Rejection of fluorescence background in resonance and spontaneous Raman microspectroscopy.

Zachary J. Smith, Florian Knorr, Cynthia V. Pagba, Sebastian Wachsmann-Hogiu

Research output: Contribution to journalArticle

Abstract

Raman spectroscopy is often plagued by a strong fluorescent background, particularly for biological samples. If a sample is excited with a train of ultrafast pulses, a system that can temporally separate spectrally overlapping signals on a picosecond timescale can isolate promptly arriving Raman scattered light from late-arriving fluorescence light. Here we discuss the construction and operation of a complex nonlinear optical system that uses all-optical switching in the form of a low-power optical Kerr gate to isolate Raman and fluorescence signals. A single 808 nm laser with 2.4 W of average power and 80 MHz repetition rate is split, with approximately 200 mW of 808 nm light being converted to < 5 mW of 404 nm light sent to the sample to excite Raman scattering. The remaining unconverted 808 nm light is then sent to a nonlinear medium where it acts as the pump for the all-optical shutter. The shutter opens and closes in 800 fs with a peak efficiency of approximately 5%. Using this system we are able to successfully separate Raman and fluorescence signals at an 80 MHz repetition rate using pulse energies and average powers that remain biologically safe. Because the system has no spare capacity in terms of optical power, we detail several design and alignment considerations that aid in maximizing the throughput of the system. We also discuss our protocol for obtaining the spatial and temporal overlap of the signal and pump beams within the Kerr medium, as well as a detailed protocol for spectral acquisition. Finally, we report a few representative results of Raman spectra obtained in the presence of strong fluorescence using our time-gating system.

Original languageEnglish (US)
JournalJournal of visualized experiments : JoVE
Issue number51
StatePublished - 2011
Externally publishedYes

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Fluorescence
Light
Raman Spectrum Analysis
Raman scattering
Optical shutters
Camera shutters
Pumps
Pulse repetition rate
Optical Devices
Optical systems
Raman spectroscopy
Lasers
Heart Rate
Throughput

ASJC Scopus subject areas

  • Medicine(all)

Cite this

Rejection of fluorescence background in resonance and spontaneous Raman microspectroscopy. / Smith, Zachary J.; Knorr, Florian; Pagba, Cynthia V.; Wachsmann-Hogiu, Sebastian.

In: Journal of visualized experiments : JoVE, No. 51, 2011.

Research output: Contribution to journalArticle

Smith, Zachary J. ; Knorr, Florian ; Pagba, Cynthia V. ; Wachsmann-Hogiu, Sebastian. / Rejection of fluorescence background in resonance and spontaneous Raman microspectroscopy. In: Journal of visualized experiments : JoVE. 2011 ; No. 51.
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