Using Photon Counting Detection Systems in Raman Research Applications

The simple room temperature PMT based photon counting system can perform sophisticated analyses, typically expected from higher cost advanced systems. Raman scattering is one such experiment that can be performed with the photon counting system using a weak and inexpensive source.

Raman Scattering Experiment

Figure 1 depicts the setup of the Raman scattering experiment using the photon counting detection system. The Raman spectrum of benzene is illustrated in Figure 2. The spectrum was acquired using a 50µm wide slit relative to a resolution of 0.5nm at an acquisition rate of 1s/point. The acquired spectrum is purposely not background subtracted, nor corrected for the spectral response of the photon counting system.

This diagram shows a typical Raman experiment using the Photon Counting Detection System.

Figure 1. This diagram shows a typical Raman experiment using the Photon Counting Detection System.

The spectrum is intended to yield ‘raw’ data in order to demonstrate the capabilities of this experimental setup. The holographic notch filter integrated into the photon counting system allowed detecting both Stokes and anti-Stokes components of the Raman emission. The corresponding intensities of the emission lines are in good agreement with estimated values for this room temperature sample. The baseline of the measurement is very near to the dark counts of the photon counting system, showing the rejection of virtually all of the stray light by the monochromator.

Raman spectrum of benzene.

Figure 2. Raman spectrum of benzene.

The photon counting system was used to measure the emission pertaining to the bending mode from a water molecule in order to test its sensitivity. The very weak emission of water makes it to serve as a solvent in most Raman scattering experiments. Hence, the ability to detect the water bending mode is a measure of the sensitivity of the Raman system to perform analytical measurements.

Figure 3 delineates emission for both water (H2O) and heavy water (D2O) samples captured in the same experimental conditions as earlier, excluding the increment in the slit width that led to a lower resolution. As can be seen, the frequency of the Raman emission from the heavy water sample is lower than the water sample owing to the variations in mass of hydrogen and deuterium atoms. The Raman shift from one water sample to the other, and their corresponding intensities, are in good agreement with the values mentioned in the literature (John Wilfred Shultz, Ph.D. thesis, Brown University, June 1957).

Raman spectrum of heavy water (D2O) and water (H2O).

Figure 3. Raman spectrum of heavy water (D2O) and water (H2O).

About Oriel Instruments

Oriel Instruments, a Newport Corporation brand, was founded in 1969 and quickly gained a reputation as an innovative supplier of products for the making and measuring of light. Today, the Oriel brand represents leading instruments, such as light sources covering a broad range from UV to IR, pulsed or continuous, and low to high power.

Oriel also offers monochromators and spectrographs as well as flexible FT-IR spectrometers, which make it easy for users across many industries to build instruments for specific applications. Oriel is also a leader in the area of Photovoltaics with its offering of solar simulators that allow you to simulate hours of solar radiation in minutes. Oriel continues to bring innovative products and solutions to Newport customers around the world.

This information has been sourced, reviewed and adapted from materials provided by Oriel Instruments.

For more information on this source, please visit Oriel Instruments.

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