Optical Parametric Oscillator Cavity Research Articles

Photoacoustic trace gas detection of ethane using a continuously tunable, continuous-wave optical parametric oscillator based on periodically poled lithium niobate

A 1.2 W, continuous-wave, continuously-tunable, singly-resonant optical parametric oscillator (OPO) (idler tuning range 3.0–3.8 μm), pumped by a 10 W continuous-wave Nd:YAG laser, is used in combination with a photoacoustic cell for the detection of ethane. An intracavity solid-state etalon (thickness 400 μm) was used to stabilize the OPO cavity and could be used to mode-hop tune the idler wavelength over 10 cm−1. The usefulness of the system was demonstrated by determining a detection limit for ethane down to 10 parts per trillion. The selectivity was achieved by making a 24 GHz wide pump laser scan over the ethane absorption line at 2996.9 cm−1, after which a Lorentzian fit determined the total area of the absorption signal. Both area value and peak value proved to be linearly depending on the ethane concentration.

An all solid-state narrow bandwidth optical parametric oscillator and its applications to the high resolution spectroscopy of free radicals

The paper describes the design, performance and illustrative spectroscopic applications of a high power, pulsed, injection seeded, narrow bandwidth and continuously tuneable optical parametric oscillator (OPO) based on two β-barium borate (BBO) nonlinear crystals. A ring cavity OPO was injection seeded with an external cavity diode laser in the spectral range 755–855 nm. The OPO generated high power transform limited nanosecond light pulses in this range and, simultaneously, at 606–667 nm. Spectral parameters of the OPO were investigated as a function of pump power for two different cavity lengths. A bandwidth of ∼120 MHz (0.004 cm-1) in the visible has been achieved with a 40-cm-long cavity. The potential of the OPO system is demonstrated by recording high resolution sub-Doppler spectra in the UV of PF and C3 radicals in a pulsed supersonic jet expansion.

Tunable single-mode operation of a pulsed optical parametric oscillator pumped by a multimode laser

High-quality single-longitudinal-mode (SLM) tunable signal radiation is generated by a pulsed optical parametric oscillator (OPO) pumped by a compact, inexpensive multimode laser. The OPO is based on periodically poled lithium niobate (PPLN) in a ring cavity that is injection seeded at its resonated signal wavelength by a single-mode tunable diode laser. Accurate control of the OPO cavity length and crystal temperature ensures a continuously tunable SLM signal output frequency range of >7.5 THz (>250 cm(-1)); the corresponding idler output remains multimode. High-resolution molecular spectra are recorded to verify OPO performance at wavelengths of ~1.55 mum. The observed signal optical bandwidth of </=120 MHz (</=0.0040 cm(-1)) compares favorably with that of a more elaborate PPLN OPO system pumped by a pulsed single-mode laser.

Narrow-linewidth middle-infrared ZnGeP_2 optical parametric oscillator

We report a narrow-linewidth ZnGeP2 (ZGP) optical parametric oscillator (OPO). It employs a Q-switched Nd:YAG-laser-pumped LiNbO3 OPO with an output at λ=2.55 µm that is used as a pump for the ZGP OPO. With the singly resonant type II ZGP OPO cavity containing a diffraction grating and a Si etalon, we achieved mid-IR tunability from 3.7 to 8 µm with an output linewidth of ∼0.1 cm-1, corresponding to ∼3 axial cavity modes. We have also demonstrated that such a narrow-linewidth OPO can be achieved with a fairly broadband (∼15 cm-1) pump.

Continuous-wave 43-μm intracavity difference frequency generation in an optical parametric oscillator

We have achieved 150 mW of cw output at 4.3mum, using difference frequency mixing in a singly resonant optical parametric oscillator (OPO). We pumped the OPO cavity, which contains periodically poled LiNbO(3) (PPLN), with a 14-W 1.06-mum Nd:YAG laser to generate a signal at 1.7 mum and an idler at 2.8 mum. Mixing of the two waves at the same crystal temperature and grating spacing yielded emission in the mid IR. This technique avoids the mid-IR absorption-high-threshold problem, which has limited the cw performance of PPLN OPO's at wavelengths beyond 4 mum. Provided that tunability is not required, this method is a simple alternative to multiple-crystal configurations.

