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The first laser was built in 1960

2026-08-08 · 09:28 UTC ·@Object_Zero_ ·2 min read

Brief

Lasers: the post explains the 1960 ruby laser built by pumping a ruby rod with a bright lamp and mirrors to create population inversion, which yields narrow-wavelength emission; stimulated emission produces coherent, in-phase photons. The author notes it is striking that lasers were not discovered during WWII (1939–1945) despite Manhattan Project physicists.

Why it matters

The first laser was built in 1960: a ruby laser assembled from a ruby rod and a bright surrounding lamp/mirror arrangement to 'pump' the crystal.

Key details

  • A laser pump floods the crystal with photons to reach population inversion (more atoms in excited than lower states), producing narrow-wavelength spontaneous emission when atoms decay.
  • Stimulated emission occurs when an incoming photon induces an excited atom to emit a second, in-phase photon (coherence); the author argues a coherent laser parallels a supercritical nuclear chain reaction and finds it curious that no lasers were discovered during WWII (1939–1945) despite the concentration of physicists in the Manhattan Project.
Source evidence

Lasers

This is actually a pretty new technology, there were no lasers in WWII which is very strange in hindsight because lasers are actually very simple devices and have a huge array of applications that would have been very useful during the war.

The first laser was put together in 1960, it was a ruby laser, and this is how it works…

You need a rod of ruby (which you can synthesise) and you just wrap a very bright lamp around it so that you can saturate the ruby with lots of photons.

When you hear about a laser being “pumped” or a “laser pump” it just means a very bright lamp and a bunch of mirrors to direct a lot of photons into a crystal.

Once the Ruby has a lot of photons inside it achieves a state called “population inversion” this just means more of the atoms are in a higher energy state or excited state than are in a lower energy state.

Usually such a state is not possible because a thermal equilibrium is reached, but in some cases you can achieve population inversion.

When this happens, there are spontaneous decay events among the atoms to the lower energy state, and yes you guessed it, these decay events emit a quantum of energy, a photon, with a very specific wavelength that depends on the type atom that changed energy state.

So a laser is just a crystal that is flooded with photons to pump it into population inversion, and then as some atoms decay to a lower state the emission is a light with a very narrow frequency band and so a very pure colour.

The decay is random and so the photons are emitted with random phase (they are incoherent).

HOWEVER, you can also get stimulated emission where a photon knocks an atom out of a higher energy state and into a lower energy state and thus produces a second photon.

Simulated emission is not spontaneous decay, and so these photons ARE in phase (they are coherent).

And so a coherent laser works a lot like the optical version of a super critical nuclear chain reaction.

And that is why it’s very strange that lasers were not discovered during WWII, because the Manhattan project essentially had every physicist of note in the Western world working on it.

So it is ever so curious that lasers were not formally discovered during WWII.

🤔