Month: March 2015

The hyperfine structure of cesium

Today in the lab of atomic spectra we built a setup for observing the hyperfine structure of cesium. It is a big deal for atomic clocks as they use this transition to “tick”. It is also a very very tiny and fine effect (as its name suggests) so it’s pretty exciting that we can see it with such simple setup.

First, here is a brief description of atomic structure notation. The source of the text and picture is http://webphysics.davidson.edu/Alumni/JoCowan/honors/section1/THEORY.htm

The electrostatic attraction between the electron and the nucleus could be described by the principal quantum number, n. The combination of l and s gives an electron’s total angular momentum, J. Magnetic coupling between the electron’s orbit and spin causes an energy splitting between levels with different J called the fine structure. The fine structure is split again into the hyperfine structure denoted by the letter F. The hyperfine structure is due to a magnetic coupling between the electron’s total angular momentum, J, and the nuclear spin, I.

In order to observe the hyperfine structure, i. e. the two distinct energy levels at F=3 and F=4, and to measure the frequency difference between them, we carried out the following experiment.

The concept is to set the laser generation exactly at the wavelengths of absorption of cesium (they are two known peaks around 895 nm). For this we use an IR laser diode and we can modulate its wavelength by changing the temperature and the supplying (triangular) current. We are thus “scanning” the laser. In order to ensure the scan is smooth – that is, the laser doesn’t “jump” from one mode to another, we add an interferometer Fabri-Perot (IFP) which also serves as an etalon for the frequencies.

scheme

So we have the laser diode, connected to a thermoregulator and powered with triangular current, which is monitored on the oscilloscope screen. The beamsplitter sends the laser beam through the interferometer and the output is detected by a photodiode, hooked to the oscilloscope. The other part of the beam is reflected by a mirror in such manner that it passes through a glass case with cesium inside. The output is again recorded with a photodiode and displayed on the oscilloscope screen.

Finally, at the right adjustment of the scan, we get our lovely hyperfine structure:

Screen Capture

Green signal is the current, yellow is the interferometer signal and blue is cesium signal with the energy level splitting

The only thing left is to process the data we recorded with the oscilloscope and plot it. Now, to find out what is the frequency difference, we’ll need two things: the FSR (free spectral range) of the interferometer and the number of peaks of the IFP signal between the two cesium split levels. The FSR = c/4L, where L is the length of the IFP and in our case 0,2 m. Thus, the FSR is 375 MHz.

Graph-cesium

As you see above, I have counted the number of peaks and they are 22. So for our final result, we multiply them and get frequency difference of 8,25 GHz which is close enough to the real one of ~9 GHz, considering how imprecisely the experiment was made and the fact that our IFP was pretty bad. Well, it is possible that I messed up somewhere, I’ll find out in a week. 🙂

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One place for science in Oslo

Greetings from Norway! I paid a visit to Lukasz and some former colleagues last weekend so I thought “Why not write a post (or a series of posts) about places for science in various cities?”. Here is where I start – the University of Oslo or to be more specific the Department of Informatics and Mathematics and to be “Swiss sharp” – the Nanoelectronics group.

The University of Oslo is one of the largest higher education institutions in Norway being the biggest in number of students in social sciences. When it comes to natural sciences it has a pretty strong competitior namely the Norwegian University of Science and Technology in Trondheim. Nevertheless, the Department of Mathematics and Informatics has a number of applied science research groups, in addition to that the pure theoretical maths and physics groups do not fade-out too much in the overall picture. The main campus (Blindern) is also merged with Oslo Science Park and dozens of applied maths/informatics private or public companies e.g. one of the major being Sintef. Besides mathematics and informatics as a “Si person” I should also mention something about the semiconductor/applied physics opportunities in that place. Unfortunately when it comes to microchips there are only a few spots in Oslo doing design, these few “spots” however on the contrary have a long history (in the context of the semiconductor industry) e.g. Texas Instruments c.a. 13 years and nowadays OmniVision (before Photobit – Micron – Aptina) about 15 years old. Some rumours about Nordic Semiconductor opening more positions in Oslo have been spreading with the speed of light recently too. Speaking of applied physics a mini-cocktail of small companies in microfluidics, optics, and nanomaterials exist, but maybe someone with broader experience should hint what actually the situation is.

Anyway, I aim to give a virtual tour of the Nanoelectronics group at IFI in UiO and provide you with some “live” pictures from my ultra-high noise, low dynamic range and shaky camera.

First stop – Department of IFI (Institutt for Informatikk) or as I often like to call it – “THE MOTHERSHIP”!

The Mothership

The Mothership

IFI - Department of Informatics @ UiO

IFI – Department of Informatics @ UiO (typical Scandinavian weather)

This place is vacated by an extremely large number of research groups, here’s a link providing an alphabetically ordered list of all research groups at the department.

