Different aspects of molecular dynamics can be understood by specifying the velocity and spatial distribution of the products, ensuing from photodissociation processes or bimolecular reactions. One method that attracted considerable interest is that of one-color velocity map imaging (VMI), which is used for probing photofragments resulting from photodissociation of jet-cooled molecules, while scanning the narrow spectral width probe beam across the Doppler profile of the resonant transition.  Here we introduced the two-color reduced-Doppler¹ (TCRD) method, which employs two counterpropagating beams at close and fixed wavelengths, for probing light and fast fragments, specifically hydrogen atoms. This technique enables to probe the entire velocity distribution of the fragments in single pulses, resulting in enhanced ionization efficiency, as well as improved sensitivity and signal-to-noise ratio, relative to that obtained in VMI.   It is anticipated that this scheme for TCRD will find a niche in measurements of H atoms and other photofragments excitation spectra, particularly when only low level signal intensities are available.

Reference

1. Enhanced sensitivity in H photofragment detection by two-color reduced-Doppler ion imaging, M. Epshtein, A. Portnov, R. Kupfer, S. Rosenwaks, and I. Bar, J. Chem. Phys. In press (2013)