Birefringence based multi-focus fs/ps-CARS spectroscopy for thermometry and hyperspectral microscopy.

We present a multi-focus fs/ps-CARS scheme to perform spectroscopy on multiple points simultaneously for gas phase measurements and microscopy, using a single birefringence crystal or a combination of birefringent stacks. CARS performances are first reported for 1 kHz single-shot N2 spectroscopy on two points set few millimeters apart, allowing thermometry measurements to be carried out in the vicinity of a flame. Then, simultaneous acquisition of toluene spectra is demonstrated on two points set 14 µm apart in a microscope setup. Finally, two-point and four-point hyperspectral imaging of PMMA microbeads in water is performed, demonstrating a proportional increase in acquisition speed.

5 kHz single shot hybrid fs/ps-CARS thermometry in an atmospheric flame.

Single shot hybrid fs/ps-CARS spectroscopy of N2 is demonstrated at repetition rate up to 5 kHz using an amplified probe delivering a constant energy per pulse between 1 and 5 kHz. We performed 5 kHz CARS thermometry in a laminar CH4/air flame and in ambient air, with a precision under 0.5% at typical flame temperature, which is 2 times more precise and 5 times faster than previous state of the art with this technique. Temperature was measured during long acquisition times up to 100 s, making the system suitable to record signals in the 0.01-2500 Hz spectral window; in our case 10 Hz temperature oscillations were probed.

Ultrafast background-free ro-vibrational fs/ps-CARS thermometry using an Yb:YAG crystal-fiber amplified probe.

A novel laser system for ro-vibrational spectroscopy using coherent anti-Stokes Raman Scattering in hybrid fs/ps regime is presented. A single Yb:KGW laser source is used as a master laser to generate the three CARS laser beams, namely the pump and Stokes femtosecond pulses and a 58 ps probe pulse. Master oscillator power amplifier (MOPA) architecture is implemented to increase the probe output power using a custom two stage free space linear amplifier. The probe is 0.37 cm-1 in width and 100 µJ in energy to allow resolving the Q-branch ro-vibrational lines of N2 and recording single shot CARS spectra at kHz repetition rate in flames. An original and simple technique based on the study of the influence of probe delay and polarization has been setup to optimize nonresonant background rejection, with no loss in resonant contribution. CARS performances are reported for N2 thermometry between 300 K and 3000 K, demonstrating state of the art precision.

Imaging Aluminum Particles in Solid-Propellant Flames Using 5 kHz LIF of Al Atoms.

Laser-induced fluorescence imaging of aluminum atoms (Al-PLIF) is used to analyze the spatio-temporal behavior of aluminized solid propellant combustion. Using alternating LIF and chemiluminescence emission images of the particles in the gaseous and liquid phase evolving close to and far above the dynamically varying propellant surface, sequences of images were recorded and analyzed. The good sensitivity achieved enabled us to track the dynamics of the flame in the vicinity of particles detected all along the flame extension and up to 1.5 MPa. Analysis of wide-field images enabled droplet velocity measurements due to the high LIF sampling rate (5 kHz). The observed typical plume structures were in good agreement with alumina-formation prediction and previous shadowgraphy visualization. High-resolution sequences of images showed gaseous distribution behavior around the molten particles. The Al vapor phase was thus found to extend between 3 and 6.5 radii around the particles. Particle detachment dynamics were captured just above the propellant surface.

Multi-line fiber laser system for cesium and rubidium atom interferometry.

We present an innovative multi-line fiber laser system for both cesium and rubidium manipulation. The architecture is based on frequency conversion of two lasers at 1560 nm and 1878 nm. By taking advantage of existing high performance fibered components at these wavelengths, we have demonstrated multi-line operation of an all fiber laser system delivering 350 mW at 780 nm for rubidium and 210 mW at 852 nm for cesium. This result highlights the promising nature of such laser system especially for Cs manipulation for which no fiber laser system has been reported. It offers new perspectives for the development of atomic instruments dedicated to onboard applications and opens the way to a new generation of atom interferometers involving three atomic species (85Rb, 87Rb and 133Cs) for which we propose an original laser architecture.