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