You can expect to lose about 1-2% per mirror if you do the pucktest at the head.  Also check your optics for purpling, or haze.  Next, pop off some of the water fittings at the heat exchangers in the resonator, see any "putty-like" substances?  Check your quartz tubes for aluminum oxide deposits.

CoffeeMan:

Another source of error:
Has the probe and meter been calibrated and inspected lately? Possible probe damage from too high of an energy density could cause power readings to be too low.

-Pete

Ideally, you should see full power from the laser. Anything less indicates deterioration of something or some several things. Those "things" can include optics, electronics, cooling (which can affect alignment and optics performance), and the power puck itself.
As Pete says above, you have to determine if your test instrument is still working correctly.

Five years is long enough that your laser may need more than "regular maintenance". Part of the question is: Does it cut well? Is the beam quality still good?
Some lasers need to be overhauled or have blowers replaced to avoiid catastrophic failure- I have no clue as the your machine's requirements.
What does the factory service department suggest?
regards
Jay

Jay Maechtlen

You should be shoot the power puc directly out of the resonator and depending on what size puc you have and the calibration you should receive the exact wattage of the laser.  2200 watts.  If the wattage is very low, then you internal mirrors inside the resonator probably need to be cleaned or replaced. Shooting into an acryllic block, and looking at the shape of the beam is the best way to tell if you need internal resonator work, shoot for a specified time probably about 3 seconds at 2200 watts.