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FrozenGate by Avery

Replace the pump diode?

W

wakko

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Aug 18, 2010
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My green pointer has decided to die on me and was producing a green splat which appeared to change shape over time and was very low on power. The pointer hasn't been dropped and just did this after being sat on the shelf for a while. The diode is pulling solid 1.48A from the driver and varies very little.

As it seems the diode has croaked I looked at the module to see if the it could be replaced. I cracked off the front of the module (this contains the crystals and optics) and as you can see, found a c-mount diode.

LD.jpg


Looking at the specs, I think this is a 1W diode and the current draw of 1.48A is about right for the 300mW of green it used to produce. The question is, should I try replacing the diode? On ebay the diode is around the £16 mark and with the crystals and optics being in one lump I'd only have to align it to the pump diode. Might be worth a shot

Any thoughts?

B.
 





Haven't got a LPM but there appears to be little power to the pump diode, to my finger anyway. I'll post up a pic of the pump diode beam pattern when I get home from work.
 
The beam patterns

The FAC looks like maybe some of the UV
glue creeped along the lens. If it was
working at one time, I doubt this is the
problem unless it was never properly cured
and the creepage occurred while it was
sitting on the shelf.
 
After using I put it on the shelf where it sat for about a month, the next time I came to use it I found it outputting a beam like the pic. The pics are a little blurred but they do show the pattern I'm seeing. I'd have expected the 808nm beam from the diode to be much stronger and more defined than it is.
 
wakko said:
I'd have expected the 808nm beam from the diode to be much stronger and more defined than it is.
Click to expand...

This is because

  1. Your camera has an IR filter
  2. Autofocus is confused by IR
  3. Sensors are not optomized to pick it up

There is nothing you can do about #3, but
#1 and #2 can be worked around by using a
camera that does not have an IR filter and
manual focus.

But all this isn't really getting us
anywhere because you don't have an LPM.
Really the only other suggestion I have is
to try setting up a lens with a third hand
tool and seeing how well the diode can
burn. If it can burn reasonably well with
a 2-3mm spot, then it's safe to say that
the diode is not your problem.

This is really not something to attempt if
you don't have an LPM. You should buy
one. You are wearing safety glasses that
block 808nm, correct?
 
I do have the correct pair of Eagle goggles but for me it's not really worth buying an LPM to repair a laser pointer worth just over £100. I do have some optics to focus the beam so I'll try that and test the burning power of the 808nm.
 
Looks like it's massively mode hopping to me in the green pic. Usually happens from excessive heat and/or an unstable/improper pump. My old aries did that until I rebuilt it. If it's drawing an amp and a half the pump is likely fine.
 
Last edited:
The 808nm pics show the same pattern as the green so it doesl ook like some issue with the pump diode. I'm not sure how it can be excessive heat as it was working one day and not the next so I'm not sure whats changed in order for the pump diode to suddenly be mode hopping. Is a thermal paste used on the mating surfaces of the diode and heatsink?
 
NO thermal paste

This is a multimode diode. Mode lines are
normal. All multimode diodes will "mode
hop" with changes in current or
temperature. This is a crystal/alignment
problem.
 
I'm inclined to agree with the above: The pattern from the pump diode may look 'odd' to you, but could be perfectly normal for a multimode like that. The only way to find fault in it would be to have the pattern of a known good one and check for differences.

Current consumption is not likely to be any indication at all: the difference in voltage/current graph for live vs cod-failed diodes is often small.

Misalignment between pump diode and crystal set would give the problem with the green as you describe. As to what may have caused this only guessing remains as you didn't drop it or anything like that. It could be something as innocent as thermal stresses that can dislodge things even when simply stored in an evironment where temperature changes between day and night.
 
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