Is absolute count of emission spectrum meaningful?

[Yinxiao Li]

I am using Renishaw confocal Raman microscope to do photoluminescence spectroscopy of some polymer inside microchannel. When I fix the laser power and exposure time, the absolute count of intensity will change from time to time even for the same sample. I was hoping the intensity should linearly reflect the concentration of polymer and why is that not the case?
(PS: I read some papers that they can use the relative intensity to tell the concentration of molecules in a solution with some other machines)

 

[mfb]

When I fix the laser power and exposure time, the absolute count of intensity will change from time to time even for the same sample.

How much? There are statistical fluctuations. If the difference is larger then something changes between your measurements (quite likely).

 

[Yinxiao Li]

How much? There are statistical fluctuations. If the difference is larger then something changes between your measurements (quite likely).

It changes about 100%...I also used plain silicon and use f-stop to help focus on the surface. Still, the result is not consistent in terms of the absolute counts...For plain silicon, I don't think anything could change..

 

[mfb]

Then something changes, but it is hard to tell what without knowing the setup.