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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi all.
Just found something interesting.
I found a broken 100mW burner diode (violet 405nm) which measured nearly open.
Having confirmed that it still drew a few uA I hooked up DMM on microamp range.
Well whaddaya know, narrow band UV sensor
1.5mV outside in the winter sun around 11am from the wire side (decanned) and 0.1mV from the front.
Confirmed no response to blue, green, red or infrared but a strong response at near UV from two different LEDs, a triple junction 405 and a 3mm 390.
Anyone can think of a use other than as a sunburn alerter?
Haven't tried it yet with a red or infrared but this makes sense, enough light must be hitting the semiconductor from the top to generate electrons via the PV effect.
EDIT:- I tried with IR 808nm diode which was damaged, still works fine. Responds most strongly to red or orange light, no detectable response at IR or UV. Different response to identical LED brightness at 670 versus 640nm.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780
the filtering is due to the laser diode facets being coated for 405nm, and furthermore the cavity length inside the diode allowing constructive interference for UV only
it would be interesting to monitor UV level along the year... a nice idea
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Yes this was my thinking too. The slight problem is that usually when diodes fail it is because some id10t has blown the bond wires.
However, a used PS3 diode of which there are lots with the 405nm on top of the stack will work without much effort. Even better it also has a nice little photodiode which also responds to visible light so it can be used to measure UV versus visible.
A nice project for someone would be to measure UV at altitude and the ground with the same sensor having first calibrated it with known UV flux over a range of temperatures.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
The comment on as to why it is only sensitive to UV is slightly off, it has nothing to do with the laser structure, but more to do with the fact that is is grown with an exotic semiconductor (Gallium Nitride) which has a bandgap in the near UV, that is to say that in order for a photocarrier (and thus current) to be generated you must have a photon with more energy that a 400nm photon. The idea to use the internal silicon photodiode to compare s actually quite clever, one could even take it to the next step and use one of the triple stack IR/Red/UV lasers (like out of a ps3) to make a sensor which can tell between UV/Visible/IR.
As to uses, perhaps testing the uv blocking performance of sunglasses?
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
a 3 in 1 sensor for characterizing light? sounds like a good addition to a sonic screw driver. Might be able to extrapolate some temperature data from the IR too.
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Dead laser diodes as UV sensors ?
