Fabry-Perot velocity

The advent of lasers allowed optical interferometry to become a useful and accurate technique to determine surface motion in shocked materials. The two most commonly used interferometric systems are the VISAR (Barker and Hollenbach, 1972) and the Fabry-Perot velocity interferometer (Johnson and Burgess, 1968 Durand et al., 1977). Both systems produce interference fringe shifts which are proportional to the Doppler shift of the laser light reflected from the moving specimen surface. Both can accommodate a speci-... 

Durand, M. (1984), Use of Optical Fibers for Velocity Measurement by Laser Doppler Interferometry with a Fabry-Perot Interferometer. In High Speed Photography and Photonics, Proc. SPIE, 491 (edited by M. Andre and M. Hugenschmidt), pp. 650-656. 

Bundy et al (Ref 13) measured the velocity and pressure of gases in a rocket flame by determining the small shift in wavelengths of the flame luminosity with a Fabry-Perot interferometer... 

Figure 4.68. Measuring system for the determination of the velocity of target motion by Fabry-Perot interferometry...

There are several types of velocity interferometers, such as ORVIS, FABRY-PEROT, VISAR, and others. They differ from each other in time resolution that is, from about 0.3 nanoseconds to a few nanoseconds. 

Determination of the velocity of a metal shim moved the explosive charge detonation using the Fabry-Perot interferometer is illustrated in Figure 4.68. 

When the target velocity is to be determined, the laser beam is sent to the moving target. The target surface is prepared to produce a diffuse reflected beam. Mirrors and lenses are used to direct the reflected beam as a parallel one to the Fabry-Perot interferometer. 

Fig. 5. Polarized Rayleigh-Brillouin spectrum of amorphous PnHMA taken with a Burleigh plane Fabry-Perot interferometer using a free spectral range of 12.4 GHz at 295 K. The two Brillouin peaks are shifted from the incident frequency by the product of the wave vector q and the sound velocity u. The line width of the Brillouin peaks is related to the attenuation of the sound waves. PnHMA.

The principle of the method is to use Fabry-Perot spectroscopy to measure the frequency shift in laser light scattered through 90° after passage through a parallel polymer sheet. The hypersonic velocity Vs is obtained from the equation... 

For an isotropic polymer, the hypersonic sound velocity is determined as a function of direction, and the elastic constants are obtained by fitting the data to a set of equations known as the Christoffel equations, which essentially relate the values of Vs to the stiffness constants Cj through Cj = pV, where p is the density [24]. For a detailed discussion of this technique, the reader is referred to papers by Kruger, Pietralla and co-workers. [25-27]. More recently, the development of non-scanning Fabry— Perot interferometry has made possible faster acquisition of data to enable study of liquid-glass transitions [28]. 

A unidirectional ring laser also avoids the unwanted hole-burning effects in inhomogeneous gain profiles of active media in Fabry-Perot type resonators, which are caused by the fact that the wave travelling into the z direction is absorbed by molecules with a velocity component v = +(v - Vq)c/vq, but the reflected wave by other molecules with v = -(v - Vq)c/vq (see Sects. 

A NEAR-INFRARED FABRY-PEROT IMAGER AT CRL 1.5M TELESCOPE AND THE STRUCTURE AND VELOCITY FIELD OF SHOCKED H2 EMISSION IN ORION KL REGION... 

Images of 2 micron molecular hydrogen emission were obtained with a newly developed Fabry-Perot imager, FINAC (see the poster by Sugai et al.). The velocity resolution of the FP was 240 km/s. The pixel size and the field of view of the camera were 1.88 arcsec and 4.0 arcmin, respectively. 

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