Antoine Godard

Dual-cavity doubly resonant optical parametric oscillators: demonstration of pulsed single-mode operation

The operating points of pulsed dual-cavity doubly resonant optical parametric oscillators have been investigated, taking into account the influence of the optical dispersion. A diagram is proposed to determine the spectral separation of doubly resonant positions for any optical lengths of both cavities. From the analysis of the distribution of doubly resonant coincidences, original conditions for stable single-mode operation are specified. This approach is validated by use of a type II phase-matched β-barium borate crystal. Frequency stability and tuning characteristics are also reported. To our best knowledge, this is the first demonstration of single-mode operation that uses a dual-cavity doubly resonant optical parametric oscillator in the nanosecond pulsed regime.

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.

Infrared quantum counting by nondegenerate two photon conductivity in GaAs

We report on infrared quantum counting of photons at optical communication wavelengths based on nondegenerate two-photon absorption in a GaAs photomultiplier tube. The detected photon energy is lower than the GaAs band gap and the energy difference is complemented by a high intensity pump field. This detection setup is simple, compact, has a broad spectral bandwidth, and benefits from the intrinsic low noise and dark counts of large band gap semiconductor junctions.

Photon extrabunching in ultrabright twin beams measured by two-photon counting in a semiconductor

For many years twin beams originating from parametric down-converted light beams have aroused great interest and attention in the photonics community. One particular aspect of the twin beams is their peculiar intensity correlation functions, which are related to the coincidence rate of photon pairs. Here we take advantage of the huge bandwidth offered by two-photon absorption in a semiconductor to quantitatively determine correlation functions of twin beams generated by spontaneous parametric down-conversion. Compared with classical incoherent sources, photon extrabunching is unambiguously and precisely measured, originating from exact coincidence between down-converted pairs of photons, travelling in unison. These results strongly establish that two-photon counting in semiconductors is a powerful tool for the absolute measurement of light beam photon correlations at ultrashort timescales.

Modal competition via four-wave mixing in single-mode extended-cavity semiconductor lasers

An analysis of the wave-coupling phenomena in extended-cavity semiconductor lasers is carried out to investigate the conditions of mode-hop-free single-mode operation. Taking into account the external cavity selectivity and the mode coupling via four-wave mixing in the active medium, we present a theoretical analysis of the modal competition and perform calculations that are in good agreement with experimental results obtained with a 1.55-/spl mu/m extended-cavity laser.

Side-mode gain in grating-tuned extended-cavity semiconductor lasers: investigation of stable single-mode operation conditions

In semiconductor lasers, nonlinear phenomena inside the active medium change the side-mode gain with respect to the static threshold-gain. For a given side mode, the sign and the magnitude of the change depend on the lasing-mode optical power and on the wavelength detuning from the lasing mode. If the side-mode gain is enhanced, mode-hopping can occur toward a side mode whose loss is higher than the lasing-mode one. Conversely, in the case of side-mode-gain suppression, the side-mode loss can be smaller with no mode-hop. In this paper, effects of carrier-density pulsation, carrier heating, and spectral-hole burning on the conditions of stable single-mode operation in grating-tuned single-mode extended-cavity semiconductor lasers are investigated. Taking into account the external cavity spectral selectivity and mode coupling, we present a theoretical analysis of experimental results. We perform calculations that compare well with the experimental data obtained with a 1.55-/spl mu/m extended-cavity laser.

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.