Quote:Original post by LessBread
Laser beams already emit waves at frequencies beyond the range of human hearing. The upper range of human hearing is ~22kHz (10^3 Hz == kHz). Visible light is in the hundreds of terahertz range (10^12 Hz == THz).

I doubt the frequency of laser beams would alter the frequency of the sound you hear coming from the plasma bursts. A higher frequency means more energy means more bursts, but it's very likely that there are already more bursts occurring than the ones you hear, so increasing the number of bursts won't likely change the frequency, just the amplitude (in other words, same pitch only louder).

I want to say its like the sound coming from a hive of bees. Add more bees and the frequency of the sound doesn't change (just it's amplitude). To change the frequency would mean getting every last bee to beat it's wings faster. The bee comparison only goes so far.

As for which gas to use, my initial thought was one of the noble gases (ie. helium, neon, argon, krypton, xenon). But the links ddn3 provided show that the technique works in air, so nitrogen and oxygen!

Quote:
The laser light source we used in this work is a high-quality and high–brightness infrared pulsed laser (repetition frequency of pulse: approximately 100 Hz), by which plasma production can be more precisely controlled, enabling brighter and higher contrast image drawing. In addition, the distance between the device and drawing points can be greatly extended (several meters).

Quote:Original post by nagromo

Quote:Original post by SteveDeFacto
Actually no they are using a infrared pulse laser that has a frequency of approximately 100Hz:

That's the pulse repetition rate, not the laser frequency, which is infrared (over 1 THz).

I think you're right, though; that buzz sounds like a square wave between 60Hz and 100Hz.

You can still hear the harmonics from the pulse edges, though; if you were able to get the pulse rate well over 20 kHz (which will be quite difficult), I expect you would still hear broadband noise/buzz from the decay of the plasma.

Quote:Original post by nagromo
that buzz sounds like a square wave between 60Hz and 100Hz.

Quote:Original post by SteveDeFacto
The heating of the air causes it to expand quickly which makes the popping sound.

Quote:Original post by ddn3
Sure you won't hear it above 20kHZ but your dog would go crazy and your cat would try to scratch ur eyes out...:)

-ddn

Quote:Original post by nagromo

Quote:Original post by SteveDeFacto

Quote:Original post by ddn3
Sure you won't hear it above 20kHZ but your dog would go crazy and your cat would try to scratch ur eyes out...:)

-ddn

Actually from what I read I do not believe it needs to pulse at all! I think the reason they are using a pulse is to allow time for the motor to readjust to a new position without leaving a trail. All they really need to do is draw the image instead of trying to create individual pixels.

I don't think they realize how useless the noise makes it and they are just going for the most dynamic approach.

I think they're using a pulse because of the incredible amount of power required to create plasma.

Each pulse is about 1ns long, and they're only doing 100 pulses per second. If they used the same average power but spread it out to continuous, the air would cool itself and never get hot enough to make plasma.

If they used the same pulse power but made it continuous, they would be generating 10,000,000 times more heat in the laser, which would burn it out really quickly.

Even just pushing it from 100 Hz to 20 kHz would require 200 times more cooling, which would make it much bigger (and also put more stress on the mirrors).

Quote:
The laser light source we used in this work is a high-quality and high–brightness infrared pulsed laser (repetition frequency of pulse: approximately 100 Hz), by which plasma production can be more precisely controlled, enabling brighter and higher contrast image drawing. In addition, the distance between the device and drawing points can be greatly extended (several meters).