotation of the H3 + sub-unit. The resulting Coriolis interactions couple the internal and end-over-end rotation of the complex and contribute significantly to the energy terms. They are observed both in experiment and theory and are, e.g., the origin of different rotational constants for states of e and f parity. Also in this respect, experiment and theory agree very well. Despite the assignment and analysis of many bands of the extremely rich IR spectrum of He-H3 +, higher levels of excitation, including the complex stretching mode, need further attention.

Nonlinear quantum behavior of ultrashort-pulse optical parametric oscillators

The quantum features of ultrashort-pulse optical parametric oscillators (OPOs) are investigated theoretically in the nonlinear regime near and above threshold. Viewing the pulsed OPO as a multimode open quantum system, we rigorously derive a general input-output model that features nonlinear coupling among many cavity (i.e., system) signal modes and a broadband single-pass (i.e., reservoir) pump field. Under appropriate assumptions, our model produces a Lindblad master equation with multimode nonlinear Lindblad operators describing two-photon dissipation and a multimode four-wave-mixing Hamiltonian describing a broadband, dispersive optical cascade, which we show is required to preserve causality. To simplify the multimode complexity of the model, we employ a supermode decomposition to perform numerical simulations in the regime where the pulsed supermodes experience strong single-photon nonlinearity. We find that the quantum nonlinear dynamics induces pump depletion as well as corrections to the below-threshold squeezing spectrum predicted by linearized models. We also observe the formation of non-Gaussian states with Wigner-function negativity and show that the multimode interactions with the pump, both dissipative and dispersive, can act as effective decoherence channels. Finally, we briefly discuss some experimental considerations for potentially observing such quantum nonlinear phenomena with ultrashort-pulse OPOs on nonlinear nanophotonic platforms.

Tunable injection-seeded fan-out-PPLN optical parametric oscillator for high-sensitivity gas detection

We demonstrate the possibility to enhance spectroscopic and lidar capabilities of mid-infrared pulsed optical parametric oscillators (OPOs) based on fan-out periodically-poled lithium niobate (fan-out PPLN) by combining their own wavelength tunability with tunable continuous-wave injection seeding. To that effect, we have developed an original test-bed singly-resonant OPO configuration in which continuous wavelength tuning via intracavity translation of the fan-out PPLN is assisted by simultaneous tuning of a narrow-linewidth fiber-coupled seed diode laser. It is shown that such an approach provides strong (at least by one order of magnitude) spectral narrowing, wavelength stabilization and beam-quality improvement for the signal and idler radiations (tunable around 1.54 μm and 3.33 μm, respectively). The achieved spectral narrowing does not noticeably affect the OPO output pulse energy, but allows fine wavelength tuning and significantly increases the power spectral density which can be available at an analyzed gas absorption line. Thus, it leads to a noticeable increase in sensitivity of the photoacoustic gas sensing carried out with the developed OPO. We have achieved an almost double (∼80%) increase in the photoacoustic response of a methane detector to the reference gas mixture with low concentration methane. The application of the method can be simply extended to many gas absorptions lines within the range 3.1–3.4 μm, due to the potentially wide tunability of the developed OPO. The demonstrated OPO features simplicity, reliability and energy efficiency. It can advance various LIDAR techniques due to the unique combination of spectral and energy characteristics.

Broadly tunable, intracavity injection-seeded, hybrid optical parametric oscillator

We report a novel, to the best of our knowledge, approach for injection seeding of pulsed optical parametric oscillators (OPOs), which can provide spectral control over the full tuning range. Bandwidth reduction down to single-mode operation is realized across the pulsed tuning range by deploying a hybrid design, where a continuous-wave (cw) OPO injection seeds the pulsed OPO in a single composite cavity. By exploiting two identical MgO-doped periodically poled lithium niobate crystals, the hybrid OPO provides signal pulses with a single-frequency linewidth as narrow as 7.2 MHz across 1510-1677 nm. The effect of cw injection seeding on pulsed OPO operation is also confirmed by reduced rise time, increased pump depletion, major reduction in threshold, and substantial enhancement in output power and extraction efficiency.

Application of a pulsed OPO seeded by a CW OPO to investigation of linewidth effects on TALIF excitation efficiency

In this article we present a widely tunable laser architecture for high-resolution nonlinear spectroscopy which incorporates a continuous wave optical parametric oscillator (OPO) for injection-seeding of a singly resonant actively-locked β-Ba(BO2)2 nanosecond OPO. Such an instrumental configuration is designed to provide near-transform-limited pulses over 450–650 nm signal, and 225–325 nm after signal doubling. Novel features that enable frequency agility and ramp-lock injection-seeding over a wide frequency range are described. System performance was demonstrated through investigations of two-photon laser induced fluorescence (TALIF) and the influence of excitation linewidth on the signal strength of the 5p6S0 - 6p[3/2]2 transition of atomic xenon at 252.49 nm. Measurements conducted at xenon partial pressures of 1×10-1-4×10-4 Torr, with and without active cavity locking and injection seeding, resulted in a 17× increased TALIF fluorescence yield during injection-seeded operation. The results are found to be consistent with modeling, taking into account the effects of lineshape, energy, and beam spatial cross-section. Modeling was informed by direct single-shot measurements of the signal beam lineshape in seeded and free-running operation using a virtually imaged phased array (VIPA) spectrometer.

