Thomas Oksenhendler

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.

Single-shot, high-dynamic-range measurement of sub-15 fs pulses by self-referenced spectral interferometry.

We explore theoretically and numerically the temporal contrast limitation of a self-referenced spectral interferometry measurement. An experimental confirmation is given by characterization and fine compression of hollow-core fiber generated sub-15 fs pulses, yielding an accurately measured coherent contrast of 50 dB on a ±400 fs time range.

Carrier-envelope phase stabilization and control using a transmission grating compressor and an AOPDF

Carrier-envelope phase (CEP) stabilization of a femtosecond chirped-pulse amplification system featuring a compact transmission grating compressor is demonstrated. The system includes two amplification stages and routinely generates phase-stable (approximately 250 mrad rms) 2 mJ, 25 fs pulses at 1 kHz. Minimizing the optical pathway in the compressor enables phase stabilization without feedback control of the grating separation or beam pointing. We also demonstrate for the first time to the best of our knowledge, out-of-loop control of the CEP using an acousto-optic programmable dispersive filter inside the laser chain.

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.

Pulse-measurement techniques using a single amplitude and phase spectral shaper

We investigate, both theoretically and experimentally, the practical use of amplitude and phase pulse shapers to characterize ultrashort optical pulses. Pulse shapers greatly simplify the optical setup required for the SH-FROG and SPIDER measurement techniques, and both methods can even be implemented with a common optical layout. We also introduce, demonstrate, and compare several new interferometric variants of these techniques, which are compatible with a basic setup comprising no more than a pulse shaper, a type I second-harmonic stage, and a spectrometer.

Jitter-free subpicosecond streak cameras (invited)

We review here our recent work on a high dynamic range, subpicosecond x-ray streak camera. Our subpicosecond streak camera (PX1) has been coupled to a 10 Hz Ti: sapphire laser system and tested with 500 fs UV light pulses (266 nm) in jitter-free accumulation mode. A novel design for the photoconductive switches that are coupled to the camera’s deflection plates has been successfully used to eliminate the jitter induced by the laser intensity fluctuations and by the temporal shape of the laser beam. Results demonstrate that this detection system gives simultaneously a high dynamic range and a subpicosecond resolution at a repetition rate of 10 Hz.

In situ measurement of nonlinear carrier-envelope phase changes in hollow fiber compression

We demonstrate a simple and robust single-shot interferometric technique that allows the in situ measurement of intensity-dependent phase changes experienced by ultrashort laser pulses upon nonlinear propagation. The technique is applied to the characterization of carrier-envelope phase noise in hollow fiber compressors both in the pressure gradient and in the static cell configuration. Measurements performed simultaneously with conventional f-to-2f interferometers before and after compression indicate that the noise emerging in the waveguide adds up arithmetically to the phase noise of the amplifier, thus being strongly correlated to the phase noise of the pulses coupled into the compressor.

Self-referenced spectral interferometry for single-shot measurement of sub-5-fs pulses

We demonstrate a novel approach for the extension of self-referenced spectral interferometry to the temporal characterization of few-optical cycle pulses. The new experimental setup is characterized by low dispersion and a collinear geometry. 4-fs pulses have been characterized by performing single-shot measurements, with high dynamic range on a broad temporal region. An independent measurement of the pulse duration, obtained by using attosecond streaking, allowed us to cross-check the experimental technique.

Local Spectral Compression method for CPA lasers

Measurement of femtosecond pulses without any reference requires three successive steps: a linear filter, a non linear interaction (e.g. SHG) and a spectral measurement of the output [1]. As previously demonstrated, the linear filtering can be performed using a pulse shaper, such as an acousto-optic programmable dispersive filter (AOPDF) [2]. Since a significant number of CPA amplifiers now include a pulse shaper in their front-end, it is highly convenient to use such a device not only to correct but also to characterize the amplified pulses by adding at the back-end a nonlinear element and a spectral detector. In this paper, we demonstrate experimentally a new phase-only measurement technique called Local Spectral Compression (LSC) on a CPA laser system (CEA Saclay) by inserting an AOPDF in front of the last three-pass amplifier and a nonlinear BBO crystal at the output. The second harmonic signal is recorded with a spectral detector.

Achromatic and Single-beam Pulse Characterization Technique for Visible-UV Pulses based on direct UV Pulse Shaping and Cross-polarized Wave Generation

40 fs pulses at 397 nm are characterized by a single-beam, achromatic, programmable and self-compensated spectrally resolved interferometric autocorrelation technique based on the conjugate use of a broadband pulse shaper and crossed-polarized wave generation.