Expérimental
Circular dichroism (CD) is the property of chiral molecules to absorb differently left- and right-circularly polarized light. CD spectroscopy is a very popular technique for analyzing the secondary structure of biomolecules at equilibrium in solution. However, despite the conceptual simplicity of static measurements, their transposition to the time domain (TRCD), especially on the sub-picosecond time scale, remains challenging due to their weak signals prone to pump-induced polarization artifacts. Recently we have developed a simple and robust method allowing simultaneous measurement of the intensity variation of the two circular polarization components of linearly polarized probe pulses. This balanced detection geometry allows femtosecond TRCD signals to be recovered from a single laser shot, which significantly increases S/N ratio and reduces the acquisition times. The objective of this internship will aim at implementing this detection over an extended spectral region spanning the visible down to the deep-UV and then to test its potentiality for the measurements of relevant chiral model systems. In this respect, a commercial 1kHz amplified Ti:sa laser source delivering 800-nm pulses of 100-fs duration will be used. Pump and probe will be generated from the combination of optical parametric amplification, sum frequency generation and second harmonic generation, allowing a tunability over 220 nm up to 700 nm.