If you're looking for a simple import and speed isn't a concern you should try:
A speedier load than this can be achieved using low-level IO functions.
Depending on your field, converting wavelength to wavenumber is achieved using either
waveNumber = 1./waveLength
waveNumber = 2*pi./waveLength
The interpolation you are looking for can be achieved using either
depending on the dimensions of your data, or using the
resample function if you want some antialiasing.
The FFT is done with the aptly named
I am not exactly sure what you're doing, but I think you could probably skip most of these steps and just fft the intensity vs wavelength data to achieve the same goal.