This Saturday Jake proposed to Louise and they are now engaged. At dinner on Saturday, Louise was given a picture of the engraved message and then Jake asked her hand in marriage.

The proposal was laser engraved using the femtosecond laser in the photon factory. The spot size used was 4 microns and the whole engraving was 100 microns high, about the thickness of a human hair.

Celebrations in the Photon Factory!  A new MSI/MBIE High Value Manufacturing and Services Sector grant was recently awarded:  “Laser Micromachining and Microfabrication” with Cather as PI.  See  http://www.msi.govt.nz/get-funded/research-organisations/2012-science-investment-round/high-value-manufacturing-and-services-research-fund/ for more details.

Congratulations to Sarah Thompson and Julie Kho for their success in the Faculty of Science Postgraduate Poster competition.

Sarah won 2nd prize and Julie won a merit award. Both Sarah and Julie’s posters will move to Exposure.

Just uploaded an online TrA simulator which you can use to make your own 3D spectrum. The program uses an opensource maths package called Sage which has great ineractive plotting abilities with matplotlib and jmol being used to do the surface plot.

So have a go making your own spectrum.

We have been busy over the last few weeks getting a video made for the RSC video competition.

Jake

Just uploaded a copy of the software PyTrA I have been writing in python to analyse ultrafast transient absorption data in the Photon Factory. It is a first release and I am still working on making it easier to use but here is the current version.

Go to the blog post to download the files.

Jake Martin

Peter the head engineer in the lab built a nice demonstration of wave motion in a multi-pendulum set-up where each pendulum has a different period leading to a 50s cycle. We are planning on building a larger demo which should reduce the frictional effects for the shorter period pendulums.

For a good write up on the physics behind this demo and how to make your own go to this link

A computer generated demo that helps you hear the patterns.

Congratulations to Sarah Thompson from the photon factory for getting into the finals of the 3min thesis competition.

Transient absorption spectroscopy (TrA) is a method for probing the details of molecular behaviour, such as movement of nuclei during a reaction, on chemically relevant timescales. In TrA, a laser pulse is first used to put a molecule in its excited state (photoexcitation), followed by a second pulse at some time delay which is absorbed by the molecule to form an absorption spectrum. By capturing spectra at many time delays, we can obtain information about behaviour of the molecule as it evolves in real time.

TrA is similar to multiflash photography: just as Edgerton pieces together various exposures to illustrate movement, one TrA spectrum pieces together spectra from various time delays to show the behaviour of a molecule

In one kind of TrA carried out at the Photon Factory, we use femtosecond (fs = 10^-15 s) pump pulses with super-continuum probe to capture the UV/Vis/IR spectra of the initial molecular structure just after photoexcitation. This tells us how the molecule absorbs energy and what happens subsequently, and will help us better understand the conversion of light energy to useful forms – heat, electronic energy and mechanical motion. For us, the relevant timescales are tens of femtoseconds to a few nanoseconds (ns = 10^-9 s). Very interesting chemical physics happens on this time scale:

The transient absorption system:

• The instrument response on the system is approximately 250fs
• Calcium fluoride crystal generates super-continuum from 350nm to 1100nm.
• Sapphire plate generates super-continuum from 420nm to 1500nm
• The delay stage gives a 1689ps of relative delay with a 0.68fs resolution.
• Travelling wave optical parametric generator TOPAS-C (by Light Conversion) provides tuneable single wavelength pulse from 280 to 2600nm.

The pump and probe beams are mechanically chopped to produce a sequence of pulses such as the following:

Absorption is calculated based on the equation

ΔOD=log₁₀[(I₀-I_B)/(I_sig-I_P)]

and the pump (IP) and stray light (IB) windows allow us to correct for pump and stray light related noise.

• The data is plotted in two and three-dimensions using PyTrA, a programme written by Jacob Martin.

When femtosecond white light pulses propagate through any medium, different wavelengths will travel at different speeds; this is called group velocity dispersion (GVD) or ‘chirp’. This is essentially the same phenomenon that allows us to split white light with a prism.

• PyTrA can correct for the chirp of the super-continuum pulse by interpolating a quadratic equation to the chirp spectrum.

• The software also handles the de-convolution of the chirp from the spectrum to get an accurate analysis of the signal.
• Single kinetic traces are fit to provide a good estimate of the kinetic parameters before a global analysis of the spectral-kinetic information is performed in IGOR (by WaveMetrics).

For those who are interested in the life and works of “Doc” H. E. Edgerton, there are several websites available, including the source of the image used in this document http://edgerton-digital-collections.org

For further reading on TrA see
Mergerle, U., Pugliesi, I., Schriever, C., Sailer, C. F., Riedle, E. Sub-50fs broadband absorption spectroscopy with tunable excitation: putting the analysis of ultrafast molecular dynamics on solid ground, Appl. Phys. B, 2009, 96, 215-231.

Andy Wang

Congratulations to Julie Kho and Sarah Thompson for winning prizes in this years Chemistry Research Showcase.

Julie Kho won the Baldwins prize (First place in the second year poster competition)

Sarah Thompson was the winner of the Fonterra Prize (First place in the general poster competition).

Kids Visiting Venus is a blog about the transit of Venus on the 6th of June. When venus will parially eclipse the sun. There are some cool solar/space experiments and blog posts will be leading up to the transit.