CH and NO planar laser-induced fluorescence and Rayleigh-scattering in turbulent flames using a multimode optical parametric oscillator.

An optical parametric oscillator (OPO) is developed and characterized for the simultaneous generation of ultraviolet (UV) and near-UV nanosecond laser pulses for the single-shot Rayleigh scattering and planar laser-induced-fluorescence (PLIF) imaging of methylidyne (CH) and nitric oxide (NO) in turbulent flames. The OPO is pumped by a multichannel, 8-pulse Nd:YAG laser cluster that produces up to 225 mJ/pulse at 355 nm with pulse spacing of 100 µs. The pulsed OPO has a conversion efficiency of 9.6% to the signal wavelength of ∼430nm when pumped by the multimode laser. Second harmonic conversion of the signal, with 3.8% efficiency, is used for the electronic excitation of the A-X (1,0) band of NO at ∼215nm, while the residual signal at 430 nm is used for direct excitation of the A-X (0,0) band of the CH radical and elastic Rayleigh scattering. The section of the OPO signal wavelength for simultaneous CH and NO PLIF imaging is performed with consideration of the pulse energy, interference from the reactant and product species, and the fluorescence signal intensity. The excitation wavelengths of 430.7 nm and 215.35 nm are studied in a laminar, premixed CH4-H2-NH3-air flame. Single-shot CH and NO PLIF and Rayleigh scatter imaging is demonstrated in a turbulent CH4-H2-NH3 diffusion flame using a high-speed intensified CMOS camera. Analysis of the complementary Rayleigh scattering and CH and NO PLIF enables identification and quantification of the high-temperature flame layers, the combustion product zones, and the fuel-jet core. Considerations for extension to simultaneous, 10-kHz-rate acquisition are discussed.

High power, twin-band mid-infrared PPMgLN optical parametric oscillator pumped at 1.679 µm.

We report on a high-power, twin-band mid-infrared (MIR) periodically poled MgO-doped ${{\rm LiNbO}_3}$LiNbO3 (PPMgLN) optical parametric oscillator (OPO) pumped by a near-infrared pulsed OPO with 20 kHz of repetition rate. The pump source has a central wavelength of 1.679 µm and a linewidth of 0.12 nm. The MIR OPO can be tuned from 2.74 to 2.80 µm for signal and from 4.34 to 4.19 µm for idler through raising the oven temperature from 30°C to 200°C, respectively. Under 100°C oven temperature, the OPO yielded maximum total output power of 15.4 W (2.76 µm signal plus 4.29 µm idler) with single-pass pumping configuration. The beam quality ${M^2}$M2 was measured to be $ \lt {2.5}$<2.5 for signal and $ \lt {4}$<4 for idler.

绿光泵浦的黄光波段可调谐窄线宽光学参量振荡器

A pulsed optical parametric oscillator (OPO) was demonstrated for the purpose of wavelength-tunable yellow output with narrow spectral line width. The OPO pumped by the green output of an acousto-optic Q-switched Nd:YAG used a type II phase-matched KTiOPO4 (KTP) crystal as the nonlinear gain medium and a folded cavity arrangement. The OPO was designed to have the idler wave tunable in near infrared oscillated in the cavity, which was further frequency doubled to generate the wavelength-tunable yellow output by using a LiB3O5 (LBO) crystal with type I non-critical phase matching scheme. A fused silica etalon was inserted in the idler wave cavity to narrow the idler wave and the resultant yellow spectral line width. The wavelength of the yellow output obtained could be tuned over 587.2-595.2 nm, within which the maximum average output power of 2.89 W was obtained at 591.2 nm, under an incident average green pump power of 24.0 W. The beam quality factor M2 was 3.4. The conversion efficiency from the green pump to the yellow output was 12.0%. The pulse width at the maximum output power was 37 ns, and the peak power was 7.8 kW. The spectral line width of the yellow output was 0.15 nm, which was narrowed effectively compared with that without etalon in the OPO cavity.

Kerr-lens mode locked, synchronously pumped, ultra-broadband breathing pulse optical parametric oscillator

Profiting from a breathing pulse design, we demonstrate a Kerr-lens mode locked non-collinear optical parametric oscillator, which is capable of delivering stable ultrabroadband signal spanning from 628 nm to 890 nm at -10 dB level.

Fully resolved lineshape measurement of a seeded and unseeded optical parametric oscillator using a virtually imaged phased array spectrometer.

Mode-resolved characterization of a nanosecond pulsed optical parametric oscillator (OPO) has been performed with a cross-dispersed virtually imaged phased array (VIPA) spectrometer during both free-running and partially injection-seeded operation. The spectrometer is designed around a 0.5 cm-1 VIPA element with a measured spectral resolution of 220MHz and a range of over 60 cm-1. Full high-resolution lineshape measurements are obtained covering over 600 oscillating cavity modes on a commercial type I beta barium borate OPO during operation of the signal beam near 632.8nm. Mean and fluctuating mode intensities are found to agree with previous studies of ultra-short OPO resonators. Furthermore, modulation of the broadband output due to the étalon characteristics of the nonlinear crystal produces clear fringes on the output lineshape, which have been observed for the first time, to the best of our knowledge. Future application of VIPA spectrometers to pulsed OPOs will allow previously unattainable characterization of the entire OPO lineshape and enable monitoring and optimization of OPO spectral purity.

