- #1
physicsninja
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When exciting a phonon mode with an evanescent wave possessing a wavevector ~100-200X larger than freespace but still ~10X smaller than fermi wavevector, would one expect a different resonance frequency for the phonon mode? I would think not.. but experiment seems to say yes.
More specifically: I am dealing with the main infrared active mode of SiO2 at 1080cm-1. I bring an evanescent probe near the surface which is capable of generating light of any frequency 900cm-1 to 1250cm-1 (enough to make a spectrum) with wavevector equal to roughly 1/probe radius ~ 1/10nm. This ends up being something like 100-200X larger than the free space wavevector. Experimentally I am seeing a large shift and I am not sure why.
Any ideas, thoughts or suggestions are welcome. Thanks!
More specifically: I am dealing with the main infrared active mode of SiO2 at 1080cm-1. I bring an evanescent probe near the surface which is capable of generating light of any frequency 900cm-1 to 1250cm-1 (enough to make a spectrum) with wavevector equal to roughly 1/probe radius ~ 1/10nm. This ends up being something like 100-200X larger than the free space wavevector. Experimentally I am seeing a large shift and I am not sure why.
Any ideas, thoughts or suggestions are welcome. Thanks!