Heat sink cooling?

[rbneville]

Hello, This is my first post but that doesn't mean im a stranger to lasers.:yh:
I have been reading many posts on the forum and most people that build their own gas lasers use water cooling. My family owns 3 co2 lasers and all use a heat sink to cool the co2 tube(2 30watt lasers and 1 15watt laser). I was wondering whats the max wattage that would be safe to use a heat sink on? (I am considering building a tube)
Also, I am not very good at glass working so I was wondering would a heat sink with water cooling coils running through it work effectively?

Thanks in advance,
Richard

 

[Benm]

If your laser has water cooling, the question boils down to 'what is sufficient to cool the water'.

If you are looking at serious power levels, and automotive cooling system comes to mind. Those are designed to cool several tens of kilowatts, and could be good candidates to cool a CO2 laser of any power level.

If you are looking at tens of watts to dissipate, any car radiator would suffice even without the fan running.

 

[Event_Horizon]

CO2 lasers are especially sensitive to temperature. A few degrees can mean the difference between 20W and 200mW. The cooler you can keep it (without forming condensation, of course), the better.

 

[anselm]

So an automotive cooling system would only ever keep it at room temperature...
Would that be cool enough?

 

[Cyparagon]

A few degrees can mean the difference between 20W and 200mW.

Sounds like total BS. Do you have s source, sir?

 

[Event_Horizon]

Sounds like total BS. Do you have s source, sir?

My degree in Photonics Engineering. We did an experiment on a 35 watt Lumonics CO2 laser which had two tubes in a folded cavity arrangement. It was cooled by flowing tap water through the tubes and into the drain (wasteful, I know). It was February at the time and so the tap water was extremely cold, and it was causing condensation on the tubes. Since it runs at high voltage, we decided to turn the water down to let the tubes warm up to room temperature. My lab partner and I weren't paying attention though and the laser got much warmer, approximately 35-40 degrees C. We noticed that it's output was extremely low (not measurable on our power meter which could only resolve in 100mW increments). After we turned the water back on full, the temperature slowly dropped back down to 10 degrees C or so and we watched the output climb with it.

Asked our professor about it later and he told us that was indeed the case. The lasing transitions in a CO2 laser are all at very, very low energy levels. It only takes a small amount of ambient heat to populate the lower level of the lasing transitions and extinguish output entirely. We later did another experiment with the whole class to demonstrate this.

That said, it's not dangerous for the tube itself. You just won't get any laser output.

 

[rbneville]

Benm, I was considering using a pc water-cooling system for the liquid cooling. A automotive cooling systems seems overboard for the power im considering (30-45 watts).

anselm, our laser tubes currently get warm to the touch but show no apparent decrease in power so keeping it at room temp should be plenty

Cyparagon, I agree that what Event_Horizon said is not true. I've experienced a increase by 7 degrees Fahrenheit with only a 45mw drop in power.

 

[rbneville]

My degree in Photonics Engineering. We did an experiment on a 35 watt Lumonics CO2 laser which had two tubes in a folded cavity arrangement. It was cooled by flowing tap water through the tubes and into the drain (wasteful, I know). It was February at the time and so the tap water was extremely cold, and it was causing condensation on the tubes. Since it runs at high voltage, we decided to turn the water down to let the tubes warm up to room temperature. My lab partner and I weren't paying attention though and the laser got much warmer, approximately 35-40 degrees C. We noticed that it's output was extremely low (not measurable on our power meter which could only resolve in 100mW increments). After we turned the water back on full, the temperature slowly dropped back down to 10 degrees C or so and we watched the output climb with it.

Asked our professor about it later and he told us that was indeed the case. The lasing transitions in a CO2 laser are all at very, very low energy levels. It only takes a small amount of ambient heat to populate the lower level of the lasing transitions and extinguish output entirely. We later did another experiment with the whole class to demonstrate this.

That said, it's not dangerous for the tube itself. You just won't get any laser output.

20 degrees is not exactally a few degrees :can:

 

[Flaminpyro]

To answer your question, Yes a heatsink with water passagas running through it will work just fine to cool most any laser, it has to be designed corectly for the job at hand though.

post 2424 wasn't there a song by Zager and Evans about the year 2424
or am I just having a big one and loosing all the blood to my brain ?

 

[Pontiacg5]

My degree in Photonics Engineering. We did an experiment on a 35 watt Lumonics CO2 laser which had two tubes in a folded cavity arrangement. It was cooled by flowing tap water through the tubes and into the drain (wasteful, I know). It was February at the time and so the tap water was extremely cold, and it was causing condensation on the tubes. Since it runs at high voltage, we decided to turn the water down to let the tubes warm up to room temperature. My lab partner and I weren't paying attention though and the laser got much warmer, approximately 35-40 degrees C. We noticed that it's output was extremely low (not measurable on our power meter which could only resolve in 100mW increments). After we turned the water back on full, the temperature slowly dropped back down to 10 degrees C or so and we watched the output climb with it.

Asked our professor about it later and he told us that was indeed the case. The lasing transitions in a CO2 laser are all at very, very low energy levels. It only takes a small amount of ambient heat to populate the lower level of the lasing transitions and extinguish output entirely. We later did another experiment with the whole class to demonstrate this.

That said, it's not dangerous for the tube itself. You just won't get any laser output.

I've run a 20W tube with water just sitting in the tube for about 5 minutes. It was still strong enough to punch 1/4" holes in balsa wood instantaneously.

Auto parts stores usually have transmission or oil cooler radiators for fairly cheap. I would pick one of those up and add a few CPU fans if I planned on running the lasers for any period of time. A large tank with a lot of water will help keep the temperature stable as well. I used to run my 20W tube with a windshield washer pump and around a gallon or so of water in the loop. The water never got above room temperature during 30 minute runs that way.

A windshield washer pump isn't meant to be run continuously though, that's just about the only part of my setup that got hot

 

[anselm]

post 2424 wasn't there a song by Zager and Evans about the year 2424
or am I just having a big one and loosing all the blood to my brain ?

You're off by 101 years (or posts).
YouTube - Zager And Evans - In The Year 2525
Great song!

 

[Flaminpyro]

Damn it must be my brain going then :crackup:
At least I can still make it to 2525 posts

You're off by 101 years (or posts).
YouTube - Zager And Evans - In The Year 2525
Great song!

 

[Cyparagon]

My CO2 has no noticeable output changes between the 65F ambient and the 95F when I turn the radiator fan on. I know the output drops a little with increased temp, but what you described is VERY drastic. It seems that for whatever reason, your lab unit was much more susceptible to temp changes than most other units out there.

 

[james1095]

Motorcycle radiators are nicely sized for this sort of thing. I've used one with a diffusion pump, cooled by a 4" muffin fan and it had no trouble dissipating the 450W of heat. Automotive transmission coolers ought to work well too, go to a junkyard and look for trucks, SUVs, some minivans, anything with an automatic transmission and towing package will tend to have one attached in front of the radiator behind the grill.