Thursday, December 27, 2018

Phase Contrast Microscope

•destructive interference patterns in the viewed image (amplitude and phase difference) 
•details in the image appear darker/brighter against a background •colorless and transparent specimen, such as living cells and microorganisms

P = S + D 
phase contrast

Optical Path Length (D) = n •t 
δ= 2πD/λ D = (n2-n 1) •t 
Living Cell

Applications of Optical Microscopy

1. Crystal morphology and symmetry
•Crystal fragments (characteristic shape) 
•Classify isotropic and anisotropic substances 
•Check possible symmetry (parallel extinction) 


2. Phase identification, purity and homogeneity
•Standard optical data (refractive indices and optical axes) for comparison 
•Phase analysis (impurities with separated crystalline/amorphous phase) 
•Single vs.twinned crystal

phase identification

3. Crystal defects –grain boundaries and dislocations
•Defects always present, even in single crystal 
•Chemical etching may preferentially occur at stress sites

crystal defect

4. Refractive index determination

Beckeline method:
•Sample ( n1) is immersed in a liquid (n2) 
•Out of focus, light is seen to emerge from region of higher n

Beekeline Method

Fluorescence Microscope

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