Questions about LEDs for Lasers

Horace · Aug 5, 2009

Ok folks, my buddy just received a blu-ray laser that Igor built for him. I noticed that the LEDs that are being used in these "pointers" are in the range of 200mw or there abouts. Im sure there must be a reason, but why are these being built with these small power LEDs compared to like an CREE XRE 1000mA (3.3w) LED? Is it just a matter of those LEDs not being able to be focused into a nice tight beam like the LEDs from Blu-rays??

I ask because if I was to find a way to focus one of the CREE XRE LEDs, I think it woudl be really easy/cheap to make a 3.3w laser.

Whats the deal?

pullbangdead · Aug 5, 2009

Laser diode != LED

An LED emits incoherent light through spontaneous emission. A laser diode emits coherent light through stimulated emission. The laser diode in your IgorT laser does not function in the same way as an LED, and an LED cannot be used in place of a laser diode.

Incoherent light, such as what comes from an LED, cannot be focused in the same way as the coherent light from a laser diode.

Horace · Aug 5, 2009

Well that answers that

. I had never heard of a "laser" diode before, when my buddy started talking about "diodes" being used in lasers, I falsely assumed they were just high power LEDs.

pullbangdead · Aug 5, 2009

Yeah, they're made out of the same stuff, but they function in very different ways as far as the light is concerned. Electrically, they're more similar. But the light output is completely different.

Horace · Aug 5, 2009

So realistically, what is the most powerful laser diode you can get your hands on, and how feasible is it to build a high powered laser (in the order of multiple watts) w/out a diode?

Tech_Junkie · Aug 5, 2009

Horace said:
Well that answers that . I had never heard of a "laser" diode before, when my buddy started talking about "diodes" being used in lasers, I falsely assumed they were just high power LEDs.

Well you know what happens when you assume LOL.

If you want to get into lasers I would suggest taking a week or three and reading the FAQ and other stickies in the forum like the rest of us did when we were new. If you dont understand something there is the search button. You will more than likely get flamed if you ask a question without doing any research first. This is because the same stupid questions get asked over, and over when all the new member had to do was click the search button. http://laserpointerforums.com/search.php

Good luck!!!

pullbangdead · Aug 5, 2009

Horace said:
So realistically, what is the most powerful laser diode you can get your hands on, and how feasible is it to build a high powered laser (in the order of multiple watts) w/out a diode?

That's one giant "depends".

If you want a visible color that's based solely on a diode, violet 500mW is the highest around here in a handheld for a reasonable price. If it can be DPSS (not a direct diode), then you can get greens over 500mW, but those are also much more expensive. If it doesn't have to be visible, a member here was built somewhere in the neighborhood of 2W-3W IR laser in a handheld for a reasonable price.

You can get into diode bars and multimode stuff with both visible and IR laser diodes, and the powers get higher; but the price increases even faster, because such things aren't generally mass-produced like the diodes we're pilfering from optical data storage drives.

If you don't need it to be handheld, lab-style lasers get a lot more powerful, especially with gas lasers. There are members on here with 40W+ power lasers in their basements, such as CO2 lasers that emit IR.

Yeah, reading around here is your friend. There is a TON of information, about everything to do with lasers around here.

Horace · Aug 5, 2009

Before the flaming gets any hotter, im well aware of typical FAQ and newbie questions. I post on several other forums with different topics and am the expert in some. If I was really serious about building one I would probably spend more time. But once I found out that the LEDs I was considering wouldnt work, that was pretty much it. Im not honestly THAT interested in making a laser given the cost involved, and the fact that I cant really think of any practical use of one even if I was to build it. In fact I totally ripped on my buddy for spending $300 on a laser that has essentially no use at all, other than to burn paper lol.

Dont get me wrong, lasers are pretty cool devices, but my wife would murder me if I spent more than a small amount of money on such a device, not to mention she would probabaly think i was a major Dork. NO OFFENSE

Tech_Junkie · Aug 5, 2009

Not true.. you can build a decent high power laser for under $80. Your buddy bought an Igor laser, which is top of the line. Thats why he paid so much.

Lasers have many uses other than burning. Light shows, unique devices like a laser lighter, and a boat load of other cool things.

Horace · Aug 5, 2009

Your absolutely right. There ARE uses for lasers no doubt. But for me, I really dont have any reason to build a laser, other than to say I did it. For the average person, a keychain laser pointer is enough

YGG · Aug 5, 2009

I was shining my 200mw red(which only costs 40-50$ btw at a pole last night and I saw this faint red crap after. I looked over and I saw a pathetic red <1mw, then it went into my eyes. I beamed mine over in that general direction(no not in their eyes), it sent them inside running, things like that make them fun and the way they look at night is stunning. For only 43$. As for the green one in my picture, it cost me only 26.50$. The red will burn the paint on my walls. It's really not that expensive, until you start an obsession. Building can be cheap to, just don't get every bell and whistle.

Horace · Aug 5, 2009

Yep, agree, lasers are fun to play with. NO doubt about it. Hell I played with my keychain laser for hours upon hours when I first got it and that is just a lame little thing. But I still want to slap my buddy for spending $300 lol. Freggin batchelors

Tech_Junkie · Aug 5, 2009

You cant put a price on craftsmanship or the love of a hobby. Like anything else, its not for everyone.

dr-ebert · Aug 6, 2009

For the power comparison in the first post: you're comparing 200mW OUTPUT power of a laser diode with the 3W INPUT power of a typical Cree flashlight diode, which are rated at around 110lm/W. It is a bit tricky to convert this to an output watt rating. However, the overall efficiency of these white LEDs is around 20%, while for LDs it's around 15%, so the difference isn't really that great.

FireMyLaser · Aug 6, 2009

Actually red LD's have an efficiency of around ~25%, and violet ~20%, if my math is right. Just a fun-fact.

dr-ebert · Aug 6, 2009

LPC-815: Vf=3.4V, I=420mA, Pin=1.43W, Pout=315mW, eta=22%
PHR-803: Vf=5.7V, I=120mA, Pin=684mW, Pout=130mW, eta=19%

I'm not too sure about the Vf of the BR (I had to extrapolate on some IgorT data; I'm pretty sure there's a graph but I didn't find it). The Pout would be without a lens, and can of course vary a bit from diode to diode. The values I used are a bit of a guesstimate and open to discussion.

The 15% was a figure I calculated some time ago, which takes the driver efficiency into account as well (for a FlexDrive type driver) - my mistake.

So with all the variables, I'd say now that ~20% would be a good overall ROT figure for all diodes.

According to wikipedia, the only light emitter that's more efficient is the low pressure sodium vapor lamp (at 29%), which however is monochromatic yellow and not too widely used. The more common high pressure sodium vapor lamp (used in streetlights, pinkish-yellow color) is at 22%.

It's pretty obvious that LEDs will be the illumination of the future.

Questions about LEDs for Lasers

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