Electronics > Projects, Designs, and Technical Stuff
Laser diode efficiency
npelov:
I recently bought a 15W blue laser diode. I was wondering if I could roughly calculate if it's close to the rated output. Does someone know how efficient are these laser diodes? The input from the power supply is 23W. I can assume driver efficiency >=90%. I know it's not the way to measure laser output, but well... I just want to know if it's close to it's rated value.
Kleinstein:
The efficiency of laser diodes can be pretty high. I remember around 50% efficiency for a 15 mW red one - though this was slightly better than genral data-sheet specs.
Still even a crude measurement is probably better than just looking at the power consumption. A poor quality diode tends to be lower output, not so much lower electrical input.
Marco:
Laser power meters all seem rather expensive.
How about taking a small plate of aluminium, painting it black, putting a resistor and temperature sensor and some insulation behind it? Then you can see how much power you have to put into the resistor to get the same steady state temperature as the laser (widen the beam a bit obviously, so you don't burn the paint off).
ejeffrey:
That's basically how power meters work.
Agree that you are not going to be getting 65% wall to beam efficiency of of an ebay blue laser. Red or IR lasers can have near 50% conversion efficiency from the DC power input to the output power, but blue diodes are considerably worse. I wouldn't be surprised if your driver was only 65% efficient for diode input power of 15 watt. The output power would be a fraction of that.
npelov:
--- Quote from: Marco on February 11, 2019, 06:37:31 pm ---How about taking a small plate of aluminium, painting it black, putting a resistor and temperature sensor and some insulation behind it? Then you can see how much power you have to put into the resistor to get the same steady state temperature as the laser (widen the beam a bit obviously, so you don't burn the paint off).
--- End quote ---
I thought about aluminium, but since I don't have laser diode with known input I didn't know what to compare it to. It didn't occur to me that a resistor would transfer 100% of the energy to heat. Now I have the problem that I need a resistor with good heat transfer. I have 50W suitable for mounting on a heat sink, but they contain a lot of aluminium themselves, so it'll take more time to transfer the heat to the plate. The only way is to keep it running while the temperature rising stops. But the laser does not really have enough cooling to run for a long time at 100% power.
I need a small resistor with good mounting point for fast heat transfer, so I can measure temperature rise above ambient for given time.
I have 5W cement resistors, but I'm not sure they have that good thermal conductivity.
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