Femto-photography

Femto-photography is a technique for recording the propagation of ultrashort pulses of light through a scene at a very high speed (up to 10¹³ frames per second). A femto-photograph is equivalent to an optical impulse response of a scene and has also been denoted by terms such as a light-in-flight recording^[1] or transient image.^[2][3] Femto-photography of macroscopic objects was first demonstrated using a holographic process in the 1970s by Nils Abramsson at the Royal Institute of Technology (Sweden).^[1] A research team at the MIT Media Lab led by Ramesh Raskar, together with contributors from the Graphics and Imaging Lab at the Universidad de Zaragoza, Spain, more recently achieved a significant increase in image quality using a streak camera synchronized to a pulsed laser and modified to obtain 2D images instead of just a single scanline.^[4][5]

Schematic of the active CUSP system for 70-Tfps imaging

In their publications, Raskar's team claims to be able to capture exposures so short that light only traverses 0.6 mm (corresponding to 2 picoseconds, or 2×10⁻¹² seconds) during the exposure period,^[6] a figure that is in agreement with the nominal resolution of the Hamamatsu streak camera model C5680,^[7][8] on which their experimental setup is based.^[9] Recordings taken using the setup have reached significant spread in the mainstream media, including a presentation by Raskar at TEDGlobal 2012.^[10] Furthermore, the team was able to demonstrate the reconstruction of unknown objects "around corners", i.e., outside the line of sight of light source and camera, from femto-photographs.^[9]

In 2013, researchers at the University of British Columbia demonstrated a computational technique that allows the extraction of transient images from time-of-flight sensor data without the need for ultrafast light sources or detectors.^[11]

Other uses of the term

Prior to the aforementioned work, the term "femto-photography" had been used for certain proposed procedures in experimental nuclear physics.^[12]