Imaging & Soldering

On my lab bench today was:

• A minature CCD camera


• A 100x oil imersion microscope


• A tube of oil


• Clear nail varnish


• Nail varnish remover

The camera and microscope form the basics of the imaging side of my experiment. I had a shot at setting these up... With quite a bit of help from Michael... The main difficulty of being a "newbie" in Tyndall is just the fact that I don't know where anything is. Secondary to that is my unfamiliarity with the various wires and cables and plugs and fittings and components. So, if I need something in the lab I either wander around blindly looking for it - not knowing what it looks like or where its found - or I ask one of the guys who are only too happy to help me which leads to me feeling extra newbie-ish and slightly guilty from bothering them. It's one of those lovely learning curves we all know, love and acts logarithmically if plotted.

Yes, so, after we discovered that the connector we were using to wire the little camera wasn't working, Michael decided that soldering was the way to go. He soldered two pins for me and I did the last. I love soldering! At least, I think I do. I'm sure I did the simplest soldering exercise possible but it's so cool!

Oh, I am so sad...

We connected the finished product to the TV and the power supply and, as expected, the camera didn't work. Hmmm.

Optical Trapping Of PolyBalls

Above is a very basic outline of the apparatus I will eventually be working with towards the end of term. My experiment will attempt to optically trap a suspension of polystyrene beads using a evanescent field produced by propagation of 1480nm light through a fibre. In a previous experiment credited to Brambilla, Murugan, Wilkinson, Richardson, some of the beads were trapped not only by the field, but also through resonance with the field in the form of a whispering gallery mode. The set-up is essentially entirely foreign to me which makes it doubly exciting - getting to grips with each component (mostly through extensive googling of their model numbers).

Sile ordered me a photodetector which I had a look at today. I have a diode laser and I'm waiting for Kieran and Michael to finish with the current and temperature drivers. I'm also waiting on an SMA adaptor because of the non-standard fitments on the detector... I was very boggled trying to locate this adaptor - blissfully unaware of the sheer amount of adaptors and cables and fittings!

While I wait for the temperature and current drivers to become available, I'm going to try and use the detector with another laser. Then, my first task is to characterise the laser as a function of driving current.

More Dots

I tried the HeNe laser on the quantum dots this morning. Just as I suspected... Extreme saturation! An enormous red peak at 633nm dominating the entire spectrum. So, I asked Michael for filters (just as he was about to go for lunch - I am so considerate). I used a 10^0.5 filter to reduce the power and it seemed to help find the little quantum dot-related emission range amongst the (still very large) red peak. I meant to spend approximately 30 minutes in the lab and I ended up there for two hours fiddling with filters and set-ups that might reduce stray red light.
Later, I'll talk about the experiment I'm going to be setting up over the next couple of months. I'm waiting on some components before I can start (attempting) to build it. I promised myself I'd spend the afternoon finishing my Nuclear & Particle homework (and look what time it is already!)...

Quantum Dots

Today I had a look at the quantum dots under table lamp light and with the green 532nm laser. I wasn't sure whether to use the HeNe laser or not (with or without filters) so that will be for another day. Here's the basic characteristics I observed -

Some of the screenshots I took are shown below. (Click for larger - and more informative - versions!) Fig. 1 shows the spectra obtained using 532nm light and Fig. 2 shows the results due to illumination with a table lamp. Interesting to note that small 532nm peak for the green laser emission due to my shoddy alignment of the laser, quantum dots and spectrometer. The absorbtion range of the quantum dots is relatively wide and this yields a large wavelength-spread in emission (see images on the right).

Fig. 1: 532nm Absorption

Fig. 2: Table Lamp Absorption

I also took spectra with the room light on. The weaker intensities are explained by the losses in intensity due to the isotropic radiation given out by the lightbulb. On the other hand, it is possible to see a hint of the emission curves already obtained through laser illumination.

Sophisticated Mecanno

After my two classes on Wednesday morning, I spent a few hours in Tyndall. Because I still have no keycard (or, rather, I do have a keycard but it doesn't give me lab access), I went through the spectrometer's instruction manual at my desk first. Then I went down to the lab with Roy and Dipankar. I had been moved to a new corner complete with shiny, black metric breadboard (whoo!). I began setting up the HeNe laser and spectrometer. After about 30 minutes of screwing posts and post holders and bases and clamps together, I realised I was failing miserably at this sophisticated form of meccano. John probably noticed my amateur set-up and dropped me over two laser-shaped clamps - they worked perfectly.

I got a spectrum for HeNe that yielded a 0.012% error, so no complaints there (see image on the right). The other laser emitted at 531nm or thereabouts. I stupidly didn't bother to check what the expected wavelength was supposed to be and I assumed it was 540nm - producing a 2% error. Eeep. Sile had to point out the correct wavelength to me.

