Raman Spectroscopy, A Few Questions

[CasualDays]

Using a PMT/Monochromator, we have Surface Enchanced Raman Vials we are using to analyze samples.

One thing I am trying to figure out: The so called finger print region is 500-3000 wavenumbers after the wavelength of the laser you are using. In our case, we are currently using a 200mW 532nm laser. So, I've set the monochromator to scan from 545-632 (approximate numbers). The problem is I am seeing around 18,000 photons at 545-547 and then it drops off to around 1,000-3,000. I think the 1,000-3,000 photons are a result of the Raman scattering, but why is the 545-547 range so high? Do you think a 532nm subtraction filter would help this problem?

Also, this is a very basic question but we are also using a photon counter to measure interrogate the signal from the PMT. What is the methodology behind determining what the Photon counter should call a photon i.e. how do I determine the amount of volts the Photon counter calls a photon? Maybe use something like E=hv?

Thanks for your time!

 

[Navin A S]

Regarding your first question, it is possible that the high photon count at 545-547 is because the laser is slightly out of alignment with the monochromator, resulting in some light being scattered at those particular wavelengths. To determine if this is the case, you could try using a subtraction filter to block any photons from the laser line. This should reduce the number of photons detected in this range and result in a smoother background signal. Additionally, you could also adjust the alignment of the laser and monochromator to ensure that the laser line is centered in the monochromator. Regarding your second question, the methodology for determining the voltage threshold for a photon count depends on the type of photon counter you are using. Generally, the photon counter will have a setting that allows you to choose the voltage threshold for a photon count. This is typically done by trial and error, so you can start with a low voltage threshold and then gradually increase it until you get a reasonable photon count.