Lasers produce light waves {coherent light}| that have same phase.
Light passed through consecutive slits {collimate}| has many light waves in phase.
Devices {laser}| {Light Amplification by Stimulated Emission of Radiation} can emit many photons in phase [1960].
light source
Flash tube excites atom electrons into highest orbital. Below highest orbital are one or two lower-energy levels, and below them is ground-state level.
light
Electrons spontaneously fall to intermediate-energy level by vibration, rotation, or radiation.
Then previous photon causes electron to fall to next-lower level {lase}, which simultaneously makes another photon, so both photons are in phase and photon number doubles. This process repeats to make many in-phase photons. Lasers can emit light axially or transversely.
collimation
Photons conserve momentum, so they have same direction.
amplitude
Mirrors can build power by repeated lasing and reflecting, until shutter opens {Q switching} and light releases. Shutter can be rotating mirror, Pockels cell, photochemical, or exploding film. Current modulation can modify laser amplitude. Lasers can pulse or be continuous. Laser can be tunable to different light frequencies.
materials
Lasers can use helium-neon, helium-cadmium, argon, krypton, carbon dioxide, and gallium arsenide. Ruby lasers emit red light. Gallium-nitride lasers emit blue light. Zinc selenide can also make blue light.
purposes
Lasers can align exactly, measure distances by reflection from corner reflectors, attach retinas by burning them on, weld, and make holographs. Lasers can separate atom isotopes, by exciting only one isotope. Lasers can measure thickness, drill holes, and carve miniature circuit blocks. Lasers can implode pellet to start nuclear fusion in tube {hohlraum}.
fiber optics
Laser light passed down non-linear optical fiber {microstructure fiber} broadens in wavelength {supercontinuum light}. Light can alter material, which then alters light {self-phase modulation}.
timing
Lasers {mode-locked laser} can make one-femtosecond microwave or light pulses at 1-GHz. Frequencies are visible light within 150-nm wavelength interval. Superposition makes pulses have few wavelengths. Phase {offset frequency} increases slightly with each pulse. Wave-train pulses have higher net frequencies until cycling again, with equal spacing. Pulses are beats, so pulse frequency is lower-frequency frequency difference. Given reference frequency, beat frequency can determine unknown frequency.
Storing light-wave interference patterns {hologram}| on photographic plates {holograph} allows display of three-dimensional images [Gabor, 1946].
production
Coherent light can shine directly on photographic plate and can reflect from static scene onto plate. Wave-front superposition makes interference pattern that photographic plate can record.
projection
Shining coherent light on or through photographic plate can project scene wave front into space. Plate positions contribute to all image points, whereas photograph points contribute to one image point. Observer sees wave front coming from three-dimensional space, rather than from surface. Observer can view image from different points to see image from different perspectives.
Shining coherent light on part of plate makes whole image but with lower resolution, because number of contributions is less, so standard error is more. Using longer-wavelength coherent light to reconstruct image can magnify image size. Using shorter wavelength coherent-light to reconstruct image reduces image size.
5-Physics-Wave-Electromagnetic
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Date Modified: 2022.0225