Postpulse Molecular Alignment Measured by a Weak Field Polarization Technique

Abstract

We report a direct nonintrusive observation of alignment and planar delocalization of CO2 after an intense linearly polarized femtosecond laser pulse excitation. The effects are measured by a polarization technique involving a perturbative probe that itself does not induce appreciable alignment. We show that this technique allows one to measure a signal proportional to <cos((2)theta>-1/3, with theta the angle between the molecular axis and the laser polarization. Simulations that support this analysis allow one to characterize the experimentally observed alignment and planar delocalization quantitatively.

Excitation of rotons in parahydrogen crystals: The laser-induced-molecular-alignment mechanism

“…The expression is the same as derived by Renard et al, 65 except for cos 2 φ instead of sin 2 φ. However, the trace operation removes the φ-dependence in the gas phase, and one obtains…”

Suppression of plasma contribution in femtosecond degenerate four‐wave mixing (fs‐DFWM) at high intensity

“…Although both effects are responsible for the alteration of the transients, the most apparent feature is the modification of the transient shape due to the interaction with the permanent alignment. 5,11 In Refs 7-9, the appearance of a strong background was observed with increasing intensity. A part of this background was due to a permanent alignment as mentioned above.…”

“…1 When short laser pulses are used, post-pulse periodic molecular realignment occurs after the pump extinction which is measured either by combining ionization-fragmentation of molecules with an imaging technique [1][2][3][4] or by using nonlinear optical properties of the molecular sample. 5,6 In the last case, the polarization state and the spatial profile of a probe pulse is perturbed as a consequence of alignment. More precisely, the refractive index shows a time-dependent nonlinear variation due to alignment.…”

“…More precisely, the refractive index shows a time-dependent nonlinear variation due to alignment. 5,6 Measuring the perturbation as a function of the delay between the aligning pulse and the probe one enables us to quantify the degree of alignment. Transients grating or degenerate four-wave mixing (DFWM) experiments can be also performed to explore molecular alignment.…”

Formation of coherent rotational wavepackets in small molecule-helium clusters using impulsive alignment

“…Laser-induced impulsive alignment can be applied to all molecules with an anisotropy of polarisability. While initially, studies were performed in small linear molecules 4,19,20 , 1D and 3D impulsive alignment of complex, asymmetric top molecules has been demonstrated [21][22][23][24][25] . Control over molecular alignment has enabled the investigation of processes such as strong field ionisation 26,27 , high harmonic generation [28][29][30] , gas-phase X-ray 31 and (photo-)electron diffraction experiments 31,32 .…”