A Tunable Optical Centrifuge for Spectroscopy and Collisional Dynamics of Superrotor Molecules

Abstract

The work presented in this dissertation utilizes a tunable optical centrifuge to study the spectroscopy and collisional dynamics of N2O and CO2 superrotor molecules. High-resolution transient IR absorption spectroscopy is used for time-dependent, polarization-sensitive, and rotational state-resolved measurements of superrotor molecules. An optical centrifuge combines ultrafast laser pulses with opposite chirp and opposite circular polarization to create a linear optical field polarization that angularly accelerates thermal molecules into extreme rotational states. The maximum rotational state populated by the optical centrifuge is related to the maximum angular frequency of the optical trap. We present a tunable optical centrifuge, which controls the final rotational state population distribution of the optical centrifuge via a systematic reduction in the spectral bandwidth of the optical pulse. In this way, the rotational population can be controlled down to a specific maximum rotational quantum state J. The studies presented here are a mixture of high-resolution spectroscopy measurements and polarization-sensitive collisional dynamics measurements of high-J N2O and CO2. First, we measure new N2O IR transition frequencies with J≤ 200 in the R-branch and J≤ 155 in the P-branch of the (0001) ← (0000) vibrational transition. New, more accurate spectral fitting parameters are reported and a combination difference analysis reveals the effects of high angular momentum on bond stretching. Next, the new N2O spectroscopy is used to measure the collisional dynamics of J= 67-180 with time-dependent and polarization-sensitive IR absorption signals. Here time-dependent measurements were performed to determine relative populations, molecular alignments and rotation-to-translation energy transfer pathways of high-J N2O. Next, we discuss measurements of new IR transitions of CO2 with J= 186-282. A spectral perturbation was discovered near J= 220. Collisional dynamics studies were then completed in the region of J= 244-282. Time-dependent and polarization-sensitive measurements of CO2 molecules in this region were performed to determine relative populations, molecular alignments and rotation-to-translation energy transfer pathways. Finally, two optical centrifuge traps were characterized to test the effects of the optical trap spectral bandwidth on the collisional relaxation dynamics of CO2 superrotors.