Diode-Pumped Lasers not using flash tubes?

Elusid · Aug 17, 2012

I’ve been working in the entertainment industry for over a decade, primarily as an electrician, so I’m always dealing with different types of lighting fixtures. I realized though I never learned how the optics work particularly lasers. I’ve been doing research on them and I have a few questions as well as a few ideas I’d like to bounce off all of you. I did a few quick searches in the forum so hopefully these haven’t been asked before.

(1) A ruby laser uses a flash tube surrounding a ruby that excites the particles inside, amplifies the energy, and emits it out the end correct? Is there any reason the same effect can’t be achieved by surrounding the crystal with a tight array of white SMD LEDs?

(2) I’ve read a bit on active laser mediums for diode-pumped lasers. They use different kinds of doped crystals and from what I’ve seen all use some kind of flash tube to excite the particles. Is there some kind of medium that when formed into a rod will absorb surrounding light and emit it out the ends but be the same color as the light source? I assume it wouldn’t excite particles and amplify them but simply absorb and reflect internally like a sort of edge lit fiber optic.

(3) I’ve seen several diagrams of a single LED being focused using a reflector and a collimating lens to create a pretty narrow beam. Is it possible to take an array of LEDs all pointing toward the center of the lens to create the same effect but brighter?

My end goal is to create a beam of light with as little divergence as possible using LEDs and adding LEDs to the array or around the rod would increase its intensity. I would like something more durable than a flash tube and using LEDs adds the option of RGB/CMY color mixing. If anyone has any other suggestions I’m all ears… Well eyes in this case.

Things · Aug 17, 2012

1. Yes. No, SMD LED's or LED's of any kind won't work. You need extremely high power densities to pump the rod. Flashlamps are used because they can produce these extremely high power densities, but only for very short times.

2. Diode pumped lasers don't use flashlamps, they use diodes, thus the name. Flashlamp pumped lasers use flashlamps

And no, I believe no such medium exists that'll actually lase.

3. No, since light bouncing into a lens at different angles will always come out at different angles, you'd need a single, high power LED. This is why LED fixtures have been struggling for the last few years, their power density vs things like metal halide are pretty poor. High power LED's tend to have a large emitting area.

For your application, I'd probably look at using a conventional discharge type lamp, dichroic filters and lenses, like the Clay Paky Sharpy's, Alternatively, you could build a laser projector which would allow multicolour beams, but they become expensive very quickly.

Elusid · Aug 17, 2012

I love Clay Paky's Sharpy. That's one of the things that got me on the idea in the first place. Have you seen the videos of ~24 of them in a row? They do some AMAZING effects when all combined.

So with a diode-pumped laser you can use rows of lower power diodes to create one high power beam right? Can you use IR diodes and depending what medium you fire them into will it create a different wavelength? Is there any medium that is preferred over another?

Oh also have you seen ETCs new S4 LED fixture? I used to work at a company called Barbizon and we were able to get our hands on a demo before they were released. They use a combination of RGBCMY LEDs in a hexagonal array. Does it work though because they aren't making a collimated beam?

Meatball · Aug 17, 2012

Elusid said:
I’ve been working in the entertainment industry for over a decade, primarily as an electrician, so I’m always dealing with different types of lighting fixtures. I realized though I never learned how the optics work particularly lasers. I’ve been doing research on them and I have a few questions as well as a few ideas I’d like to bounce off all of you. I did a few quick searches in the forum so hopefully these haven’t been asked before.

(1) A ruby laser uses a flash tube surrounding a ruby that excites the particles inside, amplifies the energy, and emits it out the end correct? Is there any reason the same effect can’t be achieved by surrounding the crystal with a tight array of white SMD LEDs?

(2) I’ve read a bit on active laser mediums for diode-pumped lasers. They use different kinds of doped crystals and from what I’ve seen all use some kind of flash tube to excite the particles. Is there some kind of medium that when formed into a rod will absorb surrounding light and emit it out the ends but be the same color as the light source? I assume it wouldn’t excite particles and amplify them but simply absorb and reflect internally like a sort of edge lit fiber optic.

(3) I’ve seen several diagrams of a single LED being focused using a reflector and a collimating lens to create a pretty narrow beam. Is it possible to take an array of LEDs all pointing toward the center of the lens to create the same effect but brighter?

My end goal is to create a beam of light with as little divergence as possible using LEDs and adding LEDs to the array or around the rod would increase its intensity. I would like something more durable than a flash tube and using LEDs adds the option of RGB/CMY color mixing. If anyone has any other suggestions I’m all ears… Well eyes in this case.

Things is completely right, but I think I have some more to add.

1. About pumping, other reasons why flashlamps and arc lamps are used include the emission tunability of gas discharge tubes, the ability to effectively couple the tube's output into a rod, and of course the possible peak power which proves to be very effective. Laser rods for instance can't absorb every wavelength to the point of stimulation - causing the population inversion. Just because you can aim lots of light into a tube doesn't at all mean that it would be absorbed. LEDs start to look very weak at this point. Early YAG rods were pumped with LEDs but stimulated emission from the rods amounted to micro-watts. Laser diodes and flashlamps were found to be much better.

2. Aside from classical optics, and some kind of nasty edge absorbing fiber, I don't know of any design that allows for that. So there's actually a relatively new material called Pr

AYAC which has strong absorption lines at 445nm. Interestingly, it can lase at 444nm. Sadly, this is not commercially produced material.

3. Simply, no. LEDs have a bandwidth ~50nm wide, so that means it could be focused to a beam. But it would be highly divergent and nothing "laser like".

Your best bet is... lasers. Probably laser diodes. Still solid state, very reliable, pretty easy to find and purchase. Combine your red, green, and blue beams with dichroic mirrors to achieve a color tunable white beam for your different colors.

Does any of that help?

Elusid · Aug 17, 2012

Yes it does. Thank you! Somewhat disappointing but it is what it is.

Diode-Pumped Lasers not using flash tubes?

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