Light-in-flight Research Articles

Ultrafast diffraction algorithms for light-in-flight holography

Digital light-in-flight (LIF) holography is an ultrafast imaging technique capable of single-shot simultaneous 3D and femtosecond time resolution acquisitions of light pulse propagation. However, the numerical diffraction algorithms used to model light on femtosecond timescales are currently limited in scope, accuracy, and efficiency. We derive an analytical model capable of modeling LIF hologram formation for various optical setup configurations, able to model 3D objects and precisely account for the limited temporal coherence of the signal. We design an efficient algorithmic implementation and validate the system in numerical simulations and with an experimental LIF holographic recording setup. We report ultrafast numerical diffraction over 10,000 times faster than the reference technique, with higher accuracy and capable of modeling 3D samples, thereby broadening its application domain.

Non-line-of-sight transient rendering

The capture and analysis of light in flight, or light in transient state, has enabled applications such as range imaging, reflectance estimation and especially non-line-of-sight (NLOS) imaging. For this last case, hidden geometry can be reconstructed using time-resolved measurements of indirect diffuse light emitted by a laser. Transient rendering is a key tool for developing such new applications, significantly more challenging than its steady-state counterpart. In this work, we introduce a set of simple yet effective subpath sampling techniques targeting transient light transport simulation in occluded scenes. We analyze the usual capture setups of NLOS scenes, where both the camera and light sources are focused on particular points in the scene. Also, the hidden geometry can be difficult to sample using conventional techniques. We leverage that configuration to reduce the integration path space. We implement our techniques in a modified version of Mitsuba 2 adapted for transient light transport, allowing us to support parallelization, polarization, and differentiable rendering.

Intensity-corrected 4D light-in-flight imaging.

Light-in-flight (LIF) imaging is the measurement and reconstruction of light's path as it moves and interacts with objects. It is well known that relativistic effects can result in apparent velocities that differ significantly from the speed of light. However, less well known is that Rayleigh scattering and the effects of imaging optics can lead to observed intensities changing by several orders of magnitude along light's path. We develop a model that enables us to correct for all of these effects, thus we can accurately invert the observed data and reconstruct the true intensity-corrected optical path of a laser pulse as it travels in air. We demonstrate the validity of our model by observing the photon arrival time and intensity distribution obtained from single-photon avalanche detector (SPAD) array data for a laser pulse propagating towards and away from the camera. We can then reconstruct the true intensity-corrected path of the light in four dimensions (three spatial dimensions and time).

Light-In-Flight Imaging by a Silicon Image Sensor: Toward the Theoretical Highest Frame Rate.

Light in flight was captured by a single shot of a newly developed backside-illuminated multi-collection-gate image sensor at a frame interval of 10 ns without high-speed gating devices such as a streak camera or post data processes. This paper reports the achievement and further evolution of the image sensor toward the theoretical temporal resolution limit of 11.1 ps derived by the authors. The theoretical analysis revealed the conditions to minimize the temporal resolution. Simulations show that the image sensor designed following the specified conditions and fabricated by existing technology will achieve a frame interval of 50 ps. The sensor, 200 times faster than our latest sensor will innovate advanced analytical apparatuses using time-of-flight or lifetime measurements, such as imaging TOF-MS, FLIM, pulse neutron tomography, PET, LIDAR, and more, beyond these known applications.

Extending recordable time of light-in-flight recording by holography with double reference light pulses.

Light-in-flight (LIF) recording by holography is a powerful technique for observing ultrashort light pulse propagation. However, the recordable time of the technique has been limited by the lateral length of the holographic plate. Then, to extend the recordable time of LIF recording by holography, we proposed a space-division multiplexing technique of holograms, which divides the holographic plate longitudinally and uses double reference light pulses. We experimentally demonstrated that the recordable time becomes twice as long as before for the first time, to the best of our knowledge, using the proposed technique. Specifically, we recorded the motion picture of the ultrashort light pulse propagation for 236ps.

Slow light in flight imaging

Slow-light media are of interest in the context of quantum computing and enhanced measurement of quantum effects, with particular emphasis on using slow-light with single photons. We use light-in-flight imaging with a single photon avalanche diode camera-array to image in situ pulse propagation through a slow light medium consisting of heated rubidium vapour. Light-in-flight imaging of slow light propagation enables direct visualisation of a series of physical effects including simultaneous observation of spatial pulse compression and temporal pulse dispersion. Additionally, the single-photon nature of the camera allows for observation of the group velocity of single photons with measured single-photon fractional delays greater than 1 over 1 cm of propagation.

