The Optical Spectroscopy of Solids (OSS) group (Institut Pascal UMR 6602 UCA/CNRS - Clermont-Ferrand) has developed an internationally recognized expertise in the field of optical spectroscopy of semiconductor nanostructures and more particularly in the field of exciton-polaritons in microcavities or waveguides which are at the basis for the optical components of the future. This research team masters the analysis of optical properties of nanostructures at the femtosecond scale and aims to develop time-resolved nonlinear optical studies under high excitation. Actually, the optical spectroscopy experimental platform is based on various excitation laser sources (continuous, quasi-continuous (Q-switched type) and femtosecond). The actual femtosecond setup, associated with an ultra-fast detection system (streak camera with a resolution of one picosecond) enables to study the dynamics of optical transitions at the picosecond scale. However, the latter only delivers pulse energies of a few nano-joules, which strongly limits its use for nonlinear optics experiments.
In order to increase the potential of the actual experimental platform and to access pulse energies greater than ten micro joules (in a wide range of wavelengths ranging from the visible to the ultraviolet), the team will acquire a new more powerful femtosecond setup consisting mainly of a power pump femtosecond laser associated with an optical parametric amplifier (OPA). The targeted temporal resolution of the “pump-probe” measurements that we propose to implement with this new equipment is only governed by the laser pulse duration and not by the bandwidth of the photodetectors or signal acquisition electronics. These pump-probe measurements therefore require a tunable laser source emitting pulses of around a hundred femtosecond duration at most. This setup will allow to study the dynamics of quantum phenomena which occur on time scales less than a picosecond and which govern the operation of new optoelectronic components; applications could ultimately concern quantum cryptography and communication with levels of transmission security never before achieved.
The recruited candidate will perform the installation of the new experimental set-up to carry out nonlinear optical pump-probe experiments resolved in time at the femtosecond scale

- Firstly, he will carry out preliminary study and technological monitoring work on “pump-probe” optical experiments under femtosecond excitation to determine the optimal architecture of the new set-up and its insertion in the actual experimental platform. He will also lead a reflexion about the choice and implementation of an optimal detection method for the measuring the differential reflectivity signal as function of time.
- He will be then in charge of (i) the reception of the new equipment, (ii) the installation of the femtosecond laser with its optical parametric amplifier for tunability in wavelength of the “pump” beam, (iii) the generation of the white light continuum up near ultraviolet (320nm) for the “probe” beam and (iv) the management of the detection system.
- He will then participate in the first “pump-probe” experiments on existing semiconductor nanostructures based on GaN and ZnO. The latters will enable to confirm and refine previous experimental results already obtained from quasi-
continuous spectroscopy results and linked to the modification of the optical properties of these structures under strong excitation. A quick publication of the first results is expected.

The person recruited will be assigned to the Institut Pascal's PHOTON axis, and more specifically to the Solids Spectroscopy Operation (OSS), which conducts research on materials and nanostructures based on large-gap semiconductors such as GaN, (Al,Ga)N and ZnO. In addition to the spectroscopy experiments at its disposal (ellipsometry, photoluminescence, reflectivity, transmission, femto-second spectroscopy and spatially resolved spectroscopy), the team has developed its expertise mainly in the following two directions: - non-linear four-wave degenerate mixing optics experiments in the UV range, - micro-photoluminescence experiments to study single objects of micro- or nano-metric size.