Apart from research groups, the first and second floors of this building are tailored for students offering all sorts of lecture halls and individual study rooms which one can book online. I really like the idea of giving names to rooms instead of using boring number-based systems, it seems like all Scandinavian universities I have visited so far follow this system and it is maybe something to consider by some institutions in the rest of Europe. It’s more fun to have laboratory exercises in e.g. “Olympen, Asgård, Egypten, Southfork, Muxen, Ada, Touring, Hopper, Mead, Volt, Kepler or Schrodinger” than “2.210, 4.311, 10.304, C.53 or 7.777 (:”.

a Practical Extraction and Reporting Language

a Practical Extraction and Reporting Language

After BASIC, my first ever official program used Pascal

After BASIC, my first ever official program used Pascal

This place is Chilly like Norway

This place is Chilly like Norway

Caml - humpy as a camel's back ?

Caml – humpy as a camel’s back ?

C - I see

C – I see

Xml - eXtensible markup language? I am sure you can do better with PERL

Xml – eXtensible markup language? I am sure you can do better with PERL

Awk - hates PERL but both go out for dinner from time to time together with bash and tcl (;

Awk – hates PERL but both go out for dinner from time to time together with bash and tcl (;

"Master! Master!  Where's the dreams that I've been after?"

“Master! Master! Where’s the dreams that I’ve been after?”

Limbo? Hell's edge, or?

Limbo? Hell’s edge, or?

The baroness of all programming languages, ever!

The baroness of all programming languages, ever!

They have even built a room dedicated to our blog, oh such an honour.

They have even built a room dedicated to our blog, oh such an honour.

Kappa - lalalapa

Kappa – the 10th letter of the Greek alphabet?

Photons hit electrons, but not before they've passed the optics.

Photons hit electrons, but not before they’ve passed though the optics.

Снимка0520

And the corridor & rooms goes to infinity

And the corridor & rooms goes to infinity

Ok, pretty lengthy, but the child in me screamed out so I had to take pictures of the room nameplates. Follow me to the 5th floor which is occupied by the Nanoelectronics group.

At the entrance we are greeted with some posters.

At the entrance we are greeted with some posters.

"The gods must have gone crazy" - stacked games, stacked sandwich, stacked chips :)

“The gods must have gone crazy” – stacked games, stacked sandwich, stacked chips 🙂

"We are the robots, we're functioning automatic and we are dancing mechanic..."

“We are the robots, we’re functioning automatic and we are dancing mechanic…”

This is what oil leads to - you guys need two more, this is not enough.

This is what oil leads to – you guys need two more, this is not enough.

The average PhD's heaven!  Just give me coffee and a white board.

The average PhD’s heaven! Just give me coffee and a white board.

Lukasz's messy desk - messy = work

Lukasz’s messy desk – messy = work

And a posted of his master's thesis

And a poster of his master’s thesis

Chips chips chips ;)

Chips chips chips 😉

And more chip (ship)s'

And more chip (ship)s’

Dungeon and no dragons

Dungeon and no dragons

The anechoic chamber!

The anechoic chamber!

Echoooo

Echoooo

Can you hear my heartbeat?

Can you hear my heartbeat?

Network analyzers, but what do we need them for?

Network analyzers, but wait, what do we need them for?

Of course, to measure rf medium quality, handy.

Of course, to measure a random cable’s rf medium quality, handy!

Smells like electronics

Smells like electronics

Lukasz' master thesis - the bio-inspired image sensor

Lukasz’ master thesis – the bio-inspired image sensor

And its camera control board

And its camera control board

And a color wheel for testing purposes

And a color wheel for testing purposes

Messy?

Another angle (now I am really suffering from comment deprivation)

Another angle (now I am really starting to suffer from comment idea deprivation)

The new testing furnace. We used the old one to bake a frozen pizza but it didn't go very well. The firefighters were not quite happy to visit us, nor the departmental head. Dear readers, in case you want to try baking a pizza in a temperature testing chamber make sure you have set the right temperature profile for your pizza indicated on the back of its package.

The new testing furnace. We used the old one to bake a frozen pizza but it didn’t go very well. I wonder why? The fire-fighters were not quite happy to visit us, nor the departmental head. Dear readers, in case you want to bake a pizza in a temperature testing chamber make sure you have set the right temperature profile for your pizza indicated on its package. Alternatively you may want to try with cookies as well, what could possibly go wrong?

A microprobing station for emergency chip surgeries.

A microprobing station for emergency chip surgeries.

A c"s"hip. Hint, Swedes pronounce ch as sh (accent) so if you say so - it's a ship.

A c”s”hip. Hint, Swedes pronounce ch as sh (accent) so, if you say so – it’s a ship.

And another emergency room

And another emergency room

Accompanied by some chip pulse and health monitors

Accompanied by some chip pulse and health monitors

And some other randomly scattered tools.

And some other randomly scattered scalpels.

A PCB printer, I wish I had one at home some years ago

A PCB printer, I wish I had one at home some years ago

With this my shaky virtual tour ends. Unfortunately the trends point that chip design loses more and more popularity amongst students (not that it has been an extremely popular science to start with but…) as opposed to computer science, physics or mathematics. So hopefully this tour would inspire you to go forward and dive into the endless river of microelectronics.