Subnanosecond time-correlated photon counting with tunable lasers

Area of Science:

• Laser Spectroscopy
• Photophysics
• Analytical Chemistry

Background:

• Time-correlated photon counting (TCPC) is a crucial technique for measuring fluorescence lifetimes.
• Existing methods face limitations in precision and stability for complex decay analysis.

Purpose of the Study:

• To present novel laser-based methods for improving TCPC.
• To characterize the performance of a tunable dye laser system in various timing configurations for TCPC.

Main Methods:

• Utilized an Ar(+) laser-pumped tunable dye laser operated in acousto-optically mode-locked, cavity-dumped, and cavity-dumped-mode-locked configurations.
• Employed a high-resolution photon counting system with a sensitive photomultiplier tube (RCA C31034).
• Developed measurement techniques for both gas and liquid phase samples, including the fluorescent dye rose bengal.

Main Results:

• Achieved sub-nanosecond, highly stable laser pulses with identical shapes over 6 hours at 15 psec channel resolution.
• Demonstrated wavelength-independent fluorescence detection across visible and ultraviolet ranges.
• Successfully determined short exponential decays (as low as 50 psec) and dual exponential decays (e.g., 390 psec and 725 psec).
• Identified photomultiplier transit time dispersion (0.8 nsec FWHM) as the primary limitation for deconvolution accuracy.

Conclusions:

• The presented laser-based TCPC system offers significant improvements in stability and resolution.
• The system is capable of accurately analyzing complex fluorescence decay dynamics in various phases.
• This advancement enables more precise investigations into photophysical processes and molecular dynamics.