I see that this is “all optical” like the “Back in 2011, researchers from MIT created a high-speed camera that captured light passing through an empty bottle in slow motion”. Great.
So far as I can tell, the process works as follows. An femtosecond laser pulse is fed into a “temporal mapping device” which turns it into a series of femtosecond laser pulses (like a strobe light). It could be that this works by giving each pulse a different frequency. This laser pulses then pass through the object to be measured. The transmitted light is picked up by a “spatial sequencing device” that deflects each pulse into a different location (If each pulse has a different frequency then a prism will do this). From there it foes to an image sensor (like a CCD or CMOS chip) and to a computer.
So it’s a transmission optical microscope.
Not surprisingly, the faster it’s run, the more difficulty the “temporal mapping device” has in separating out the different times. It struggles with a frame interval of 230 femtoseconds but gives good temporal separation at a frame interval of 800 femtoseconds, and perfect temporal separation at a frame rate of 15500 femtoseconds (15.5 picoseconds). A plasma burst generated by a femtosecond laser hitting a glass plate was photographed at a frame rate of 15.5 picoseconds. In a second experiment, a heat pulse wave induced in a crystal by a femtosecond laser blast caused light scattering that was picked up by the camera.