OPERATIONAxiolab 5 Illumination and contrast methods in transmitted light ZEISS05/2019 430037-7444-001 894.2.4 Configuring transmitted light polarization microscopy4.2.4.1 Detecting birefringence(1) ApplicationThe transmitted light polarization method is used for samples which change the polarization of the light.Such samples are called birefringent. Examples include crystals, minerals or polymers. If such birefringentsubstances are observed between crossed polarizers, the birefringent portion of the sample appearsbright while its surroundings remain dark.A birefringent substance can be recognized by rotating the sample by 360° between crossed polarizers.The sample should show four bright and four dark appearances during the rotation procedure. Duringthe rotation procedure, interference colors appear that range from gray (mostly for biological samples)through white, yellow and red to blue, depending on the birefringence, thickness and orientation of thesample. The interference colors may be of the first or a higher order.(2) InstrumentationPolarization methods can be used in the transmitted light on Axiolab 5 microscopes for transmitted lightpolarization and conoscopy.− Strain-free objectives− Pol rotary stage− Polarizer D (rotatable or fixed)− Analyzer slider D, fixed, or lambda compensator or lambda/4 compensator− Depolarizer (for screwing into Axiolab 5 tubes) to avoid undesirable polarization effectsNOTEThe depolarizer is already incorporated in the Axiolab 5 stand for conoscopy.A depolarizer (quartz depolarizer) should be incorporated in all microscopes used to examinemineralogical/geological specimens.A depolarizer extinguishes undesirable polarization effects (e.g. false or pseudo-pleochroism) that mayoccur behind the analyzer (e.g. on prism surfaces in the tube), or shifts them to higher orders.
