Picosecond pulse-shaping for strong three-dimensional field-free alignment of generic asymmetric-top molecules

TL;DR

This paper demonstrates a method for achieving strong three-dimensional, field-free alignment of asymmetric-top molecules using shaped, elliptically polarized laser pulses, enabling detailed molecular imaging.

Contribution

It introduces a novel pulse-shaping technique combining chirping and phase/amplitude control to align complex molecules in 3D without external fields.

Findings

Achieved 3D alignment with .89 in .89 in .89 measure

Validated experimental results with computational simulations

Demonstrated applicability to complex asymmetric-top molecules

Abstract

Fixing molecules in space is a crucial step for the imaging of molecular structure and dynamics. Here, we demonstrate three-dimensional (3D) field-free alignment of the prototypical asymmetric top molecule indole using elliptically polarized, shaped, off-resonant laser pulses. A truncated laser pulse is produced using a combination of extreme linear chirping and controlled phase and amplitude shaping using a spatial-light-modulator (SLM) based pulse shaper of a broadband laser pulse. The angular confinement is detected through velocity-map imaging of H$^+$ and C$^{2+}$ fragments resulting from strong-field ionization and Coulomb explosion of the aligned molecules by intense femtosecond laser pulses. The achieved three-dimensional alignment is characterized by comparing the result of ion-velocity-map measurements for different alignment directions and for different times during and after the alignment laser pulse to accurate computational results. The achieved strong three-dimensional field-free alignment of $\langle \cos^{2}\delta \rangle=0.89$ demonstrates the feasibility of both, strong three-dimensional alignment of generic complex molecules and its quantitative characterization.