Resolving Power: The resolving power of a device is the minimum linear separation (s ) ,or angular separation (), between two resolvable objects observed by that device

Resolving power of human eye: Θ ~ 0.0001 radian  smaller, means better device

Factors affecting Resolving Power: Quality of the lens Chromatic aberration Spherical aberration Diffraction of wave

Diffraction at a circular aperture: Sin θ = (1.22) / D θ = (1.22)/D Diffraction at a narrow slit: Sin θ = /d if θ small, θ = /d Diffraction at a circular aperture: Sin θ = (1.22) / D θ = (1.22)/D

circular lens ~ circular aperture light diffracts when it passes through a lens of an optical device

The diffraction patterns of the two point sources overlap: difficult to resolve them.

The Rayleigh criterion Two objects are just resolvable when the first minimum of one diffraction patterns falls on the central maximum of the other.

For circular aperture, the minimum angular separation of two resolvable objects is

Verify resolving power of human eye

Increase D but very limited: D  10m Decrease  How to increase resolving power (decrease ) of a device? Increase D but very limited: D  10m Decrease 

Visible:  ~ 10 −7 m , observe bacterium, virus Use matter wave:  of a electron ~ 10 −10 m, observe simple molecules, atoms

Transmission electron microscopes (TEM) The transmission electron microscope (TEM) uses electron beams of short wavelengths instead of visible light.

Salmonella bacteria (沙門氏菌) E. Coli (大腸桿菌) Salmonella bacteria (沙門氏菌)

Summary: Definition of resolving power Factors affection resolving power of a device Use matter wave to increase the R.P. Structure of TEM