Pierre Tournois

Amplitude and phase control of ultrashort pulses by use of an acousto-optic programmable dispersive filter: pulse compression and shaping

We demonstrate experimentally that an arbitrary phase and amplitude profile can be applied to an ultrashort pulse by use of an acousto-optic programmable dispersive filter (AOPDF). Our filter has a large group-delay range that extends over 3 ps and a 30% diffraction efficiency over 150 THz. Experiments were conducted on a kilohertz chirped-pulse amplification laser chain capable of generating 30-fs pulses without additional pulse shaping. Compensating for gain narrowing and residual phase errors with an AOPDF in place of the stretcher results in 17-fs transform-limited pulses. Arbitrary shaping of these 17-fs pulses is also demonstrated in both the temporal and the spectral domains.

Acousto-optic programmable dispersive filter for adaptive compensation of group delay time dispersion in laser systems

Abstract It is demonstrated in this communication that using an acousto-optic interaction in an anisotropic birefringent medium it is possible to produce a chirped optical signal reproducing an original acoustic signal. This acoustic signal can then be used to generate a pre-distorted optical signal at the input of a laser chain to compensate for group delay time dispersions within the chain. The first experiments achieved with such a device are reported.

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.

Ultraviolet acousto-optic programmable dispersive filter laser pulse shaping in KDP

An acousto-optic programmable dispersive filter pulse shaper has been designed using KDP material for operation in the 200-500 nm wavelength range. With an acousto-optic interaction length of 72 mm, a spectral resolution of 0.15 nm has been measured to be consistent with theoretical predictions. Theory and experiments indicate that diffraction efficiencies up to 50% are expected in practical experimental conditions.

Time-domain interferometry for direct electric-field reconstruction by use of an acousto-optic programmable filter and a two-photon detector

We introduce a new approach to the characterization of femtosecond optical pulses based on a remarkably simple setup combining a two-photon detector and a pulse shaper consisting of a longitudinal acousto-optic programmable filter. The operation of this setup is demonstrated through the use of a new version of spectral phase interferometry for direct electric-field reconstruction based on time-domain instead of on frequency-domain interferometry.

Superluminal asymptotic tunneling times through one-dimensional photonic bandgaps in quarter-wave-stack dielectric mirrors

It is shown that the time needed for light to pass through the optical barrier associated with an antiresonant quarter-wave-stack dielectric mirror, as measured by the group-delay, or phase time, asymptotically reaches a limit that is independent of the barrier thickness and hence of the number of layers. This limit, which scales as the inverse of the refractive-index difference between successive layers, is equal to the mean value of the asymptotic group delays needed for light to reflect off each side of the barrier. This superluminal transmission does not violate causality, as the transmitted intensity is always lower than the intensity that would have been transmitted in vacuum in the absence of the barrier.

Negative group velocities in metal-film optical waveguides

Abstract It is demonstrated that the group velocity of the frustrated transverse magnetic modes in an optical waveguide including a metal is negative when the power flow inside the metal is larger than the power flow inside the dielectric medium, while the phase velocity remains positive. The energy and the phase are then contrapropagating.

Direct mid-infrared femtosecond pulse shaping with a calomel acousto-optic programmable dispersive filter

Direct amplitude and phase shaping of mid-infrared femtosecond pulses is realized with a calomel-based acousto-optic programmable dispersive filter transparent between 0.4 and 20 μm. The shaped pulse electric field is fully characterized with high accuracy, using chirped-pulse upconversion and time-encoded arrangement spectral phase interferometry for direct electric field reconstruction techniques. Complex mid-infrared pulse shapes at a center wavelength of 4.9 μm are generated with a spectral resolution of 14 cm(-1), which exceeds by a factor of 5 the reported experimental resolutions of calomel-based filters.

Grism compressor for carrier-envelope phase-stable millijoule-energy chirped pulse amplifier lasers featuring bulk material stretcher.

We demonstrate compression of amplified carrier-envelope phase (CEP)-stable laser pulses using paired transmission gratings and high-index prisms, or grisms, with chromatic dispersion matching that of a bulk material pulse stretcher. Grisms enable the use of larger bulk stretching factors and thereby higher energy pulses with lower B-integral in a compact amplifier design suitable for long-term CEP control.

Chirped-mirror pairs for ultra-broadband dispersion control

Summary form only given. Since their recent introduction by Szipocs et al. dispersion controlled mirrors (DCM) or chirped mirrors have proved to be essential devices for the production of ultra-short pulses directly from the oscillator, and more generally for many aspects of femtosecond laser sources. Further reduction of the pulse duration is still expected for such oscillators, as the whole gain bandwidth of Ti:sapphire has not been utilized yet. Simultaneously, progress in femtosecond optical parametric amplification (OPA) has made possible the production of tunable sub-10-fs pulses in the visible and near infrared.