Frédéric Louradour

Spectro-temporal imaging of femtosecond events

We demonstrate a new technique for the direct, real-time, femtosecond scale temporal measurement based on the conversion of temporal information to the spectral domain. The potential of the method has been experimentally investigated with an optical fiber spectral compressor device, first stretching and up-chirping the pulses in a prism dispersive delay line, and afterwards compensating the induced chirp by means of cross-phase modulation in a single-mode fiber. Spectro-temporal imaging (STI) reduces the problem of high-resolution temporal measurements to standard spectrometry.

Development of a versatile multiphoton microendoscope for in vivo deep-tissue label-free biomedical imaging

We report the optimization of a miniaturized multiphoton endomicroscope enabling high resolution label-free in vivo imaging of deep cellular and tissular intrinsic constituents at the output of a very long and flexible custom-designed optical fiber.

Passive mode locking of a flash lamp Nd:YAG laser with nonlinear rotation polarization in type II frequency doubling crystal

We report an experimental study of passive mode-locking of a flash-pumped Nd:YAG laser using for the first time a non- linear polarization rotation effect in a type II crystal cut for second harmonic generation. The mode-locking regime is self-starting and produces pulses of 20 ps duration with more than 100 uj per pulse. We developed a numerical model to calculate laser pulse steady-state temporal profile as a function of group velocity mismatch between fundamental and second harmonic pulses and group velocity dispersions in the nonlinear crystal. It takes also into account on laser medium and resonator characteristics insuring perfect second order dispersion compensation during one round trip in the cavity.

Diode-pumped solid state laser sources of picosecond UV pulses for photobiology

We realized three different configurations for the production of picoseconds pulses in the UV by a diode-pumped solid-state laser. The first one is based on a diode-pumped Cr:LiSAF oscillator delivering tunable picosecond pulses in the near infrared. A Ti:Sapphire regenerative amplifier increased IR pulses energy up to 4.5 (mu) J. After doubling and tripling in two LBO crystals, we obtained pulses with an energy up to 0.14 (mu) J tunable between 273 and 286 nm. In the second scheme, based on a modelocked Nd:YAG laser, the SHG (KTP) and SFG (LBO) crystals are both inserted inside the cavity. The laser operated in a Q-switched mode-locked regime and produced 1.2 mW of UV average power in pulse of 60 picoseconds duration and 4 W peak power. In the last architecture, we used a resonant enhancement with a ring- cavity. We obtained 54% conversion efficiency in the green for picoseconds pulses at 1064 nm at 100 MHz rep. rate. A special arrangement was implemented for compensation of the birefringence and walk-off of the KTP crystal in the resonant cavity. Conversion to UV in the same cavity is in progress.