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Old 05-02-2009, 09:38 AM #1
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Default Question about "under-driving" a laser diode...

I bought some laser diodes; the spec sheet says the operating current range is 25 to 75 mA. (they're 904nm)

I'm using a ddl-type constant current driver.

Tinkering around, I discovered that they still lase as low as 17mA.

What's the conventional wisdom on "under-driving" a laser diode. Is it safe, or will it damage the diode or shorten it's life?

Thanks.


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Old 05-02-2009, 11:37 AM #2
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Default Re: Question about "under-driving" a laser diode..

What you need to check on the Data Sheet is not only the Operating Current...
but the Threshold Current...
That is the minimum current required to start that particular Laser Diode to
Lase.. 8-)


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Old 05-02-2009, 01:13 PM #3
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Default Re: Question about "under-driving" a laser diode..

As Jerry said, you just found the threshold current. Underdriving is fine. It won't hurt the diode. In fact, if anything, it will lengthen the diode's life. But, most here don't have the restraint to not push the laser diode to it's absolute limit, or beyond ;D
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Old 05-02-2009, 01:33 PM #4
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Default Re: Question about "under-driving" a laser diode..

The treshold current is also the lower end of the operating current range (i.e. below it, it will not operate in the sense of produce any laser output). No harm will come from operating a diode at or near treshold current, but you should keep in mind that theshold current depends on temperature.

If you would design a driver to provide current just above threshold at, say, 20 degrees, chances are your device will not lase at all at 30 degrees. The treshold current rises about 10% typically over a 0 to 50 degree temperature range.
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Old 05-02-2009, 05:33 PM #5
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Default Re: Question about "under-driving" a laser diode..

Quote:
Originally Posted by Benm
The treshold current is also the lower end of the operating current range (i.e. below it, it will not operate in the sense of produce any laser output). No harm will come from operating a diode at or near treshold current, but you should keep in mind that theshold current depends on temperature.

If you would design a driver to provide current just above threshold at, say, 20 degrees, chances are your device will not lase at all at 30 degrees. The treshold current rises about 10% typically over a 0 to 50 degree temperature range.
Awesome! Thanks to all for the replies, but thanks in particular to Benm! That helped my understanding tremendously.

The temperature curve is particularly useful info. Were you speaking in C or F ?

Thanks!
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Old 05-02-2009, 11:15 PM #6
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Default Re: Question about "under-driving" a laser diode..

Figures are in celcius.

One of the bad things that can happen is that you drive a diode just over treshold, slightly heating it up, afte which it fails to lase and appears dead - until you let it cool and retry.

With the burning lasers made here mostly this is hardly a problem since most people drive those at 2x treshold or (lots) more, but with something delicate that isn't designed to handle much more then treshold it can be, and optical feedback is required to get it to work properly.
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