I was inspired to ask such a question by this New York Times article, which basically says blue sparks creativity while red may help accuracy, among other things.
That led me to wonder why red is always the color of choice for laser sights, red dot sights on firearms, etc. Why not green or any other color?
Red lasers are cheap and easy to make, and we’ve been able to make them cheaper and easier than other colors for a long time. I’m not saying that I know that’s the reason, but it would argue in favor of it.
Got it in one. The first lasers were a ruby rod, surrounded by a strobe light, gradually we added different colors, but for the longest, red dominated, because those could be made with LEDs. Other colors required complex things like assorted gases to be pumped into the laser.
Interesting. So what about moving past “what’s the cheapest option?” and on to “which color makes aiming the easiest?” Is it even possible to study that?
There might also be the (unrelated) advantage that red light is least scattered by the atmosphere, dust and fog, and therefore gives you the longest range from your laser pointer. That alone might make it the easiest and most useful colour to have on a sight.
You can see that scattering through the green lasers that are becoming more and more popular. One of the fun things with them is that you can use them outside to point out stars as they cause a “light trail” up into the sky due to diffraction.
Well, laser sights are past they heydays. Gun people realized that they have a couple of serious drawbacks, like:
So, while we could make study “what color make aiming easies”, the answer nowadays is “collimator/holographic sights are better for quick target acquisition on short to medium range, and low-magnification scopes are best for medium to long range”. Most agencies and armies are either moving away from laser sights or moving towards universal laser devices that integrate infrared laser, rangefinder and painting laser.
Having said all that, laser sights are still quite often purchased by hobbyist because of their coolness factor, and I’ve seen green laser sights available.
Up until recently, infrared and red LEDs had the highest efficiency compared to other color LEDs. That made them perfect candidates for use in laser applications.
This is also the reason blue laser disks (Blu-ray) took so long to reach the market. The technology was there, but there was no way to make a cheap enough high powered blue LED for the laser.
Nowadays they put those annoying blue LEDs everywhere.
Nitpick. Its not due to diffraction (well very little), its due to scattering and reflection (which I guess if you really want to get technical are due to diffraction).
You are right in that laser pointers are VERY handy in pointing out stuff in the night sky out to folks. When you use a laser pointer at night, this nice long thin pencil of light projects way up into the sky. If someone is standing close to you, where the beam appears to “end” in the sky appears to pretty much be in the same place in the sky for both folks.
It sure as heck beats saying “see that bright star over there?”…“which one?”…“that one”…“no, not that one, THAT one”…blah blah blah
Other posters are right that red is pretty much the easiest, cheapest color “to make”, which is just the way physics shook out.
At one point in the past, green and blue lasers were all the bomb, and it wasnt that long ago that blue leds were breakthough news.
A LED and a solid-state LASER or two different things. The ability to manufacture a blue LED doesn’t mean one will be able to manufacture a blue LASER.
True enough, but if you’re going to want a cheap blue laser, you need the cheap blue LED first.
Fight my ignorance, please. Why were/are red lasers cheaper and easier to make?
Please be very careful when doing this: pilots really do not like it and you can end up in court.
See this Pprune thread.
Red lasers, as noted, were easiest to make (it was easier to get the band gap for red and Near Infrared LEDs, if you want to know – it’s harder to push that to the higher energies needed for Green and Blue LEDs). Even now, the green laser pointers that you see don’t use a direct green transition – you’re seeing the result of an infrared laser diode being squeezed through a frequency-doubling crystal. The beam starts out as 1.06 microns and is doubled (with very high efficiency) to 533 nm. That’s why red LEDs for playing with your cat are dirt cheap, while green laser pointers are still pretty pricey. (All that volume of the pointer, by the way, is taken up with the batteries that power the laser. The actual laser and the frequency doubling crystal are incredibly thin).
Shorter wavelength laser diodes are available, but the technology is still expensive. Here, for example, is a direct blue laser pointer (not a frequency-tripled NIR laser). But it’s $669. Either pay up, or wait a few years for the price to come down:
I have to disagree with this to an extent. The ability to make a blue LED is absoultely a prerequisite to the ability to make a blue diode laser since the emitted wavelength is dependent upon the semiconductor chemistry. The light-emitting p-n junction is, for all practical purposes, identical in both devices; the main difference between an LED and an injection-type diode laser is the optical cavity–and that’s entirely mechanical.
And if you want to impress your friends, you tell them it’s a DPSS (diode-pumped solid-state) laser .
Well, not quite. Frequency doubling isn’t the same thing as diode pumping – the frequency-doubling crystal isn’t another laser being pumped by the Infrared Laser – it’s a nonlinear crystal that provides output at 1/2 the frequency.
Besides, you can’t pump a visible laser with an infrared laser because of the Stokes shift. Not enough energy*
*unless you use two-photon pumping, which I’ll give you long odds against building a practical laser using. The efficiency just isn’t there.
(bolding mine)
Am I the only one who read this and thought, “Huh, optical physics pr0n”?
Just me, then? Ah, well.
Optics is filled with potentially salacious terms:
**Stimulated Emission
Spontaneous Emission
Degenerate Perturbation Theory
Blackbody Emission
Graybody Emission
Excited States
**
Heck, we measured radiometry in Nits, Lux, and Phots. Don’t try to say them fast.
Not for driving a laser, maybe, but two-photon pumping does have its share of practical applications. I’ve seen some work on using an infrared laser to activate chemotherapy agents using two-photon pumping, for instance-- Activation of the chemical by light allows for more precise targetting, and using two-photon pumping lets you do it with infrared rather than visible light, which penetrates more deeply through tissue.