Sunday, October 5, 2014

Greenlight HPS Part 2: First Light

So we had this beautiful laser, and no clue how to turn it on...

The first step was to plug it in and see what happened. We knew it had a chiller error, and indeed, after a few minutes warming up, it threw an "error 611", which was a flow error.

After some fiddling with the internal valves we were able to clear the flow error - it turned out that one of the flow restrictors was set improperly, which resulted in the diodes receiving too little flow. At this point, the laser booted, and, as expected, we could do nothing without a fiber and a smart card.

However, at some point during the weekend, one of us decided to pull the lid off of the resonator before booting the laser, at which point we saw this:

It turned out that part of the boot process was to check actual power against the internal open-loop P/I (power/current) table, and that involved turning on the laser.

Unfortunately, somewhere during the process the laser threw an error 210, "Diode Stack Overvoltage". This sounded ominous, and indeed, after we disassembled the head it turned out one of the diodes had shat itself and failed open circuit. Undaunted, we replaced the open diode with a blob of solder paste and reassembled the stack, and the laser kept going. Little did we know...

With the diode stack fixed, it was simple to put a turning mirror in the resonator and get a beam out of the head:

Really ass photo
This self-test mode would prove critical to getting the laser to turn on under our control, as you will soon see.

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