Optical wedge

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 This is basically the Michelson interferometer technique except that the end mirrors have been replaced by optical wedges mirrored on the back side.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. 

Optical wedge A device used in optical spectroscopy whose transmission decreases linearly along its length. 

When the sample absorbs light, its intensity is lowered. Thus the photo electronic cells will receive an intense beam from the reference cell and a weak beam from the sample cell. This results in the generation of pulsating or alternating currents which flow from the photoelectric cells to the electronic amplifier. The amplifier is coupled to a small servo motors which drives an optical wedge into the reference beam rmtil the photo electric cell receive light of equal intensities from the sample as well as the reference beams. 

Optical attenuator A nick or irregularity in the teeth of the optical wedge will give rise to a false step or shoulder on the side of an absorption band. This effect is most pronounced in the 0-10 / transmission range. 

Fig. 9.96 (a) Mach-Zehnder interferometer with variable phase delay (p realized by an optical wedge, (b) Detected mean intensity (I) measured at / = 0, and phase-independent photon noise power density, measured at / = 10 MHz with and without input intensity Iq... 

Coherent light shows phase-independent noise. This can be demonstrated by a two-beam interferometer, such as the Mach-Zehnder interferometer shown in Fig. 9.96. The monochromatic laser beam with the mean intensity /q is split by the beam splitter BSi into two partial beams bi and b2 with amplitudes E and E2, which are superimposed again by BS2. The beam b2 passes a movable optical wedge, causing a variable phase shift 0 between the two partial beams. The detectors PDl and PD2 receive the intensities... 

Using data processing, the thickness variety values of measured objects at any point on the X-Y surface can be got. In Fig.40 shows the thickness variety of measured objects got by processing the experiment results shown in Fig.39(a,b). And the tilt angles of the optical wedge and of axicon are calculated as 1.83°and 1° respectively. Form Fig.39(c,d) it can be calculated that the rotation angle of optical wedge is 7.91°and the movement of axicon is 1.86 mm [U]. 

Fig. 40. (a) thick variety of optical wedge, (b) thick variety of axicon... 

As mentioned above, the design of the standard cuvettes allowed us to use them as the working cells of a Fizeau interferometer. However, imperfection of fabricated cuvette cases made it impossible to adjust the cuvettes to a band of infinite width. The adopted adjustment procedure produced an optical wedge of 10 bands for cuvette N2 and of 150 band for cuvette Nl. The bands were parallel to the illuminated facet. 

The use of the optical wedge filter has the further advantage that since its angular motion is directly proportional to the log of the transmittance movement, the wedge can be used to drive a pen recorder so that linear motion of the pen is proportional to the weight of fineparticles in the beam. 

The energy radiated by the source SO is split into sample and reference beams by the plane mirror Ml. Mirror M2 focuses the sample beam on a comb-shaped device used to adjust the 100 % transmittance level. Since the photometer compares sample- and reference-beam transmittances, the setting of this 100% comb is relative and a matter of convenience. Mirror M3 focuses the reference beam on the optical wedge, whose function is explained below. 

In Figure 2(a), typical interference patterns of the aerial ambient space (Air) and the aqueous solution (Solution) are presented. Vertical black lines show the image of the cuvette corner (its size is 1 x 1 x 4 cm3). We have been able to observe an alteration of n in the surface zone 1x2 cm2 of the cuvette (the cuvette size) and the aperture of laser beam. Deformations of the interference pattern in different points of the solution have been caused by changes in n in these points. The resolution is defined by a location of the optical wedge, namely, by a sum of horizontal interference lines. The space resolution is about 2 mm. 

A. Source B. Reference Beam and Optical Wedge C. Sample Beam D. Chopper E. Detector... 

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