Electronics > Projects, Designs, and Technical Stuff
Laser diode efficiency
Psi:
15W :o, and to think i'm scared of my 300mW
Kleinstein:
--- Quote from: Psi on February 12, 2019, 11:52:34 am ---15W :o, and to think i'm scared of my 300mW
--- End quote ---
A high power laser is scary and may need a special permit.
I remember getting scared from the first blue laser pointer made from a diode laser. Not that bright (probably due to 408 nm wavelength), but the presentation showed a curve for the laser diode to be able to go up to 120 mW. With a fluorescent paper it got quite bright - so it was probably above todays legal limits for this use - though maybe not in 1999.
So for some reason even the first blue laser diodes where quite powerful.
npelov:
--- Quote from: blueskull on February 12, 2019, 05:38:21 am ---The state of the art 808nm pump laser has around 40% efficiency. This should say something.
Lasers, unlike LEDs, rate optical output power instead of electrical input power. If it rates 15W, it draws at least 37.5W. With a 90% efficiency driver, it should suck in 41.7W.
Your 23W looks more like an 6W NUBM144 over driven to 7W~8W.
Some laser modules rate peak power, that is the peak power when operated in QCW mode. Many so called high power Chinese laser engravers do so.
--- End quote ---
That was the kind of answer I was looking for. I don't care if I assume it's 6W while it's actually anywhere between 4 and 8. It's roughly 3 times less so I can submit my return request.
Also actual power doesn't matter to me. All that matters is that the laser should be able to mark steel as I saw in a video of AppliedScience.
duak:
In the 90's I worked with systems containing 830 nm IR laser diodes ranging in power from 15 mW to 20 W. Here's a few points I picked up over the years. It should be applicable to blue lasers but as I haven't worked with them I'd like others to chime in.
AFAIK, all laser diodes have a threshold current which has to be exceeded to produce coherent light ie., make them "lase". Below the threshold, they work as LEDs, often with a different wavelength. Above the threshold, the additional current goes into radiation and so the incremental efficiency is remarkably high. Diode lasers emit from a very small area on the edge of the die called a facet. Small diodes have a power limit because the power density at the facet can get so high that it damages the facet and the diode stops lasing. This limit was usually just above the rated power and could be easily exceeded with a power supply surge. We joked that the burn rate of laser diodes was measured in dollars per nanosecond because it happened so fast. Larger bar lasers were a bunch of small lasers that had an overall power dissipation limit and were rarely damaged except by large, fast current pulses.
I prepared a few of the laser safety reports and applications to the CDRH to get approval to sell our equipment in the US. There are a lot of misconceptions about what Brightness really means in physics. (hopefully I have the correct terminology) Brightness is the power intensity received divided by the solid angle subtended by the emitter. In other words, how much power received per area per the apparent size of the source. This is very important for laser safety. For an unfocussed system, ie. no lenses, it doesn't matter too much if the power falling on a surface comes from a point source or from something much larger. For a focussed system, such as the eye, the lens can concentrate the power in a much smaller area. A laser has a very small exit aperture and the solid angle it subtends is very small. This means that the power intensity where an image has been formed is very high and can cause damage. Laser beams usually have small divergence and so any spot formed is also quite small and can also be a hazard.
We used laser power meters with black corrugated sensors to measure the laser power outputs. They were accurate everywhere except for the film plane where the power intensity was too high. We also had some integrating spheres and silicon sensors to more accurately measure lower intensities. I don't know what sort of sensor could accurately measure laser radiation that can ablate metal. Perhaps a defocussing lens to spread the beam out and a larger area sensor? Large area silicon photodiodes have a fairly well defined response to radiation of various wavelengths and produce a photocurrent proportional to incident power so it should be possible to build a power meter with available parts.
Cheers,
james_s:
I don't see how you're gonna mark steel with even a true 15W visible diode laser, most of the energy will just bounce off. 15W far IR from a CO2 laser might do it. In order to mark something, it has to absorb the energy, most metals make pretty good reflectors at visible wavelengths.
Regarding pointers, in the US I believe the legal limit has always been 5mW but nobody seems to enforce that. You can easily buy pointers from China that are well over 100mW.
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