21 October 2009

Little Nudges from Light – Measuring the Recoil of Photons

Radiation pressure – the force light exerts on matter – is so slight that it’s usually evident only in the atomic world or in the vacuum of space. With a common laser-and-microscope technique P4L-scientists from ICFO - the Institute of Photonics Sciences from Barcelona have now shown that it is possible to measure the recoil of light emitting molecules. The researchers around Prof. Dmitri Petrov in collaboration with colleagues from the Moscow State University were the first to measure this effect and published their exclusive findings in the renowned Physical Review E and Physical Review Letters highlighted recently by Physical Review Focus.

A fluorescent molecule emits a photon (yellow) resulting in a recoil (black) of the bead. (Source: http://focus.aps.org)

To measure the effect the researchers use a photonic force microscope (PFM) to trap a small metal covered dielectric sphere in a laser beam. The surrounding liquid contains fluorescent molecules that attach to the surface of the sphere. Excited by the light of the laser the molecules themselves start to emit light. Just like a soldier feels the recoil of his gun after firing a projectile, the small molecules pass their momentum they get from light emission on to the sphere. During this process the scientists measure two values: the forces acting on the bead (described by a tiny dithering in the trap) and the intensity of light generated by the molecules coating the bead's surface. As the intensity of the emitted light fades over time due to bleaching the scientists can observe a decline of the recoil as well.

What initially was the set-up for a different experiment turned out to deliver the first direct proof of the correlation between light emission and recoil and also allowed the calculation of the power of light emitted. In their experiment the researches measured a force of 240 femtonewtons, which equals a power coming from the bead of 1 microwatt. "Until now it has been really difficult to say how much light eventually comes off this material", says Dmitri Petrov from ICFO, “but by looking at the recoil we have a completely new approach to quantify light emission by a mechanical force”. Possible applications of the PFM-setup could be to offer a more precise way of measuring the efficiency and intensity of other light-emitting molecules, including the bleaching of fluorescent dyes.

Round Robin Experiment

Raman spectroscopy has already proved its effectiveness in many cases for medical diagnostics such as for cancer, cardiovascular diseases and infections. However, there are no standards in the different working groups, e.g. for sample preparation, implementation of the Raman experiments, spectra pre-treatment, data evaluation, etc.In a round robin experiment, the required groundwork will take place in order to define standardised Raman measurement methods, which will be fundamental for establishing Raman spectroscopy for clinical diagnostic procedures.

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5th International Conference on Biophotonics

20 March 2017

Continuing the success of the previous meetings held in Sacramento, Ottawa, Jena, and Florence, the 5th conference will come to Perth, Western Australia, running over two full days, and back-to-back with the Science on the Swan medical research conference, which delegates are strongly encouraged to also attend, at discounted rates. [more]

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