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Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Well that is my only claim to fame so far! I was in fact the first person to build a Blu-ray pointer from a ps3 laser, and am the author of the original article. Sam Goldwasser (laserfaq.org) , Mike Harrison, and I, then proceeded to reverse engineer the rest of the optics. It is some piece of engineering!
When I first wrote the article, Ith was determined by eye. A piece of bleached white copier paper was placed in front of the laser diode, and current gradually increased until the paper fluoresced. I still setup violet laser diodes this way, before using the power meter for final calibration In order to produce a meaningful graph, I had to invest in a laser power meter, but since these are expensive, you could try a reverse biased photodiode, in series with a milliameter. There will be a sudden marked increase in output once Ith is reached.(this simple method does an excellent job of ignoring LED emission!)
76mA is way too high a current for the diode, call it 40, tops! Anything more is running into dangerous ground in terms of lifetime.
405nm is indeed a wierd wavelength, as it apparent brightness varies depending on its environment. For example if you direct the beam at clean teflon, 405nm appears quite dim, whereas copier paper will brilliantly fluoresce. Oddly at this wavelength the beam is quite visible in the dark, since the wavelength is so short, the light will scatter off of air molecules!
As for speckle, well, the eye has a real problem focusing at 405nm too (the reason those horrid blacklights give you eyestrain) plus the speckle is quite `fine grained` due to the short wavelength.
Another clue to when your diode starts lasing is in the 5th picture you posted, of a raw diode shining off a work surface. The straiations either side of the beam, only become visible once Ith is reached.
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
plazmatron wrote ...
Well that is my only claim to fame so far! ...
Actually your x-ray stuff is pretty cool too.
plazmatron wrote ...
When I first wrote the article, Ith was determined by eye. A piece of bleached white copier paper was placed in front of the laser diode, and current gradually increased until the paper fluoresced. I still setup violet laser diodes this way, before using the power meter for final calibration In order to produce a meaningful graph, I had to invest in a laser power meter, but since these are expensive, you could try a reverse biased photodiode, in series with a milliameter. There will be a sudden marked increase in output once Ith is reached.(this simple method does an excellent job of ignoring LED emission!)
I'll do a plot sometime myself. Currently (pun intended) I run at 37mA.
plazmatron wrote ...
76mA is way too high a current for the diode, call it 40, tops! Anything more is running into dangerous ground in terms of lifetime.
I am a man of action and excitement - "go for 76mA" I said.
plazmatron wrote ...
...the speckle is quite `fine grained` due to the short wavelength. Another clue to when your diode starts lasing is in the 5th picture you posted, of a raw diode shining off a work surface. The straiations either side of the beam, only become visible once Ith is reached. To me your diode looks quite healthy!
It looked better when I got the focusing fixed. Unfortunately I have killed the red and IR lasers by running them at 36mA or by ESD due to the switching as there would have been current spikes as the protection caps charged.
Still, a fun project. Perhaps next a bank of DVD writer diodes for a couple of watts of red power... TDU
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
wrote ...
It looked better when I got the focusing fixed. Unfortunately I have killed the red and IR lasers by running them at 36mA or by ESD due to the switching as there would have been current spikes as the protection caps charged.
Still, a fun project. Perhaps next a bank of DVD writer diodes for a couple of watts of red power... TDU
The red and IR diodes are mounted on to of the Violet laser diode chip, in some weird integrated fashion. Killing one diode will at the very least damage the other, if not kill it entirely.
Hmm now a bank of DVD diodes sounds fun! Apparently Sony now does 650nm upto a watt or so, that would be nice to see!
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
The violet diode is made of a different substrate (GaInN) than the red/IR diodes (GaAs), and likewise they are quite separate inside the can. The violet diode (easily recognizable by the fact that the substrate is clear) is soldered down to the can, and then red/ir diodes are mounted on top of the violet diode. I haven't powered it up under a camera to see where the IR light is being emitted from, but judging by the structure of the GaAs block both the red and IR diodes are grown on a single substrate.
However, I would be surprised that you managed to kill both the IR and red diodes in a single blow, as individual emitters are quite separate from each other, and damaging one of them does not affect surrounding emitters. If you really wanted to you could remove the GaAs chip and cleave it into a separate red/IR diode, and it wouldn't affect the lasing operation. Unless of course you managed to catastrophically damage the chip (put so much power through it that it melted the entire substrate or something) I would say that you damaged the diodes seperatley, and that you might want to rethink your driver design before the violet diode gets taken out...
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
The diodes arent as seperate as you might think. The red and infrared diodes, are bonded to the GaN diode at the molecular level. They arent just soldered on. Sony patented this process, as it is unbelievably difficult to match the crystal lattices of GaAlA/GaIAs to GaN. In effect what you have almost constitutes an integrated circuit. It has been observed that damaging just one of the laser diodes will invariably damage another. I would imagine that thermal shock would be a big player (since the crystals have differing thermal expansion coefficients). There are likely to be more subtle effects such as ion migration through neighboring lattices, when one of the diodes overheats, or in the case or the red/infrared diodes damage to their shared substrate.
Registered Member #10
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
Both the IR and red LED are down to 0.1mW so I suspect overcurrent rather than over voltage. The red LED at least lases as it still produces a holographic picture. I don't think I ever took them above 36mA but having the meter in the circuit does drop the current because at least with the voltage drop of the violet diode, the constant current unit can only just regulate particularly when I have the protection diode in the circuit.
I measured the red led at 3.5mW so it aint' burnin' nuthin'.
The violet diode should still be fine and not at risk with current as it is now set.
Hard not to pick it up and shine it around the room every so often...
Pic shows me crouching a bit so the beam hits my fluoro cycling shirt.
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Blu-ray laser
