It’s currently 10pm. I’ve spent 30mins of the last 14hours not in the physics building, and the end is far off…
Most of the morning was spent pumping systems down. I’ve got a spectrometer built around a continuous flow cryostat.
The spectrometer sends a short pulse of light through the system. This pulse is measured in time and a Fourier transform taken. This yields a frequency domain trace of the pulse.
The cryostat is a vacuum cylinder, into which a sample is placed on the end of a lump of brass. The lump of brass is connected to another tube, into which liquid helium is pumped through the system at a continuous flow. This simple system allow for temperatures down to just over 2K, or -271.15Deg C. Pretty cool
I’m investigating the material properties of a device as the temperature is reduced and its interaction with light.
Why so late and why so long. Well the first few hours of the day were spent aligning the spectrometer and making the cryostat fit. This involved moving a slightly more traditional cryostat out of the way, one that’s about 8times larger and works by filling with helium and then pumping to create the low temperatures. This large cryostat doesn’t work in the frequency range I require which is why I couldn’t just pop my sample in and hit run. Once in place the cryostat needs the sample chamber evacuating. This is done so that the system doesn’t just fill with ice (and frozen CO2 or liquid oxygen or nitrogen). Having done this the transfer tube needs all it’s air sucked out so that when the gas flow starts it doesn’t just freeze up and stop everything working before it’s even gotten started.
Having done these things which took me to around 1.30pm. The cryostat is then connected via the pumped transfer line to the dewer of liquid helium, this is just a tank full of the stuff. The pumping then begins and so does the waiting. This is the longest wait of the day, a few hours for it to drop down to 6K, the lowest temp I need today. This doesn’t give me a chance to escape the building though because our semi-clean laser lab needs to be cleaned so me and another guy spend most of the time hovering and wiping down the surfaces.
The first scan can then take place this takes around an hour and is followed by 10 more, each taking at least an hour. If I left and started again tomorrow, I’d probably get it done a bit earlier in the evening as everything is in place, but I’d still be here till around midnight…
The time is now 10:40.
I’ve spent some time in the lab since I began writing this.
I’m not alone though, three others are around in the physics building tonight. Tom, he came in a little late today and to make up for it is sat two desks away from me in our four desk office, he’s working on some modelling and finalising a paper. Al, he’s upstairs running some sound experiments, he runs them at night out of courtesy for his lab mates because the buzzing noise that his system makes is really off putting. And Fred, he’s in and out of the clean room making some graphene samples, not sure why he’s here so late…
I’m sorry I’ve gone on a bit and there’s nothing really interesting in here. It’s late, I’ve been busy for a long time now, tiredness is setting in. Looking forward to going home, having some hot food and getting a good few hours sleep.