A. Migus

Generation of spatially incoherent short pulses in laser-pumped neodymium stoichiometric crystals and powders

We have developed mirrorless quasi-monochromatic laser sources made of stoichiometric neodymium compounds (Nd0.75:La0.25P4O15 and NdCl3· 6H2O) pumped by nanosecond laser pulses. We find that short subnanosecond and narrow-bandwidth (0.15-nm) pulses are generated in both compounds when they are pumped at high intensities. This emission is spatially incoherent as shown by a speckle statistics analysis. Its origin is discussed in terms of collective effects. This shows that poor optical materials with strongly quenched emission may be useful for generating incoherent short pulses.

Generation of ultrabroadband femtosecond pulses in the mid‐infrared by optical rectification of 15 fs light pulses at 100 MHz repetition rate

Quasi‐single‐cycle near‐infrared light pulses with a measured spectrum extending from 7 to 15 μm have been generated, opening up new perspectives in IR spectroscopy. The method is based on the rectification of 0.8 μm 10–15 fs light pulses from a 100 MHz oscillator, using the instantaneous second‐order polarizability of bulk semiconductors such as GaAs.

Generation of high-peak-power tunable infrared femtosecond pulses in an organic crystal: application to time resolution of weak infrared signals

High-intensity femtosecond pulses tunable in the 0.8–1.6-μm range have been generated by parametric amplification of a continuum white light in a new organic crystal, N-(4-nitrophenyl)-L-prolinol (NPP). The traditional concept of noncritical phase matching was revised in view of requirements linked to the observation of ultrafast subpicosecond nonlinear phenomena. The notions of θ (noncritical) and λ (noncritical) phase matching are introduced together with their applications. An experimental determination of phase-matching curves for both second-harmonic generation and three-wave mixing has been carried out. A θ noncritical phase-matching configuration for second-harmonic generation at 1.15 μm and a quasi-λ noncritical phase-matching configuration in the near IR for three-wave mixing were evidenced. Frequency and pump-intensity dependences of the gain have also been studied. Parametric emission at degeneracy was observed, with the emitted bandwidth extending from 1.0 to 1.4 μm. Time resolution of the amplified signal has been carried out by cross correlating the pump with the incoming signal, evidencing a reduced time broadening of the interacting pulses; a new spectroscopic method with subpicosecond time resolution is derived from the previous nonlinear optical characterization experiments by replacing the IR continuum from the water cell by any sample emitting in the same frequency range. This method, termed parametric amplification and sampling spectroscopy, was used for temporal analysis of amplified and emitted infrared signals generated in an NPP crystal.

Generation of 50-TW femtosecond pulses in a Ti:sapphire/Nd:glass chain

Femtosecond pulses in the 50–60-TW power range have been generated at 1064 nm by using the chirped-pulse-amplification technique applied to a Ti:sapphire/Nd:silicate glass (90-mm output aperture) power chain. We have identified the spectral gain narrowing to be one of the main issues, and we show how to solve it.

Arbitrary dispersion control of ultrashort optical pulses with acoustic waves

Acousto-optic programmable dispersive filters (AOPDF) can compensate in real time for large amounts of group-delay dispersion. This feature can be used in chirped-pulse amplification femtosecond laser chains to compensate adaptively for dispersion. An analytical expression relating the group delay at the output of the AOPDF to the input acoustic signal is obtained with coupled-wave theory in the case of collinear and quasi-collinear bulk acousto-optic interactions and also in the case of planar waveguides and optical fibers. With this relation, the acoustic signal that will induce an arbitrary group-delay variation with frequency can be easily obtained. Numerical simulations are shown to support the principle of arbitrary group-delay control with an AOPDF.

Femtosecond spectroscopy with high-power tunable optical pulses

Femtosecond techniques permitting the generation of intense optical pulses tunable from the near UV to the near IR are presented. Implications for chemistry, biology, and solid-state physics are discussed. Specific cases are developed for applications such as the comparison of time-resolved polarization and absorption studies in photoexcited GaAs or malachite green in water.

Efficient generation of narrow-bandwidth picosecond pulses by frequency doubling of femtosecond chirped pulses

We demonstrate efficient generation of picosecond narrow-bandwidth pulses by frequency mixing of broadband opposite chirped pulses in a type I doubling crystal. This procedure allows us to produce picosecond pulses that are perfectly synchronized with femtosecond pulses. The experiment shows a decrease of the initial bandwidth by a factor of more than 30, while a high conversion efficiency is maintained.

Temporal aberrations due to misalignments of a stretcher-compressor system and compensation

Sensitivity of alignment is one of the major issues in the stretcher-compressor devices used for chirped pulse amplification. In this paper we discuss the temporal aberrations induced by the different kinds of misalignments of the gratings and we emphasize the importance of spatially transverse effects. We discuss simple criteria for minimizing these faults. Finally, we introduce the basic principles of self-compensation and present such a set-up based on symmetry considerations. >

ONE-PICOSECOND OPTICAL NOR GATE AT ROOM TEMPERATURE WITH A GaAs-AlGaAs MULTIPLE-QUANTUM-WELL NONLINEAR FABRY-PEROT ETALON.

The speed of a GaAs‐AlGaAs optical logic gate is time resolved using a 100‐fs laser system. It shows that the gating operation can be performed in ≂1 ps, the fastest reported for such a low‐energy optical device. The lowest incident switching for such a device is ≲3 pJ.

Optoelectronic sampling in the picosecond range

Abstract We describe a sampling technique utilizing an Auston switch to determine the time response of a fast oscilloscope, and to resolve the impulse response of two fast photodiodes.