Viewing light at four trillion frames per second

[zincshow]

TL;DR

These researchers appear to be imaging a pulse of light travelling at the speed of light. Unfortunately, the detail is behind a paywall. Why does the light appear to pulse bright to dark over about a 5ps timeframe?
https://www.nature.com/articles/d41586-019-01625-5?utm_source=Nature+Briefing&utm_campaign=567cff556e-briefing-wk-20190524&utm_medium=email&utm_term=0_c9dfd39373-567cff556e-42247907

 

[phinds]

The are not viewing a light beam, they are viewing the scattered light as the beam travels through a material. I'd guess that the scattering is variable based on the characteristics of the material.

 

[Wrichik Basu]

The article under discussion has been published in Phys. Rev. Lett. From the news article by APS, the caption of the video says:

In this 33-picosecond clip produced with the new technique, a light pulse (red blob) travels through a transparent solid. Upon reaching the edge of the material (dashed line), the pulse travels invisibly through air, hits a mirror, and then re-enters the material.

(Emphasis added)

The reference to the paper (for future visitors, in case the link is unavailable) is:
Yu Lu et al., Compressed Ultrafast Spectral-Temporal Photography, Phys. Rev. Lett. 122, 193904 – Published 17 May 2019
https://doi.org/10.1103/PhysRevLett.122.193904

 

[member 656954]

In what seems to be a similar technique, this YouTube clip makes it easier to appreciate the making of such "light speed" imagery as reflections from within a plastic water bottle (diluted with a trace of milk) track the movement of a laser pulse.