The optical table, which was used at the very end, features a lot of hidden physics as well. The most important is probably at the very heart of the table, namely the laser. Lasers are still a fairly recent invention, only having been invented in the 1960s, but are now used in a large variety of fields. This ranges from medical purposes, to microchip production (in the way of photolithography) or even something as mundane as printers. Fundamentally, lasers work on a similar principle as any other form of light, as it excites electrons. This can be done by using thermal energy, like when something is burned, or by letting a current pass through it, like for traditional light bulbs. However, as mentioned briefly in the explanation for spectroscopy, the wavelength of light that is emitted depends heavily on the precise substance that is used, so it is very hard to produce a specific wavelength. Moreover, in these basic emissions, light is spread in all directions. Both of these are addressed by using lasers. Lasers produce light at a specific wavelength and the light is bundled in one direction. This has as a consequence that a laser can be a lot more powerful than other light sources. Unlike traditional light sources, in a laser electrons are made to emit light by interacting with another photon in a process called stimulated emission. There is already some excited material that then interacts with a single photon. Due to quantum mechanics, this photon can affect the state of the material without being absorbed by it. Therefore, the electron returns to a less excited state and in the process emits a photon that is identical to the original, meaning it has the same direction, wavelength and polarization. There are now two photons, which can undergo the same process, which quickly leads to a cascade. So, a large bundle of identical photons are produced which is eventually emitted by the laser. To keep the material in an excited state, there needs to be a constant supply of energy, which is usually provided by electricity. Of course, before the process can be started, the original photon needs to be produced. These components then lead to the most powerful source of light we currently have access to.
