Femtosecond laser-induced circular dichroism in silica: Dependence on energy and focusing depth

The paper addresses the creation of strong circular dichroism from a femtosecond laser light with a linear polarization strongly focused in silica glass and perpendicular incidence. All aspects of the experiment are therefore achiral and should not give rise to chiral property creation if taken themselves alone. We investigate the laser-induced circular dichroism according to orientation of the laser polarization, pulse energy and focusing depth. It appears that deep focusing under high numerical aperture conditions leads to higher ellipticity when compared to shallow focusing or low numerical aperture focusing. Strong circular dichroism can be imprinted when polarization is at ±45° of the horizontal scanning direction in reference to the laser plan. In addition the generation of circular dichroism appears to be closely related to the spatial aberration, spatial chirp and beam elongation under strong focusing conditions.