Sujet de stage / Master 2 Internship

The aim of this internship is to install and test a new experimental setup to measure the spectral phase of the laser high order harmonic generation radiation resulting from the interaction between femtosecond laser pulses and semiconducting crystals, in the deep ultraviolet spectral range, inaccessible to standard detectors.

Using light to control the motion of electrons in a semiconducting crystal opens the way towards petahertz optoelectronics, which would relies on electronic devices switching 1000 times faster than the current fastest transistors. In a semiconducting or dielectric crystal, the excitation of electrons from the valence to a conduction band generate charge carriers, which can carry electric current in electronic devices. Using intense laser light, those carriers can be accelerated in the different electronic bands in a controllable and reversible way. By shaping the laser electromagnetic field at the optical cycle level, these processes can be controlled at the attosecond time scale (1 attosecond = 10-18 second).

When those electrons accelerate in the strong laser field inside the conduction bands or recombine towards the valence band, a short wavelength radiation is emitted. In the spectral domain, this coherent radiation consists in successive high order harmonics of the incident radiation [1]. In the temporal domain, this corresponds to the emission of ultrashort pulses, in the attosecond scale, although this measurement has not been performed yet. The harmonic emission is a direct consequence of the electron dynamics in the laser field. The temporal characterization of the emission would therefore allow to know precisely the dynamics of the electrons, in particular by differencing the intra and inter band processes. However, the spectral domain of this radiation (in the vacuum ultraviolet (VUV, 200-120 nm) and the extreme ultraviolet (EUV, 120-50 nm) domains) complicates this measurement. The DICO group from LIDYL has the expertise for this measurement in the EU [2,3], but the VUV range has not been accessible up to now. The aim of the internship will be to modify an electron time of flight spectrometer to gain access to this spectral range, and to integrate this tool in an experimental setup for temporal characterization through the RABBITT technique [2]. The first tests will be performed in usual semiconducting crystals. Depending on the progress, samples with strong electronic correlations may be studied. Indeed, temporal characterisation of the harmonic emission will enable the study of their specific electron dynamics.
This internship will take place in the NanoLight facility, a brand new laboratory of the Attophysics group, equipped with a new OPCPA laser system that delivers intense ultrashort pulses of just a couple optical cycle duration at a 100kHz repetition rate, in the near infrared spectral domain.

[1] Ghimire et al., Nature Physics 7, 128 (2011)
[2] Mairesse et al., Sciences 302, 1540 (2003)
[3] Boutu et al., Nature Physics 4, 545 (2008)