Time-correlated single photon Raman spectroscopy at megahertz repetition rates

Abstract

Significant improvements in time-correlated single photon counting (TCSPC) Raman spectroscopy acquisition times can be achieved through exploitation of megahertz (MHz) laser repetition rates. We have developed a TCSPC Raman spectroscopy system based on a high peak power ( > 40 W ) pulsed laser, a high pulse repetition rate (40 MHz), a custom f / 1.5 spectrometer, and a 512 spectral channel × 16 time bin single photon avalanche diode line sensor. We report millisecond Raman spectrum acquisition times, a peak Raman count rate of 104 kcps, and a linewidth aggregated count rate of 440 kcps with a diamond sample. This represents a three-order-of-magnitude increase in measured Raman count rate in comparison with a 104 kHz pulsed laser operating at 300 W and a four-order-of-magnitude increase over a 0.1 W pulsed laser operating at 40 MHz. A Raman-to-fluorescence ratio of 4.76 is achieved with a sesame oil sample at a 20 MHz repetition rate. Achieving high count rates and Raman-to-fluorescence ratios unlocks the potential of combined Raman/fluorescence lifetime spectroscopy for imaging and other short acquisition time applications.

CMOS SPAD Line Sensor With Fine-Tunable Parallel Connected Time-to-Digital Converters for Raman Spectroscopy

“…In comparison to previous work, the presented line sensor has the least timing skew, the highest output data rate, and good performance in terms of power consumption, temporal resolution, DCR, and IRF. When Raman measurements are compared to recent studies, significantly better spectral quality was achieved for a water sample than in [9], and acquisition time could be reduced by 90% for a diamond sample when compared to [33]. To the best of the authors' knowledge, the Raman spectrum of roasted sesame oil measured with CMOS SPAD sensor and 532-nm excitation has not been presented in literature before.…”

“…The Raman spectrum of diamond achieved in 1-ms measurement in Fig. 17 shows a higher Raman hit count (276 > ∼230) and noticeably lower background noise without any postprocessing when compared to the 10-ms acquisition time spectrum with background subtraction in [33]. The largest factors for such a big difference in required acquisition times are excitation pulse energy (ratio ∼1:335, higher in this work) and active area of SPADs in a sensor channel (∼1:3, higher in this work).…”

“…Hits from bins 23-37 (∼430-ps time window) were summed to spectra without any post-processing. Raman spectra of a diamond sample measured with a CMOS SPAD-based spectrometer were recently reported in [33]. The Raman spectrum of diamond achieved in 1-ms measurement in Fig.…”

“…In previous work, the performance of CMOS SPAD line sensors in Raman spectroscopy has been demonstrated with various sample types including oils, minerals, water, paracetamol, and diamond [7], [8], [9], [10], [28], [33]. To achieve comparable results and to demonstrate how the different sample types set different requirements for a sensor, Raman measurements are here divided into three categories.…”

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

“…13,36,42 Despite this benefit, it is important to note that laser pulse repetition rate effects remain important. While high pulse repetition rates have been shown to offer significant improvements in spectrum acquisition times, 43 as an overly excited PMT (i.e., one that is not given an opportunity to return to is baseline state) can suffer from pulse pile-up and after-pulsing effects, 12 as well as compromised gain due to increased charge distribution in the dynode chain, which adversely impact output linearity. 2 In the experiments performed herein, the laser pulse repetition rate (5 kHz) and short pulse duration (<600 ps) were more than adequate to avoid these complications.…”