Stimulated Scattering - Revision history

Lwcamp at 19:06, 7 March 2026

2026-03-07T19:06:22Z

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	==References==		==References==

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

Tshhmon at 21:53, 23 April 2024

2024-04-23T21:53:57Z

← Older revision		Revision as of 14:53, 23 April 2024
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	==References==		==References==

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

Tshhmon at 21:53, 23 April 2024

2024-04-23T21:53:46Z

← Older revision		Revision as of 14:53, 23 April 2024
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	==References==		==References==

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

Lwcamp at 02:01, 13 January 2022

2022-01-13T02:01:02Z

← Older revision		Revision as of 19:01, 12 January 2022
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	It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.		It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.

			A less complicated method is to do what the laser fusion people do, and just use laser pulses with a large spread in frequencies. Any one frequency of your laser now has a much lower intensity to stimulate the Raman scattering.

	==Credit==		==Credit==

Lwcamp at 22:18, 12 January 2022

2022-01-12T22:18:36Z

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	There is a physical phenomenon called Raman scattering where a photon can bounce off an atom or molecule and create two lower energy photons that add up to the same energy. Usually one of them will be deep in the infrared, the other just has all the energy that wasn’t used up making that infrared photon (which is usually most of it). This is usually a very weak process, and for practical purposes we wouldn’t usually need to worry about it. However ...		There is a physical phenomenon called Raman scattering where a photon can bounce off an atom or molecule and create two lower energy photons that add up to the same energy. Usually one of them will be deep in the infrared, the other just has all the energy that wasn’t used up making that infrared photon (which is usually most of it). This is usually a very weak process, and for practical purposes we wouldn’t usually need to worry about it. However ...

	~~Now, if~~ you have a whole bunch of photons of the same energy (like a laser beam) going past atoms (like if the beam is in the air), and a photon of just the right energy happens to come past corresponding to the Raman scattered photons (like if one of the other photons in the beam had undergone Raman scattering), it can make a photon that normally would have just minded its own business undergo Raman scattering to give a photon that matches the incoming scattered photon. Then this scattered photon can make even more of the original photons also scatter. This is just the same stimulated emission process that makes lasers work, but now it is removing photons from your beam!		If you have a whole bunch of photons of the same energy (like a laser beam) going past atoms (like if the beam is in the air), and a photon of just the right energy happens to come past corresponding to the Raman scattered photons (like if one of the other photons in the beam had undergone Raman scattering), it can make a photon that normally would have just minded its own business undergo Raman scattering to give a photon that matches the incoming scattered photon. Then this scattered photon can make even more of the original photons also scatter. This is just the same stimulated emission process that makes lasers work, but now it is removing photons from your beam!

	In order for this to become an issue, you need high powers and long distances over which the scattering amplification can occur. Unfortunately, the two things a laser weapon wants to have are high powers and long ranges, Oops.		In order for this to become an issue, you need high powers and long distances over which the scattering amplification can occur. Unfortunately, the two things a laser weapon wants to have are high powers and long ranges, Oops.

Lwcamp at 05:03, 12 October 2021

2021-10-12T05:03:15Z

← Older revision		Revision as of 22:03, 11 October 2021
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	It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.		It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.

			==Credit==
			Author: Luke Campbell

			==References==

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

Lwcamp at 15:19, 29 September 2021

2021-09-29T15:19:18Z

← Older revision		Revision as of 08:19, 29 September 2021
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	It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.		It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.

			[[Category:Lasers]]

Lwcamp: Created page with "What happens when your laser turns the air into a laser? You get stimulated scattering, and it can be a big problem for some kinds of beams. There is a physical phenomenon c..."

2021-09-29T04:50:39Z

Created page with "What happens when your laser turns the air into a laser? You get stimulated scattering, and it can be a big problem for some kinds of beams. There is a physical phenomenon c..."

New page

What happens when your laser turns the air into a laser? You get stimulated scattering, and it can be a big problem for some kinds of beams.

There is a physical phenomenon called Raman scattering where a photon can bounce off an atom or molecule and create two lower energy photons that add up to the same energy. Usually one of them will be deep in the infrared, the other just has all the energy that wasn’t used up making that infrared photon (which is usually most of it). This is usually a very weak process, and for practical purposes we wouldn’t usually need to worry about it. However ...

Now, if you have a whole bunch of photons of the same energy (like a laser beam) going past atoms (like if the beam is in the air), and a photon of just the right energy happens to come past corresponding to the Raman scattered photons (like if one of the other photons in the beam had undergone Raman scattering), it can make a photon that normally would have just minded its own business undergo Raman scattering to give a photon that matches the incoming scattered photon. Then this scattered photon can make even more of the original photons also scatter. This is just the same stimulated emission process that makes lasers work, but now it is removing photons from your beam!

In order for this to become an issue, you need high powers and long distances over which the scattering amplification can occur. Unfortunately, the two things a laser weapon wants to have are high powers and long ranges, Oops.

So will it affect your laser? Let’s calculate it! The distance <math>z_0</math> where we expect stimulated scattering to ruin your beam is about
<ref name=Nielsen-2012>Philip E. Nielsen, “Effects of Directed Energy Weapons”, (2012)</ref>
<div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><math>
z_0 = \frac{25 \, \pi \, S \, D }{ 4 \, g \, P}
</math></div>
where <math>S</math> is the spot diameter at the target, <math>D</math> is the diameter of the focusing aperture, <math>P</math> is the beam power, and <math>g</math> is the gain. In Earth-like air, the gain for any particular wavelength <math>\lambda</math> and pulse duration <math>t</math> can be estimated with
<ref name=Zemlyanov_2004>A. A. Zemlyanov and Yu. E. Geints, "Effect of Diffraction on Stimulated Raman Scattering of Laser Radiation in the Middle Atmosphere", Optics and Spectroscopy, Vol. 99, No. 4, 2005, pp. 620–629. Translated from Optika i Spektroskopiya, Vol. 99, No. 4, 2005, pp. 644–654.</ref>
<ref name=Ruhua_1995>Song Ruhua and Yue Shixiao, "Stimulated Rotational Raman Scattering of N<math>_2</math> in the Atmosphere", National Air Intelligence Center NAIC-ID(RS)T-0443-93</ref>
<ref name=Rokni_1986>M. Rokni and A. Flusberg, Stimulated Rotational Raman Scattering in the Atmosphere, IEEE Journal of Quantum Electronics, Vol. QE-22, No. 7, pg. 1102-1108, (1986)</ref>
<ref name=Ori_1990>A. Ori, B. Nathanson, and M. Rokni, The Threshold for Transient Stimulated Rotational Raman Scattering in the Atmosphere, J. Phys. D: Appl. Phys. 23 (1990) 142-149</ref>
<div class="center" style="width: auto; margin-left: auto; margin-right: auto;"><math>
g = g_0 \, \frac{\lambda}{\lambda_0} \, \frac{t}{t+\tau}
</math></div>
where <math>g_0 = 2.6 \times 10^{-14} \mbox{m}/\mbox{W}</math>, <math>\lambda_0 = 1.057 \times 10^{-6} \mbox{m}</math>, and <math>\tau = 5 \times 10^{-9} \mbox{s}</math>.

It may be possible to preempt unwanted stimulated scattering by emitting small amounts of light in the Raman-shifted wavelengths in laser modes that focus along with the main pulse. Now these additional modes will cause all the stimulated scattering first, before random Raman scattering from the air can build up. So even though you still get runaway Raman scattering, it will still be adequately focused on your target. If this mode will in turn succumb to stimulated scattering before it reaches its target, inject a second mode to preempt its stimulated scattering, and so on.