Time-resolved Raman spectrometer with high fluorescence rejection based on a CMOS SPAD line sensor and a 573 nm pulsed laser

Tuomo Talala, Ville A. Kaikkonen, Pekka Keränen, Jari Nikkinen, Antti Härkönen, Vasili G. Savitski, Sean Reilly, Łukasz Dziechciarczyk, Alan J. Kemp, Mircea Guina, Anssi J. Mäkynen, Ilkka Nissinen

Research output: Contribution to journalArticlepeer-review

Abstract

A time-resolved Raman spectrometer is demonstrated based on a 256 × 8 single-photon avalanche diodes fabricated in CMOS technology (CMOS SPAD) line sensor and a 573-nm fiber-coupled diamond Raman laser delivering pulses with duration below 100-ps full-width at half-maximum (FWHM). The collected backscattered light from the sample is dispersed on the line sensor using a custom volume holographic grating having 1800 lines/mm. Efficient fluorescence rejection in the Raman measurements is achieved due to a combination of time gating on sub-100-ps time scale and a 573-nm excitation wavelength. To demonstrate the performance of the spectrometer, fluorescent oil samples were measured. For organic sesame seed oil having a continuous wave (CW) mode fluorescence-to-Raman ratio of 10.5 and a fluorescence lifetime of 2.7 ns, a signal-to-distortion value of 76.2 was achieved. For roasted sesame seed oil having a CW mode fluorescence-to-Raman ratio of 82 and a fluorescence lifetime of 2.2 ns, a signal-to-distortion value of 28.2 was achieved. In both cases, the fluorescence-to-Raman ratio was reduced by a factor of 24–25 owing to time gating. For organic oil, spectral distortion was dominated by dark counts, while for the more fluorescent roasted oil, the main source of spectral distortion was timing skew of the sensor. With the presented postprocessing techniques, the level of distortion could be reduced by 88%–89% for both samples. Compared with common 532-nm excitation, approximately 73% lower fluorescence-to-Raman ratio was observed for 573-nm excitation when analyzing the organic sesame seed oil.

Original languageEnglish
Article number6004110
Number of pages10
JournalIEEE Transactions on Instrumentation and Measurement
Volume70
DOIs
Publication statusPublished - 26 Jan 2021

Keywords

  • fluorescence
  • fluorescence rejection
  • measurement by laser beam
  • oils
  • photonics
  • Raman laser
  • Raman scattering
  • Raman spectrometer
  • Raman spectroscopy
  • single-photon avalanche diodes
  • SPAD sensor
  • time gating
  • time-correlated single photon counting
  • timing skew
  • wavelength measurement

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