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.

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.

Multispecies high-energy emitter for CO2, CH4, and H2O 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.

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.

Random quasi-phase-matching in bulk polycrystalline isotropic nonlinear materials.

Three-wave mixing in nonlinear materials--the interaction of two light waves to produce a third--is a convenient way of generating new optical frequencies from common laser sources. However, the resulting optical conversion yield is generally poor, because the relative phases of the three interacting waves change continuously as they propagate through the material. This phenomenon, known as phase mismatch, is a consequence of optical dispersion (wave velocity is frequency dependent), and is responsible for the poor optical conversion potential of isotropic nonlinear materials. Here we show that exploiting the random motion of the relative phases in highly transparent polycrystalline materials can be an effective strategy for achieving efficient phase matching in isotropic materials. Distinctive features of this 'random quasi-phase-matching' approach are a linear dependence of the conversion yield with sample thickness (predicted in ref. 3), the absence of the need for either preferential materials orientation or specific polarization selection rules, and the existence of a wavelength-dependent resonant size for the polycrystalline grains.