Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Akin to dispersive Fourier transform spectroscopy (29), free-induction decay s-SNOM (15), and nano-FTIR (17, 20), we use an asymmetric Michelson interferometer to frequency resolve the scattered near-field signal and amplify the weak, tip-scattered light.
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