Ultrafast Optical Gating by Molecular Alignment

Abstract

Field-free alignment of gaseous molecules could function as an ultrafast polarization optical gating with periodic revivals originated from quantum wakes of the impulsively excited molecular wave packets. Recent experimental explorations have revealed some unique applications of ultrafast optical gating from pre-excited molecular rotational wave packets, such as molecular-alignment-based cross-correlation frequency-resolved optical gating (M-XFROG) for ultrashort pulse characterization, and molecular-alignment-based ultrafast optical imaging and optical buffer with revivable optical storage in molecular rotational wave packets. The M-XFROG technique employs the impulsive transient alignment of gaseous molecules as a gate function to characterize the ultrashort pulse and exhibits the advantage of no phase-matching constraint and applicability to pulses at any wavelength ranging from ultraviolet to far-infrared. Ultrashort pulse meaurements of ultraviolet pulse, supercontinuum pulse, optical parametric amplifier, and multi-colored pulses were experimentally performed by using the M-XFROG technique. Ultrafast optical imaging by periodic molecular alignment was also demonstrated, involving the optical image storage in the pre-excited molecular wakes followed by periodic readout and display. For diatomic molecules in air, both raised and intagliated monochromatic images were observed with periodic revivals of aligned molecules. Ultrafast time-encoded holographic-like imaging was realized to encode the phase information of a three-demensional object in the molecular revivals. The monochromatic images could be transformed into colorful optical imaging by using a spatially chirped supercontinuum laser pulse to chromatically encode the stored images with different colors at different delays with respect to the molecular alignment revivals.