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A littile laser diode help...

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Wilson

Thu Dec 21 2006, 01:41PM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

Hello. With festivities on their way, I decided on an early Christmas present, and succumbed to the urge of buying 2 IR (980nm) laser diodes off ebay
Set it up as shown below - a simple power supply filter, a battery pack of 2 or 3AA batteries, and a laser assembly from an old laser printer, replacing the old laser diode with my new ones

Started with 3V in, 5ohm resistance, got about 0.4A current...had some black plastic in front, nothing happened

Tried paper, nothing. Thinking that i might still be below the lasing threshold, I increased the power to 4V, observing a 0.8A current draw...still nothing

Could it be that the beam is not focused? Although i'm pretty sure the laser heatsink assembly is inbuilt with a collimating lens..
Or have i somehow blow the diode through ESD? (I did touch ground b4 handling it...)
Voltage drop across the diode reads 1.2V
Any help will be greatly appreciated, as I am pretty much a noob in this field...

Thank you,
Wilson

...

Thu Dec 21 2006, 02:59PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

1.2v sounds right for a diode, and I doubt that is was ESD (ir diodes really aren't all that sensitive). But running at at 2x its rated current, even for a few ms, might have done it in. Finally, capacitors and laser diodes are a very dangerous combination. You must be SURE that any cap you may connect to a laser diode is 100% empty before connecting the diode to it, or you can get huge spike that will fry the diode. If you were connecting the laser to your board, then connecting the board to a power supply your were probably ok, but if you even connected the laser to the board while it was powered then there is a decent chance your fried the diode that way.

What you need to do it try getting out a digital camera (still/digital doesn't matter, but if you can find one that has a 'nightshot' mode it would be idea) and pointing the laser at it. If you actually are lasing then it will glow green (nightshot) or purple (normal), about as bright as if it were a normal red diode of that power.

I am thinking that your problem is that you do not have enough collimation. Looking at that mount, it looks like it came out of a laser printer, which means that it isn't focused down to a spot but rather collminated like a laser beam. In order to get any burning action with 200mw you will need to focus the laser down to a pretty small spot (well under a mm).

Be careful and have fun!

Simon

Sat Dec 23 2006, 04:17AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

You really need to find a way to look at the beam, like how ... suggests. (Or buy a cheap webcam and remove the IR filter, or at least an IR photodiode.) This way you'll know when the thing is working and you'll know how focussed it is.

If you're going spend this kind of money on laser diodes, spending a few dollars on equipment will save you money very quickly. (That includes driver circuitry.)

Cranking up the power with laser diodes can be tempting but ultimately leads to RIP diodes.

Madgyver

Sat Dec 23 2006, 03:00PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

I think you have ruined the diodes already. The ebay text says clearly that they are meant or usage in the 150-300mA region. You initial test with 400mA might have severely damaged them, 800mA have clearly killed them. Like a main battle tank driving over an snail.

Try one of these:

Wilson

Mon Dec 25 2006, 06:36AM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

Oh dear :(
Oddly enough, the ebay'er recommended 4-5ohms with 3-4.5V input. I used 5ohms and 3V and the current was around 0.4A already...

Are normal digital video camcorders and cameras able to detect 780nm laser light (ie, CD IR laser). I've hooked 2 up, feed a controlled 25-30mA into them and detected nothing

(I'm connecting the 2 legs with a 1.4V drop)
Am I killing the diodes somehow? or is the wavelength just not detectable?

Thanks,
Wilson

Madgyver

Mon Dec 25 2006, 02:38PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

Actually 780nm Diodes can be seen with the human eye as a very dimm red light (we are not actually seing the 780nm but red light near the 780nm with very little intensity.)

Maybe you are doing something very odd here. Checked Diode polarity?

This might help:

especially:

Marko

Mon Dec 25 2006, 05:58PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

They are all pretty visible trough digital camera. CD rom ones are really puny but are still seen well with digital camera and even naked eye in dark.

If they aren't, they ar either blown or connected improperly.

Steve Conner

Tue Dec 26 2006, 11:37AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

780 is visible, sure, but Wilson said his diodes were 980, which is invisible. I asked my boss, and he said that a digital camera may well be able to see 980. Those IR cards for testing TV remotes can definitely see it. When I get back to work, I can grab my digital camera and a 980 laser, and see if it shows up.

You'll probably not achieve burning unless the beam is focused just right. My own experience of this was that I was playing with a 980nm fibre coupled pump laser, and running at about 100mA, when the fibre end was held against black plastic it would glow white hot and send up tiny puffs of smoke. But the fibre concentrates it to a very fine spot. It also lit an IR test card very brightly.

I actually design laser diode drivers in my day job, and it horrifies me to see how mean you guys are to the poor things

Mine have all sorts of soft-start, current limiting and protection circuits.

Also when hooking up to a new laser for the first time, we always ramp the current up gradually while looking to see if any light comes out. That way, if we hooked something up wrong, we'll hopefully find out before we've passed too much current through it and trashed it.

Carbon_Rod

Mon Jan 22 2007, 08:23PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Steve, do you work with any semi-laser pumped YAG units?
I do agree current sensing drivers are better at preserving the diode lifespan.

A cheap ccd camera will pick up most IR diodes from CD/DVD/DVD-RAM drives.

And yes, some CD/DVD burners can burn holes in things... including your retina if your not careful around incident rays. There is an IR active phosphor testing card sold that will work with most IR devices.

Cheers,

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