Senarmont compensators

A polarizing microscope for transmitted light usually has a polarizer at a fixed azimuth beneath the substage condenser, and an analyzer in the microscope tube above the objective. Typically, a compensator is inserted at 45° beneath the analyzer. Some compensators (such as the de Senarmont) are fixed in azimuth, and measurements are made with a rotary analyzer with a variable azimuth. For other compensators, the analyzer is fixed and the compensator is rotated or tilted to make measurements in the axis of the microscope. 

The optical system used to assess flow-induced birefringence consisted of a 2-mW polarized He-Ne laser focused by a condenser lens on the center of the flow field. The birefringence patterns are observed between crossed polars by using a quarter wave (X/4) retardation plate as a Senarmont compensator. The polarized laser has an extinction ratio of 100 1 the polarizer and analyzer are Carl Zeiss components with extinction ratios of approximately 10... 

A standard polarized-light microscope equipped with a Senarmont compensator, having magniflca tions up to 400X, and a rotatable analyzer with a graduated scale are used by the writer. All the obser vations are made with the use of the upper element of the substage condensing lens on the microscope. 

To measure alite birefringence using a Senarmont compensator and the upper element of the substage condensor, Ono recommends the following steps ... 

Insert the Senarmont compensator, properly oriented so that the darkness of the background results in cross-polarized light. Place a green filter in the path of the incoming light. The green filter facilitates observation of the alite crystal compensation point determined in the next step. 

Polarized-light microscope Senarmont compensator Reflected-light (metallo-graphic) microscope Petrographic slides (46x24 mm)... 

The Senarmont compensator has two parts, an accurate A/4 plate inserted above the specimen in the parallel 0° position and a rotating calibrated analyzer. Range is 150 nm. 

FIGURE 6.32 Polariscope arrangement for Senarmont compensation. (H. W. McKenzie and R. J. Hand, Basic Optical Stress Measurement in Glass, Society of Glass Technology, Sheffield, England, 1999, p. 41.)... 

Figure 11.9 (a) Edge stress meter principle www.sharplesstress.com/.) (c) Strainoptics Inc. with a Senarmont compensator, (b) Sharpies edge stress meter. (Photograph courtesy of edge stress meter. (Photograph courtesy Strainoptics Inc., www.strainoptics.com.)... 

Next consider a 1/4 wave plate (as used for a Senarmont compensator Chapter 11) inclined by 45° from principal directions 1 and 2 of a specimen, say, parallel to initial linear polarization (Figure A.3). The polarization vector... 

That is, a linear polarized light with polarization vector forming an angle of ///2 with initial polarization vector. Hence, an analyser allows determination of ///2 after rotating to darkness as done when using a Senarmont compensator. 

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