Serial time-encoded amplified imaging for real-time observation of fast dynamic phenomena

Abstract

Ultrafast real-time optical imaging is an indispensable tool for studying dynamical events such as shock waves, chemical dynamics in living cells, neural activity, laser surgery and microfluidics. However, conventional CCDs (charge-coupled devices) and their complementary metal-oxide-semiconductor (CMOS) counterparts are incapable of capturing fast dynamical processes with high sensitivity and resolution. This is due in part to a technological limitation-it takes time to read out the data from sensor arrays. Also, there is the fundamental compromise between sensitivity and frame rate; at high frame rates, fewer photons are collected during each frame-a problem that affects nearly all optical imaging systems. Here we report an imaging method that overcomes these limitations and offers frame rates that are at least 1,000 times faster than those of conventional CCDs. Our technique maps a two-dimensional (2D) image into a serial time-domain data stream and simultaneously amplifies the image in the optical domain. We capture an entire 2D image using a single-pixel photodetector and achieve a net image amplification of 25 dB (a factor of 316). This overcomes the compromise between sensitivity and frame rate without resorting to cooling and high-intensity illumination. As a proof of concept, we perform continuous real-time imaging at a frame speed of 163 ns (a frame rate of 6.1 MHz) and a shutter speed of 440 ps. We also demonstrate real-time imaging of microfluidic flow and phase-explosion effects that occur during laser ablation.

Unveiling multi-scale laser dynamics through time-stretch and time-lens spectroscopies

“…Apparently, a real-time high-resolution spectro-temporal analyzer operating in a continuous mode is yet to be demonstrated for better understanding the nonlinear optical physics as well as optimizing the laser performances. Photonic time-stretch through dispersive chirp has recently been demonstrated as a highthroughput single-shot spectral analyzer [31][32][33] and has greatly enriched researches on nonlinear physics, e.g., supercontinuum generation [34], optical rogue wave observation [24,35,36], soliton explosion [37,38], as well as mode-locking and soliton-molecule formation [39,40]. Despite its superior performance in fs-ps regime, typically for transformlimited short pulses, time-stretch spectroscope (TSS) is inadequate for CW/quasi-CW optical signal, see Appendix 1.…”

Locating and classifying fluorescent tags behind turbid layers using time-resolved inversion

“…The technique is implemented non-invasively in reflective mode. This opens a new set of possibilities for applications such as tracking and locating probes in photocytometry 20 , endoscopy 21 and larger-scale industrial tomography 22 .…”

Power efficiency of time-stretch imaging system by using parallel interleaving detection

“…Since photodetectors with more than 40 GHz bandwidths are commercially available nowadays, the image can be read out at an ultrafast speed. The STEAM technique's ability to acquire images at a frame rate of more than 6 MHz and at a line-scan rate of 1 GHz were demonstrated [3,7] . Besides, the STEAM technique actively captures images using spatially dispersed optical pulses.…”

“…Recently, a novel ultrafast imaging technique, serial time-encoded amplified microscopy (STEAM), was proposed [3][4][5][6] . In the STEAM technique, a broadband optical pulse is first spatially dispersed in free space for space-to-wavelength mapping to record the spatial pattern of an object into the spectrum.…”