News Finding: Kepler surmised the pressure of the solar rays caused comets' tails to always point away from the sun.
Paper Finding: Due to its finite aperture, all detected displacements are spatially averaged by the sensor.
News Context: The breakthrough confirmed light possesses momentum, an idea first proposed by the great German astronomer Johannes Kepler in 1619. Kepler surmised the pressure of the solar rays caused comets' tails to always point away from the sun. "We were able to trace the features of those waves back to the momentum residing in the light pulse itself, which opens the door to finally defining and modelling how light momentum exists inside materials."
Paper Context: These comparisons further suggest that the surface displacement measurements are driven almost exclusively by normal radiation pressure, as opposed to absorption or shear optical forces NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05706-3 ARTICLE picometer with a reasonably flat frequency response between 10 kHz and 5 MHz while minimizing ultrasonic and electromagnetic distortion effects. Due to its finite aperture, all detected displacements are spatially averaged by the sensor. The tip is covered by a protective nickel foil, but due to its inadequate reflectivity (R = 73% at 1064 nm) a soft gold foil (R = 99% at 1064 nm, thickness: 20 μm) was inserted between the sensor tip and the substrate to further suppress absorption of the scattered laser pulse and to provide a good contact.