# Focusing a bar diode...



## mm85 (Nov 10, 2004)

I recently found a 20w 808nm bar diode that I'm interested in but I'm unsure of one thing, how do I bring the bar of light it emits into colimation? What kind of lenses would it take?


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## Spec (Nov 11, 2004)

Wow, your opening up a giant can of worms there...

That diode bar is absolutely dangerous. I would reccomend sending an email to Sam Goldwasser of LASERFAQ fame asking him to professionally test it for you before you start messing with that. He charges a completely reasonable fee for his time and services.

To answer your original question, the professionals hand allign fiber optics infront of each emitter and then "squeeze" the fibers together to get a pretty uniform beam. Keep in mind that the beam will be bouncing all over the inside of the fiber and when it finally gets to the end it should be "tamed" with optics to make a uniform dot.

While the output wont technically be a single point there will be enough overlap to make it appear it is.

-Spec


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## mm85 (Nov 11, 2004)

Many things are dangerous, I think that's what makes them interesting, isn't it?

All jokes aside, I knew it was common to use fiber optics, I just didn't know if there was any other ways to collimate this form of light. 

Can diodes like this output continuously with proper cooling or only pulsed?


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## Spec (Nov 11, 2004)

Hi there, Im going to need the model number and manufacturer of the diode to be able to tell you anything else about its operating mode or electrical requirements.

-Spec


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## mm85 (Nov 11, 2004)

It's a Spectra Diode Labs (SDL) part number 3470-S-807-2.5-S-20. Thanks.


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## Spec (Nov 11, 2004)

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=7287&item=3850312814&rd=1

Spectra Physics doesnt produce that model anymore, its primary output is at 807nm and might be able to be temperature tuned to 808. Thats going to require some expensive peltier cooling.

It is CW and takes a lot of "Clean" current to get it to produce the 808nm beam.

IF your going to make a green laser with this thing your in for one hell of learning experience!

-Spec


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## mm85 (Nov 11, 2004)

Sorry I should have stated, I am interested in building a very high power ir device. Like possibly coupling two of these bar diodes. Is peltier cooling the only way of efficiently cooling these? What about water?


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## sharkeeper (Nov 11, 2004)

Most bars are watercooled. TE cooling is only necessary to shift the wavelength for pumping, etc.

They are very dangerous devices. I had a 240W bar here and we were joking about using it for many things. 

Cheers!


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## Spec (Nov 12, 2004)

Exactly right. However, the weird part about this bar is that the watercooling block doesnt exist. He would have to get a preform and lowtemp solder to make it stick to a sink with peltier elements for cooling and shifting of frequency, if needed.

I seriously doubt just a fan and heat-sink would provide adequate cooling for this unit.

I might get one soon to play with. Problem is I can not in good conscious buy a laser diode like this off ebay because they are so amazingly easy to destroy. Ie: an errant 3volts can destroy it, not to mention static shock, thats COMPLETELY lethal as far as the diode is concerned.

-Spec.


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## mm85 (Nov 12, 2004)

How do you work with the fiber optics on these things? They look like they would be as small as a hair.


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## sharkeeper (Nov 12, 2004)

Yes I've seen these suffer facet damage from careless handling and you can bet the house that was ESD related...

The power density is too high for forced air cooling unless you like to hear the sound of a vacuum cleaner running.

You would easily use a water-cooling setup similar to what pc enthusiasts use - over clocked processors put out well over 100W of heat and up to triple that if a TEC is brought into the equation.

The thought of "hobbyist" use of a 20W bar makes me squeamish. I know the dangers and have seen firsthand what can happen. You can never be too careful around these things - short of not buying one!


Cheers!


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## Spec (Nov 13, 2004)

mm85: In comparison a standard fiber is massive compared to what your trying to "cram" in it. "Car in a 12 lane tunnel" image comes to mind.

In the documentation it states the bar is a bunch of emitters about a micron wide. Keep in mind that an average SC fiber is 65microns in diameter, quite a lot of "play"

sharekeeper: All the watercooling stuff I have dealt with for computers is designed to disapate less than 100w/cm2. This bar appears to be pushing that quite a bit more when at full tilt.

And, your right, its amazing how affordable high power lasers have become because of surplus. A 20w bar 5 years ago could have easily cost as much as a furnished house. /ubbthreads/images/graemlins/wink.gif

-Spec


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## tonmomon (Jul 27, 2010)

Hi there.

Sorry to unearth this topic but I'd need to know the retail price of this item you're talking about:



> Spectra Diode Labs (SDL) part number 3470-S-807-2.5-S-20


Also, I'd like to know how much for a YAG crystal (9.4mm/115mm/Brewster angle).

Thanks


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## everphotonics (Aug 24, 2010)

Usually the 20W Laser Diode Bar contains 19 emitters with a pitch of 0.5mm between emitters. For each emitter, there will be a divergence of 8~10 degrees in horizontal direction (we call it Slow Axis), and a divergence of 60~70 degrees in vertical direction (we call it Fast Axis). Each emitter gives Gaussian beam.

So in principle, it is impossible to focus all the 19 emitters into a single spot. But we can try to focus it as small as possible.

The way is to use 2 kinds of micro-lenses as Fast Axis Collimator (FAC) and Slow Axis Collimator (SAC).

Usually FAC is a simple cylinderical lens or rod lens. The SAC is a group of very small cylinderical lenses which are used to collimate each emitters.

After FAC and SAC, the beam divergence of the Laser Diode Bar will be abviously reduced. And then, you can try to use a cylinderical lens to focus it into a small spot area (not spot in fact).



Any questions, you can email me at: [email protected]

We work on High Power Laser Diode Bars, Arrays, Stacks and high power DPSS lasers.





mm85 said:


> I recently found a 20w 808nm bar diode that I'm interested in but I'm unsure of one thing, how do I bring the bar of light it emits into colimation? What kind of lenses would it take?


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