Martin-Puplett interferometer

An example of a Martin-Puplett interferometer is schematically illustrated in Figure 19.1. The important characteristic of the Martin-Puplett interferometer lies in its use of a wire-grid polarizer (WGP) as the beamsplitter this is free from the effects of interference arising from multiple internal reflections occurring inside a PET film. The WGP used for the Martin-Puplett interferometer is an array of parallel metallic wires, each having a diameter of about 10 pm and separated by intervals of about 12.5 pm. A beam of far-infrared radiation incident on the WGP is divided into two orthogonal polarized components that is, a component with its plane of polarization parallel to the wires, which is reflected, and a component with its plane of polarization perpendicular to the wires, which is transmitted. Thus, the WGP performs the role of a beamsplitter. 

The Martin-Puplett interferometer illustrated in Figure 19.1 has two further WGPs (Pj, and Pom) in addition to that used as the beamsplitter (B). The plane of P , located before B is set to be perpendicular to the x-axis, while the plane of B is set at an angle of 45 to both the x- and y-axes. Pm has its wires parallel to the y-axis, so that only x-polarized radiation is transmitted from P and advances toward B. The wires in B are arranged in a direction rotated clockwise by 45° from the x-axis, when viewed from the side of P, so that the component of the beam of radiation incident on B with its plane of polarization rotated clockwise by 45° from the x-axis is reflected by B, and advances toward the fixed mirror Rf along the positive direction of the y-axis. It should be noted that the plane of polarization of this beam, when viewed in the direction toward Rf, is rotated anticlockwise... 

Figure 19.1 Schematic illustration of a Martin-Puplett interferometer. For details, see text.

Another important ingredient of the Martin-Puplett interferometer is a reflector that rotates the plane of polarization of the returning beam by 90° with respect to the incident beam. Two metal mirrors, set at 90° with respect to each other, can rotate... 

Fig. 5.8.16 Completely symmetrical Martin-Puplett interferometer with two outputs and two inputs for difference measurements.

A very promising technique is the measurement of circular dichroism (and linear dichroism) by means of a polarizing interferometer (Martin and Puplett, 1969). The Martin-PupIett-interferometer uses a linear polarizer as beamsplitter. If the interferogram produced at the detector is Fourier transformed, the sine FT gives directly the circular... 

Ohta et al. (2006) theoretically proposed to apply a Martin-Puplett-type Fourier-transform spectrometer to the aperture synthesis system in millimeter and submil-limeter waves. They succeeded in proving that this system is capable of performing broadband imaging observations (Ohta et al. 2007). Also a laboratory prototype spectral-spatial interferometer (Chap. 3) has been constructed to demonstrate the feasibility of the double-Fourier technique at far infrared (FIR) wavelengths (0.15-1 THz) by Grainger et al. (2012). 

The Martin Puplett polarizing interferometer lends itself readily to the implementation of a balanced two input - two output beam interferometer where the difference between the two beams is only the axis of polarization. This highly balanced system allows a direct interferometric ratio determination between the two inputs at both output beams separately. In the far I.R. this feature is currently exploited by Mather et al. and separately bu Gush in an attempt to measure the residual cosmic background radiation in outer space. This is believed to follow approximately a 3° K blackbody radiation distribution. The balanced dual beam eliminates the radiation contributed by the spectrometer and the actual measurement consists of a direct comparison of the space field of view with a calibrated 3°K blackbody source in the second input beam. 

Fig. 5.8.15 Simple Martin-Puplett polarization interferometer. Pi and P2 are polarizers with the wires normal to the plane of the paper. B.S. is a beamsplitter with the wires rotated at 45° with respect to that plane. R.R. are roof reflectors that rotate the plane of polarization by 90°. Symbols in the circles indicate the plane of polarization.

It has been established that an interferometer design first proposed by Martin and Puplett [2] is the most effective FT-IR spectrometer configuration for far-infrared measurements, particularly in the wavenumber region lower than 150 cm [3],... 

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