another hello from france

Hello I'm sebastien, ham call F4GRX

I'm new here, I want to share my beginner experiments and get advices from you. It seems you have the best laser forum of the intarwebs!

I have to say that lasers are only one of my hobbies, so I play with them from time to time. There are so many things to do! Radio for example! or PIC programs!

First of all I browsed other "hello" threads and unfortunately no, I don't have safety googles yet, but I read the "1000mW blue laser retina damage" story, and I was quite scared, so one on my initial questions is about this. All my experiments so far were with relatively small (but yet dangerous, I know) diodes.
As a beginner in the laser world, I'm quite hesitant to invest $100+ on googles; I would need a pair to protect from blue lasers, and another one for red lasers.
I saw the nice "orange" model on amazon, I'll get it soon to continue my hobby research on blue lasers, but I need advice for "blue" googles to protect my eyes from red lasers. On ebay, I see that "CE" advertised googles are at least $30, but sometimes it just means "china export". Maybe cheaper googles are still ok? Do you have any advice on red-laser googles?
For example what about these? eBay | 638nm 650nm 660nm Red Laser Protection Goggles Safety Glasses Eyewears

Some time ago when I still was a physics student (2004), I got into a laser diode harvesting operation, gathering diodes from discarded laser printers. I learnt it was infrared diodes after a quick google search. I powered one of the mounted IR diodes with a LM317 system, in a shoebox, and monitored the thing with a webcam! I noticed it was not so dangerous if handled properly, so I dropped the shoebox and played a bit with IR lasers. But that was not very interesting, since I needed a webcam to see the spot. But I also got a bunch of very nice laser diode mounts!

In 2010, after a lot of other occupations, I came across the famous SAM's laser FAQ, I knew that DVD used red visible diodes, but I discovered that DVD burners used *powerful* red diodes. This brought me back to the laser hobby and I started gathering "dead" DVD drives from around me (people were really curious about what I could do with them!)

I finally got a decent red laser diode from a dvd burner (some of these are not in a standard package, which is quite disappointing), which I installed in a laser printer diode mount, and this was my first serious homemade laser pointer. It was rather powerful since I could see the beam when pointed outside of my window, thanks to the diffusion on the faint outside air humidity.

Then came the blue laser diode, and by chance I got one from a broken blu-ray drive (not a recorder) in 2012.

Recently, I mounted my blue diode in an old laser printer diode mount, and powered that with an LM317, which resulted in a very nice, but not very powerful, blu-ray pointer. I noticed that the blue pointer activated glow-in-the-dark paint, and other fluorescent product like white paper and clothes. Awesome! Then I discovered that oil was also fluorescing (yellow) and olive oil was producing a red glow!

A few weeks ago, I wanted to create a driver that was more intelligent than a simple LM317. I reviewed schematics from sam's laser faq, and tried to understand photodiode power feedback. But I did not like that because I had diodes with different wirings (dvd diodes are often common-cathode, and no simple driver could work with that) and I could not imagine a simple schematic to use the internal photodiode in all possible situations.
I let that go and focused on constant current drivers.
In another project, I had built a constant current driver for a YIG microwave oscillator, so I reused that. It was based on a bipolar transistor whose base was driven by an op amp comparing the voltage on a shunt resistor and a voltage set by a potentiometer. This driver worked okay with the test LED, but I burnt 4 diodes, including the blue one

Re-reading sam's FAQ, I understood that transient current spikes at driver's startup were the problem, and I noticed a "soft start" circuit could be used.
So here I am, I now have a working driver using a soft-start circuit, a maxim rail to rail "precision" op amp, a n-channel FET instead of a bipolar transistor, and the same potentiometer. I added RC networks in a few places to prevent transients. The current is limited to 80mA because of the 8-Volts regulated supply. The new dvd burner red diode I tested with this driver is still alive
So, I have another question here:

The soft start circuit is strange. Input is 12V, but output is 9V... It worked when I tested with a simple LED, but now the transistor does not seem to saturate when I connect a LD. I think the BD175 transistor does not have enough current gain so the base current is not sufficient to turn the transistor full-on? I used a 33K resistor and a 47uF capacitor to have plenty of startup time. Would a darlington solve the base current problem?

One of the biggest mysteries in front of me right now is: how to know the maximum current I can feed in a diode? I can estimate the threshold current when I see the light output "step", but how to know the maximum current? Sam's FAQ says 10% over the threshold is a maximum, but that does not seem much. Any thoughts about that?

Next question is how to measure the light output. I saw on this forum that the best power detectors use photopiles, but I don't have that. I have some BWP34 photodiodes. Do you know any use of that component to measure laser power? I think a relative measurement is OK for a start, I'll calibrate later

Final question is about diode mounts. I got a nice (and cheap) "C-mount" with a massive aluminium body and a 16-mm lens. I built a small brass thingy to mount a normal 5.6mm diode inside, and tried to focus the beam. I was a bit disappointed, because I could not get a nice spot. I think that this mount is not very efficient because of internal reflections. Do anyone of you have experience with this sort of mount? How are you using them? As of now, the old laser printer thing does a better job! I think this "C-mount" has a lens with a too long focal length, so it does not intercept the full beam.

