Sub-Nanosecond Digital Signal Processing of Photomultiplier Tube Response Enabling Multiphoton Counting in Raman...

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Photonics

Background:

• Conventional Raman spectroscopy treats photon arrivals as binary events.
• This binary approach overlooks multiple photons arriving simultaneously, limiting signal gain.
• Existing methods sacrifice potential signal enhancement by using a single threshold.

Purpose of the Study:

• Introduce a novel multiphoton counting approach for Raman spectroscopy.
• Enhance Raman detection sensitivity and signal gain.
• Improve the analysis of low-concentration samples and high Raman-yield compounds.

Main Methods:

• Utilized a time-resolved Raman spectroscopy system with a pulsed laser.
• Implemented a high-speed data acquisition system.
• Developed and applied a multiple threshold digital signal processing counting algorithm for multiphoton counting, differentiating photon events by amplitude and time.

Main Results:

• The multiphoton counting algorithm significantly improved Raman detection sensitivity.
• Achieved 2.0-, 2.0-, and 3.1-fold sensitivity increases for nitrate, isopropanol, and rhodamine 6G, respectively.
• Extended the upper analysis limit for high Raman-yield compounds by shifting the saturation threshold to higher concentrations.

Conclusions:

• Multiphoton counting offers a substantial advancement over traditional single-threshold methods in Raman spectroscopy.
• The developed algorithm enables lower concentration detection, greater sensitivity, and improved noise rejection.
• This technique broadens the applicability of Raman spectroscopy for sensitive quantitative analysis.