Polarising Microscope
Definition
Compound microscope fitted with a polariser below and an analyser above the stage. Used to study birefringent materials like fibres, minerals and crystalline drugs.
- Field
- Optical microscopy, mineral and fibre analysis
- Components
- Polariser below stage, analyser above
- Sample types
- Fibres, minerals, crystalline drugs
Common questions
What is the difference between a polarising microscope and a comparison microscope?+
A polarising microscope is built to reveal optical properties like birefringence using crossed polarisers, while a comparison microscope joins two separate optical paths into one eyepiece so an examiner can view two samples side by side. Some casework requires both instruments for different stages of an examination.
Why is a polarising microscope used on synthetic fibres in trace evidence work?+
Man-made fibres show characteristic birefringence values tied to their polymer type and manufacturing draw ratio, so measuring birefringence under the polarising microscope helps classify and compare fibre evidence beyond what color and diameter alone can establish.
Related terms
- Comparison Microscope
- Two compound microscope bodies connected by an optical bridge that presents one half of each body's image in a single split eyepiece...
- Depth of Field
- Axial thickness of the specimen that appears acceptably in focus at one time. High in stereoscopic microscopes, very low in oil-immersion compound...
- EDX / EDXRF
- Energy-dispersive X-ray detector attached to an SEM. Identifies elements from characteristic X-rays emitted when the beam strikes the sample. Backbone of GSR...
- Fluorescence Microscope
- Uses UV or short-wavelength excitation to make fluorophores emit longer-wavelength light. Used for semen, saliva, fibres and ink discrimination.
- Numerical Aperture (NA)
- The product of the refractive index of the medium between objective and specimen and the sine of the half-angle of the maximum...
- Resolution
- The ability of a mass analyser to distinguish two ions of nearly equal m/z, defined as m/Δm at a given peak. A...
- SEM
- Scanning electron microscope. Focused electron beam raster-scans the sample surface; resolution down to a few nanometres with great depth of field. Paired...
- Stereoscopic Microscope
- Two separate light paths producing a true 3D image at low magnification (typically 7x to 40x). Used for trace recovery, gross examination...
- TEM
- Transmission electron microscope. Electrons pass through an ultra-thin section; resolution below 1 nm. Rare in routine forensic casework, common in research.