Lasers and the electromagnetic spectrum - Revision history

Lwcamp at 19:03, 7 March 2026

2026-03-07T19:03:33Z

← Older revision		Revision as of 12:03, 7 March 2026
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	==References==		==References==

	[[Category:Lasers]][[Category:Beams]][[Category:Physics]][[Category:Physics & Engineering‏‎]]		[[Category:Lasers]][[Category:Beams]][[Category:Physics]][[Category:Physics & Engineering‏‎]][[Category:Physics & Math & Engineering]]

Lwcamp: /* The Nature of Light */

2025-04-08T23:18:19Z

The Nature of Light

← Older revision		Revision as of 16:18, 8 April 2025
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	You knew we had to go through this, didn’t you? Lasers are made of light, so we need some understanding of some of the basic physics of light in order to really grok lasers. Light is made when an accelerating charged particle shakes off some of its electric or magnetic field. These bits of free field naturally end up re-making themselves in such a way that they fly off and propagate through space as a wave. All the stuff that you see is actually wiggling bits of electric and magnetic fields continually re-making themselves almost like they were dragging themselves along by their bootstraps.		You knew we had to go through this, didn’t you? Lasers are made of light, so we need some understanding of some of the basic physics of light in order to really grok lasers. Light is made when an accelerating charged particle shakes off some of its electric or magnetic field. These bits of free field naturally end up re-making themselves in such a way that they fly off and propagate through space as a wave. All the stuff that you see is actually wiggling bits of electric and magnetic fields continually re-making themselves almost like they were dragging themselves along by their bootstraps.

	As you might guess from the name, these wiggling waves zip around at the speed of light. But we need to be a wee bit careful here, because light goes a bit slower through a transparent medium like water or glass or even air than it does through the vacuum of space. In air, light moves so close to the speed of light in vacuum that we can usually ignore the difference. But in transparent condensed materials like water or glass, the light might only be going ~~<math>\frac{~~2}{3~~}</math>~~ or ~~<math>\frac{~~1}{2~~}</math>~~ or even less of the speed in vacuum.		As you might guess from the name, these wiggling waves zip around at the speed of light. But we need to be a wee bit careful here, because light goes a bit slower through a transparent medium like water or glass or even air than it does through the vacuum of space. In air, light moves so close to the speed of light in vacuum that we can usually ignore the difference. But in transparent condensed materials like water or glass, the light might only be going 2/3 or 1/2 or even less of the speed in vacuum.

	As a wave, light has a number of properties that can be used to describe it. One is the wavelength - how far it is from the crest of the wave to the crest of the next cycle. This is closely related to the frequency - if you are staying in one spot, how many times does the light wave go up and down in a given amount of time. If you multiply the frequency and wavelength together, you will get the speed of the wave. So with a bit of algebra and knowing that light moves at the speed of light, if you know the wavelength you can find the frequency, and vice versa. When light goes from one material to another, the frequency stays the same but the wavelength changes. Many people characterize light by its wavelength - almost always they are talking about its vacuum wavelength, not the wavelength it has in any particular medium.		As a wave, light has a number of properties that can be used to describe it. One is the wavelength - how far it is from the crest of the wave to the crest of the next cycle. This is closely related to the frequency - if you are staying in one spot, how many times does the light wave go up and down in a given amount of time. If you multiply the frequency and wavelength together, you will get the speed of the wave. So with a bit of algebra and knowing that light moves at the speed of light, if you know the wavelength you can find the frequency, and vice versa. When light goes from one material to another, the frequency stays the same but the wavelength changes. Many people characterize light by its wavelength - almost always they are talking about its vacuum wavelength, not the wavelength it has in any particular medium.

Lwcamp: /* Short-wave infrared */

2025-02-15T01:22:06Z

Short-wave infrared

← Older revision		Revision as of 18:22, 14 February 2025
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	==Short-wave infrared==		==Short-wave infrared==
	Short-wave infrared is a good choice when you are looking for a color of light that [[Diffraction\|focuses well]], [[Attenuation\|can get through air]], can maintain a tight focus without [[Two-Photon Absorption\|two-photon ionization]] messing it up, and that won’t pose a severe blinding hazard to anyone nearby. It is the shortest wavelength (and thus longest ranged) color of infrared that is eye-safe. You won’t get eye-safe colors again until you are up into the ultraviolet.		Short-wave infrared is a good choice when you are looking for a color of light that [[Diffraction\|focuses well]], [[Attenuation\|can get through air]], can maintain a tight focus without [[Two-Photon Absorption\|two-photon ionization]] messing it up, and that won’t pose a severe blinding hazard to anyone nearby. It is the shortest wavelength (and thus longest ranged) color of infrared that is mostly eye-safe - your eye is more sensitive to heat than your skin so your eye still might get cooked, but at least it can't get through your eye gunk to directly burn your retina. You won’t get eye-safe colors again until you are up into the ultraviolet.

