Jean-Pierre Faleni

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.

Tunable ultraviolet intracavity tripled Ti:sapphire laser

We present what we believe to be the first intracavity tripled Ti:sapphire laser. This source is tunable in the 275-285-nm range and will be useful for applications in the detection of important atmospheric species such as OH and NO radicals. Single-frequency operation and high optical yield (>50%) are obtained in this system after it has been injected by a laser diode.

In Situ Measurement and Validation of Gaseous Species Concentrations of a Gas Turbine Model Combustor by Tunable Diode Laser Absorption Spectroscopy (TDLAS)

In the framework of a European research project, ONERA and DLR have studied the applicability of infrared laser techniques to gas turbine combustor measurements. The final goal is to replace gas analysis with probe measurements by optical techniques fulfilling the ICAO standards for engine emission measurements. Infrared laser absorption spectroscopy has the potential for fast, high spatial resolution measurements of combustion species with rugged equipment and therefore might contribute to the reduction of combustor development time and cost. Furthermore, the measurement of minor species in the combustor could help the understanding of the combustion process in the gas turbine. The tunable diode laser absorption technique of ONERA was used to probe CO, CO2, NO and H2O. The apparatus and measurement procedure including the upgrades for the combustor measurements are described. Successful measurements were achieved with CO inside and outside of the combustor. The reactive flow field of the model combustor was characterized with conventional measurement techniques. The CO measurements by TDLAS were compared with probe measurements that could be weighted by temperature and velocity measurements. Furthermore, temperature information was derived from the Laser measurements. The results are compared and further improvements are discussed.

Cross resonant optical parametric oscillators: theoretical and experimental study in nanosecond regime

We investigate theoretically and experimentally a two-crystal optical parametric oscillator where signal and idler are outcoupled after the first and second crystal, respectively. Difference-frequency generation in GaAs slabs from the two beams is also reported.

Wind Tunnel Experimental Study Of Optical Beam Degradation Through Heterogeneous Aerodynamic Flows

This paper deals with the influence of aerodynamic disturbances on the quality of images obtained by an airborne optical system. A wind-tunnel experiment has been carried out in order to simulate aero-optical phenomena in transsonic and supersonic flows. The characterization of such effects is obtained by studying the propagation of a laser beam (λ : 0.63 pa) through optical aerodynamic configurations. The influences of turbulent mixing zone and shock waves have been studied. Each aerodynamical configuration has been qualified by both Schlieren visualization and wall pressure probing test. For each configuration, images are recorded and then processed to obtain point spread functions (PSF), optical transfer functions (OTF), modulation transfer function (MTF) and Wiener spectrum of the images. This study should lead to match optical and aerodynamical considerations in designing future airborne imaging systems.

Optical Fibers Application To Visualization Of Flow Separation Inside An Aircraft Intake In Wind Tunnel.

We describe an experiment to visualize air flow separation in an aircraft air-intake. This experiment was realized in a large industrial wind-tunnel. It uses optical fibers to bring a laser beam into the model and an optical fiber endoscope to visualize images of the phenomenon. Some pictures showing changes of the air flow separation are presented for several aerodynamic conditions.