Broadly tunable noncollinear optical parametric oscillator with periodically poled KTiOPO4

ABSTRACT Here we report on a noncollinear optical parametric oscillator (OPO) in periodically poled KTiOPO4. The noncollinear OPOcavity consisted of a 10 mm-long periodically poled KTiOPO4 crystal placed between two flat mirrors and pumped at532nm by a frequency doubled Q-switched Nd:YAG. The OPO threshold for the collinear configuration was reached at thepump pulse energy of 10 jtJ and increased monotonically when increasing the noncolinear interaction angle. The efficiencyof the OPO with PPKTP reached 50% in the collinear configuration and about 40% in the noncollinear configuration. Thenoncollinear OPO generated two signal-idler pairs. Only one of the waves in each pair was resonated in the OPO cavity,while the complementary waves were generated at different angles as required by momentum conservation. The OPO could be tuned over a range of about 290 nm around 1064 nm wavelength by adjusting the cavity angle and the PPKTP temperature. Narrowing of the OPO spectrum was observed for small noncollinear interaction angles.Keywords: Nonlinear optical materials, Periodically poled KTiOPO4, Optical parametric oscillators, Noncollinearinteractions.

Stability and frequency tuning of thermally loaded continuous-wave AgGaS_2 optical parametric oscillators

We analyze and investigate experimentally the output stability and the frequency tuning characteristics of weakly triply resonant silver gallium sulfide (AgGaS2) optical parametric oscillators. These oscillators are subject to thermally induced bistability and passive self-frequency-locking phenomena. The robust self-frequency-locking on a single-mode pair (thermal lock) originates from the material’s ability to correct external cavity-length perturbations, which would normally cause a mode hop, by increasing or decreasing the optical path length of the cavity through the thermo-optic effect triggered by the intracavity signal–idler power fluctuations. The Fourier frequency bandwidth of this passive servo is limited to ∼1 kHz by the thermal diffusion time constant, which is proportional to the ratio of the specific heat to the thermal conductivity Cp/Kc. A thermal feedback servo gain as high as 180 is obtained, owing to the large thermal figure of merit η=(dn/dT)/Kc of AgGaS2, leading to routine passive mode-hop-free operation for more than 30 min, without the need for an external cavity-length servo. Analysis of the stability range of the thermally loaded standing-wave resonator shows that thermal lensing is less critical for shorter doubly resonant optical parametric oscillator cavities employing shorter-curvature mirrors, in agreement with experimental observations. When a doubly resonant oscillator operates near the boundary of the power stability range a self-pulsing behavior is observed on a number of axial mode pairs. This self-pulsing is found to originate from the destabilization of a self-locked cw state, and the transition from self-pulsing to the stable self-frequency-locked state is found to be controlled by the pump frequency detuning. The passive stability allows the single-parameter frequency tuning to be studied. Under pure thermal lock operation the oscillators show a tendency to resist the pump frequency and temperature tuning processes. When an external cavity-length servo is implemented continuous tuning over 850 MHz, by means of the pump frequency tuning (Δνs/Δνp≈0.66), and over 100 MHz, by means of the crystal temperature (Δνs/ΔT≈250 MHz/°C), is obtained. These tuning ranges are in good agreement with calculations based on a cold doubly resonant oscillator.

Low-threshold, self-frequency-stabilized AgGaS_2 continuous-wave subharmonic optical parametric oscillator

We report the demonstration of a cw AgGaS(2) optical parametric oscillator (OPO). The subharmonic (3omega ? 2omega + omega) OPO is configured as a doubly resonant oscillator with weak pump enhancement. The temperature-tuned, noncritically phase-matched crystal is pumped by a diode laser at lambda(p) approximately 845 nm . Oscillation at lambda(s) approximately 1267 nm and lambda(i) approximately 2535 nm is observed at an input threshold power of 60 mW. Crystal thermal loading induces a robust passive self-frequency stabilization of any single-axial-mode pair to the OPO cavity resonance. The conversion efficiency is limited by thermal effects to 2% for a 200-mW pump input.

