Myriam Raybaut

Compact, single-frequency, doubly resonant optical parametric oscillator pumped in an achromatic phase-adapted double-pass geometry.

We report on a nested-cavity, doubly resonant optical parametric oscillator (NesCOPO) architecture for widely tunable, mid-IR, single-frequency generation. By use of an achromatic phase-adapted double-pass pumping scheme, this new, low-threshold, semimonolithic architecture only requires two free-standing cavity mirrors and a nonlinear crystal with a mirror coating deposited on its input facet while the other facet is antireflection coated. It is thus as simple and compact as any basic linear optical parametric oscillator cavity, is easily tunable, and displays low sensitivity to mechanical vibrations. Using a high-repetition-rate (4.8 kHz) microlaser as the pump source of the NesCOPO, we demonstrate a compact source that provides pulsed, stable single-frequency output over a wide spectral range (3.8-4.3 μm) with a high peak power (up to 50 W), which are properties well suited for practical gas sensing applications.

High-energy single-longitudinal mode nearly diffraction-limited optical parametric source with 3 MHz frequency stability for CO2 DIAL

We report on a 2.05 microm nanosecond master oscillator power amplifier optical parametric source for CO2 differential-absorption lidar. The master oscillator consists of an entangled-cavity nanosecond optical parametric oscillator based on a type II periodically poled lithium niobate crystal that provides highly stable single-longitudinal-mode radiation. The signal emission is amplified by a multistage parametric amplifier to generate up to 11 mJ in a nearly diffraction-limited beam with an M2 quality factor of approximately 1.5 while maintaining single-longitudinal-mode emission with a frequency stability better than 3 MHz rms. This approach can be readily applied to the detection of various greenhouse gases.

Intersubband resonant enhancement of second-harmonic generation in GaN∕AlN quantum wells

This letter reports on the observation of resonant enhancement by intersubband transitions of the second-harmonic generation of ∼1μm radiation in GaN∕AlN quantum wells grown on AlN∕c-sapphire templates. Quantum wells with a nominal well thickness of 10 ML have been investigated in terms of intersubband linear and nonlinear optical properties. A strong increase of the second-harmonic conversion is observed at a pump wavelength of ∼2μm, which is attributed to double-resonance enhancement of the nonlinear susceptibility by intersubband transitions. The second-order susceptibility at resonance is of the order of 114pm∕V, in good agreement with calculations.

Multispecies high-energy emitter for CO 2 , CH 4 , and H 2 O monitoring in the 2 μm range

We demonstrate the first emitter, based on a single optical source device, capable of addressing three species of interest (CO₂, CH₄, and H₂O) for differential absorption Lidar remote sensing of atmospheric greenhouse gases from space in the 2 μm region. It is based on an amplified nested cavity optical parametric oscillator. The single frequency source shows a total conversion efficiency of 37% and covers the 2.05-2.3 μm range.

Management of thermal effects in high-repetition-rate pulsed optical parametric oscillators

We report on the investigation of thermal effects in high-repetition-rate pulsed optical parametric oscillators emitting in the mid-IR. We find that the thermal load induced by the nonresonant idler absorption plays a critical role in the emergence of thermally induced bistability. We then demonstrate a significant improvement of the conversion efficiency (more than 30%) when a proper axial temperature gradient is applied to the nonlinear crystal by use of a two-zone temperature-controlled oven.

Spectrotemporal dynamics of a picosecond OPO based on chirped quasi-phase-matching

We report on the first experimental investigation of the spectral dynamics of a synchronously pumped optical parametric oscillator (OPO) by use of dispersive Fourier transformation. For standard pumping rates, we observe a reproducible steady-state pulse-to-pulse spectrum. However, at high pumping levels, the OPO delivers pulse trains with nontrivial oscillatory spectral patterns. So as to benefit from a tailored broadband gain spectrum, the investigated OPO contains a chirped quasi-phase matching (QPM) nonlinear crystal. We explore the specific impacts of using such a remarkable parametric amplification medium where nonlinearly coupled frequencies vary with position. Depending on the QPM chirp rate sign, a red- or blue-shift of the emitted wavelength occurs when the OPO is switched on, leading to different spectral steady-states. These singular spectrotemporal dynamics are evidenced and explained for the first time.

Longwave infrared, single-frequency, tunable, pulsed optical parametric oscillator based on orientation-patterned GaAs for gas sensing.

We demonstrate a nanosecond single-frequency nested cavity optical parametric oscillator (NesCOPO) based on orientation-patterned GaAs (OP-GaAs). Its low threshold energy of 10 μJ enables to pump it with a pulsed single-frequency Tm:YAP microlaser. Stable single-longitudinal-mode emission is obtained owing to Vernier spectral filtering provided by the dual-cavity doubly-resonant NesCOPO scheme. Crystal temperature tuning covers the 10.3-10.9 μm range with a quasi-phase-matching period of 72.6 μm. A first step toward the implementation of this device in a differential absorption lidar is demonstrated by carrying out short-range standoff detection of ammonia vapor around 10.4 μm. Owing to the single-frequency emission, interferences due to absorption by atmospheric water vapor can be discriminated from the analyte signal.

Microsecond fiber laser pumped, single-frequency optical parametric oscillator for trace gas detection

We report on the first microsecond doubly resonant optical parametric oscillator (OPO). It is based on a nested cavity OPO architecture allowing single longitudinal mode operation and low oscillation threshold (few microjoule). The combination with a master oscillator-power amplifier fiber pump laser provides a versatile optical source widely tunable in the 3.3-3.5 μm range with an adjustable pulse repetition rate (from 40 to 100 kHz), high duty cycle (~10(-2)) and mean power (up to 25 mW in the idler beam). The potential for trace gas sensing applications is demonstrated through photoacoustic detection of atmospheric methane.

Cross-resonant optical parametric oscillators: study of and application to difference-frequency generation

We revisit both theoretically and experimentally the study of a two-crystal optical parametric oscillator (OPO) for which the signal and the idler beams are totally and exclusively output coupled after the first and the second crystals, respectively. This geometry, referred as cross-resonant OPO, is useful for applications that require the production of two beams that can be independently adjusted. A theoretical analysis is carried out by use of a plane-wave semianalytical rate-equation approach that completely includes pump depletion and reconstruction effects. We also report on an experimental investigation of a 1.064 µm pump-pulsed KTP cross-resonant OPO whose performance is compared with that of a singly resonant OPO with a similar oscillation threshold. To illustrate the practical advantages of such a configuration, we performed difference-frequency generation in a CdSe crystal by mixing the signal and idler beams of the cross-resonant OPO to produce mid-infrared radiation over the 8-12 µm range.

Analysis of cavity-length detuning in diffraction-grating narrowed picosecond optical parametric oscillators

We report on the detailed investigation of picosecond synchronously pumped optical parametric oscillators (OPOs) with a Littrow-mounted diffraction grating as the tuning element, operating close to and far from degeneracy. In addition to the expected line-narrowing effect, we observe a fivefold increase of the resonator-length detuning tolerance when compared to conventional mirror-based OPOs. When the OPO resonator length is altered, we also measure reproducible variations of the emitted wavelength associated with lateral beam displacements that were not reported before. We show that all of these effects can be explained by a geometric adaptation of the resonant beam path within the cavity to maintain a constant cavity round-trip time.