Here Lies the Laser

From Bec's Eureka Diary that gets mailed to the Polar Sunrise Campagin team:

March 7 2009
Farewell DIAL

We have sad news to report today. The DIAL (ozone lidar) at PEARL finally
died last night. It has served EC well since PEARL was first started as the
Arctic Stratospheric Ozone (AStrO) Observatory in the early 1990s, and has
been a great member of the ACE Validation campaigns for the last few years.
Its death by old age was not unexpected, and its successor is already in the
planning, but we are thankful that it chose to survive through a record 17
nights of high-quality measurements this campaign before dying as the sun
was getting too high for great measurements anyway. Emily and Bernard are
obviously very disappointed that it stopped before the end of the campaign,
and did their best to revive it, but to no avail. RIP DIAL!

So as you see, the dial has finally died. Friday night, we went to the lab as usual, ready for another night of measurements. We filled up the laser, turned it on, and it sounded like an airplane in low gear. The power was also really unstable. We've been getting around 50W out of it usually (one day up to 58W), but this day the power was all over the place, and dropping down past 40W. That is not how it usually sounds, and that's not what the power is supposed to do, so we turned it off, pumped it down, filled it back up with a new fill of gases. Sometimes if we don't get the mix just right, strange things happen with the power. This time, it sounded even worse - more like an airplane in low gear that is having some troubles and maybe you'd like to get off the plane before it takes off because it, not to mention you, might not survive the flight- so we turned it off again. We tried most of the stuff in the book to see what might be wrong. We did leak checks of various sorts, flushed the system with Helium, and it's currently filled with an HCl mixture. It is a very sick puppy and we will be closing it up tomorrow.