Ray - path of the light wave

Cone of light is focused by a lens on the object

Ibn Sahl 

Wellebrord Snellius

Law of Refraction

n1 sin(theta1) = n2 sin(theta2)

Huygens principle states that a wavefront can be thought of as an infinite number of hemispherical wavefronts

allowed scientists to understand particle-wave duality of light

invented after 1600

followed the invention of the telescope in 1608

no reliable date of invention, given to prominent people

Hans Maartens

Developed the early electron microscope

Invented osciolloscope to prevent power surges

used oscilloscope to create the electron microscope

equation for resolution

cannot see details smaller than wavelength of light

detail resolved in sample  is about half the wavelength at best

the point at which light (parallel rays) converges after passing through a biconvex lens 

fixed in light microscopes

variable in electromagnetic microscopes

ray tracing: rays arriving on axis go parallel to their direction in the front space

all other rays are refracted, converged in biconvex lens

1/v-1/(-u)=1/f becomes 1/v+1/u=1/f

M (magnification) = v/u

if u=v=2f, then M = 1x

1. In SEM, the lenses only exist to focus the beam from the source

2. resolution depends on spot size. you don't want to magnify the image of the source very much

3. magnification relationship not too far from reality

1. electron spirals through the lens

2. no change in velocity as in the light lens

3. same lens equations hold true

large spot = better gathering power, low resolution

small spot = poor gathering power, high resolution

occurs whenever waves interact with matter

huygens' principle

lowest in polepiece lens

intermediate in shrouded lens

greatest in simple solenoid

electrons spent too much time in lens

coated lens in iron with brass piece

entire field emitted through brass piece, making smaller, thinner lens (better)

condensed electron field thin as pancake, close to ideal lens

rays far from axis converge close to the lens

rays near axis converge further from lens

creates a circle of minimum confusion instead of a focal point

different wavelengths of light converge differently

blue focuses closer, red is further away

opposite in electron microscope

stigmator

charged poles pull the beam on one direction or another, can change the direction and magnitude of the pull

elastic - bouncing off protons

inelastic - knocks electrons out of electron shell

IR, visible, UV

fluorescence

electron orbitals

differ in terms of energy

n = quantum number of electron shell

increasing energy with increasing n

E = nhf

electrons move around nucleus in energy levels

more energy at higher levels

equation for angular momentum

explains frequency of hydrogen irradiance spectrum

n=/=0

couldn't solve anything other than hydrogen

No 2 electron orbitals can have the same quantum signature

azimuthal, spin

increasing voltage increases interactions (zone of interaction)

low voltage = minimal elastic and inelastic scattering

how far the electron moves without colliding (elastic)

shorter for larger atoms, reason for coating

positive field

electrons are "lazy" and change trajectory easily

boost +10kV before scintillator, to keep from getting stuck

scintillator made of scintillin produces photons when electrons strike

made of scintillin

beta emmitter

converts electrons into photons

some electrons lost on the sides of the scintillator

photomultiplier tube

amplifies the signal at each dynode and sends it to the CRT

Two different types of scattering

Emission energy as a fraction of beam energy

Region I. backscatter, Region II. backscatter with energy loss, Region III. secondary emission

electron beam will go deep into sample with low density and atomic weight

can go a long distance without colliding

signal bounces off specimen (100 electrons)

scintillator boosts signal strength

60-70 quanta per 100 quanta