Two-beam reflection

Thus, the two beams reflected by Rf and R are mixed at B, although their planes of polarizations are orthogonal to each other, and advance to Pout- The plane of Pout is rotated anticlockwise by 45° about the x-axis, and its wires are parallel to the x-axis. Therefore, only the z-polarized component is transmitted from Pout and advances to the detector. Interference between the two beams refleeted by Rf and R occurs during this step. The spectroscopic measurement process after this is exactly the same as that of a conventional FT-IR spectrometer. The x-polarized component reflected by Pout along the z-axis is not utilized for any purpose. 

In order to ensure perpendicular beam incidence on the cylindrical specimen, the circular B-scan profiles were acquired by high frequency (narrow beam) transducers in a synthetic circular aperture array. From these profiles two-dimensional reflection tomograms were reconstructed using a filtered backprojection technique. Straight line propagation was assumed. Several artificial discontinuity types in a cylindrical Plexiglas (Perspex) specimen were compared with similar artificial discontinuities in a cylindrical A/Si-alloy [2]. Furthermore, examples of real discontinuities (an inclusion and a feed head) in the cylindrical AlSi-alloy are presented. 

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... 

In an FTIR spectrometer, a source (usually a resistively heated ceramic rod) emits infrared radiation that is focused onto an interferometer whose main components consist of a beamsplitter, fixed mirror, movable mirror, and detector. The beamsplitter divides the beam into two beams. One beam is reflected off the beamsplitter toward the fixed mirror and is then reflected back through the beamsplitter to the detector. The other beam is transmitted through the beamsplitter toward the movable mirror and is then reflected off of the beamsplitter and to the detector [1],... 

The collision process can be captured by a high speed video camera as shown in Fig. 6 [14]. The slurry is about 50 mm apart away from the solid surface at 0 s (Fig. 6(a)), and reaches the surface at 0.018 s (Fig. 6(b)). Then the slurry reflects at an angle as same as the incidence angle (Fig. 6(c)). As time goes, the reflected liquid beam is divided into two beams, one is in the reflected direction and another is parallel to the solid surface as shown in Fig. 6(d). When time reaches 0.068 s, most of the reflected slurry moves along the solid surface. 

In a reflectance or ellipsometry experiment, measurements are always referred to the physical plane of incidence, as defined in Fig. 27.24. If the polarization is parallel to this plane of incidence, the parameters related to it are denoted by the subscript p. For polarization perpendicnlar to the plane, the subscript s is used. When a linearly polarized beam is reflected, one often finds that the parallel and perpendicular components nndergo changes in amplitude and phase. Thus, two beams that are in... 

Nanobeam optics with beam diameters of several nanometers are presently developed at the ESRF. Using a Kirkpatrick-Baez optical system (cf. Fig. 4.9) beam diameters of 80 nm have been achieved. The Kirkpatrick-Baez system is made from two successively reflecting, orthogonal mirrors that are bent into elliptical shape by mechanical benders. The focused flux is strongly increased by deposition of a graded multilayer structure similar to that used with the parabolic Gobel mirror. 

The beams are backreflected by the cube corner prisms which are fixed, respectively, on the sample and on the sample holder. Since the cube corner prisms are able to make reflected beam exactly parallel to incident beam, this interferometer is tilt independent. The reflected beams get back to the beam splitter through the same path, but shifted by about 2 mm in the vertical direction. The beam splitter lets a part of the two beams go towards the photodiode sensor and lets the other part of beams reach the laser source (off axis, therefore giving no feedback effect). 

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... 

When the reflectivity of the two end faces is low (e.g., 4% from an air-glass interface), the multiplex reflections in the cavity have negligible contribution to the optical interference. Under this circumstance, the FP cavity is commonly referred to as the low-finesse cavity and the signal can be modeled using a two-beam interference model, given by5,6 ... 

The second type of double-beam instrument is one where the light source is divided into two beams by a rotating sector mirror that alternately reflects and transmits the light. This results in a chopped beam of light that alternately passes through the reagent blank and the sample as shown in Fig. 5.18. 

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.

The two beams are subsequently reflected on a rotating segmented mirror called chopper C. The chopper rotating = 10 times per second helps the sample beam and the reference beam to be reflected alternatively to the monochromator grating D. 

---