|Description||2017 Fall Graduate Colloquium Series|
Light by Light Scattering
Light-by-light scattering is a phenomenon in quantum mechanics in which photons interact indirectly, through shared leptons or quarks. This was accomplished by individuals at the Large Hadron Collider, by accelerating lead nuclei to relativistic speeds, which in turn, generated electromagnetic fields strong enough to produce the interaction. With 480 µb-1 of lead-lead collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, a total of 13 potential events were observed, with an expected background of 2.6±0.7 events. Further analysis yielded the cross section of the process in lead-lead collisions for a photon transverse energy ET > 3 GeV, a photon absolute pseudorapidity |η| < 2.4, a diphoton invariant mass > 6 GeV, and a diphoton transverse momentum < 2 GeV. These results provide evidence for light-by-light scattering that agrees with predictions from the standard model.
Broadband Achromatic Optical Metasurface Devices
Metasurface, a type of flat optical device, has presented an ability in efficient manipulation of light fields. Metasurfaces are proposed for variety of devices with specific functionalities. Unfortunately, metasurfaces have large chromatic aberration caused by high phase dispersion of their building blocks. We have a proposed design principle to realize achromatic metasurface devices which successfully eliminate the chromatic aberration for a continuous wavelength region from 1200 to 1680 nm. We demonstrate broadband achromatic metalenses with the efficiency on the order of ∼12%. These metalenses are capable of focusing light with arbitrary wavelength at the same focal plane. A broadband achromatic gradient metasurface is also implemented to deflect wide-band light by the same angle. Through this approach, various flat achromatic devices that were previously impossible can be realized, which will allow innovation in full-color detection and imaging.
For more information contact: Dr. Ken Hatakeyama 254-710-2511