What is the main cause of power drop off ? Updated with new info

[Accutronitis]

What is the main cause of power output drop off bellow 60 seconds run time ?

assuming it's not batteries draining down.....

Is the diode getting hot ?

Is it something to do with the driver ?

I guess it has to do with one of the two because what else is there ?

 

[HydroSean]

Re: What is the main cause of power drop off ?

basically the diode gets hot. heat creates more resistance, therefore less current travels through the diode (i.e. V=IR)

 

[Eracoy]

Re: What is the main cause of power drop off ?

Hopefully, if you have a proper driver, it would keep the current constant by upping the voltage when the resistance rises. DPSS are much more sensitive to temperature, but you might be experiencing the same with your diode. How much is it dimming by, approximately? Also, I'd be interested in hearing your battery/driver setup before ruling that out.

 

[Accutronitis]

Re: What is the main cause of power drop off ?

I don't have a power output meter, I see it visually that it dims but I guess that's not surprising because it's a Chinese laser so the driver most likely isn't a really good one....

My batteries are 2ea 16340 3.7v 2800mAh

 

[dden4012]

Re: What is the main cause of power drop off ?

I thought resistance drops in a laser diode as it get hotter. I thought I read that on this forum. Am I right?

 

[Rivem]

Re: What is the main cause of power drop off ?

I thought resistance drops in a laser diode as it get hotter. I thought I read that on this forum. Am I right?

No.

Resistance increases in all conductors in almost all situations with heat. That isn't the entire story though as the heat also can effect the semiconductor and lasing cavity to decrease efficiency. That's the bigger reason for the dropoff.

Edit: A hot driver also suffers losses due to resistance that can diminish output if its rating is barely enough.

 

[Accutronitis]

Re: What is the main cause of power drop off ?

"heat also can effect the semiconductor and lasing cavity"

I was wondering if something like that was going on and I'm thinking the poorer the diode quality the more heat with effect it ?

 

[Rivem]

Re: What is the main cause of power drop off ?

"heat also can effect the semiconductor and lasing cavity"

I was wondering if something like that was going on and I'm thinking the poorer the diode quality the more heat with effect it ?

Right. Poorly made diodes won't account for thermal expansion very well, and they'll typically expand in a way that makes the cavity far less optimal for lasing at their target wavelength.

Edit: This is also one of the reasons you might see a redshift in overdriven diodes.

 

[Crazlaser]

Re: What is the main cause of power drop off ?

No.

Resistance increases in all conductors in almost all situations with heat. That isn't the entire story though as the heat also can effect the semiconductor and lasing cavity to decrease efficiency. That's the bigger reason for the dropoff.

Edit: A hot driver also suffers losses due to resistance that can diminish output if its rating is barely enough.

This is why supercooling helps lessen resistance.

 

[Sta]

Re: What is the main cause of power drop off ?

Not all lasers like it cold, though - for example, my 561 takes around 5-10 minutes to warm up to full power! It likes it **very** warm.

 

[Rivem]

Re: What is the main cause of power drop off ?

Not all lasers like it cold, though - for example, my 561 takes around 5-10 minutes to warm up to full power! It likes it **very** warm.

Yep. That's actually an excellent example. Unlike diode lasers which also involve electrical efficiencies directly, DPSS doesn't. You'll still see similar issues though. They'll change mode and diminish/increase output depending upon their temperature.

Just as I said with diode lasers, the temperature can effect the mechanical properties of the lasing cavity and change the efficiencies of the optical materials.

Of course, ideal operating temperature is a much more definite range in DPSS than diode lasers.

 

[Accutronitis]

Re: What is the main cause of power drop off ?

Very interesting posts guys !

 

[Accutronitis]

Re: What is the main cause of power drop off ?

I was just messing around with it and after 60 seconds it gets quite a bit weaker but nothing feels even a little warm, could it be a cheap a$$ driver ? or a very poor quality diode ?

 

[Accutronitis]

Re: What is the main cause of power drop off ?

I started a new thread with the updated info