Mitt liv som Tobin

Today is the last day of "Enhanced LIGO," the project I have been working on since I arrived at Caltech in January 2007. The mood is very quiet. I think the Enhanced LIGO people are worn out and ready to move on. (I am!) Tomorrow morning the two LIGO detectors will be shut down and within hours the disassembly will begin. Almost all of the equipment is being sent away to other labs, surplussed, or thrown away. Then begins a many-year process to build "Advanced LIGO".

Tomorrow afternoon I fly to Germany to check out a post-doc opportunity there.

We have so far failed in our efforts to fix the detector. The patient has refused all transplants; something is wrong with our procedure. Electrostatic damage? Microscopic bits of metal from the can-opening procedure? Some kind of strange damage in shipping? We've used up all our spare photodiodes. The Project's last two spares are being overnighted from Caltech.

Big day at work tomorrow.

On friday we blew up a photodiode, the very sensitive component of our gravitational wave detector that senses the intensity of the laser light. This particular photodiode is hard to reach and is inside the vacuum enclosure.

Coming from each arm of the LIGO interferometer there's about 200 watts of laser power. While operating, the detector keeps these two beams very close to being perfectly out of phase, so that they cancel out, leaving only ~0.1 W for the photodiodes. But when there's an earthquake or something we lose control of the instrument and the the high power beams "spill" for an instant. We have a system that's supposed to shutter the photodiodes within 2 milliseconds of this happening, but it didn't work this time. So the photodiode got burned.

Fixing this is kind of an Apollo-13 style operation. The folks in Pasadena and Hanford have overnighted us replacement parts (Okay, so I guess it's not like Apollo 13), and even made a video showing how to disassemble a particular component.

We'll fill the vacuum enclosure with clean air and open it up, then dress up in bunny suits and very carefully try to fix it.

If you were a real nerd (a real nerd with too much time on your hands), you'd already know this from reading the elog (username:reader/password:readonly).

In other LIGO news, we just got an email from an editor at Nature saying:

We are delighted to accept your manuscript "An Upper Limit on the Amplitude of Stochastic Gravitational-Wave Background of Cosmological Origin" in Nature. Thank you for choosing to publish your interesting work with us.

I'm pretty sure I had almost nothing to do with this, but, still, it has my name on it! Along with the names of ~4×10² other people.

I don't know either.

mom and dad at ligo

Yesterday I took my parents to LIGO, dressed them up like this, and took them into the Pre-Stabilized Laser (PSL) and Large Vacuum Equipment Area (LVEA) for a LIGO tour. My advisor Gaby gave them a tour of the Science Education Center (our little mini-Exploratorium), and then they were off to Mandeville to see my great aunt Pooh for the evening.

Today we went to the nearby Bluebonnet Swamp, where the city maintains a nature center and boardwalk trail. It turns out that the nature center has a large collection of native and exotic snakes, with a complete collection of Louisiana's venemous snakes, including an enormous timber rattlesnake, not to mention the largest python (not native) that I've ever seen. A nice boy who works there (Will) gave us a personal tour of the swamp and we found several small snakes in the wild.

Breakfast: at Zeeland Market, by my house. The food was good but I still find this place disappointing.

Lunch: delicious delicious hot pastrami sandwich and shrimp and corn soup at George's, also by my house. <3 <3 <3

Work at the lab lately has been quite satisfying. Working with Stefan and Hartmut, our current visitors, has been quite a pleasure. I feel more confident, and have had more time to think about things on my own. Also, we've made a lot of progress.

Part of today's excitement was in replacing a photodiode.



Our gravitational wave detector consists mainly of vacuum, enclosed by a steel tube and bounded by a collection of mirrors, and full of photons. The photons, little packets of light, carry all of the information. When the photons come out of the machine, we detect them with photodiodes, which turn streams of photons into streams of electrons, which feed through electrical circuits.

We use many photodiodes, several at each place where light comes out of the machine. A photodiode itself is a tiny piece of semiconductor, carefully mounted and connected via tiny wires to some bigger wires that poke out of its little can, and connect the photodiode to a collection of electronic circuits who are sensitive to variations in the intensity of the light at radio frequency, who gather this information, and send it out over a wire to more electronics, who feed the signal into computers, and servo systems, and data analysis algorithms. Servo systems that hold all our mirrors in exactly the right places. Data analysis algorithms that will tell us when we see a gravitational wave.

I don't know how much our photodiodes cost, or where we get them, but it is clear that they are very precious.



One of our photodiodes went bad recently, and today we replaced it. The new photodiode came as all new photodiodes do, mounted in a little metal can with a glass cover on top.

The glass cover protects the delicate photodiode and its delicate wires. But for us it is a problem; the small amount of light that gets reflected by the glass window instead of going through it corrupts our measurements. We have to take off the window, exposing the delicate photodiode.

This is done with a tool known as the "can opener," because it is used for opening photodiode cans. It is from ThorLabs, an company that makes scientific optical equipment, and as far as I can tell, it is specifically for this purpose.

I strongly appreciated Stefan's tutelage in this matter; he described how to perform the delicate operation, and then promptly left the room, leaving me to perform it. Trust leads to confidence. He's soloed an airplane; maybe the philosophy comes from there.

With the new photodiode, our gravitational wave detector is able to see 8.5 megaparsecs into space.

The summer students' whiteboard:


"Do not feed or caffeinate!"

(Previously)

Driving to work


Waiting for the coffee


Eating breakfast/lunch


Rana in the control room

Stefan B., who took me up flying with the Caltech Aero Club in Pasadena, recently visited Livingston to work on the interferometer. While visiting, he went flying and took this photo of the lab where we all work.

Sam Waldman has posted some excellent photos of the work we've been doing over the last week at the lab (the installation of the Enhanced LIGO Output Mode Cleaner (OMC)).