General Properties of Light Light as a wave Speed Wave properties: wavelength, frequency, period, speed, amplitude, intensity Electromagnetic wave

EM Spectrum

Diffraction – the bending of waves at an aperture or obstacle

Double-slit pattern of water/sound waves

Interference – double-slit, speckle y D  I peak =4I o I average =2I o

Polarization

Light as a particle Photon Energy packet Photoelectric effect Double slit- revisited

Double Slit Experiment with Electrons Detections come in lumps = quanta Intensity exhibits interference Reducing intensity of the light, so that only one electron arrives at the slits at a time

Questions? Why do no electrons (or photons) ever arrive at some locations? Clearly How can we get interference when only 1 particle at a time is going through the slits? What does that particle interfere with? Suppose we actually check which slit each particle went through and know with certainty – what happens then? How can this be? Resolution comes from QED with Feynman

Electron diffraction

How is light produced? Chemical energy - fire Electrical energy - lightning Nuclear energy - stars –Incandescent –Electric discharge – continuous vs discrete spectrum –Fluorescence

Special Properties of Laser Light Monochromatic Intense Pencil beam – collimated Coherent Can be cw or pulsed

Prototype Laser Energy levels Absorption, spontaneous emission Stimulated emission Population inversion Metastable state Pump – optical, electron excitation, atom- atom collisions, chemical Resonant cavity – gain, cavity modes, beam

Types of Lasers 3-level vs 4-level Ruby, first, a 3-level pulsed laser He-Ne, gas, 4-level

Argon ion, gas

CO 2 – molecular gas laser Neodymium – solid-state

Diode laser Dye – liquid laser

Laser Applications Communications Coding information, fiber optics

Medical uses

Materials processing Science

Laser Tweezers

Holography