Hi Elie,

If you are using dark field (DF) microscopy with transmission illumination, then the best method is to use a objective lens with a variable numerical aperture(NA). Take the DF spectrum of your sample at high NA, and then twist the objective collar to lower the NA---this will allow the transmitted light into the spectrometer to get the lamp spectrum. I am assuming your polymer doesn't absorb much light.

Two Caveats: (1) At the beginning of the session you should make sure the intensity of the lamp isn't too strong at low NA, otherwise you will saturate your detector. (2) After taking the sample spectrum ONLY change the NA before acquiring the lamp spectrum. Do Not change the intensity of the lamp or the focus of the objective or move the stage as this will change the lamp spectrum.

A less ideal method is to use a sample that uniformly scatters light  (ie. milk, etc) and put a dried drop of it next to your sample. You can take the spectrum of your sample then move the stage and take a spectrum of the scatterer. Again, I do not recommend this method but if you lack the funds for an expensive ~$10K variable-NA objective then this is your best bet. Good Luck!

Joel

Article Manipulating the Optical Properties of Pyramidal Nanoparticle Arrays

Article Anisotropic Etching of Silver Nanoparticles for Plasmonic St...

Article Oriented assembly of polyhedral plasmonic nanoparticle clusters

Hi Joel,

Thank you for your advices. Unfortunately i don't have funding for a variable-NA objective!

I take spectra in a reflection configuration but I will try the milk and see how it goes.

Tanks again,

Cheers,

This is a well-known issue. The variable NA is probably the best like Joel says. Otherwise you can use polystyrene beads as "reference scatterers". This means that the k^4 (wavevector) dependence will be normalized away as well, which may or may not be desirable...