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daguin said:As I was writing a note to someone who bought a laser from me, I realized that I was "teaching" him about the eccentricities of 405nm laser light. I thought that it would be a good thing to collect these thoughts here. I will start. Please add your knowledge to this
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1) It is not blue. It is violet. The misunderstanding comes from the "marketing" name Blu-Ray. This name was developed by the manufacturer to help the sale of the new technology. The light is NOT blue. Blue would be around 473nm. The light is violet (405nm). The light may seem to change colors because it causes many things to fluoresce. That fluorescence may be different colors, but the laser light is violet
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2) High powered blu-ray lasers require a limited duty cycle. 150mA is NOT too much current for the PHR-803T diode. For every one that you read about failing, there are 20 that are doing fine. Plus, one must be aware how much efficient and fast harvesting can effect these diodes. Also, how long was the failed diode burned for? If you run them for 20 minutes at a time, they will fail. It continues to amaze me that people that would never think of running their red laser for more than 2 minutes before allowing it to cool down, think that they can run a blu-ray for 20 minutes at a time, several times a night! Then they get angry that the diode was "weak" or that the builder must have messed it up.
When you read about somebody's red laser (with a long open can), that is running at 420mA burning out, do you hear anyone crying, "We should run these diodes at no more than 380mA?" No. People accept that sometimes diodes just fail or that the operator probably did something to kill it. Why do people think that the 405nm diodes are somehow "magic" enough that they should never fail? [/rant]
Harvest the diode without excessive heat or impact. Heat sink it well. Make very fast solder connections. Limit your burns to under 2 minutes (I limit mine to under one minute). Using these guidelines I have had one blu-ray running at 190mA, with several burns a night, for over three months and one running at 200mA for over two weeks now. Will they fail? Eventually they probably will. When they do, I will have to replace them. Just like we do with red diodes.
If you want your diode to "live forever" then run it at 110mA (although even that is not a guarantee that the diode won't fail). However, there is a significant difference in the beam of one at 110mA and one run at 150mA. You decide what you want. Conservative use means longer use
If you turn it on for a very short time (short 5-10 second burns), then you do not need to wait (unless you do several short burns in rapid sequence). There is a lot of metal in these builds. They can dissipate quite a bit of heat. If they begin to feel warm (not hot) in your hand, you have taken them to the limit. Feeling "heat" does not mean that they have started to degrade. It just means that you have reached the limit of the host's ability to draw heat away from the diode. Heat is drawn very quickly and efficiently from the diode into the host. It is NOT transferred very quickly or efficiently from the host into the air. Hence it takes longer to cool down than it took to heat up. Smaller, lighter, hosts (like Leadlights or pen lasers) require shorter duty cycles than more massive, heavier hosts
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3) Higher currents require higher voltage. At currents under 110mA the 803T diode needs about 5V. As the current is increased they require more voltage. The diode MAY require over 6V at higher (over 180mA) currents. When figuring the needed voltage to run the diode, don't forget that the driver requires voltage as well. If your driver needs 2.2 volts and the diode needs 6 volts, you MUST have a minimum of 8.2 volts coming from the power source, to run the diode effectively. They will also require significantly more heat sinking and shorter duty cycles, at these currents.
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4) The laser MUST be focused. It is an absolute requirement with diode type lasers that the beam be focussed. All light diverges. We can limit that divergence with laser light, but it still diverges. For looking at the beams and spots as far away as possible, you will want to focus to "infinity." Realistically what that means is that you want to focus it to as small a dot as you can as far away from you as you can and then leave it there. Unfortunately, that leaves the "close-up" spot very large and out of focus. If you want to "burn" things with it up close, you will leave the beam very out of focus just a few feet away.
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5) The eye has trouble seeing 405nm light. 405nm is "Near Ultra Violet" light. Blu-ray lasers are at the very edge of our eye's ability to see. Older people have more trouble and glasses with UV coatings filter it. Your eyes will get tired quickly when you first start using the blu-ray and the beam and dot may look "strange" to you. If you have read about IgorT's experiences you will have a better understanding.
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6) The laser "looks" dimmer than you thought it would. The beam and dot may appear to you to be very low powered -- until you hit something fluorescent with it!!!! I use a little 11mW blu-ray in lecture. When the dot is on the wall, you can barely see it. However, as soon as the dot hits the projector screen (white) it "seems" to jump exponentially in power. If you first shine it on your wall, it may appear to be "broken." However, shine it at a white shirt that has had "fabric softener" used on it. The whole room will light up! One of the cool things to do with the 405nm is to shine it on rocks, plants, and insects to see the different fluorescent colors out there. This activity is when most people "burn up" their blu-rays. It is very easy to lose track of time when one is "searching out" glowing things
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7) The beam will look "large" (especially outside). Some people have described the beam as "as wide as a baseball bat." This is simply an illusion caused by the eye's inability to focus on the beam AND the light being scattered in the air.
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8) The dot looks like it has "stuff" all around it. This caused by the same processes as described above. Also, these diodes have some "artifacts" surrounding the beam.
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9) The beam isn't "round." When looking at the unfocused beam, the spot will appear "flat", elongated, or oval. This is normal. The shape of the beam is an artifact of the construction of the crystal and the diode. When you focus the beam the small dot will be a pinpoint.
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10) It doesn't look "dangerous." Since it appears dim, people are lulled into a false sense of safety. Your laser is probably putting out over 100mW of light! No matter how "dim" it looks (when shining on a non-fluorescent surface), it is bright enough to blind a person or animal!!! Use caution with it. Be mindful of shiny, smooth surfaces especially when using the laser inside. Specular reflections are just as dangerous as a direct hit. If you are going to use the laser in an enclosed space or surrounded by reflective surfaces, use eye protection. If you are going to "burn" things, use eye protection. Educate anyone around you about the danger that the light poses. They will NOT have read this warning.
Peace,
dave
Could I (or you) put this on the wiki please?
