The first hyperpolarizability of the aromatic amino acid Tyrosine has been obtained by Hyper Rayleigh Scattering (HRS) in aqueous environment and under non resonant conditions. The rather large value determined is in agreement with previous HRS studies and confirms that Tyrosine can be targeted as an endogenous molecular probe for the second harmonic studies of biological molecules. The same experiment was also performed in an aqueous environment containing 20 nm diameter gold metallic nanoparticles. The resulting first hyperpolarizability measured with the fundamental wavelengths of 815 nm and 1050 nm in these conditions for Tyrosine is reduced as compared to that obtained in absence of metallic nanoparticles.
The Second Harmonic Generation (SHG) response from Tyrosine-containing peptides at the air-water interface is presented. First, the quadratic hyperpolarizability of the aromatic amino acid Tyrosine obtained by Hyper Rayleigh Scattering is reported, demonstrating its potentiality as an endogenous molecular probe for SHG studies. Then, the single Tyrosine antimicrobial peptide Mycosubtilin is monitored at the air-water interface and compared to another peptide, Surfactin, lacking a Tyrosine residue. Adsorption kinetics and polarization analysis of the SHG intensity for the peptide monolayers clearly demonstrate that the SHG response from Mycosubtilin arises from Tyrosine. Besides, it confirms that indeed Tyrosine can be targeted as an endogenous molecular probe.
Second Harmonic Generation was used to study the optical properties of molecular films formed at the air-water
interface. The technique was first applied to a two-dimensional film of 4-(4-dihexadecylaminostyryl)-N-methylpyridinium
iodide (DiA) formed at the air-water interface in a Langmuir trough. The SHG intensity was measured
as a function of the incident fundamental and outgoing harmonic wave polarization angles at different states of the
monolayer compression. The film revealed chirality arising from the formation of molecular aggregates and it was
demonstrated that this chirality property arose from the coupling of the electric and magnetic fields at the fundamental
frequency. In a second stage, we applied the SHG technique to follow the emergence of chirality during the compression
of a molecular film of the amphiphilic compound 5-(octadecyloxy)-2-(2-thiazolylazo) phenol (TARC18). A similar
behavior was observed and it was shown that the same origin was responsible for the appearance of chirality.
Polarization resolved intensity measurements demonstrated that the magnetic dipole contribution was the dominant one.
The initiation and propagation of a filament generated by ultrashort laser pulses in both fog and turbulent air is
investigated experimentally. Filaments can propagate through dense fog, supported by the surrounding photon bath,
which is transmitted and re-feeds the filament after he diffracts on a water droplet. Filaments can can also be generated
and propagated even after the beam has propagated through strongly turbulent regions, with structure parameters Cn2 up to 5 orders of magnitude larger than encountered in usual atmospheric conditions. Moreover, the filament position within
the beam is not affected by the interaction with a turbulent region. This remarkable stability is allowed by the strong Kerr
refractive index gradients generated within the filament, which exceed the turbulence-induced refractive index gradients
by 2 orders of magnitude.
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