Béatrice Chatel

A newcomer's guide to ultrashort pulse shaping and characterization

This tutorial gives an overview of the most widespread techniques of both ultrashort pulse shaping and pulse characterization.

Spatio-temporal focusing of an ultrafast pulse through a multiply scattering medium.

Pulses of light propagating through multiply scattering media undergo complex spatial and temporal distortions to form the familiar speckle pattern. There is much current interest in both the fundamental properties of speckles and the challenge of spatially and temporally refocusing behind scattering media. Here we report on the spatially and temporally resolved measurement of a speckle field produced by the propagation of an ultrafast optical pulse through a thick strongly scattering medium. By shaping the temporal profile of the pulse using a spectral phase filter, we demonstrate the spatially localized temporal recompression of the output speckle to the Fourier-limit duration, offering an optical analogue to time-reversal experiments in the acoustic regime. This approach shows that a multiply scattering medium can be put to profit for light manipulation at the femtosecond scale, and has a diverse range of potential applications that includes quantum control, biological imaging and photonics.

New phase and amplitude high resolution pulse shaper

We present the first realization of a femtosecond pulse shaper in phase and amplitude using two liquid crystal devices with 640 pixels, leading to a wide temporal window around 25 ps at 800 nm. Several examples illustrate the high resolution of such device. The use of a folded zero dispersion line is also successfully demonstrated.

Quantum State Measurement Using Coherent Transients

We present the principle and experimental demonstration of time resolved quantum state holography. The quantum state of an excited state interacting with an ultrashort chirped laser pulse is measured during this interaction. This has been obtained by manipulating coherent transients created by the interaction of femtosecond shaped pulses and rubidium atoms.

Robust quantum dot exciton generation via adiabatic passage with frequency-swept optical pulses.

The energy states in semiconductor quantum dots are discrete as in atoms, and quantum states can be coherently controlled with resonant laser pulses. Long coherence times allow the observation of Rabi flopping of a single dipole transition in a solid state device, for which occupancy of the upper state depends sensitively on the dipole moment and the excitation laser power. We report on the robust population inversion in a single quantum dot using an optical technique that exploits rapid adiabatic passage from the ground to an excited state through excitation with laser pulses whose frequency is swept through the resonance. This observation in photoluminescence experiments is made possible by introducing a novel optical detection scheme for the resonant electron hole pair (exciton) generation.

Factorization of Numbers with the temporal Talbot effect: Optical implementation by a sequence of shaped ultrashort pulses

We report on the successful operation of an analogue computer designed to factor numbers. Our device relies solely on the interference of classical light and brings together the field of ultrashort laser pulses with number theory. Indeed, the frequency component of the electric field corresponding to a sequence of appropriately shaped femtosecond pulses is determined by a Gauss sum which allows us to find the factors of a number.

Evaluation of infrared femtosecond laser ablation for the analysis of geomaterials by ICP-MS

The capabilities of an infrared (IR) Ti:sapphire femtosecond laser (≈800 nm) to ablate and analyze geomaterials such as monazite, zircon and synthetic glass reference materials is evaluated, with emphasis on U/Pb ratio determinations useful for dating accessory minerals in rocks. We particularly discuss the influence of pulse duration (respectively 60, 200, 350, 500, 670, 830, 2000 and 3000 fs) on the internal precision (2 min ablation), reproducibility over two weeks and accuracy of quadrupole ICP-MS measurements. The best results for all these criteria are obtained when using the shortest pulse duration (60 fs). It was found that internal precision and reproducibility were improved by a factor of 3 and 4, respectively, from picosecond to 60 fs pulsewidths. Reproducibility at this pulse duration for U/Pb ratio determinations is of 2% RSD or better, depending on the material analyzed, and this ratio is accurate within this uncertainty. Lead isotopic ratios also benefit from the shortest pulsewidth. They are measured at 60 fs with a precision (<0.5% RSD) approaching the limitations of quadrupole ICP-MS. Preliminary data were also obtained using the 3rd harmonic (≈266 nm) of the Ti:sapphire fundamental wavelength and they are compared with the infrared mode. There seems to be no obvious analytical benefit to switch from IR to UV in the femtosecond laser ablation regime. Analyses of zircon 91500 with IR pulses led to better repeatability, around 0.9% (10 values, 1σ), compared to 3% for the UV pulses. The accuracy appears to be comparable for the two wavelengths.

AOPDF-shaped optical parametric amplifier output in the visible

Time shaping of ultra-short visible pulses has been performed using a specially designed acousto-optic programmable dispersive filter of 50% efficiency at the output of a two-stage non-collinear optical parametric amplifier. The set-up is compact and reliable. It provides a tunable shaped source in the visible with unique features: a 4-ps shaping window with preserved tunability over 500–650 nm, and pulses as short as 30 fs. Several-μJ output energy is easily obtained.

Controlling the Polarization Eigenstate of a Quantum Dot Exciton with Light

We demonstrate optical control of the polarization eigenstates of a neutral quantum dot exciton without any external fields. By varying the excitation power of a circularly polarized laser in microphotoluminescence experiments on individual InGaAs quantum dots we control the magnitude and direction of an effective internal magnetic field created via optical pumping of nuclear spins. The adjustable nuclear magnetic field allows us to tune the linear and circular polarization degree of the neutral exciton emission. The quantum dot can thus act as a tunable light polarization converter.

Factoring numbers with interfering random waves

We report on the successful operation of an analogue computer designed to factor numbers. A sequence of shaped femtosecond pulses is used to implement a Gauss sum . N = 1psila340psila333psila404psila807 has been successfully factorized.