Hello,
I was measuring my sample - cellulose impregnated with polyethyleneimine, on a Raman microscope that has back-illuminated CCD. I used 633 nm excitation laser. In my spectrum, I got wavy fringes (due to interference?), but I don't know what causes them. I thought the etaloning effect was prominent only when using NIR laser, but I got the same results using 633 nm, 532 nm, and 455 nm laser (and not with 780 nm or 785 nm).
This may suggest the observation of rotational Raman spectra (since the spectra appears to be repeating with regular periodicity ). For example see following references:
http://astro1.panet.utoledo.edu/~relling2/teach/4780/20101101_lecture_10_phys4780.pdf
https://ocw.mit.edu/courses/physics/8-13-14-experimental-physics-i-ii-junior-lab-fall-2016-spring-2017/experiments/raman-spectroscopy/MIT8_13-14F16_ramanproposal.pdf
https://faculty.fiu.edu/~mebela/chm3411_chapter16_vib.pdf
The phenomenon of fluorescence is observed in the measurements of cellulose. If fluorescence is generated, it is often much more intense than Raman scattering, hiding Raman features. One method to avoid it is to select the laser excitation wavelength. You can used exciting line 1064 nm. For most examples, the choice a NIR laser wavelength can avoid exciting fluorescence - the laser photon does not have enough energy to excite fluorescence.
Magdalena Król Thank you for your answer. I appreciate it. I knew that fluorescence can be generated by cellulose, but I've never seen such a wavy fluorescent pattern in Raman spectrum (usually I've seen just one broad band of high intensity). Is the wavy pattern "normal" or is it due to some resonances or interferences (as it seems to be periodically repeated)?
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