We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending the well known technique of Optical Kerr-Effect (OKE) spectroscopy to excited electronic states. The third-order non-linear response of the excited molecular ensemble is highly sensitive to details of excited state character and geometries and is measured using two femtosecond pulses following a third femtosecond pulse that populates the S 1 excited state. By measuring this response as a function of time delays between the three pulses involved, we extract the dephasing time of the wave-packet on the excited state. The dephasing time measured as a function of time-delay after pump excitation shows oscillations indicating oscillatory wave-packet dynamics on the excited state.From the experimental measurements and supporting theoretical calculations, we deduce that the wave-packet completely leaves the S 1 state surface after three traversals of the inter-system crossing between the singlet S 1 and triplet T 2 states.
Graphical TOC Entry
We describe a software implementation of a multi-channel, multifrequency Lock-in Amplifier (SILIA) to extract modulated signals from noisy data distributed over multiple channels of arbitrary number and size. This software implementation emulates the functionality of a multi-channel, multi-frequency lock-in amplifier in a post-processing step following data acquisition. Unlike most traditional lock-in amplifiers, SILIA can work with any number of input channels and is especially useful to analyze data distributed over many channels. We demonstrate the versatility and performance for extracting weak signals in spectroscopy and fluorescence microscopy. We also discuss more general applications and exhibit a method to automatically estimate error from a lock-in result.
We report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecules by probing the third-order nonlinear optical susceptibility. A non-colinear 3-pulse scheme is developed to probe the ultrafast dynamics of excited electronic states using the optical Kerr effect by time-resolved polarization spectroscopy. Optical homodyne and optical heterodyne detection are demonstrated to measure the 3 rd -order nonlinear optical response for the S1 excited state of liquid nitrobenzene, which is populated by 2-photon absorption of a 780 nm 40 fs excitation pulse.
Milliwatt average power terahertz quantum cascade lasers (THz-QCLs, 2 THz to 5 THz) have been developed for spectroscopy and as local oscillators for heterodyne receivers. Novel DFB THz-QCLs have been fabricated and show single-mode operation. The narrow line widths of <10 MHz and stark shift tuning of of 6 GHz, allows for wavelength modulation spectroscopy of low pressure gasses in the unexplored THz frequency band. The same devices also act as local-oscillators for heterodyne receivers for remote-sensing and astronomy. Lastly we report on improved tunable DFB devices for use in spectroscopy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.