Ultrafast spectroscopy with sub-10 fs deep-ultraviolet pulses

Area of Science:

• Physical Chemistry
• Spectroscopy
• Ultrafast Dynamics

Background:

• Understanding photochemical dynamics is crucial for biologically significant molecules.
• Deep-ultraviolet (DUV) absorption is characteristic of DNA and amino acids.
• Previous spectroscopic methods lacked the resolution to capture ultrafast dynamics in the DUV region.

Purpose of the Study:

• To report, for the first time, time-resolved transient absorption spectroscopy using sub-9 femtosecond ultrashort laser pulses in the DUV region.
• To simultaneously observe electronic excited state and vibrational dynamics.
• To extract initial phase information of molecular vibrations.

Main Methods:

• Generation of single 8.7 fs DUV pulses (255-290 nm) via chirped-pulse four-wave mixing.
• Application of DUV pulses as pump and probe in transient absorption spectroscopy.
• Simultaneous observation of electronic and vibrational dynamics using a 128-channel lock-in detector.

Main Results:

• Successfully implemented time-resolved DUV spectroscopy with sub-9 fs pulses.
• Observed electronic excited state and vibrational dynamics in aqueous thymine.
• Identified vibrational modes of electronic ground and excited states.
• Extracted vibrational mode phase information from oscillatory structures in absorbance traces.

Conclusions:

• Sub-9 fs DUV spectroscopy provides unprecedented insight into ultrafast photochemical processes.
• This technique is valuable for studying molecules like DNA and amino acids that absorb in the DUV region.
• Complements existing methods like time-resolved infrared spectroscopy for a comprehensive understanding of molecular dynamics.