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Green laser makes LEDs glow!

Benm

Benm

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thejunkmonger said:
I think the circuit would be much better if it was designed with 2 L.E.D's instead of one. One to capture the light and one to emit it.
Click to expand...

That actually works when just putting them paralel - just a red and an orange high brightness 5mm led. Aim a green laser into the orange led and the red one will light up visibly.

The circuit above actually works btw, i just rigged it on a breadboard. The problem is that the flashes from the LED are so dim you cannon see them with the naked eye. I tried feeding it some current from 2 AA batteries and a 10k resistor, then it works like a charm. I can see the same thing happening electrically (on a scope) when i shine a laser into the LED, but its not bright enough to make out by eye.
 





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thejunkmonger

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LOL hook it up to a digital multimeter and we have just discovered a poor mans power meter. Great that you have all that stuff on hand i've had that <Schematic for years and never got around to finding the stuff to make it.
 
Switch

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Maybe if you shine a highpowered laser at the LED and use high OD goggles you can see the blinking better :p
 
Benm

Benm

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thejunkmonger said:
Great that you have all that stuff on hand i've had that <Schematic for years and never got around to finding the stuff to make it.
Click to expand...

I didnt build it to exact specifications, but it still works to a degree. I just used it little toroid for the coil but actually even a tiny coil from a flahslight driver seems to work.

Maybe if you shine a highpowered laser at the LED and use high OD goggles you can see the blinking better
Click to expand...

I tried using a KD50 laser and a red gel (as in 3d glasses red film) to look through. I can see the blinking a bit that way, but its all far from spectacular...
 
pullbangdead

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Instead of throwing together some band diagrams and a few paragraphs now to illustrate all this from the physics/semiconductor point of view, I've decided that I would like to put together a whole tutorial on the parts of semiconductor and device physics that are pertinent to photonics (lasers, LEDs, and photovoltaics) that I can post so everyone can hopefully learn a little something about these devices that we all love so much. This way, it can all be out there, in one easy to read page, with some helpful diagrams, and I can try to cover all the background you need to get a good overview of these topics. What things are actually made of, what's happening when you apply a voltage to something, what is happening when a photon hits a pn junction or when a photon leaves a pn junction, all that great stuff. Only problem is, I don't have time in the next couple weeks. So, I'm going to start working on it, and maybe in a few week's time, this will be posted in the Help/Repair/Tutorials section.

If you'd be interested in something like this, basically learning what's really happening inside our laser diodes and LEDs and such, pm me and I can let you know when it's all finished and posted. Also, if there's any aspect of semiconductors in particular you want to know or want to be included in such a tutorial, I would be more than happy to oblige. Sorry I can't just do it right now, but I was sick last week and now only have 2 weeks to finish a little more than 3 weeks of school work so that I can graduate.
 
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pullbangdead said:
Instead of throwing together some band diagrams and a few paragraphs now to illustrate all this from the physics/semiconductor point of view, I've decided that I would like to put together a whole tutorial on the parts of semiconductor and device physics that are pertinent to photonics (lasers, LEDs, and photovoltaics) that I can post so everyone can hopefully learn a little something about these devices that we all love so much.  This way, it can all be out there, in one easy to read page,  with some helpful diagrams, and I can try to cover all the background you need to get a good overview of these topics.  What things are actually made of, what's happening when you apply a voltage to something, what is happening when a photon hits a pn junction or when a photon leaves a pn junction, all that great stuff.  Only problem is, I don't have time in the next couple weeks.  So, I'm going to start working on it, and maybe in a few week's time, this will be posted in the Help/Repair/Tutorials section.  

If you'd be interested in something like this, basically learning what's really happening inside our laser diodes and LEDs and such, pm me and I can let you know when it's all finished and posted.  Also, if there's any aspect of semiconductors in particular you want to know or want to be included in such a tutorial, I would be more than happy to oblige.  Sorry I can't just do it right now, but I was sick last week and now only have 2 weeks to finish a little more than 3 weeks of school work so that I can graduate.
Click to expand...


PLEASE DO.
i will be waiting for it :)

take your time.
 
FireMyLaser

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Yeah please do it, it will make this forum even better! [smiley=2vrolijk_08.gif]
+1!
 
Benm

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More information on semiconductors is always nice to have - let me know when you put it online!

For now, just an entertaining picture of a green laser shining into an orange led, which powers a red led in turn.

The alligator clamps are just mechanical support and not connected to anything... its a bit tricky to aim the laser into the led as these leds have rather narrow opening angles and you need to hit the die just right..,
 

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phenol

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i put together the blinking self-powered led cct, too. it did work, but i could only veify that with a scope. the 500uF cap took forever to charge to a level where the circuit oscillates, but i used an incandescent lamp as a source of light, hence the meager current the LED produced
 
FireMyLaser

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Benm, nice picture!
Another thing worth telling is that if you short the leads on the LED it won't glow. So it is not fluorescence.
 
pullbangdead

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FireMyLaser said:
Hehe, your avatar is a LED, right?
Click to expand...

And yes, it is a new kind of GaN blue LED being worked on by the group I 'm going to be working with in graduate school. The technique grows the GaN in a new direction, such that the crystal structure is oriented differently. By doing this, the LED is grown on a different plane of atoms (the "m-plane", where most all GaN devices are grown on the "c-plane" now) and the device has a lot more potential output. It solves some problems, but still has to be optimized and worked on to catch it up with current c-plane devices. It basically isn't as good now, but should have higher potential for how good it can get.

*Sorry for the double post, but just saw this question, and it is a topic very pertinent to all photonic devices.
 
Benm

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phenol said:
i put together the blinking self-powered led cct, too. it did work, but i could only veify that with a scope. the 500uF cap took forever to charge to a level where the circuit oscillates, but i used an incandescent lamp as a source of light, hence the meager current the LED produced
Click to expand...

I tried with a LED flashlight at first, but couldnt get enough light into it to make it work at all. I went straigt for a laser from there on, and its oscillations show up on the scope nicely.

Next i did a bit of a trick to demonstrate it: I used 1 idential red leds paralel, one as the target for the laser, and the other as an indicator - see the attached video for the result!

It will flash a lot faster than it does on the video if you aim the laser exactly right. Also, there are some components on the breadboard that arent part of this circuit but i didnt feel like removing for this test either. Suffice it to say that it doesnt get any external power and the led you see blinking is powered by only its twin exposed to the laser. The one facing the laser also blinks, but this is impossible to make out on the video.
 

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