What Determines Laser Reliability/Durability?

I am building a laser tripwire system but it constantly goes on and off several times an hour. Currently we have some cheap Chinese 50mw green lasers inside some metal heasink housings with a 1.5cm fan on the back. We are finding that over a month, their intensity starts dropping and they start failing.

I don't really have any experience with lasers, what determines their overall reliability/durability? They seem to be dying and having to be replaced every month.

well, first things first: these laser modules are "DPSS" or Diode Pumped Solid State lasers. green ones in particular operate like this; a infrared laser diode emitting light at a wavelength of 808nm, has its beam focused onto a Nd:YAG or Nd:YVO crystal (depending on the module and application) which is excited by the infrared light and starts lasing at a wavelength of 1064nm, which is also infrared. the 1064nm light is then passed through a KTP crystal which doubles the frequency (halving the wavelength) to 532nm, which is a very green color.

there are many things to go wrong here, as you can see. there are also many places where power is lost, so a high power IR laser diode is needed.

so, after considering that, those modules could be failing for 2 reasons:

1. the infrared laser diode is over driven (meaning the driver is set to feed it a higher current than the diode is supposed to handle) in order to make a higher IR output, instead of spending more on a diode with a higher rated output power. this overall decreases the lifespan of the module, and causes the laser diode to slowly degrade until it dies

and/or 2. the fact that DPSS lasers slowly, over time, drop in output power if they are not under optimal conditions in a very stable environment. they are also very temperature sensitive, this may play a role in whats happening.

if you could give more details about what type of laser you need i could definitely give you a recommendation on what you need to get for your application.

edit: what determines a lasers durability is operating method (Gas, solid state (crystal and DPSS), dye, free electron, semiconductor, diode, optically pumped semiconductor... there are many) and a few other things, but mainly operating method.

That's what mass produced junk gets you, unfortunately. If you can use lower powers and different wavelengths, try these. if you search for the, you can find 50-100 packs for dirt cheap. They are low power, 5V input, relatively low output (someone metered some once, and found some do almost 40mW), and are surprisingly reliable, going against my first sentence someone has one hooked up to a USB wall charger that's been running for something like 10000 hours. Sorry I can't find links for you, I'm on my mobile.

well use green diodes laser instead.