	Some modern lasers can output high power short-wave infrared beams, primarily fiber lasers.		Some modern lasers can output high power short-wave infrared beams, primarily fiber lasers.

Lwcamp: /* Near ultraviolet */

2025-02-15T01:19:42Z

Near ultraviolet

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	This region of the spectrum is made up of invisible colors with shorter wavelengths than we can see that [[Attenuation\|can still go through air]]. But although these colors can get through sea level air, ozone in the upper atmosphere does a pretty good job of absorbing ultraviolet light with wavelengths shorter than 0.34 μm. So if you want to use your laser to shoot things on the ground from your spacecraft, choose a wavelength longer than 0.34 μm. Ultraviolet light is scattered more by air than visible light, which makes it more favorable to use visible light for shooting things on Earth from a spacecraft. But on an alien planet, the scales may tip in favor of ultraviolet.		This region of the spectrum is made up of invisible colors with shorter wavelengths than we can see that [[Attenuation\|can still go through air]]. But although these colors can get through sea level air, ozone in the upper atmosphere does a pretty good job of absorbing ultraviolet light with wavelengths shorter than 0.34 μm. So if you want to use your laser to shoot things on the ground from your spacecraft, choose a wavelength longer than 0.34 μm. Ultraviolet light is scattered more by air than visible light, which makes it more favorable to use visible light for shooting things on Earth from a spacecraft. But on an alien planet, the scales may tip in favor of ultraviolet.

	Ultraviolet light is eye-safe at wavelengths ~~shorter than~~ 0.35 μm. Some ultraviolet-A colored light can get through window glass, but ultraviolet-B or C cannot. So if you are shooting your laser gun at someone on the other side of a window, choose ultraviolet-A or longer wavelengths.		Ultraviolet light is reasonably eye-safe at wavelengths between approximately 0.35 μm to 0.38 μm. Longer waves can get through the eye to burn your retina. Shorter waves risk causing cataracts. The eye is more sensitive to heat than skin, so at intensities where the UV light is painful but non-burning to your skin it might be cooking your eye. And of course any true laser weapon will instantly destroy your eye (and much of the rest of your head) on a direct hit. But UV light in this range might be attractive for allowing your soldier to use lasers and not be at as much risk of eye injury as with other colors.

			Some ultraviolet-A colored light can get through window glass, but ultraviolet-B or C cannot. So if you are shooting your laser gun at someone on the other side of a window, choose ultraviolet-A or longer wavelengths.
	<table border=1>		<table border=1>
	<tr><td>Color <td>Frequency <td>Wavelength <td>Energy		<tr><td>Color <td>Frequency <td>Wavelength <td>Energy

Lwcamp: /* Near ultraviolet */

2025-02-15T01:13:30Z

Near ultraviolet

← Older revision		Revision as of 18:13, 14 February 2025
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	==Near ultraviolet==		==Near ultraviolet==
	This region of the spectrum is made up of invisible colors with shorter wavelengths than we can see that [[Attenuation\|can still go through air]]. But although these colors can get through sea level air, ozone in the upper atmosphere does a pretty good job of absorbing ultraviolet light with wavelengths shorter than 0.34 μm. So if you want to use your laser to shoot things on the ground from your spacecraft, choose a wavelength longer than 0.34 μm. Ultraviolet light is scattered more by air than visible light, which makes it more favorable to use visible light for shooting things on Earth from a spacecraft. But on an alien planet, the scales may tip in favor of ultraviolet. And if you are shooting down within the atmosphere, the optimum color depends on the range to the target. And there is also the issue that high powered ultraviolet pulses are likely to be absorbed due to [[Two-Photon Absorption\|two-photon absorption]] before they get to their target.		This region of the spectrum is made up of invisible colors with shorter wavelengths than we can see that [[Attenuation\|can still go through air]]. But although these colors can get through sea level air, ozone in the upper atmosphere does a pretty good job of absorbing ultraviolet light with wavelengths shorter than 0.34 μm. So if you want to use your laser to shoot things on the ground from your spacecraft, choose a wavelength longer than 0.34 μm. Ultraviolet light is scattered more by air than visible light, which makes it more favorable to use visible light for shooting things on Earth from a spacecraft. But on an alien planet, the scales may tip in favor of ultraviolet.

