DPSS stability

[norty303]

How stable should DPSS lasers be after warmup time? Is there an acceptable level of power fluctuation (e.g. 10% or so) or should they settle down to within a few 10's of mW after a while? Or is a lot of this purely down to manufacturer?

[ElektroFreak]

It depends on the model and the manufacturer. As a example, each model of DPSS laser that CNI sells comes in several stability levels. You can get a 1W 532nm laser system with 1%, 3%, 5% or 10% stability, with price increases for each increase in stability. Most of the ones we use in projectors are either 10% or 5%.

I don't recommend trying to measure stability until the laser has been powered up on a baseplate for at least 15 minutes.

[norty303]

Ok, so would 20% after 20 mins warmup time on a well respected Chinese brand green be considered excessive?

[ElektroFreak]

I would consider it so, yes.

The issue with that is that I have never seen TRULY accurate Chinese specifications. It seems that very often (especially at the lower end of things, which is where most of us laser show types buy from, regardless of manufacturer) the Chinese companies embellish specs. I frequently see claims of TEM00 from high-powered linear cavity DPSS lasers that are not really possible, and many other specs are embellished as well, such as divergence and stability. Even the leading Chinese manufacturers seem to get their lower-end systems "close enough" (in their opinion) and ship 'em out.

I should add that while a stability rating is important, once you put a DPSS laser under modulation the stability goes out the window. None of the ratings apply. Really as long as the laser is still running over spec in terms of average power and the scanned beams and images look good I wouldn't worry.

[frothychimp]

What wavelength is that? It's jumping around like a 473nm.

[norty303]

It's a 532nm head

[frothychimp]

I think there may be a problem with the temperature feedback. You have to work hard to get even a Chinese lab system at 532nm to jump around that much. Can you do a graph after the laser warm up period and post the average output and the standard deviation? That will at least give us an idea how much instability we really have here.

[taggalucci]

What is the ambient temperature? I've recently had issues with my greenie and it had to go back, though I did need to factor in the ambient temperature (which is quite low in Melbourne at the moment) before calling it.

[norty303]

Can you do a graph after the laser warm up period and post the average output and the standard deviation? That will at least give us an idea how much instability we really have here.

Well I would guess the graph already shows that if you take the warmup period as after midpoint (in fact this is around 20mins so well warmed up by then). After that you can see that it still varies from a high of just over 500mW to a low of just under 400mW and you can probably guess a slowly decreasing average starting around 450mW to the end of the measurement, based on the pattern you can see.

[ElektroFreak]

He estimated 20% instability, but if we take into account average power and standard deviation we might only have ~ +-10% instability.