Spiking in pump enhanced idler resonant optical parametric oscillators

We report on time-resolved measurements of the output power of an idler resonant optical parametric oscillator (OPO) with resonator internal pump power enhancement. The experiments are performed with a two-mirror, pump and an idler resonant OPO based on a RbTiOAsO 4 (RTA) crystal, pumped with a single-frequency Ti:sapphire laser. When the length of the OPO cavity is piezoelectrically tuned through pump resonance, we observe a strong transient spiking in the output of the signal wave with a repetition rate of about 7 MHz. This spiking was also observed in the pump power transmitted by the OPO cavity. The observed transient spiking is in agreement with the predictions of a numerical analysis based on the equations of motion for the intracavity electric fields. This analysis also indicates the possibility to obtain pulsed operation of an OPO with a cavity resonant for the cw pump and the idler wave, by Q-switching the idler cavity loss.

The compound cavity optical parametric oscillator: theory and experiment

We present the time dynamics of a compound-cavity optical parametric oscillator (OPO) using a mathematical model for the modes under the gain profile of the oscillator which accounts for pump depletion and the cavity-Q factors. The computational results show that this type of cavity is superior in that its threshold is lower than that of a simple narrow-band cavity with dispersive elements and its efficiency is increased, while its narrow linewidth remains nearly the same across the tunable range of the nonlinear crystals used. A diagram illustrating the operation state of a compound-cavity OPO is presented, which is applicable to the simple narrow-band cavity, simple broad-band cavity, compound cavity, and traveling-wave amplification. The theoretical results are compared to the experimental data from a compound-cavity OPO using a grazing-incidence prism and grating as dispersive elements.

Narrow Linewidth, Nanosecond Pulsed Optical Parametric Oscillator with a Compound Cavity

We report a new type of optical parametric oscillator (OPO) cavity, i.e., a compound cavity OPO. Both the numerical simulation and experimental results show that this type of cavity is superior, in that its threshold is lower than that of a simple narrow-band cavity with dispersive elements, and its external efficiency is increased while its narrow linewidth remains nearly the same across the tunable range of the nonlinear crystals used.

Widely tunable optical parametric oscillator with electrical wavelength control

A LiNbO(3) optical parametric oscillator (OPO) pumped at 930nm shows a wide phase-matching curve. Each pulse produced by the OPO has a very broad natural linewidth, from 1480 to 1800 nm for the signal and from 1950 to 2550 nm for the idler. The emission wavelength is controlled thanks to an electrically tunable Fabry-Perot interferometer inserted into the OPO cavity. The signal wavelength is electrically tuned in the range 1450-1850nm without crystal rotation.

Optical parametric oscillator pumped by a Bessel beam

We demonstrate operation of a KTP optical parametric oscillator (OPO) pumped by a Bessel beam for the first time to our knowledge. It is shown that the output of the OPO has a transverse profile, which is consistent with noncollinear phase-matching relations defined by a conical pump. The central spot and ring related to the pair of signal and idler beams were generated in the OPO. By adjusting the OPO cavity mirrors, we easily selected the lowest-order mode as well as the higher-order transverse modes in the central spot. Bessel beam pumping was shown to be useful, providing tubular beam coupling into OPO cavity modes. The OPO threshold pump energy was ~100 muJ in a 6-ns pulse.

Backconversion in a pulsed optical parametric oscillator: evidence from injection-seeded sidebands

A pulsed optical parametric oscillator (OPO) is pumped at 355 nm and injection seeded at two distinct idler wavelengths at ∼855 nm; these are separated by a frequency interval Δ falling within the 350-GHz free-running OPO bandwidth. Above-threshold operation of this dual-frequency seeded OPO causes sidebands to be observed at multiples of Δ in the spectrum of the 607-nm signal radiation. The sideband spacing varies smoothly as Δ is tuned (with the injection-seeded OPO cavity misaligned to reduce its effective finesse), and corresponding sidebands are observed on the transmitted 355-nm pump radiation. This is interpreted as direct evidence of backconversion of signal and idler waves in a pulsed OPO, consistent with previous temporal observations and other aspects of OPO performance. Signal-wave sidebands are observed well beyond the regular free-running OPO gain profile, which is understood in terms of the different phase-matching conditions for the various OPO pump and idler (seed) frequencies that are involved.

