my laser and laser building questions thread

[iroquois]

OK. So first I'd like to say I own and operate some 1W laser projectors and I also make and sell some laser frames and animations. I've taken a laser safety course and understand the laser dangers, risks and safety.
But it all started as a wallet-blackhole hobby and still is a hobby. Jut nothing out there I can compare to the awe from cool bright laser graphics and beams.
I've been more into making abstracts and other animations for laser projectors. My electronics knowledge is very limited. Though I've replaced fans and taken apart complete laser projectors and replaced damaged laser modules and power supplies so not a complete noob either I guess.

Now I want to make my own lasers and learn some more how the tools I've used work internally. I don't want to make my own laser projectors or real laser modules with modulation etc control, nor a handheld laser. Just my own home lasers I can turn on/off and see how much I can improve and how bright I can get them

The tutorials on Youtube on making a red laser from old dvd burners were a piece of cake to follow.
But they don't go any deeper than that.

I want to know how to make brighter lasers (found only multi-diode lasers allow that so far...), and actually have some idea how I should set up proper cooling and stuff like that. And info on those are hard to find, limited or if any, a bit confusing for me at least.

I know this is going to be difficult, time consuming and costy, but most importantly fun
So hope you guys will be patient with all the questions I have now and help me get somewhere. I'll post pics and videos of my results as I progress.

BTW, I also have two 3d printers, another newer hobby of mine. Taken those apart several times already as well.

OK, so I guess my first questions will be:

1) What are the methods of combining several same color laser diodes? I've seen videos with homemade lasers reaching all the way up to 7W, but can't get in contact with the creators and learn from them.
I've only found out the particular method they've used for their multi-diode lasers is called "knife edge array" and a sticky in this forum explains it (along with dichros and polarizing cubes) but what tools and what do they use to make such array, or how they decreased the diameter of the combined laser beam and stuff like that?
Knowing if there are other beam combining methods other than dichoric mirrors, polarizing cubes and arrays would be nice too.

2) What is the basic things I should know about laser cooling? All I know now is they should be cooled or will die after certain amount of time and the commercial laser modules use heatsinks, fans and TEC coolers (I've taken apart few 300mW dead laser modules and examined what was inside), but what's the desired temps, how temperature affects laser power and other parameters, etc I don't know.

Thanks!

(I should have joined and posted this in LPF from the beginning...)

 

[daawood123]

Can only answer first question lol, knife edge arrays are mostly used for same wavelength combining, so if one was to want 5W of blue, they would usually use knife edge arrays to get that using indivudal blue diodes. Dichroic mirrors can be used to combine different wavelengths to achieve exotic colours and such.

I'm not too sure about the combined laser beam focusing, but I'm pretty sure you just use a special lens to focus all the rays into bigger/smaller ones.

In terms of tools, all of above can be achieved with not much apart from the components themselves, simple as a couple diodes with a mirror all aligned in place.

It depends what your wanting to do

EDIT: Copy pasted from Pi R Squared's post on this thread http://http://laserpointerforums.com/f51/what-heatsink-test-load-92490.html

"The duty cycle is very important for hand held battery powered lasers, if you don't stick to it you can kill the diode, it's because it will overheat, not just the diode but sometimes the driver too. If the duty cycle is 30sec on/30sec off it means you must only have the laser on for at most 30 seconds and then give it 30 seconds to cool off before you can turn it on again. If you exceed the duty cycle too many times you will burn out the diode or sometimes they can also degrade over time and have a reduced output, and you don't want that."

 

[iroquois]

Thanks for the reply man.

I should have been more specific: I'm interested in making a powerful laser by combining *same* diodes, so dichro mirrors like in my RGB laser projectors won't work. And polarizing cubes won't work with more than two same color diodes right? This is something I'm less familiar with, I guess a third beam with say 45 degree angled wave won't work huh?
So the knife edge combining method is the only way currently to do same color beam combination?

I'd like it to not die or lose power running for an hour or so.

'm not too sure about the combined laser beam focusing, but I'm pretty sure you just use a special lens to focus all the rays into bigger/smaller ones.

What kind of special lens are we talking about here?
I'm not experienced with lenses either too much. In my laser projectors those are hidden inside the laser module boxes, except the dichoric mirrors.

In terms of tools, all of above can be achieved with not much apart from the components themselves, simple as a couple diodes with a mirror all aligned in place.

Yes, but what should hold the diode, the mirror which will be attached to the base plate?
You know, something like this (this is used in 3d printers/cncs).

My cheap projectors just have 90 degree aluminum sheets with holes where the mirrors go. There's no screws to fine tune the angle of the mirror. is there a mirror holder which does?

As for heatsinks, I understand how they work, but are they sufficient for my purpose? Why do companies add extra fans and TEC coolers? How can I know I'll need them? Again, would be interesting to know how temperature change (both hot and cold) affects the diode. because I wouldnt mind wasting power on extra cooling just to be on the safe side if that doesn't have negative side effects itself.

 

[daawood123]

Depends how many diodes and such you want, if your looking at combining more than a few, then knife edging would probably be a better choice price wise, because yes, only 2 beams can be used with polarizing cubes. Do some research on knife edging lasers, it should explain the bit about the lenses and such also in good depth.

These will probably be fine for holding the diode modules.

http://odicforce.com/WebRoot/Store1...551/FB7B/DCDB/01D4/0A48/3538/B26F/Slide23.jpg

If your going to use those however you may want to add a fan or 2 due to the high amount of heat that will probably be given off from all those diodes.

Yes there are mirror mounts, search optical mirror mounts in google, should come up with plenty of products.

