Rotating interferometer

In a rotating interferometer, fringe shifts have been observed between light beams that propagate parallel and antiparallel with the direction of rotation [4]. This Sagnac effect requires an unconventional explanation. 

Figure 1. shows the measured phase differenee derived using equation (6). A close match between the three sets of data points can be seen. Small jumps in the phase delay at 5tt, 3tt and most noticeably at tt are the result of the mathematical analysis used. As the cell is rotated such that tlie optical axis of the crystal structure runs parallel to the angle of polarisation, the cell acts as a phase-only modulator, and the voltage induced refractive index change no longer provides rotation of polarisation. This is desirable as ultimately the device is to be introduced to an interferometer, and any differing polarisations induced in the beams of such a device results in lower intensity modulation. 

More usual is the kind of vibration-rotation band shown in Figure 6.8. This spectmm was obtained with an interferometer having a resolution of 0.5 cm and shows the v= 1-0... 

Inertial sensors are useful devices in both science and industry. Higher precision sensors could find practical scientific applications in the areas of general relativity (Chow et ah, 1985), geodesy and geology. Important applications of such devices occur also in the field of navigation, surveying and analysis of earth structures. Matter-wave interferometry has recently shown its potential to be an extremely sensitive probe for inertial forces (Clauser, 1988). First, neutron interferometers have been used to measure the Earth rotation (Colella et ah, 1975) and the acceleration due to gravity (Werner et ah, 1979) in the end of the seventies. In 1991, atom interference techniques have been used in... 

In the case of a space separation of the laser beams (i.e. if the atomic velocity is perpendicular to the direction of the laser beams), the interferometer is in a Mach-Zehnder configuration. Then, the interferometer is also sensitive to rotations, as in the Sagnac geometry (Sagnac, 1913) for light interferometers. For a Sagnac loop enclosing area A, a rotation Q, produces a phase shift ... 

Figure 2. Diagram of the atomic Sagnac interferometer at Yale (Gustavson et al., 2000). Individual signals from the outputs of the two interferometers (gray lines), and difference of the two signals corresponding to a pure rotation signal (black line) versus rotation rate.

Laser cooling can efficiently reduce the velocity of the atoms but cannot circumvent the acceleration due to gravity. On the ground the 1-g gravity level sets clear limitations to the ultimate sensitivities. The HYPER project (Hyper precision cold atom interferometry in space) will follow precisely this line and will benefit from the space environment, which enables very long interaction time (few seconds) and low spurious vibrational level. The sensitivity of the atomic interferometer can achieve few 10 rad.s. Hz to rotation and to acceleration. This very sensitive and accurate apparatus... 

The high sensitivity of atomic Sagnac interferometers to rotation rates will enable HYPER to measure the modulation of the precession due to the Lense-Thirring effect while the satellite orbits around the Earth. In a Sun-synchronous, circular orbit at 700 km altitude, HYPER will detect how the direction of the Earth s drag varies over the course of the near-polar orbit as a function of the latitudinal position 9 ... 

J. Kauppinen, J. Heinonen and I. Kauppinen, Interferometers based on rotational motion, Appl. Spectrosc. Rev., 39, 99-129 (2004). 

Most detector systems require that the IR beam be modulated, where the source energy is adequately differentiated in the measured signal from the ambient background. One of the traditional approaches is to use some form of mechanical chopper , usually in the form of a rotating sector wheel, which modulates the beam by blocking the radiation in one or more sectors during a rotation. Note that this is not a requirement for FTIR systems where the interferometer naturally modulates the beam. 

One of the greatest advantages of matrix isolation IR (or Raman) spectroscopy is that vibrational bands are inherently very narrow, because rotations are largely suppressed, which means that much more detailed information can be obtained than in the liquid phase at room temperature. However, this additional information can only be obtained if the spectrometer offers high enough resolution, which in the case of interferometers translates into sufficient displacement of the movable mirror. For most practical purposes, a resolution of 1 cm is adequate for matrix work, altough it is good to have 0.5-cm resoution available in case one needs it, say, for the elucidation of site structures. 

Bergdolt (Ref 12) used the Mach-Zehnder interferometer and a short duration light source with a rotating mirror cameraito obtain interferograms of projectiles and the air flow patterns around them... 

At the beginning of the twentieth century, there were several isolated voices claiming for a revision of the Michelson-Morley interpretation. Hicks [52] performed a theoretical analysis of the Michelson-Morley experiment and concluded that data were consistent with a somewhat larger magnitude of the difference of speeds. More importantly, he noted that the data followed a periodic curve proportional to cos 20, where angle 0 refers to a rotation of the interferometer relative to the presumed direction of orbital velocity. The functional dependence present in the results is of the form to be expected if there existed E. 

M-M experiments typically yielded finite (nonzero) differences of speed along two perpendicular positions of the interferometer s reference arm. Such difference is consistently lower than the value to be expected from orbital motion alone (30 km/s), within the naive conventional approximation of not taking into account diurnal variations due to earth rotation. With the exception of Miller, all authors consistently interpreted their observations as nullresults. 

Figure 17. (a) Transverse electrooptic modulator that rotates polarization of an incoming light beam as a function of applied electric field and (b) a travelling Mach-Zehnder interferometer that introduces a phase shift to the light beam in one arm as a function of applied field. 

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