After having built a UV filter for my camera I was able to confirm that we should, without any problems, be able to see stars in the night sky. After some small adjustments to the telescope, the stars suddenly appeared and we were all very happy to see them.

Our hope is obviously to be so lucky that we will be able to observe an Air shower. However, in order to run, we first have to learn how to walk, and before we learn how to walk we need to learn how to crawl. Basically what we just had done was making an attempt to sit up.

Located about 20 km from our telescope was a powerful laser. This laser was aimed in the zenith direction and could fire multiple bursts of laser shots into the night sky. Given the inclination of our telescope we have a time frame of about 20 µs during which a laser pulse is within our field of view. 20 µs is the same as 0.00002 s, i.e. you can have 50 000 such time frames, back to back, in a single second. This might sound very fast, and it is, but it’s no problem for our detector. The timing resolution of the telescope is 2.5 µs i.e. we should be able to see a single laser pulse in about 8 frames.

At the moment our telescope has no internal trigger, this is actually what I’m working on at the moment. So in order to see the laser we needed the trigger from the TA-FD. A “trigger” is just a signal saying “it’s time to read out the detector”.

A very intense wait followed after we were ready to try to observe the laser shot until it actually was time for the laser to fire. The seconds ticked by slowly, really slowly. But suddenly the screen started showing output that the detector was triggering the readout and shortly thereafter we could start looking at the data…

And there it was, we could clearly see the laser pulse ascending to the night sky across our field of view!!

This might not seem as much of a thing, although being able to show that we can see the laser proves that the detector principle is correct and that we’ve built it correctly! An email with the data was soon sent to the collaboration and shortly thereafter congratulatory emails started dropping in from the PIs (PI is Principle Investigator i.e. Boss) from all over the world. Below you can see how the laser pulse ascends across our focal surface on the way into the night sky.

(For some reason the gif doesn’t play so click here on it to see the animation.)

The EUSO-TA March 2015 campaign at Telescope Array could be classified as a success.