Stationary mirror

Thermometer periscope. In front of the thermometer, this periscope lets you read a small magnified section of the thermometer scale. By turning the small knob at the lower right of this assembly, you track the movement of the mercury thread, and an image of the thread and temperature scale appear in a stationary mirror just above the sample viewing area. 

The heart of a Fourier transform infrared spectrophotometer is the interferometer in Figure 20-26. Radiation from the source at the left strikes a beamsplitter, which transmits some light and reflects some light. For the sake of this discussion, consider a beam of monochromatic radiation. (In fact, the Fourier transform spectrophotometer uses a continuum source of infrared radiation, not a monochromatic source.) For simplicity, suppose that the beamsplitter reflects half of the light and transmits half. When light strikes the beamsplitter at point O, some is reflected to a stationary mirror at a distance OS and some is transmitted to a movable mirror at a distance OM. The rays reflected by the mirrors travel back to the beamsplitter, where half of each ray is transmitted and half is reflected. One recombined ray travels in the direction of the detector, and another heads back to the source. 

In Fourier transform spectrometry, the wavelength components of light are not physically separated. Instead, the light is analyzed in the time frame of reference (the time domain) by passing it through a Michelson interferometer. The Michelson interferometer is so constructed that light is separated into two beams by a beamsplitter. One beam strikes a stationary mirror and is reflected back to the beamsplitter. 

The light-measuring portion of an FT-IR spectrometer. The light is split into two beams. One beam is reflected from a stationary mirror, and the other from a moving mirror. The beams are recombined to form an interference pattern called an interferogram. Fourier transformation of the interferogram gives the spectrum, (p. 520)... 

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.

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.

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... 

The development of Fourier Transform IR (FTIR) spectrometers led to the ability to measure vibrational spectra of supramolecular coinpounds with increased speed and sensitivity. The main feature of an FTIR instrument is the interferometer, which modulates the IR input waves by a moving mirror, M, moving back and forth toward and away from the beam splitter. Depending on the position of Mm, recombination of waves from Mm and the stationary mirror, Ms, at the beam splitter creates constructive or destructive interference that results in an output wave of varying intensity, i.e. the interferograin (see Fig. I). 

The interferometer was developed by Michelson in 1887 and used by him to measure the wavelength of light. Figure 3-13 shows the essential features of an interferometer. It consists of two plane mirrors and a beam splitter. The beam splitter transmits approximately half of all incident radiation to a movable mirror and reflects half to a stationary mirror. Each component reflected by the two mirrors returns to the beam splitter, where the waves are combined. 

FIG. 8. Profiles of the density of dissociated atoms, p/Po ( ) of Fig-7, vs lattice plane number at different times. Data have been smoothed by averaging over 2 neighboring planes ahead of the reaction front, and 6 behind the reaction front, and over 15 time steps. Solid lines are the steady-state trajectories of the head and foot of the reaction front. Dashed lines are the corresponding trajectories of the shock front obtained from a similar plot of the stress profiles vs time and distance. Dotted line marks the trajectories of some local reaction sites initiated by shock compression. Velocities refer to the stationary mirror plane. From reference [38b]. 

Fig. 2 Schemes of the optical part in the LICRM system. 1, Laser light source 2, movable plane mirror or corner reflector 3, polarizer 4 and 5, photocells 6 and 7, semi-transparent (half-sUvered) mirrors 8 and 9, stationary mirrors 10, the directions for the reflector 2 displacement...

Infrared radiation from the light source is divided into two beams by the beam splitter. One beam is reflected onto a moving mirror and the other onto a stationary mirror. Both beams are then recombined and pass through the sample to the detector. Fourier transformation of the resulting interferogram yields an infrared transmission spectrum. 

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