Frequency-stable operation of a diode-pumped continuous-wave RbTiOAsO_4 optical parametric oscillator

Frequency-stable operation of a diode-pumped continuous-wave optical parametric oscillator (OPO) of RbTiOAsO(4) is demonstrated. Piezoelectric and fast electro-optic control of the optical length of the two-mirror OPO cavity (resonant for the pump and the idler waves) compensates for thermal changes in the refractive index of the OPO crystal (induced by absorption of pump light) and acoustic perturbations of the cavity length. Pumped by 405mW of the 810-nm output of a GaAlAs masterf-oscillator-tapered-amplifier diode laser system, the OPO generates a power-stable single-frequency signal wave at 1.24microm with an output of 84mW and a spectral bandwidth of less than 10MHz.

Optical parametric system with a compound cavity and a grazing-incidence prism

We report a new type of optical parametric oscillator cavity, i.e., a compound cavity with a grazing-incidence prism. The optical parametric oscillator is based on a β-BaB2O4 crystal and is pumped by the third harmonic of a Nd:YAG laser. Compared with the grazing-incidence-prism optical parametric oscillator (narrow-band cavity), the compound cavity has the same linewidth, whereas its threshold is only half as high and its external efficiency is an order of magnitude greater.

CW optical parametric oscillators: single mode operation and frequency tuning properties

In this paper we review the main properties of CW optical parametric oscillators (OPO) and in particular the output power values and the frequency tuning properties of the singly, doubly and triply resonant configurations. We study the mode coupling and competition between the different Gaussian modes sustained by the OPO cavity, and show that in the stationary regime and for a non-degenerate cavity the oscillation on a single pair of modes is the only stable configuration.

Coherent anti-Stokes Raman scattering spectroscopy using an optical parametric oscillator

A -barium borate optical parametric oscillator (OPO) pumped by the third harmonic of a pulsed Nd:YAG laser was developed and its potentials and limits to carry out coherent anti-Stokes Raman scattering spectroscopy are studied. Spectral properties of the OPO operated in a noncollinear phase-matching configuration are detailed, demonstrating that the OPO bandwidth can be controlled and considerably enlarged from the classical value of 1 nm up to 40 nm. The broadband signal wave emitted in this case fulfils the requirements of the tunable source needed for coherent anti-Stokes Raman scattering experiments in liquids. For gas phase studies, where the Raman linewidths are narrower than the distance separating the OPO cavity modes, scanning CARS is preferable. Injection seeding of the OPO with an external-cavity tunable diode laser reduces the signal wave linewidth to less than 500 MHz. Using this seeded OPO and its continuous tunability over 100 GHz, coherent anti-Stokes Raman scattering spectroscopy experiments are performed and molecular hydrogen Q(5) line profiles at different pressures and temperatures are measured.

93% pump depletion, 35-W continuous-wave, singly resonant optical parametric oscillator

We report two cw, singly resonant optical parametric oscillator (OPO) configurations based on periodically poled lithium niobate that result in significantly higher efficiency and output power than in previous studies. Using four-mirror OPO cavities and pumping with a 1.064-microm Nd:YAG laser, we observe 93% pump depletion and obtain ~86% of the converted pump photons as useful idler output. The single-beam, in-the-bucket idler output power of 3.55 W at 3.25 microm corresponds to ~80% of quantum-limited performance. We measure and compare the amplitude noise and spectral bandwidth of the two configurations. We also demonstrate >1 W of tunable cw output over the 3.3-3.9-microm spectral range.

Subharmonic-pumped continuous-wave parametric oscillator

We have operated a doubly resonant optical parametric oscillator (OPO) whose pump wave is generated in the OPO cavity itself by resonant frequency doubling of an injected subharmonic wave. The subharmonic-pumped oscillator employs a miniature monolithic MgO:LiNbO3 resonator and is pumped by a single-frequency Nd:YAG laser at 1064 nm. The threshold power was 120 mW at 1064 nm, and an efficiency of 7% for the conversion from 1064 to 1063/1065 nm via the nonresonant 532 nm wave was reached at 300 mW infrared input power. Single-frequency operation for up to one-and-a-half hours was observed.