Heatsinks and fans, well that completely depends on the laser. The point is to keep the laser diode cool, and if I was to build a laser that puts out 50mw, its not going to release a reasonably large amount of heat, therefore I could use a simple small heatsink to keep it cool. However if I wanted to make a laser that was 2W, its going to need a considerably larger heatsink to take away all that heat, and a fan wouldnt be a bad idea to extend the duty cycle a lot more.

Its always better to have extra heatsinking than you think you will need, which is why companies may add TEC coolers or fans to increase the duty cycle (how long you can keep it on without killing the diode). But if you was making a 100mw laser, adding TEC's, couple of fans, chunky heatsinks, is overkill and expensive. Its just about finding a balance really, however they wont have any negative effects apart from drawing more power and taking up space. For your purpose if your after 1 hour of continuous runtime, depending on what diodes your using then your going to need a reasonably large heatsink for each diode, 1 or 2 fans blowing over the heatsinks and TEC cooling wont be a bad idea

If you plan on having 1 big heatsink, or having all the heatsinks connected in some way, then you could add a temperature sensor with a readout if you have the budget for it, and if you go over a certain temperature a fan/TEC turns on automatically etc, or you could just check the temperature readout and if it gets too warm switch your fan/TEC on manually. With the latter your reducing a lot of circuitry and money spent. The possibilities are endless, its all upto what your most comfortable with.

Different temperatures as far as I know dont have too much effect on a laser, unless we'r talking about lower temperatures, which DO affect green lasers e.g may need a period of time where the laser "warms up" and during this period the output of the laser will be significantly reduced. I do not know whether cold will affect different wavelengths aside from green.

Higher temperatures wont do much aside from reduce the duty cycle, unless its a extremely high temperature in which case you will have dangers of the batteries exploding, diode burning out, solder connections melting, but unless your planning on taking your laser to a volcano you shouldn't have these problems

 

[iroquois]

Thanks for all the help.

These will probably be fine for holding the diode modules.

http://odicforce.com/WebRoot/Store1...551/FB7B/DCDB/01D4/0A48/3538/B26F/Slide23.jpg

That really looks like a "shaft support". Is it? shaft support | eBay

if I use those, what kind of heatsinks I can use and where should they be?
Found some photos of laser arrays here but don't see any cooling systems on them to get some ideas.

And this is probably a noob question, but what's the point of having the diode in the laser diode module if it goes in an array? Isn't the module for laser pointers and putting focusing lenses on it?


All laser diodes probably have a "min and max operating temperature (℃)" in their specification. Just checked the specs from Osram, will probably need to ask for one from other manufacturers as I don't see it on their sites.
http://www.osram-os.com/Graphics/XPic9/00093340_0.pdf/PL 450B.pdf
(-40C - +70C)

But not sure what's the recommended temp then.

And can't find anything for the "duty cycle".

Can't find any info on shrinking the combined beam diameter either...

 

[daawood123]

If you look at the pic you can see the laser modules are in one giant heatsink, attached to a baseplate of solid metal. This is sufficient heatsinking for short duty cycles. For 1 hour continuous runtime you'd be looking to need some form of extra cooling, namely either TEC or fans. Finned heatsinks would also greatly help.

And if you dont put it into the module...where else you going to hold the diode?
The modules (AiXiz etc) are made so the diode can be held and heatsinked at the same time. Unless you get direct press fit heatsinks this is probably the easiest way to hold and heatsink the diode in one. If this is your first build I wouldnt venture too far from using the diodes in modules and then clamps for the modules.

Essentially it is a shaft support because a module is in the shape of a shaft anyway so it does "support" a "shaft", but I wouldnt buy a shaft support and expect it to work with this, better to buy the specialised holders that you know are made for laser projects.

 

[iroquois]

Didn't know the term heatsink can be used for any good thermal conductor, but specially shaped one.
Okay then.

Looking at some commercial several watt "modules", even the base plate seems to have fins, interesting. Thought I'd share some photos.

And if you dont put it into the module...where else you going to hold the diode?

Let me think about this some.

Essentially it is a shaft support because a module is in the shape of a shaft anyway so it does "support" a "shaft", but I wouldnt buy a shaft support and expect it to work with this, better to buy the specialised holders that you know are made for laser projects.

I'll probably get both and see if there's any difference in the process, this got me curious.
A good shaft support shouldn't be any worse, a cnc/3d printing thing I know.

 

[daawood123]

Didn't know the term heatsink can be used for any good thermal conductor, but specially shaped one.
Okay then.

Looking at some commercial several watt "modules", even the base plate seems to have fins, interesting. Thought I'd share some photos.

Those look good, for the build your looking for they are a prime candidate

if you wanted to be on the safe side you could have fans blowing air through the fins, this would help your duty cycle a lot.

I'll probably get both and see if there's any difference in the process, this got me curious.
A good shaft support shouldn't be any worse, a cnc/3d printing thing I know.

If you get the right diameter (12mm) you should be fine

 

[iroquois]

I'll start first with some scavanged dvd diodes to not destroy anything expensive.
But i didn't waste my time and send diode price quotes to the companies that made the diodes in my laser projectors.

I'm gonna need some help with the electronics for this project though, hehe.

I'm thinking of maybe finding something like a copper or brass tube to place the diodes in for now maybe?

 

[iroquois]

This might be a stupid question as I know little about fiber optics, but to not dig too much where I maybe don't need to, I'll ask this now:

Can fiber optics be used instead of knife edging for "joining beams" a bit easier?
I mean instead of having to align mirrors on mirror holders so beams end up closer to each other just let each initial beam get inside a fiber, then have the fibers stacked along each other in the other end?