Angle and time-resolved polarization change induced by Kerr effect in amorphous and crystalline SiO2

TL;DR

This study addresses ultrafast polarization dynamics in SiO2 induced by a femtosecond pump, using time- and angle-resolved Kerr measurements in both reflection and transmission for amorphous and crystalline (α-quartz) samples. It develops two complementary models: a phase-retardation description for the transmission geometry and an anisotropic tensorial framework for reflection, with an additional piezo-photoelastic mechanism needed to explain quartz. The results show strong, pump-polarization–dependent polarization rotations well below damage thresholds, revealing distinct mechanisms in amorphous vs crystalline SiO2 and suggesting avenues for ultrafast, polarization-controlled optical components. The work provides insight into the role of retarded Kerr responses and carrier dynamics, including a connection to transient self-trapped excitons in quartz, and demonstrates how polarization-based measurements can probe ultrafast light–matter interactions beyond simple intensity-based observables.

Abstract

We measure the polarization change of a beam reflected from the surface of both crystalline alpha and amorphous SiO2 samples while they are photo-excited by an intense light pulse, at intensities above the nonlinear excitation threshold yet below the damage threshold. The polarization change varies with the angle between the polarization of pump and probe light, but is found to be independent of their orientation relative to the crystal axes. This behavior differs between the reflected and transmitted beams, and can be modeled by taking into account a birefringence induced by the electric field of the pump. These polarization-change effects can be very strong, with polarization rotation exceeding 90°, at pump intensities well below the damage threshold. We also observe a markedly different behavior of the reflected beam depending on whether the material is crystalline or amorphous.

Figures (9)

• Figure 1: Schematic representation of the experimental setup. BS (beam-splitter), DL (delay line), MC (modulating chopper), DW (density wheel), L (lense), S (sample), SH (sample holder), BB (beam blocker), F400nm (high pass filter blocking 400nm), WP (Wollaston prism).
• Figure 2: Principle of the Kerr polarisation measurements.
• Figure 3: a) Schematic representation of relative angle $\theta_{ps}$ between pump and probe polarisation on the $\alpha$-quartz sample. Here the probe is toward the 1120 axis ($\Gamma-K$). b, c, d) Time-resolved reflectivity measurement on $\alpha$-quartz at $500mJ/cm^2$ of $\Delta\theta$, the photo-induced polarisation angle change, for three values of $\theta_{ps}$ at $0^{\circ}$, $45^{\circ}$ and $90^{\circ}$. The data in green and purple are taken for two different high-symmetry orientations of the probe polarisation on the sample, namely $\Gamma-K$ (1120 axis) and $\Gamma-M$ (1210 axis).
• Figure 4: Amorphous $SiO_2$ : Symmetries of the time-resolved signals in reflection and transmission for two pump fluences at $100$ and $500mJ/cm^2$. All polar graphs have time delay for radial axis (in green), relative angle $\theta_{ps}$, for the azimuthalaxis and $\Delta\theta$ values for the colorbar. These graphs are referenced as $\Delta\theta(t,\theta_{ps})$ graphs. The registered polarisation angle change $\Delta\theta$ is scaled with blue-grey-red colors for negative-zero-positive values.
• Figure 5: $\alpha$-$SiO_2$ : Symmetries of the time-resolved signals in reflection and transmission for two pump fluences at $100$ and $500mJ/cm^2$. All polar graphs have time delay for radial axis (in green), relative angle $\theta_{ps}$, for the azimuthalaxis and $\Delta\theta$ values for the colorbar. These graphs are referenced as $\Delta\theta(t,\theta_{ps})$ graphs. The registered polarisation angle change $\Delta\theta$ is scaled with blue-grey-red colors for negative-zero-positive values.