Question

Describe the following techniques (Fourier transform spectroscopy):

a. Michelson interferometer

b. Diffuse reflectance

c. Attenuated total reflectance method

Answer 1

We will be discussing following techniques with respect to Fourier transform spectroscopy.

1. Michelson interferometer – This technique uses Interferometry, in which wave is split into two as example electromagnetic waves (light) and then again superimposed using mirrors which then will give constructive information about the waves.

In Fourier transform, light waves are split and then with using moving mirror, interferogram is generated by measuring a signal at different positions. Which then creates a spectrum.

2. Diffuse reflection

Simple ray of light reflect at same angle as the incident angle. But on rough surface as plaster or paper, light ray reflected at many angles. This surface will then have equal luminance from all directions

This technique is used to illuminate the sample.

3. Attenuated total reflectance

This technique uses evanescent wave. Evanescent wave is concentrated at one point rather than propagating. This type of wave result in total internal reflection.

In this technique a crystal with high reflective index is used. When light passes through crystal, it undergoes many internal reflections. Wavelength of light, incident angle and refractive indices can be converted to characterize samples after collecting beam of light at the detector.