Michelson interferometer moving mirror

Developed in the late 19th century by Michelson, the moving mirror interferometer was initially designed to determine the speed of light. While using the instrument, Michelson noticed some differences in the interference pattern when various materials were placed in the beam. However, it was not until roughly 1960 when the math treatment of Fourier was applied to the interferogram produced by the device that an infrared... 

To measure an interferogram using a Michelson interferometer the mirror is moved back and forth once. This is called a scan. The interferograms measured while scanning are Fourier transformed to yield a spectrum, hence the term Fourier Transform Infrared (FTIR) spectroscopy. 

In an industrial-design FTIR spectrometer, a modified form of the G enzel interferometer is utilized.A geometric displacement of the moving mirrors by one unit produces four units of optical path difference (compared with two units of optical difference for a Michelson type interferometer). The modified Genzel design reduces the time required to scan a spectrum and further reduces the noise effects asstxiated with the longer mirror translation of most interferometers. 

A diagram of a typical interferometer (Michelson type) is shown in Figure 7.8. It consists of fixed and moving front-surface plane mirrors (A and B) and a beamsplitter. Collimated infrared radiation from the source incident on the beamsplitter is divided into two beams of equal intensity that pass to the fixed and moving mirrors respectively. Each is reflected back on itself, recombining at the beamsplitter from where they are directed through the sample compartment and onto the detector. Small... 

Figure 4.5 Schematic diagram of a Fourier transform infrared (FTIR) spectrometer. Infrared radiation enters from the left and strikes a beam-splitting mirror (BS) angled such that half of the beam is directed towards a fixed mirror (Mi) and half towards a moveable mirror (M2). On reflection the beam is recombined and directed through the sample towards the detector. M2 is moved in and out by fractions of a wavelength creating a phase difference between the two beam paths. This type of device is called a Michelson interferometer.

Fourier-transform infrared (FTIR) spectrometers encode infrared wavenumbers by moving a mirror in a Michelson interferometer which results in a unique, path-dependent pattern of interference for each light wavelength in the IR beam. FTIRs have come to totally dominate the IR market and are the means by which most of the work described in this review was accomplished. Only for some special applications (modulation spectra and time-dependence studies) are dispersive-based (scanning monochromator or tuned laser) spectrometers still used. The advantages of the FTIR approach are that the entire spectral region of interest can... 

One of these devices that is typically used in infrared spectroscopy is the Michelson interferometer (Fig. 6.22). This device works by splitting the beam into two components perpendicular to each other. Then each beam gets reflected by minors in such a way that the reflected beams recombine again at the beam splitter. In one of these beams a path difference is introduced by moving the mirror on which it reflects. This... 

Figure 10.11—Optical arrangement of a Fourier transform IR spectrometer, a) A 90c Michelson interferometer including the details of the beam splitter (expanded view) b) optical diagram of a single beam spectrometer (based on a Nicolet model). A weak intensity HeNe laser (632.8 nm) is used as an internal standard to measure precisely the position of the moving mirror using an interference method (a simple sinusoidal interferogram caused by the laser is produced within the device). According to the Nyquist theorem, at least two points per period are needed to calculate the wavelength within the given spectrum.

Fourier transform (FT) IR spectroscopy is one of several nondispersive optical spectroscopies based on interferometry. A two-beam interferometer first proposed by Michelson is the basis of most modern FT-IR spectrometers, as exemplified by the schematic of the Bruker Equinox 55 spectrometer (Bruker Optik, Ettlingen, Germany) in Fig. 2. Simply described, the interferometer comprises a beam splitter and two mirrors. A collimated beam of IR energy is split at the beam splitter into equal halves. Half of the energy travels through the beam splitter to one of the mirrors, which is positioned at a fixed distance away from the beam splitter. The reflected beam travels perpendicular to the incident beam to a moving mirror. IR radiation reflects off the fixed and moving mirrors and recombines at the beam splitter. The recombined IR beam projects from the interferometer towards the detector on an optical path perpendicular to the source beam. 

A Michelson interferometer is generally the device used in an FTIR spectrometer. The Michelson interferometer is composed of two mirrors and a beam splitter positioned at an angle of 45° to the fixed and moving mirrors. 

Figure 7.19 Fringe pattern and fringe shift resulting from moving one of the mirrors in a Michelson interferometer.

Figure 1. Schematic of a Michelson interferometer. The dashed lines show the paths of light which return to the source and the solid lines show the rays which propagate to the detector. The signal at the detector is the result of two light waves which have each been reflected and transmitted once by the beamsplitter. BF and BM are the respective distances of the fixed mirror and the moving mirror from the beamsplitter. Note that 8 = 2(BM - BF).

A collimated light beam from the 1R source is directed to the Michelson interferometer where it is divided by the beam splitter. One half of the beam is reflected from a fixed mirror and the other half from a moving mirror. The two light beams recombine after returning from the mirrors and give rise to a reconstructed beam which is optically an interference wave. The interference light beam passes through the sample and is modified by its interaction with the... 

The Michelson interferometer consists simply of two mutually perpendicular plane mirrors one of which is fixed and the other able to move at 90° to its plane. A semi-reflecting film or beamsplitter ... 

Fig. 7.1. Layout of the infrared spectrometer showing the Michelson Interferometer Optical System. An FTIR spectrometer s optical system requires two mirrors, an infrared light source, an infrared detector and a beamsplitter. The beamsplitter reflects about 50% of an incident light beam and transmits the remaining 50%. One part of this split light beam travels to a moving interferometer mirror, while the other part travels to the interferometer s stationary mirror. Both beams are reflected back to the beamsplitter where they recombine. Half of the recombined light is transmitted to the detector and half is reflected to the infrared source.

The Michelson interferometer is shown schematically in Figure 1. It consists of two mutually perpendicular plane mirrors, one of which can move at a constant rate along the axis and one of which is stationary. Between the fixed mirror and the movable mirror is a beam splitter where a beam of radiation from an external source can be partially... 

Figure 1. Diagram of a Michelson interferometer. Key l, unmodulated incident beam A, moving mirror B, stationary mirror E, modulated exit beam D, detector MD, mirror drive.

A schematic diagram of a Fourier transform instrument is given in Fig. 1. The simplest form of the Michelson interferometer consists of two mutually perpendicular mirrors, one of which can move in the direction of the beam. Between both mirrors there is a beam-splitter where the radiation is partially reflected (to the moving mirror) and partially transmitted (to the fixed mirror). Both parts of the beam return to the beam-splitter where, because of the difference in path ([Pg.127]

The interferometer used in a non-dispersive instrument is a device that divides the beam of radiation into two paths and recombines the two beams after a path difference has or has not been introduced. The basic concept of the interferometer was introduced by Michelson almost a century ago (Fig. 2). It consists of a stationary mirror, a moving mirror, and a beam splitter. The radiation from the infrared source is divided at the beam splitter half the beam is passed to a fixed mirror and the other half is reflected to the moving mirror. The two beams are later recombined at the beam splitter and passed through the sample to the detector. For any particular wavelength, the... 

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