Two-color resonant four-wave mixing (RFWM) shows great promise in a variety of double- resonance applications in molecular spectroscopy and chemical dynamics. One such application is stimulated emission pumping (SEP), which is a powerful method of characterizing ground-state potential energy surfaces in regions of chemical interest. We use time-independent, diagrammatic perturbation theory to identify the resonant terms in the third- order nonlinear susceptibility for each possible scheme by which two-color RFWM can be used for double-resonance spectroscopy. After a spherical tensor analysis we arrive at a signal expression for two-color RFWM that separates the molecular properties from purely laboratory-frame factors. In addition, the spectral response for tuning the DUMP laser in RFWM-SEP is found to be a simple Lorentzian in free-jet experiments. We demonstrate the utility of RFWM-SEP and test our theoretical predictions in experiments on jet-cooled transient molecules. In experiments on C3 we compare the two possible RFWM-SEP processes and show that one is particularly well-suited to the common situation in which the PUMP transition is strong but the DUMP transitions are weak. We obtain RFWM-SEP spectra of the formyl radical, HCO, that probe quasibound vibrational resonances lying above the low threshold for dissociation to H+CO. Varying the polarization of the input beams or PUMP rotational branch produces dramatic effects in the relative intensities of rotational lines in the RFWM-SEP spectra of HCO; these effects are well described by our theoretical analysis. Finally, RFWM-SEP spectra of HCO resonances that are homogeneously broadened by dissociation confirm the predicted lineshape and give widths that are in good agreement with those determined via unsaturated fluorescence depletion SEP.
Vibrational overtone excitation of single rovibrational eigenstates followed by laser-induced fluorescence (LIF) detection of the collisionally populated quantum states in single collision conditions provides a method for directly measuring state-to-state rotational and vibrational energy transfer rates in highly vibrationally excited acetylene. There are several advantages in collecting the data in vibrational overtone excitation spectra with LIF detection (scanning excitation laser wavelength with probe laser wavelength fixed) rather than collecting LIF excitation spectra (scanning the probe laser wavelength with the excitation laser wavelength fixed) of the collision-induced transitions. We compare the spectra produced by these two methods and use the technique to acquire a spectrum of state-to-state vibrational energy transfer in single collision conditions as well.
Conference Committee Involvement (9)
Dimensional Optical Metrology and Inspection for Practical Applications VII
18 April 2018 | Orlando, FL, United States
Dimensional Optical Metrology and Inspection for Practical Applications VI
13 April 2017 | Anaheim, CA, United States
Dimensional Optical Metrology and Inspection for Practical Applications V
20 April 2016 | Baltimore, MD, United States
Dimensional Optical Metrology and Inspection for Practical Applications IV
20 April 2015 | Baltimore, MD, United States
Dimensional Optical Metrology and Inspection for Practical Applications III
5 May 2014 | Baltimore, MD, United States
Dimensional Optical Metrology and Inspection for Practical Applications II
25 August 2013 | San Diego, California, United States
Optical Metrology and Inspection for Industrial Applications II
5 November 2012 | Beijing, China
Dimensional Optical Metrology and Inspection for Practical Applications
22 August 2011 | San Diego, California, United States
Optical Metrology and Inspection for Industrial Applications
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