Laurent Lefort

Efficient coherent combining of widely tunable fiber lasers

We have experimentally demonstrated coherent combining of 2 and then 4 fiber lasers, with respectively 99% and 95% combining efficiency. The combining method investigated here is based on a multi-arm resonator of interferometric configuration. In spite of its interferometric nature, the multi-arm laser operates without significant power fluctuations, even in an unprotected environment. This occurs when the arm length difference is large enough to introduce spectral modulations of period smaller than the laser bandwidth. We have also experimentally shown that the combining method is compatible with wavelength tuning. A Mach- Zehnder Fiber Laser was tuned over a wide spectral range of 60nm. Theoretically then, we confirm that the combining method can be scaled to a large number of lasers without decreasing the combining efficiency.

Spatial trapping of short pulses in Ti-indiffused LiNbO(3) waveguides.

We show numerically and experimentally that spatial trapping can be induced in quadratic media even if the pump pulses duration is shorter than the group-delay mismatch between fundamental wave and second-harmonic components. The influence of phase mismatch and pulse power on the trapping effect is discussed. Spatial, temporal, and spectral behaviors that accompany self-trapped propagation are highlighted.

High-energy femtosecond pulses from an ytterbium-doped fiber laser with a new cavity design

A new architecture which is based on the chirped pulse amplification scheme is proposed to increase the pulse energy of the mode-locked fiber laser. The idea was applied to a passively mode-locked laser using an ytterbium (Yb/sup 3+/)-doped double-clad silica fiber. Mode-locking was achieved by nonlinear polarization evolution associated to frequency-shifted feedback technique for self-starting. A compressor and a stretcher, based on diffraction gratings, permitted us to manage the dispersion and to reduce the pulse power in the fiber. The laser delivered chirped pulses at 1050 nm with 11.8-nJ energy at a 9.3-MHz repetition rate (110-mW average power) which were subsequently compressed to 196-fs duration.

Highly stable 68-fs pulse generation from a stretched-pulse Yb/sup 3+/-doped fiber laser with frequency shifted feedback

We report on the development of a passively mode-locked and highly-stable stretched pulse laser based on Yb/sup 3+/-doped silica fiber. Mode-locking is achieved by nonlinear polarization evolution coupled with the frequency-shifted feedback technique for ensuring robust self-starting. The Fabry-Perot (F-P) cavity incorporates also a diffraction grating pair to compensate for the normal dispersion of the fiber. The laser generates chirped pulses with energies of 100 pJ at a repetition rate of 23 MHz (2.3 mW average power) around 1055 nm which were subsequently compressed to near-bandwidth-limited pulses of 68 fs duration.

Generation of quadratic spatially trapped beams with short pulsed light

We report a numerical and experimental investigation on the generation of spatial self-narrowed beams with short temporal pulsed excitation in quadratic film waveguides. The impact of temporal group-velocity mismatch between the quadratic multiple interacting signals is shown. We accurately studied the spatial, temporal and spectral signals dynamics versus pulse power and phase mismatch. We show that spatial self-trapping can be induced even if the pump pulse duration is significantly shorter than the group delay mismatch between interacting waves for large enough positive phase mismatches.

Mid-infrared laser source with high average power and high repetition rate

An amplified passively Q-switched laser at 35kHz pumps an optical parametric generator to generate 1.5W around 1.5μm. Proper control of thermal lensing due to absorption of idler beam is critical for power scaling.

Adaptive spectral selection of a super continuum source using optical MEMS for biomedical diagnosis

We present an innovative approach for digital selection of precise spectral regions from a super-continuum beam using an array of electrostatically-actuated micro-mirrors. The device allows spectral and temporal encoding of selected spectral bands.

High Repetition Rate, High Average Power, Mid-Infrared Laser

An optical parametric generator pumped by an amplified passively Q-switched laser at 35kHz generates 1.5W around 1.5µm. Management of thermal lensing due to residual absorption of idler beam is critical for power scalability

Self-trapping of short pulses in Ti:PPLN waveguides at 1550 nm

We experimentally and numerically studied the excitation of quadratic spatially self-trapped beams in a Ti:PPLN film waveguide in presence of large group velocity mismatch.

Highly stable 68 fs pulse generation from a stretched pulse Yb/sup 3+/ doped fibre laser with frequency shifted feedback

We report on the development of a passively mode-locked and highly-stable stretched pulse laser based on Yb/sup 3+/-doped silica fiber. Mode-locking is achieved by nonlinear polarization evolution coupled with the frequency-shifted feedback technique for ensuring robust self-starting. The Fabry-Perot (F-P) cavity incorporates also a diffraction grating pair to compensate for the normal dispersion of the fiber. The laser generates chirped pulses with energies of 100 pJ at a repetition rate of 23 MHz (2.3 mW average power) around 1055 nm which were subsequently compressed to near-bandwidth-limited pulses of 68 fs duration.