Versatile photoacoustic spectrometer based on a mid-infrared pulsed optical parametric oscillator.

We demonstrate the usefulness of a nanosecond-pulsed single-mode mid-infrared (MIR) optical parametric oscillator (OPO) for photoacoustic (PA) spectroscopic measurements. The maximum wavelength ranges for the signal and idler are 1.4μm to 1.7μm and 2.8μm to 4.6μm, respectively, with a MIR output power of up to 500mW, making the OPO useful for different spectroscopic PA trace-gas measurements targeting the major market opportunity of environmental monitoring and breath gas analysis. We perform spectroscopic measurements of methane (CH4), nitrogen dioxide (NO2), and ammonia (NH3) in the 2.8μm to 3.7μm wavelength region. The measurements were conducted with a constant flow rate of 300mL/min, thus demonstrating the suitability of the gas sensor for real-time trace-gas measurements. The acquired spectra are compared with data from the HITRAN database, and good agreement is found, demonstrating a resolution bandwidth of 1.5 cm1. An Allan deviation analysis shows that the detection limit for methane at optimum integration time for the PA sensor is 8ppbV (nmol/mol) at 105s of integration time, corresponding to a normalized noise equivalent absorption coefficient of 2.9×10-7 W cm-1 Hz-1/2.

Laser-Based Metastable Krypton Generation.

We demonstrate the generation of metastable krypton in the long-lived 1s^{5} state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p^{6} state using a pulsed optical parametric oscillator laser operating near 215nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.

A narrowband infrared source based on orientation-patterned GaAs for standoff detection of chemicals

This paper presents our work on a pulsed single-frequency tunable optical parametric oscillator based on orientation-patterned gallium arsenide. Owing to crystal temperature tuning, this source covers the 10.2–11.2 and 7.6–8.6 $$\upmu \hbox {m}$$ ranges in single-longitudinal mode operation with a linewidth below 30 MHz. Standoff detection of ammonia around 10.35 and 10.5 $$\upmu \hbox {m}$$ is performed by implementing this source in an Integrated Path Differential Absorption Lidar (IP-DIAL) setup.

Double Blind Ultrafast Pulse Characterization by Mixed Frequency Generation in a Gold Antenna

Ultrafast pulse characterization requires the analysis of correlation functions generated by frequency mixing of optical pulses in a nonlinear medium. In this work, we use a gold optical nanoantenna to generate simultaneously Four Wave Mixing and Sum Frequency Generation across the tuning range of a Ti:Sapphire and Optical Parametric Oscillator (OPO) system. Since metal nanoparticles create remarkably strong nonlinear responses for their size without the need for phase matching, this allows us to simultaneously characterize the unknown OPO pulse and its pump pulse using a single spectrogram. The nonlinear mixing is efficient enough to retrieve pulses with energies in the picojoule range.

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

We report a pulsed singly-resonant optical parametric oscillator (OPO) based on the new nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched Nd:YAG laser at 1064nm, and using a 40-mm-long OP-GaP crystal with a single grating period of Λ=16 μm, the OPO generates signal and idler output across 1.6-1.7μm and 2.8-3.1μm, respectively, under temperature tuning. For an average pump power of 4.8W at 50kHz pulse repetition rate, mid-infrared idler powers of up to ∼20 mW have been obtained at 2966nm with high output stability. For pump pulses of ∼13 ns duration, the OPO generates ∼6 ns output signal pulses. From temperature-dependent wavelength tuning measurements at two different pump powers of 4.2W and 1.2W, a discrepancy of 11-17°C in the internal crystal temperature is estimated, implying that the OP-GaP sample suffers from increasing thermal effects at higher pump powers due to absorption.

Frequency Stabilization of Pulsed Injection-Seeded OPO Based on Optical Heterodyne Technique**Supported by the National Key Research and Development Program of China under Grant No 2016YFC1400902, the National Natural Science Foundation of China under Grant Nos 61505230 and 61475170, and the Shanghai Natural Science Foundation under Grant No 15ZR1445000.

A frequency stabilizing system for a pulsed injection seeded 1550nm optical parametric oscillator (OPO) at 20 Hz repetition rate is demonstrated. The optical heterodyne method is used to measure the frequency difference between the seed laser and the OPO output. Using the frequency difference as the error signal, a proportionalintegral controller in combination with a scanner is applied to stably match the OPO cavity length to the seed laser frequency. The root-mean-square (rms) error of the frequency discrimination method is <0.07MHz according to a ‘frequency shifting-chopping-beat’ evaluation. The frequency fluctuation of the frequency-stabilized OPO is 0.29MHz (rms), and the Allan deviation is less than 20 kHz for averaging time of more than 3 s.