I've been trying to measure the spectral response of a nanohole array to see the resonance in reflection spectrum.
The size of the nanohole array is 200um*200um. The resonance is designed to be around 780nm wavelength for the reflestion spectrum in case of normal incidence.
I tried to measure it using LED's, since I need a relatively large bandwidth because of the multilayer structure I have in my design. However, I haven't succeeded to see any resonance feature so far.
I also measured the nanohole array using Cary 7000 Universal Measurement Spectrophotometer. Still can't see any resonance in the measured spectrum.
I was wondering if I am doing it the right way or my nanohole array is too small to be detected by an LED light.
Thanks in advance for helping.
Dear Parinaz
It is difficult to say something meaningful from your too concise description. At first, your nanohole array is small and placed on a substrate. How do you suppress reflection from this substrate? Otherwise your measured reflection spectra will effectively hide your resonance structures. At least, you have to make the image of your structure by the reflected beam and to put into image plane diaphragm that pass only part of reflected beam from your nanohole array area and you should to search resonant features only into light passed such diaphragm.
As well, it is not clear, did you measured spectra of reflected LED beam?
Next, similar question:
> I also measured the nanohole array using Cary 7000 Universal Measurement Spectrophotometer.
How do you measure it? What layout was applied? How did you discriminated beams from nanohole and flat areas?
Another important point, what are angular divergences of you beams for both cases you have mentioned? Usually plasmonic effects are very sensitive to such parameters.
What were angles of incidence? Did you study angular dependence of reflection spectra?
What is the situation with light polarization?
All of those conditions and parameters are important and can reveal effect you searching
Good luck!
Since this works only for normal incidence, I would spatially filter the LED using a pinhole (~10-20 um diameter) and then collimate the light before incidence on your sample. You probably want to use some apertures and 3d stages so you can get the alignment right and make sure light is incident only on the region of interest. Further, it might be useful to have a sensitive photodetector in case you're going to end up losing light in all the collimation and alignment.
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