A laser that can maintain a perfect lasing environment/condition suitable for stable lasing is a laser that has no duty cycle. So like Dave said, something with a large heatsink that radiates heat away from the laser, and then has it blown away is one way to get a laser with no duty cycle.
This TEC cooled laser built by a PL member 300evil may have very little to no duty cycle.
My noob impression/answer of the question would be a laser that is built with components allowing it to have virtually continuous operation without failure.
This is assuming all lasers will fail at some point in time do to the diode life expectancy.
Please correct me if my assumption is wrong for future reference.
Then my laser should operate without shutting down to cool it down. hardly gives off heat even after having made pot-mod. I've come to have two minutes continuously without heating. mmmm
I have a good laser when only cost me a $ 8?
Stick a something like a 50mw in one of these hosts we use for ~1000mw+ and you have a continuous duty cycle , well continuous until the battery runs down. For instance, when I first put mine together it was running at 65ma, pretty sure it coulda run like that forever.
There is only one cheap laser that I have and have observed no duty cycle with (keep it on for hours): www.rayfoss.com
Duty Cycle = No Limitation
Of course any lab-style module with good heatsinking and/or a fan will have a continuous duty cycle.
Keep in mind that a duty cycle isn't just a period of time intervals without device failure, it also has to do with stability. As long as it has batteries, any greenie to run indefinitely until the diode takes a poop. But the duty cycle comes from the fact that while a diode may be able to run hot, the non-linear optics inside aren't. Some duty cycles require a warm up period, and some require a cool down period. While a greenie can lase and lase and lase, it may not do so with great stability. DPSS systems have duty cycles that must also account for stability.
Went to your build thread. Nice one. I have the DX 200mw module. They look virtually identical. My brass housing unscrews in the middle exposing a coated lens, it has the same 33ohm resistor, but the switch button is red and it does have a diff part no. on the sticker.
It doesnt really get hardly warm either, but the beam is way more than my 25-30mw overspec penstyles......I was just surprised they were so close in looks. I can post a pic, but would probably be more appropriate in your thread, just as a comparison thing. The 33ohm is right off the power lead so it seems its limiting the driver.