Light-in-flight imaging

Light-in-flight imaging — a set of techniques to visualize propagation of light through different media.

500 ps laser pulse propagation in air visualized by a single-photon detector arrays^[1]

A video demonstrating a superluminal light-in-flight observation captured with megapixel SPAD camera^[2]

History and techniques

Light was first captured in its flight by N. Abramson in 1978,^[3] who used a holographic technique to record the wavefront of a pulse propagating and being scattered by a white-painted screen placed in its path. This high-speed recording technique allowed the dynamic observation of light phenomena like reflection, interference and focusing that are normally observed statically.^[4][5] More recently, light-in-flight holography has been performed in a scattering medium rather than using a reflective screen.^[6][7] Light can also be captured in motion in a scattering medium using a streak camera that has picosecond temporal resolution, thus removing the need for interferometry and coherent illumination but requires additional hardware to raster scan the two-dimensional (2D) scene, which increases the acquisition time to hours.^[8][9] A few other techniques possess the temporal resolution to observe light in motion as it illuminates a scene, such as photonic mixer devices based on modulated illumination, albeit with a temporal resolution limited to a few nanoseconds.^[10] Alternatively, time-encoded amplified imaging can record images at the repetition rate of a laser by exploiting wavelength-encoded illumination of a scene and amplified detection through a dispersive fibre, albeit with 160 ns temporal and spatial resolution.^[11] Recent studies based on computer tomography using data from multiple probe pulses enabled reconstruction of picosecond pulse propagation phenomena in condensed media.^[12] In 2015 a method to visualize events evolving on picosecond time scales based on single-photon detector arrays has been demonstrated.^[1]

See also

• Femto-photography