Single-shot ultrafast tomographic imaging by spectral multiplexing

Abstract

Computed tomography has profoundly impacted science, medicine and technology by using projection measurements scanned over multiple angles to permit cross-sectional imaging of an object. The application of computed tomography to moving or dynamically varying objects, however, has been limited by the temporal resolution of the technique, which is set by the time required to complete the scan. For objects that vary on ultrafast timescales, traditional scanning methods are not an option. Here we present a non-scanning method capable of resolving structure on femtosecond timescales by using spectral multiplexing of a single laser beam to perform tomographic imaging over a continuous range of angles simultaneously. We use this technique to demonstrate the first single-shot ultrafast computed tomography reconstructions and obtain previously inaccessible structure and position information for laser-induced plasma filaments. This development enables real-time tomographic imaging for ultrafast science, and offers a potential solution to the challenging problem of imaging through scattering surfaces.

Ultrafast optical imaging technology: principles and applications of emerging methods

“…This situation is analogous to the longitudinal spatial resolution of conventional wide-field microscopy given by ∼λ/NA 2 , where λ is the optical wavelength and NA is the numerical aperture of the objective lens used for imaging. In the previous demonstration [7], the NA was relatively small, resulting in limited spatial resolution, in particular in the longitudinal direction.…”

“…The temporal resolution is constrained by the time required for the probe beams to traverse the imaging object, the arrival time ambiguity of the probe beams reaching the object, and the coherence time of the beams. In the previous demonstration of SMT [7], the second factor is dominant, resulting in the temporal resolution of 12 ps. On the other hand, the spatial resolution of SMT is limited by the divergence angle of each fan beam.…”

“…SMT [7] is a nonscanning tomographic imaging method that enables single-shot cross-sectional image acquisition on a femtosecond time scale. This method is based on spectral multiplexing of a single laser beam to conduct tomographic imaging over a continuous range of illumination angles simultaneously.…”

“…Unfortunately, conventional cameras based on electronic image sensors, such as the charge-coupled device (CCD) and complementary metal-oxide-semiconductor (CMOS), fall short in providing such high frame rates under desirable imaging conditions, as their image acquisition speed is significantly constrained by their electrical operation and limited storage. Over the recent years, several unique and unconventional approaches to high-speed optical imaging have been reported to circumvent these technical hurdles and achieve a frame rate and shutter speed far beyond what can be reached with the conventional image sensors [5][6][7][8][9][10]. Serial time-encoded amplified imaging / microscopy (STEAM) [5,11] is a continuous imaging method with a built-in optical image amplifier that enables continuous image acquisition at a high frame rate of~100 Mfps without sacrificing sensitivity.…”

“…Sequentially timed all-optical mapping photography (STAMP) [6,12] is an ultrafast burst imaging method capable of achieving motion-picture femtophotography at a frame rate of~1 Tfps with its all-optical operation that overcomes the electrical limitations of the conventional image sensors. Single-shot multispectral tomography (SMT) [7] is a high-speed tomographic imaging method based on spectral multiplexing for simultaneous illumination of the imaging target at multiple angles of incidence. Fluorescence imaging by radiofrequency-tagged emission (FIRE) [9] is a high-speed fluorescence imaging method that achieves~100 times higher frame rates than conventional methods by frequency-modulating the excitation light spatially and demodulating the fluorescence signal after detecting it with a sensitive single-pixel photodetector.…”