Kay Nietfeld/picture-alliance/dpa/AP Images
By Daniel Clery
This year’s Nobel Prize for physics has been awarded to three researchers for devising tools made from light. Arthur Ashkin of Bell Laboratories in Holmdel, New York, is honored for his invention of optical tweezers, a technique which uses focused laser beams to hold and manipulate microscopic objects, including biological samples, as might be done with tweezers. Gerard Mourou of the École Polytechnique in Palaiseau, France, and Donna Strickland of the University of Waterloo, Canada, won for the invention of chirped pulse amplification (CPA), a technique for hugely boosting the power of laser pulses which is widely used in physics research and could have applications in cancer therapy and particle acceleration.
Optical tweezers trap a tiny object by using focused laser beams to exert very small forces on it. The beam is shaped to have a narrow waist where there is a strong electric field gradient. If the object is a dielectric material that is polarized in an electric field, it will feel a force towards the area with the strongest field—the center of the beam. Vertically, the photons of the beam exert pressure on the object to hold it up. Although Ashkin, in the mid 1980s, originally intended to use the technique to manipulate atoms, he soon moved onto larger particles and then biological objects, including viruses and living cells. Others used the technique to unravel how a flagellum works to propel a bacterium and other molecular motors, as well as resolving how motor RNA polymerase, a molecule that copies DNA into mRNA in the process of gene transcription, makes one-basepair steps along the DNA. Researchers have even used optical tweezers to make a microscopic reflecting mirror.
Mourou and Strickland, working at the University of Rochester in the 1980s, sought to increase the power of laser pulses, which had grown slowly since the mid-1960s. The problem was that high-powered pulses damaged the material used for the amplification process. In work that formed Strickland’s PhD thesis, she and Mourou took inspiration from a radar technique. They first stretched out the laser pulse in time by several orders of magnitude, thereby reducing their peak power, then passed the stretched pulse through an amplifier, and finally compressed the pulse again in time to produce a short pulse with much enhanced power.
First of all, you have to think it is crazy!
Using the CPA technique, the peak power of laser pulses grew much more rapidly and it is now a regular feature at laser labs around the world. CPA has heralded the field of attosecond physics, where extremely short and powerful laser pulses are used to take snapshots of chemical reactions or the behavior of particles in extreme electric field conditions. Researchers are investigating whether trains of laser pulses can be used to accelerate particles to vastly higher energies than current accelerator facilities. CPA systems have also found applications in industry, for high-precision treatment of materials, and in medicine for corrective eye surgery and, potentially, cancer treatment.
“First of all, you have to think it’s crazy!” Strickland said when asked for her reaction this morning. Only two women have won a Physics Nobel before: Marie Curie in 1903 and Maria Goeppert-Mayer in 1963. “Is that all? Really?” Strickland said when told she was only the third. But she expressed hope that the gender balance would get better in the future.
Source: Science Mag