BTW, I ordered a pair of 12mm Aixiz mounts to check if that's better.

Okay, I wrote a lot, so here are some pictures to let you see what I did!

best mount so far, from a laser printer, with a 5mm lens and a red diode.


laser spot from this mount, photographed with a sony dsc-f826, 1/2000th of a second, black background, 2 meters distance


blue diode mount before the diode died (but I found other ones on ebay)


the working driver, and the not-so-nice "C-mount" case


brass mount to fit the 5.6mm diode in the "c-mount" case
http://www.mirari.fr/deCi

another nice mount from a printer, but the lens aperture is very small and it's made for a 9mm diode!
http://www.mirari.fr/iyUC

same one, with a nice brass 9mm to 5.6mm a friend made for me
http://www.mirari.fr/rdeM

nice looking laser diode killer... now dismantled!
http://www.mirari.fr/piru

blu ray beam generating fluorescence in walnut oil!
http://www.mirari.fr/ge4p

fun with a block of glass. the glass is fluorescent on the optical path.
http://www.mirari.fr/muvN

light output from the un-focussed burnt blue ray diode...


light output from the un focussed burnt red diode... the diode has floaters! it's not dust, there is nothing between the bare diode package and the wall!


Is that what you call COD?


In the coming weeks I'll try to improve my driver by using a high-side current sensing circuit from TI. This will allow me to ground the FET source and use a smaller value shunt resistor. I'll also have a look at the soft-start problem, and build a photodiode amplifier to test my BWP34, which I just glued on a black heatsink.

best regards!

Welcome to the LPF forum ! :wave:

That is an impressive introductory. I answer a few questions. May other fill in the rest.
The maximum output of the laser diode is determine by trail and error. We push the diode until it dims or dies. Sometime the member of the LPF are gathering a murder funds for s specific diode in order to test it to the death if that is possible. From the data we can make some assumptions about the diode.

The output is done with a LPM. It works the best with heattransfer of the sensor instead of a photodiode.

Have a nice stay here !

Hello,

thanks for the warm welcome!

Dim or die... This is a nice idea, but it's not really doable for harvested diodes, when I only have one available and I have no idea of the part number

Just like a radio power amplifier saturates when the input is too high, is it possible to detect a change in the "light output versus current" curve linearity?

I'll do some tests

I see that you have already done a lot of reading on
the Forum before posting...:yh:

to the Forum....
Don't forget to read the FAQs...the Stickies and the
Forum Rules..
http://laserpointerforums.com/tou.htm


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Welcome to the forum! :wave:

Hello,

more experiments:

1) -got aixiz modules from dtr-lpf on ebay, thanks! I realize these ones are not made for experiments, but rather for final installation. I used one to mount the diode I found in the 18x drive below. However I have a problem: I see rather powerful batwings in the form of a line, I'm sure one of you know that and have a solution. It's not very pretty! Maybe it's because of my capless diode?

2) -got two out of order dvd drives (that's very nice, the diodes are never the culprit in failed recorders!)
* one was a 18x recorder, I got a nice but capless diode! I was quite afraid to break the bondings!

There is only one bonding wire for each connection, can this be an indication of maximum power? I pushed it to 100 mA without any problem; I measured the lasing threshold to be 72 mA. Does this give any information about the power of this diode?

the other recorder is a 24x, so it should be more powerful right? The problem is that this diode is not in a round package, but in a strange flat package I only saw once before (for a weak IR diode), and it's combined with an IR diode. Do you have experience with these diodes? For the moment I kept it in the small heatsink module from the recorder. Clearly it was a very-low-cost reader, because the optical pickup is a plastic one (not a molded aluminium one) and the optical path is kept as simple as possible!

3) Small question: Do you know of a table somewhere that would cross reference dvd burners with diodes inside?

4) I played with a OPT101 light sensor from Texas Instruments (thank you texas for your fast samples). This is a photodiode and an amp in the same package. I found it to be a weak light sensor, I could measure the light output from my 18x diode in LED mode, but as soon as lasing started, the sensor saturated. So that's not a very nice test. I'll have a try with my own PD+amp circuit.

A friend gave me an oscilloscope (thanks to him!) and I made some measures on my old driver. I found noise everywhere!

I made a new one, using an INA286 high-side current sensing opamp, a OPA2704 comparator and an IRF622 FET.
I struggled a bit with oscillations and noise, but all went well, the oscilloscope shows that the noise is much lower than the one in my previous driver. I used huge filtering caps on the FET gate, so this makes a nice slow start

Anyways, thanks to this trustful new driver, I just perpetrated one nice achievement: first smoke!



No idea of the power, I was throwing 200 mA in the 18x burner diode and the voltage across the diode was 2.46V, so the electrical power was 492mW. No idea of the diode efficiency. at 50% it would be a 200mW beam.

I focused the beam with a small magnifier lens. I estimate the spot to 1mm in diameter, as seen on the black shrink tube. I'm impressed by the small size of the cut.

Now, I need glasses. Seriously.