Interferometer technique

Spark photography with shadowgraph, schlieren and interferometer techniques (such as described in. Vol 2 of Encycl, under CAMERAS) showed that density is uniform in zones I-TP-M and I-TP-R, but not in the zone R-TP-M, which includes the Mach region. The Mach shock M appears to be followed by rarefaction. Above the slipstream there is an angular variation of density so that, if measured at points farther and farther behind R, the density first rises to a maximum and then falls again For more detailed description of Mach waves etc, see Refs 2a, 3, 4, 5, 6, 7 and 8 Refs 1) Anon, "Military Explosives , TM9-1910 (1955), PP 74-5 2) Dunkle s... 

Ladenburg et al (Ref 10) described the application of the interferometer techniques to the study of faster than sound phenomena. 

L)lnterferometer Camera. E.Mach and his son L.Mach were the first to apply interferometer techniques to study of ballistic problems (Ref 1, p 275), The camera devised by them was improved by Zehnder and became known as "Mach -Zehnder Interferometer (Ref 2,p 173 Ref 18,p 141 and Addnl Ref dd). Bennett et al (Addnl Ref cc)gave the theory of interferometric analysis and described the procedure used at BRL(Ballistic Research Laboratories), Aberdeen, Md for analysis of airflow around projs in flight. The app of... 

Optical System. As shown in Figure 11, the optical section of the instrument consists of a beamsplitter, two optical wedge mirrors and a detector section with associated detector collection mirror. This is basically the Michelson interferometer technique except that the end mirrors have been replaced by optical wedges mirrored on the back side. The two windows are necessary only to maintain an ambient pressure in the Interferometer section, and a vacuum in the detector section. The window on the detector can be replaced with an optical filter if only a selected spectral region is to be investigated. 

The surface free energy of thin foils can be determined at temperatures between the melting point and approaching the Tammann temperature of the metal using the zero creep/laser interferometer technique. The use of the laser interferometer allows smaller sample strains to be measured with a higher level of confidence. 

Optical interferometer techniques can achieve resolution far beyond 1 nm. Because of this high sensitivity of the interferometer sensor, the direct detection of small molectdes at low concentrations should be possible [15]. Detection is generally limited by electronic and mechanical noise, thermal drift, light source instabilities, and chemiced noise. But interferometric devices have an intrinsic reference channel which ofiers the possibility of... 

The third method for endpoint detection uses a mass spectrometer that monitors a particular species whose concentration changes dramatically at the endpoint. In all three methods, the etch rate for a particular material can be determined. However, the interferometer technique has two advantages over the other methods. Changes in the etch rate with time can be detected and quantified, and significant etching of photoresist can be detected from the output of the strip chart recorder. In the next section, we take up the applications of plasma etching. 

Measurements using laser interferometer techniques now allow displacement resolutions of less than a nanometer [Mammano and Ashmore, 1995] and have aided investigations of the cochlea s active tuning... 

A much better way would be to use phase contrast, rather than attenuation contrast, since the phase change, due to changes in index of refraction, can be up to 1000 times larger than the change in amplitude. However, phase contrast techniques require the disposal of monochromatic X-ray sources, such as synchrotrons, combined with special optics, such as double crystal monochromatics and interferometers [2]. Recently [3] it has been shown that one can also obtain phase contrast by using a polychromatic X-ray source provided the source size and detector resolution are small enough to maintain sufficient spatial coherence. 

On metals in particular, the dependence of the radiation absorption by surface species on the orientation of the electrical vector can be fiilly exploited by using one of the several polarization techniques developed over the past few decades [27, 28, 29 and 30], The idea behind all those approaches is to acquire the p-to-s polarized light intensity ratio during each single IR interferometer scan since the adsorbate only absorbs the p-polarized component, that spectral ratio provides absorbance infonnation for the surface species exclusively. Polarization-modulation mediods provide the added advantage of being able to discriminate between the signals due to adsorbates and those from gas or liquid molecules. Thanks to this, RAIRS data on species chemisorbed on metals have been successfidly acquired in situ under catalytic conditions [31], and even in electrochemical cells [32]. 

For radiofrequency and microwave radiation there are detectors which can respond sufficiently quickly to the low frequencies (<100 GHz) involved and record the time domain specttum directly. For infrared, visible and ultraviolet radiation the frequencies involved are so high (>600 GHz) that this is no longer possible. Instead, an interferometer is used and the specttum is recorded in the length domain rather than the frequency domain. Because the technique has been used mostly in the far-, mid- and near-infrared regions of the spectmm the instmment used is usually called a Fourier transform infrared (FTIR) spectrometer although it can be modified to operate in the visible and ultraviolet regions. 

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-... 

Experimentally, this technique is very similar to the TDI technique described above. A laser beam is incident normally on a diffraction grating or a preferentially scratched mirror deposited on the surface to obtain the normally reflected beam and the diffracted beams as described above. Instead of recombining the two beams that are located symmetrically from the normally reflected beam, each individual beam at an angle d is monitored by a VISAR. Fringes Fg produced in the interferometers are proportional to a linear combination of both the longitudinal U(t) and shear components F(t) of the free surface velocity (Chhabildas et al., 1979), and are given by... 

The SFA, originally developed by Tabor and Winterton [56], and later modified by Israelachvili and coworkers [57,58], is ideally suited for measuring molecular level adhesion and deformations. The SFA, shown schematically in Fig. 8i,ii, has been used extensively to measure forces between a variety of surfaces. The SFA combines a Hookian mechanism for measuring force with an interferometer to measure the distance between surfaces. The experimental surfaces are in the form of thin transparent films, and are mounted on cylindrical glass lenses in the SFA using an appropriate adhesive. SFA has been traditionally employed to measure forces between modified mica surfaces. (For a summary of these measurements, see refs. [59,60].) In recent years, several researchers have developed techniques to measure forces between glassy and semicrystalline polymer films, [61-63] silica [64], and silver surfaees [65,66]. The details on the SFA experimental procedure, and the summary of the SFA measurements may be obtained elsewhere (see refs. [57,58], for example.). 

Fabry-Perot interferometer is an optical resonator consisting of two parallel mirrors. Fabry-Perot interferometers can be made by silicon bulk microma-chining." " Silicon surface micromachining is also a suitable technique for making interferometers for infrared wavelengths. 

In this lecture we recall the basic principles of the two main coating families dielectric and metallic coatings. In a second part, we describe the coatings deposition techniques and we address their performances and limitation. Most of the examples given in this lecture have been developed for the gravitational waves interferometers VIRGO and LJGO (see Ch. 18). 

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... 

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