The acousto-optic tunable filter AOTF analyzer

3 The acousto-optic tunable filter (AOTF) analyzer 

Note that this condition is extremely wavelength selecting. For a given angle of incidence between the input optical beam and the acoustic wave front, and a given value of the acoustic wavelength, only one value of A is permitted. 

So far a modulator device has been described, not a filter. In order to understand how an AOTF device goes further than this, it is necessary to look at the effect of Bragg regime diffraction and the impact of the anisotropy of the AOTF crystal medium. 

In an AOTF analyzer the input optical beam to the crystal is polychromatic from a broadband source. For a given acoustic frequency and angle of incidence, only a very narrow band pass of wavelengths from the 

Near-infrared Spectroscopy for Process Analytical Technology 125 

---