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Univ. Paris-Saclay

Sujet de stage / Master 2 Internship

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Temporal characterization of attosecond electron dynamics in crystals for petahertz electronics

Contact: BOUTU Willem, , willem.boutu@cea.fr, +33 1 69 08 51 63
Summary:
The internship aims at studying ultrafast electron dynamics in semiconducting crystals during their interaction with a strong femtosecond laser. More specifically, the objective will be to obtain the attosecond temporal structure of the resulting emission, direct signature of those dynamics.
Possibility of continuation in PhD: Oui
Deadline for application:31/05/2021

Full description:
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 up to now. 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 precisely know the dynamics of the electrons, in particular by differentiating the intra and inter band processes. However, the spectral domain of this radiation (in the extreme ultraviolet domain, i.e. between 100 and a few 10s nm) complicates this measurement. Based on the expertise of the Attophysics group from LIDYL [2,3], the aim of the internship will be to perform temporal characterization of the emission using the RABBITT technique, adapted to the specificity of high order harmonic generation in crystals. Moreover, we will study electron dynamics in strongly correlated materials, where correlations between electrons dictate the global properties. More specifically, VO2 crystals have a reversible ultrafast metal to insulator phase transition that can be optically addressed. This additional degree of freedom and of control makes this type of crystals serious candidates for the future smart devices for petahertz electronics. The temporal characterization of the harmonic emission will allow us to study this specific 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)
Technics/methods used during the internship:
XUV optics, RABBITT, photoelectron spectroscopy

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