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How much waste heat does a laser diode produce? (Cooling)

TacoCat

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Jun 12, 2021
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Greetings!

I am trying to make a small handheld laser in a (hopefully) 3d printed abs plastic case. However, I am unsure of how much heat energy lasers of different wattages and wavelengths produce and no amount of internet browsing seems to help.

So here are my questions:

-How much heat do lasers of different wattages produce

-Secondly, what is the most powerful continuous laser that doesn’t (hypothetically) get warmer than 150c without a cooler

Any help or guidance would be appreciated
 
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bostjan

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It depends.

Direct diode lasers are super efficient. Still, don't count on them outputting (much) less heat than light. Blues and greens are less efficient than reds and infrareds, as a general rule, and the higher the power rating, the lower the overall efficiency, generally. Also, driving the laser at maximum efficiency is different than driving it for maximum power output (generally maximum efficiency is slightly lower power).

But think of it this way, if the laser is powerful enough to burn stuff, it's powerful enough to burn itself up without proper heat management. If you just want the laser for pointing, why not use one of the ubiquitous <5mW reds?
 

paul1598419

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The multi-mode laser diodes tend to output more heat than the single-mode ones do. If you are trying to make a CNC cutter those diodes tend to output more heat.
 

Sowee7

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The multi-mode laser diodes tend to output more heat than the single-mode ones do. If you are trying to make a CNC cutter those diodes tend to output more heat.
As he said, singlemode diodes usually need way less (in some cases no) heat sinking compared to multimode diodes. The strongest singlemode diode I know of is a 900mw 405nm diode but that does produce a lot of heat even though it is a singlemode diode so you still do need a big heatsink for it
 

RA_pierce

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The only way to understand the waste heat produced by a laser diode is to calculate it. It's very simple to do.

Pt = Po + Ph = I * V
or
Ph = Pt - Po
or
Ph = I * V - Po

Pt = Total output power
Po = optical power (light) measured in Watts
Ph = heat output power measured in Watts
I = Current input measured in Amperes
V = Voltage input measured in Volts

Using this information and data on heat capacity, thermal conductivity, radiative heat dissipation, etc. of different heat-sink materials, you should be able to estimate the cooling requirements of your design.

I made a whole thread about efficiency some time ago with some graphs. Unfortunately, the image hosting service has removed my plots.
I'll repost it here as an attachment. The main plot shows efficiency (the ratio of optical power and total power) as a function of power output. Essentially what this shows is the output power setting where a diode is performing optimally - in other words, the peak for each diode on the y-axis (efficiency) is the power output you want to set the laser diode to (on the x-axis) in order to achieve the best balance of output power and waste heat.

You may notice that these plots show that multimode diodes are sometimes more efficient than single-mode diodes and that long wavelength diodes (red) are more efficient than shorter wavelength diodes with greens being the least efficient.
These curves demonstrate the different patterns of "behavior" of different diode types including how the efficiency penalty differs for each diode type as you increase power output beyond the design parameters of the diode.
 

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