The science and engineering of light!
When dealing more specifically with individual photons, we usually call it photonics.
Often just called collimated light due to the collimator being the main procedure to obtain it.
However, you move very far away from the source, e.g. the Sun, you also get essentially parallel light.
The most important type of lens is the biconvex spherical lens.
Focal length
Each side is a sphere section. They don't have to have the same radius, they are still simple to understand with different radiuses.
The two things you have to have in mind that this does are:
  • converges parallel light to a point at center at distance known as the focal length.
    This is for example why you can use lenses to burn things with Sun rays, which are basically parallel.
    Conversely, if the input is a point light source at the focal length, it gets converted into parallel light.
  • image formation: it converges all rays coming from a given source point to a single point image. This amplifies the signal, and forms an image at a plane.
    The source image can be far away, and the virtual image can be close to the lens. This is exactly what we need for a camera.
    For each distance on one side, it only works for another distance on the other side. So when we set the distance between the lens and the detector, this sets the distance of the source object, i.e. the focus. The equation is:
    where and are the two distances.
If you pass parallel light.
For a biconvex spherical lens, it is given by:
  • n: f nidnex
Video 1. Carl Zeiss, Explained by Asianometry (2021) Source.
Video 2. How Carl Zeiss Crafts Optics for a $150 Million EUV Machine. Source. Difficulty: light at those frequencies get absorbed by lenses. So you have to use mirrors instead.
Subsidiary of Carl Zeiss AG and also part owned by ASML, sole optics vendor of ASML as of 2020.
Can be approximated with a diaphragm.
The science and engineering of photons!
A bit more photon-specific than optics.
Video 1. Silicon Photonics: The Next Silicon Revolution? by Asianometry (2022) Source.
Video 2. Running Neural Networks on Meshes of Light by Asianometry (2022) Source.
Video 3. Silicon Photonics for Extreme Computing by Keren Bergman (2017) Source.
The knowledge that light is polarized precedes the knowledge of the existence of the photon, see polarization of light for the classical point of view.
The polarization state and how it can be decomposed into different modes can be well visualized with the Poincaré sphere.
One key idea about photon polarization is that it carries angular momentum. Therefore, when an electron changes orbitals in the Schrödinger equation solution for the hydrogen atom, the angular momentum (as well as energy) change is carried out by the polarization of the photon!
Video 1. Quantum Mechanics 9b - Photon Spin and Schrodinger's Cat II by ViaScience (2013) Source.
  • clear animations showing how two circular polarizations can make a vertical polarization
  • a polarizer can be modelled bra operator.
  • light polarization experiments are extremely direct evidence of quantum superposition. Individual photons must be on both L and R states at the same time because a V filter passes half of either L or R single photons, but it passes all L + R photons
This section discusses the pre-photon understanding of the polarization of light. For the photon one see: photon polarization.
People were a bit confused when experiments started to show that light might be polarized. How could a wave that propages through a 3D homgenous material like luminiferous aether have polarization?? Light would presumably be understood to be analogous to a sound wave in 3D medium, which cannot have polarization. This was before Maxwell's equations, in the early 19th century, so there was no way to know.
A device that modifies photon polarization.
Particularly cool is to see how Fresnel fully understood that light is somehow polarized, even though he did not know that it was made out of electromagnetism, clear indication of which only came with the Faraday effect in 1845.
At the beginning of the nineteenth century the only known way to generate polarized light was with a calcite crystal. In 1808, using a calcite crystal, Malus discovered that natural incident light became polarized when it was reflected by a glass surface, and that the light reflected close to an angle of incidence of 57° could be extinguished when viewed through the crystal. He then proposed that natural light consisted of the s- and p-polarizations, which were perpendicular to each other.
Matches the quantum superposition probability proportional to the square law. Poor Étienne-Louis Malus, who died so much before this was found.
A more photon-specific version of the Bloch sphere.
In it, each of the six sides has a clear and simple to understand photon polarization state, either of:
  • left/right
  • diagonal up/diagonal down
  • rotation clockwise/counterclockwise
The sphere clearly suggests for example that a rotational or diagonal polarizations are the combination of left/right with the correct phase. This is clearly explained at: Video "Quantum Mechanics 9b - Photon Spin and Schrodinger's Cat II by ViaScience (2013)".
Figure 1. Poincare sphere. Source.
An optical multiplexer!
Video 1. Control Light with Sound! by Les' Lab (2021) Source.
Video 1. Fabry Perot Interferometer by JFC UCL (2016) Source. Description only, reasonable animations. Considers the case of two nearby beam splitters.
Video 2. Fabry-Perot Introduction by Williams College Physics (2020) Source.
Shows a working device. Confocal optical cavity, one of the mirrors scans back and forward moved by a piezoelectric motor, this is called a "scanning Fabry-Perot interferometer".
Does not produce an interference pattern, only an on/off blob, which is then fed into an oscilloscope for analysis. The oscilloscope shows both the mirror displacement (which is given by a voltage) and the light detector output.
Video 3. Aligning a Scanning Fabry-Perot Interferometer by University of South Florida (2016) Source. Very detailed, and shows of some nice equipment and techniques.
Video 1. The Story of Light by Bell Labs (2015) Source. A ultra quick and Bell Labs focused overview of the development of optical fibre.
For example, that is how most modern microscopes are prototyped, see for example Video "Two Photon Microscopy by Nemonic NeuroNex (2019)".
This is kind of why they are also sometimes called "optical breadboarbds", since breadboards are what we use for early prototyping in electronics. Wikipedia however says "optical breadboard" is a simpler and cheaper type of optical table with less/no stabilization.
Video 1. A simple refracting telescope built on an optical bench by plenum88 (2013) Source.

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