Abstract
In this paper we describe a new technique for the generation of multiple pulse phase coherent sequences in optical spectroscopy. The technique is an extension of the acousto-optic modulation and fluorescence detection methods developed for optical transitions by Zewail and Orlowski (Zewail et al., Chem. Phys. Lett.48, 256 (1977); Orlowski et al., Chem. Phys. Lett.54, 197 (1978)). Application of these multiple pulse trains (of different phases) to optical transitions of two-level and multilevel systems is demonstrated experimentally. It is shown that they can be used to (i) suppress spontaneous emission background, (ii) enhance coherent transients such as photon echoes, (iii) measure additional relaxation parameters in systems with complex rotational-vibrational levels, and (iv) enhance the effective laser bandwidths through composite pulse trains, as demonstrated on I2 gas. Finally, the potential of this development is extended to the possibility of observing selective multiquantum excitation in molecules.
Highlights
INTRODUCTIONA molecule which is irradiated with intense coherent pulses (for example, from a laser) can absorb energy and coherently reradiate it
A molecule which is irradiated with intense coherent pulses can absorb energy and coherently reradiate it
We have shown in recent papers[29,30,31,32,33] that the strong mathematical similarities between coherent effects in NMR or optical spectroscopy imply that laser analogs of these multiple pulse sequences will be extremely valuable as probes of energy transport, dephasing mechanisms, and collisional dynamics
Summary
A molecule which is irradiated with intense coherent pulses (for example, from a laser) can absorb energy and coherently reradiate it. Electronic or vibrational transitions can be treated (in the semiclassical limit)) as fictitious "spin flips, ’’5’6 and laser pulse sequences analogous to those derived for NMR have been used to measure T1, T2 and the transition dipole moment [ix[ for these transitions These parameters are in principle sufficient to completely characterize any two-level system, so simple laser pulse sequences have frequently been used to study energy transfer,[7,8,9] collision effects, 1-12 and laser propagation in optically dense media. We have shown in recent papers[29,30,31,32,33] that the strong mathematical similarities between coherent effects in NMR or optical spectroscopy imply that laser analogs of these multiple pulse sequences will be extremely valuable as probes of energy transport, dephasing mechanisms, and collisional dynamics. Optical transitions often display long-range inhomogeneities which are greater than the available laser pulse bandwidth (Rabi frequency2), so only the central portion of the lineshape is properly refocused. In each part the fluorescence after the final weak pulse, minus the fluorescence produced when the final pulse is phase shifted by 180 is the observed signal ZEWAWA sequence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