I also had a meeting with Sile yesterday afternoon and she went through an idea about my project involving polystyrene microspheres rather than glass microsheres. I've found a couple of papers using polystyrene spheres, but nothing with the sort of set-up I'll be using. Hopefully I'll obtain some nice results!

First Day In The Lab

I spent approximately 1 hour in the lab today - nowhere near as long as I wanted, but I had to go for my eye test in the afternoon (which required me to bring my car back home first - don't want to be leaving her in Pouladuff overnight!). Sile set me up with some basic optics devices - two lasers, a USB spectrometer and a whole array of screws and metal clamps and insulating tape. I had to obtain an ambient-light spectrum and a spectrum for each of the lasers. The first laser emitted at 540nm - I found the emission to be approximately 531.99nm on-screen (with pixel-limiting resolution) and have not examined the data file yet for the proper peak value. I took a screenshot of the spectra of the ambient light and this green laser. I had to leave before I got a chance to run the larger red laser. I was also running out of clamps to secure it to the breadboard. I'm going back tomorrow to finish this off and copying my spectra to my flash pen - will post some pictures then.

The End Of An Era (Of Lab Reports)

I finally finished my 4th year lab reports today. At 8:40am this morning, I uploaded the last of four very, very long lab reports up to RapidShare. I had intentions of getting them bound but I completely forgot to bring a wallet to college with me. I've been working solid on them for 7 days - not eating, sleeping, showering. Not even taking midday interludes for Guitar Hero! Combined, the reports are 120 pages long, have 19500 words, too many images and even more graphs. Now I can finally launch myself into my WGM project (something which will incur just as much work at the end of term no doubt)!

I have been doing a bit of Googling for the project every time I got sick of the sight of Origin / Word / Scion Image / Excel in the past week and I have found some very nice web pages and PDFs about the geometry of WGMs to complement the papers I have already.

• http://www.etsu.edu/math/preprints/oe2004.pdf


• www.chm.bris.ac.uk/~chjpr/Research/WGM.htm


• metrology.hut.fi/courses/s108-j/Nano2.pdf


• http://www.photonics.com/content/spectra/2007/October/research/89207.aspx


• http://www.uoregon.edu/~noeckel/microlasers.php

Today, we had a seminar by Phil Jones from UCL titled Optical Tweezers: Microbubbles, nanotubes and super-resolution and it was essentially a variation on the applications of what my project is about. Very interesting to actually see clips of the optical trapping of microbubbles - a project I had orginally choosen for fourth year. One part that fascinated me was the group's wish to 'squeeze' these microbubbles, which results in a supersonic "microjet" - a very destructive force for biological cells!

First Day At Tyndall

After my two classes in the morning, I walked down to Tyndall at 11:30 to meet Sile. Roy was already there - we both waited in the lobby until one of the guys in the Photonics group took pity on us and brought us upstairs. Sile showed us our desks and computers - the desk to be shared between Roy and me (but the desks are huge so it doesn't make a difference!). The was a pile of reference material on each side of our desk relevant to our projects. I have nine papers to read through for the next few weeks.

• Feron, P., Whispering Gallery Modes and Applications as Laser Sources - a short review.


• Feron, P., Whispering Gallery Mode Lasers in Erbium doped fluoride glasses.


• Ward, J. M., O'Shea, D. G., Shortt, B. J., et al, Heat-and-pull ring for taper fabrication.


• Ward, J. M., Feron, P., Nic Chormaic, S., A Taper-Fused Microspherical Laser Source.


• Shortt, B., Carey, R., Nic Chormaic, S., Characterisation or Er:ZBNA microspherical lasers.


• Shortt, B., Ward, J., O'Shea, D., Nic Chormaic, S., Spectral characterisation of erbium doped microspherical lasers.


• O'Shea, D. G., Ward, J., Shortt, B., Nic Chormaic, S., An All-Fibre Coupled Multicolor Microspherical Light Source.


• O'Shea, D. G., Shortt, B., Nic Chormaic, S., Optical bistability in Er-Yb codoped phosphate glass microspheres at room temperature.


• O'Shea, D. G., Ward, J. M., Shortt, B., et al, Upconversion channels in Er3+:ZBLALiP fluoride glass microspheres.

Wow! I'd like to get them all read before next week, but I have a feeling that the lab report deadline will take priority. I've already read two of them and need to look up some terminology that I'm not familiar with.

Both Roy and me have to wait to get our key card passes. Without them, we have no access to the building. My lab is on the ground floor - it's a Class 4 laser lab which means there are alot safety rules to abide by. These are mostly to do with me not entering the room when the Class 4 laser is switched on.