	Ultraviolet light is eye-safe at wavelengths shorter than 0.35 μm. Some ultraviolet-A colored light can get through window glass, but ultraviolet-B or C cannot. So if you are shooting your laser gun at someone on the other side of a window, choose ultraviolet-A or longer wavelengths.		Ultraviolet light is eye-safe at wavelengths shorter than 0.35 μm. Some ultraviolet-A colored light can get through window glass, but ultraviolet-B or C cannot. So if you are shooting your laser gun at someone on the other side of a window, choose ultraviolet-A or longer wavelengths.

Lwcamp: /* Visible */

2025-02-15T01:12:31Z

Visible

← Older revision		Revision as of 18:12, 14 February 2025
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	Yeah baby! Now we’re talkin’! Flashing beams lighting up the sky for stunning visual effects, strobing flashes where the beams hit. These are the beams you can really see! Except for the minor detail that if you ever do actually see one in person, there’s a good chance you won’t ever see anything again. But we’ll ignore that for the sake of a good special effects loaded sci-fi extravaganza.		Yeah baby! Now we’re talkin’! Flashing beams lighting up the sky for stunning visual effects, strobing flashes where the beams hit. These are the beams you can really see! Except for the minor detail that if you ever do actually see one in person, there’s a good chance you won’t ever see anything again. But we’ll ignore that for the sake of a good special effects loaded sci-fi extravaganza.

	[[Attenuation\|The air is very transparent to visible light]]. It turns out that water is also at around its optimal transparency to visible light in the green, blue, and violet colors, so lasers of these colors might be the choice for underwater combat (or at least, underwater combat where you are close enough to see your enemy). ~~If you want maximum range in air without [[Two-Photon Absorption\|two photon absorption]] making your life miserable when your beam reaches close focus, visible light is the color choice for you.~~		[[Attenuation\|The air is very transparent to visible light]]. It turns out that water is also at around its optimal transparency to visible light in the green, blue, and violet colors, so lasers of these colors might be the choice for underwater combat (or at least, underwater combat where you are close enough to see your enemy).

	Visible light is where you start having significant losses due to [[Attenuation#Scatter\|Rayleigh scattering]] for light going all the way through an Earth-like atmosphere. Shorter wavelengths (the closer to violet) are scattered more than longer wavelengths (closer to red). But still, the shorter wavelengths focus better because of diffraction. When shooting straight down through Earth’s atmosphere, you still get the best laser intensity with violet light (even though your beam will have less energy, that energy will still be more concentrated). But as you shoot at more and more of an angle, the best choice goes toward longer and longer wavelengths. And for alien planets, all bets are off.		Visible light is where you start having significant losses due to [[Attenuation#Scatter\|Rayleigh scattering]] for light going all the way through an Earth-like atmosphere. Shorter wavelengths (the closer to violet) are scattered more than longer wavelengths (closer to red). But still, the shorter wavelengths focus better because of diffraction. When shooting straight down through Earth’s atmosphere, you still get the best laser intensity with violet light (even though your beam will have less energy, that energy will still be more concentrated). But as you shoot at more and more of an angle, the best choice goes toward longer and longer wavelengths. And for alien planets, all bets are off.

Tshhmon at 21:41, 23 April 2024

2024-04-23T21:41:16Z

← Older revision		Revision as of 14:41, 23 April 2024
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	==References==		==References==

	[[Category:Lasers]][[Category:Beams]][[Category:Physics]][[Category:Physics ~~& Math~~ & Engineering‏‎]]		[[Category:Lasers]][[Category:Beams]][[Category:Physics]][[Category:Physics & Engineering‏‎]]

Lwcamp at 18:50, 26 August 2022

2022-08-26T18:50:09Z

← Older revision		Revision as of 11:50, 26 August 2022
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	==References==		==References==

	[[Category:Lasers]][[Category:Beams]][[Category:Physics]]		[[Category:Lasers]][[Category:Beams]][[Category:Physics]][[Category:Physics & Math & Engineering‏‎]]

Sevoris at 15:42, 26 August 2022

2022-08-26T15:42:42Z

← Older revision		Revision as of 08:42, 26 August 2022
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	==References==		==References==

	[[Category:Lasers]][[Category:Beams]]		[[Category:Lasers]][[Category:Beams]][[Category:Physics]]

Lwcamp at 01:06, 20 August 2022

2022-08-20T01:06:13Z

← Older revision		Revision as of 18:06, 19 August 2022
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	==References==		==References==

	[[Category:Lasers]]		[[Category:Lasers]][[Category:Beams]]