Retroreflectors

In certain types of mirror surfaces the reflected beam is returned in the same direction from which the incident beam arrived. This is maintained over a wide range of directions of the incident beam (Fig. 2.40). The phenomenon is called retroreflection [258]. Retroreflectors are various kinds of catadioptric stractures ( cat s eyes ). Basically, a retroreflector may be a surface-diffractive structure with triangular, pyramidal, spherical, etc. shapes of the grating. Incident light typically reflects twice before returning in the direction it came from. 

The patterns may also be comparable to the operating wavelength or larger, even much larger, and actually many retroreflector stractures in everyday life are macroscopic. However, retroreflectors can also have subwavelength dimensions [259]. 

Instead of the conventional geometrical optics approach, one can use instead the transformation optics [243] which allows one to tailor the heam path at will. In this way one use the mapping of the optical space to arrive at optical components with vastly improved characteristics, in this case a retroreflector with omnidirectional operation [260]. 

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The Topex oceanographic satelHte used a laser-based retroreflector array for positioning. The retroreflectors were manufactured from Corning Code 7958 fused siHca, a sol—gel-derived low water vitreous siHca material (248). 

Fig. 25-2. Double-beam, double-pass transmissometer for measuring smoke density in stacks. A[, chopper wheel A, beam gating wheel A3, aperture D, detector Fj, spectral filter F2, solenoid-activated neutral density filter L, lamp M, half-mirror/beam splitter Rj, solenoid-activated zero calibration reflector R2, retroreflector (alignment bullseye not shown). Design patented. Source Drawing courtesy of Lear Siegler, Inc.

The LPA instrument of Mount (42) uses a XeCl laser to monitor absorption near the Qi(S) line group. The laser beam, expanded in a telescope to an initial area of 150 cm2, is reflected from a retroreflector array for a total optical path of 20.6 km. The returned beam and a portion of the outgoing beam follow symmetric paths through an echelle spectrograph to a pair of photodiode array detectors, thus providing both I and Z0 spectra for the... 

Figure 3.25 Cube-corner retroreflector interferometers with rotational scanning.

There are two types of optical communication systems passive reflective systems and active-steered laser systems [War 01, War 05], A passive reflective system, such as a comer-cube retroreflector (CCR), consists of three mutually orthogonal mirrors that form the comer of a cube. Light entering the cube bounces off the mirrors and is reflected back to the sender. By electrostatically actuating the bottom mirror, the orthogonalty can be disturbed and the reflection is no longer returned to the sender. 

The measurements by ultraviolet analyzers can utilize (1) single-beam (2) split-beam (3) dual-beam, single-detector (4) dual-beam, dual-detector (5) flicker photometer (6) photodiode and (7) retroreflector designs. The standard errors of these measurements are 2% FS, whereas it is 1% FS for the fiber-optic diode-array designs. These analyzers can handle process pressures up to 50 barg (750 psig) and temperatures up to 450°C (800°F). 

Fig. 8. Femtosecond two-beam pump-probe experimental set-up for Kerr gate and transient absorption measurement. P polarizers M mirrors PBS Pellicle beam splitter Ap aperture RR retroreflector... 

In this example, the desired angular response is achieved by improving the package. Fig. 7.13.18 and Fig. 7.13.19 show the package and angular response [3], To produce a reduced response when the sun is overhead, the package has a diffuser called a retroreflector molded into the outer lens cap. 

Figure 6 (a) Absorption remote sensing apparatus. (1) Tunable laser, (2) polluted region, (3) remote retroreflector, (4) telescope, (5) detector. (b) Backscatter remote sensing apparatus. (1) Laser, (2) polluted region, (3) telescope, (4) spectrometer and detector (Reproduced by permission from Analyt. Chim. Acta, 1974, 71, 277)... 

Fig. 9. Diagram of a fluorescence up-conversion apparatus. NLC, Nonlinear crystal for sum-frequency generation BS, beam splitter R, retroreflector.

Measurement of retroreflectors and prisms Fizeau interferometers have been available... 

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