Ultrashort pulse propagation recording by using the transmission-type light in flight holography

Ultrashort pulse propagation recording by using the transmission-type light in flight holography

Relativistic effects in imaging of light in flight with arbitrary paths.

Direct observation of light in flight is enabled by recent avalanche photodiode arrays, which have the capability for time-correlated single photon counting. In contrast to classical imaging, imaging of light in flight depends on the relative sensor position, which is studied in detail by measurement and analysis of light pulses propagating at different angles. The time differences of arrival are analyzed to determine the propagation angle and distance of arbitrary light paths. Further analysis of the apparent velocity shows that light pulses can appear to travel at superluminal or subluminal apparent velocities.

Multiple-return single-photon counting of light in flight and sensing of non-line-of-sight objects at shortwave infrared wavelengths.

Time-of-flight sensing with single-photon sensitivity enables new approaches for the localization of objects outside a sensor's field of view by analyzing backscattered photons. In this Letter, the authors have studied the application of Geiger-mode avalanche photodiode arrays and eye-safe infrared lasers, and provide experimental data of the direct visualization of backscattering light in flight, and direct vision and indirect vision of targets in line-of-sight and non-line-of-sight configurations at shortwave infrared wavelengths.

Light in Flight: Optical Applications in Civilian Aviation

Optical technologies such as head-up displays, fiber sensors and quantum dots will help build 21st century airplanes, connect pilots to crucial information and ensure the structural health of aircraft.

Love light in flight [The Big Picture

Love light in flight [The Big Picture

Digital recording and numerical reconstruction of holograms: a new method for displaying light in flight

We present a new method for displaying light in flight. Fresnel holograms are recorded directly on a CCD sensor, electronically stored, and numerically reconstructed. Experimental results are shown. From different parts of a single holographic recording, different views of a wave front can be reconstructed. This means that the temporal evolution of a wave front can be observed by numerical methods.

Three-dimensional shape recognition using computer-generated holograms and temporal light-in-flight technique

Visualization of light propagation and light in flight are general names for viewing a pulse of light traveling through an optical system. Abramson suggested [Appl. Opt. 30, 1242 (1991)] the use of light-in-flight techniques for holographic comparison of different objects. His system is based on sending picosecond pulses in such a sequence that, if the object has the desired shape, all the scattered light arrives simultaneously at an ultrafast detector. The result is that the shortness of the detected pulses is a measure of the similarity between a holographically recorded master object and the test object. The reference hologram is recorded from a master surface, which is not always available. This method suffers from low-contrast results. A computer-generated-hologram technique is suggested and mathematically analyzed. This technique overcomes the low-contrast problem, and a master object is not needed.

Single pulse light-in-flight recording by holography

We have succeeded we believe for the first time, in making a light-in-flight (LIF) recording using one single pulse of a mode-locked frequency doubled Nd:YAG laser. Many experiments made earlier with multiple picosecond pulses have been repeated and the results were the same. New experiments have become possible such as the contouring of a fast moving object and recording through a nonrigid scattering medium. We demonstrate a LIF transmission method for rejecting scattered light which can be developed into a method for diagnostic imaging inside living tissue.

Synthèse d'impulsions subpicosecondes et visualisation holographique

Subpicosecond pulses have been synthesized with a dye laser. The 8000 GHz broadband source corresponds to a temporal resolution of Δt = 1/ Δv = 0.12 ps. The holographic recording set-up proposed by N. Abramson has been used to visualize the light in flight, but the wavelength dependence of the hologram introduces a dispersion in the reconstructed image. Compensation techniques have been applied and an other recording system has been developed. Experimental results of the reconstructed holographic wavefront are presented. The interesting possibility to obtain a reconstruction in white light is compared with the coherent case. The signal-to-noise ratio of the image is discussed. Metrological applications have been outlined.

Light-in-flight recording by holography

A flat object surface and a hologram plate are both illuminated at an oblique angle by laser light of short pulse duration or short coherence length. Only those parts of the object surface are holographically recorded that correspond to a small-pathlength difference between object beam and reference beam. The holographic plate therefore corresponds to an infinite set of gated viewing systems triggered by the traversing reference beam. Scanning along the processed plate produces a continuous-motion picture of the light in flight. This new technique probably represents the ultimate in high-speed photographic recording, as no mechanical or electrical inertia is involved.