Polarized light microscopy

Polarized light microscopy can mean any of a number of optical microscopy techniques involving polarized light. Simple techniques include illumination of the sample with polarized light. Directly transmitted light can, optionally, be blocked with a polariser orientated at 90 degrees to the illumination. More complex microscopy techniques which take advantage of polarized light include differential interference contrast microscopy and interference reflection microscopy. Scientists will often use a device called a polarizing plate to convert natural light into polarized light.As polarised light passes through a birefringent sample, the phase difference between the fast and slow directions varies with the thickness, and wavelength of light used. The optical path difference (o.p.d.) is defined as o . p . d . = Δ n ⋅ t {displaystyle {o.p.d.}=Delta ,ncdot t}  , where t is the thickness of the sample.Cross-polarized light illumination, sample contrast comes from rotation of polarized light through the sample.Bright field illumination, sample contrast comes from absorbance of light in the sample.Dark field illumination, sample contrast comes from light scattered by the sample.Phase contrast illumination, sample contrast comes from interference of different path lengths of light through the sample.