Atomic notes

Signal to noice

Thomas Lennartsson — Wed, 12 Mar 2008 20:01:28 +0000

Time-resolved spectroscopy, that is what I am hired to do. And up until today I was really worried that all I was able to do was just rather crappy time-resolved spectroscopy. The problem has been that my signal from my light source has been very weak, which has led to that I have not been able to slice up the signal in short, short pieces. Instead I have reached a resolution of just, say, 50 microseconds for the weakest (and, unfortunately, the most interesting) transitions. And 50 microseconds when it comes to atomic transitions is not much.

Today, however, I changed a few things in my experimental setup, and whooaa. Suddenly I could get down to 1 microsecond, without any struggle at all. All I have to be able to do is being patient, since one run takes about 3 hours or so, but there is a lot of things one can do when waiting. Blogging, for instance. Oh, did I just say that? Sorry, I meant correcting undergraduate lab reports…

Some idea about some sort of experiment

Thomas Lennartsson — Thu, 06 Mar 2008 15:10:32 +0000

One of the articles which I found yesterday proved to be very interesting. The authors are measuring the concentration of Hg and Ar in a fluorescent tube, both in the negative glow and the positive column. In the cathode phase the concentration of Hg⁺ was five times bigger than in the anode phase; the amount of excited Hg was however only half as large. This implies that there are different excitation mechanisms behind the existence of Hg ions in the negative glow and the positive column. The authors suggest that the Hg ions are produced by Penning ionization, induced by metastable excited Ar.

When returning to the lab (yes, I am still at home, ill), I think I will try to detect this type of process. I will probably not be able to detect exactly the same reaction, since the dominant noble gas in my fluorescent tubes is not Ar, but Kr. But we will see what I can do…

On the hunt for articles

Thomas Lennartsson — Wed, 05 Mar 2008 19:32:27 +0000

When I was working on my diploma project, finding information was not a big issue. The thing was that I was working with measurement of femto- and attosecond laser pulses, which is a large field in atomic physics. Ergo: Much had already been written on the subject, and if you were looking for a review article about the latest attosecond pulse-characterization algorithm, you almost stumbled upon one instantaneously.

That was good.

Now, when doing my PhD, the situation is not as good as it was a couple of years ago. Atomic physics in combination with fluorescent tubes does not seem to attract as much excitement and interest as ultrafast laser physics. (I have no idea of why fluorescent lamps is not regarded as as sexy as attosecond pulse trains. But I am not bitter about that, not at all. Mrghhhgflgh. Uhm, where was I?) This leads obviously to lesser articles on the subject, making it harder to dig up anything useful. Of course, we have Waymouth’s “Electric Discharge Lamps”, but it does not go that deep into exotic atomic physics and was written over 35 years ago. Yes, I know that the aim of my PhD studies is not just to find information about experiments already done, but to produce new knowledge. However, I am not interested in reinventing the wheel, so I feel I need as much information about previous experiments and theories as possible.

Anyways, since I have been somewhat ill today, I have been at home. This has given me the opportunity to search the net for some information, without having to bother about doing other things like teaching, meddling around in the lab, and so on. And I have actually found a few more or less useful articles. Also, most of them I had never seen before, which is a plus. (I have a tendency to forget about the existence of articles which I have found in the past, which is somewhat of a minus.) Here is a list of articles which in different ways might to be relevant to my work:

G. G. Lister et al., Rev. Mod. Phys. 76, 541 (2004)

R. C. Wamsley et al., Appl. Phys. Lett. 57, 2416 (1990)

R. C. Wamsley et al., Appl. Phys. Lett. 59, 2947 (1991)

R. C. Wamsley et al. Phys. Rev. E 47, 3540 (1993)

Especially the first (a nice review of the subject which hopefully can lead my to other good sources of information) and the last I find interesting. The focus of the last article is actually almost exactly the same as what my current project is about: Penning ionization in the plasma of a fluorescent tube. Yesss.

Intro

Thomas Lennartsson — Wed, 05 Mar 2008 14:49:43 +0000

Greetings. I am Thomas Lennartsson, a PhD student at Lund Observatory. My research focuses on plasma spectroscopy, mainly of low-density plasmas like in fluorescent lamps. I started this blog since I have a tendency not to remeber stuff, so if I have an interesting (or not that interesting) idea or if I read something interesting in connection to my research, my thought is to note this in this blog. Hopefully, I will remember to do this, and also that I have this blog in the first place.