Via Physical Review Focus:

What you see is an optical fiber recoiling due to pulse of light flowing through it.  The abstract:

Phys. Rev. Lett. 101, 243601 (2008)

Observation of a Push Force on the End Face of a Nanometer Silica Filament Exerted by Outgoing Light

Weilong She, Jianhui Yu, and Raohui Feng

 There are two different proposals for the momentum of light in a transparent dielectric of refractive index n: Minkowski's version nE/c and Abraham's version E/(nc), where E and c are the energy and vacuum speed of light, respectively. Despite many tests and debates over nearly a century, momentum of light in a transparent dielectric remains controversial. In this Letter, we report a direct observation of the inward push force on the free end face of a nanometer silica filament exerted by the outgoing light. Our results suggest that Abraham's momentum is correct.

 URL:
http://link.aps.org/doi/10.1103/PhysRevLett.101.243601