Journal Article

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

Jalali, B., Tsia, K. K., Goda, K.

2009

Overview

An ultrarapid camera Ultrafast real-time optical imaging is used in many areas of science, from biological imaging to the study of shockwaves. But in systems that undergo changes on very fast timescales, conventional technologies such as CCD (charge-coupled-device) cameras are compromised. Either imaging speed or sensitivity has to be sacrificed unless special cooling or extra-bright light is used. This is because it takes time to read out the data from sensor arrays, and at high frame rates only a few photons are collected. Now a UCLA team has developed an imaging method that overcomes these limitations and offers frame rates at least a thousand times faster than those of conventional CCDs, making this perhaps the world's fastest continuously running camera, with a shutter speed of 440 picoseconds. The technology — serial time-encoded amplified microscopy or STEAM — maps a two-dimensional image into a serial time-domain data stream and simultaneously amplifies the image in the optical domain. A single-pixel photodetector then captures the entire image. Ultrafast real-time optical imaging is used in diverse areas of science, but conventional imaging devices such as CCDs are incapable of capturing fast dynamical processes with high sensitivity and resolution. This imaging method overcomes these limitations and offers frame rates that are at least 1,000 times faster than those of conventional CCDs. The approach is applied to continuous real-time imaging of microfluidic flow and phase-explosion effects that occur during laser ablation. Ultrafast real-time optical imaging is an indispensable tool for studying dynamical events such as shock waves 1 , 2 , chemical dynamics in living cells 3 , 4 , neural activity 5 , 6 , laser surgery 7 , 8 , 9 and microfluidics 10 , 11 . 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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Cameras / Charge coupled devices / Diagnostic Imaging - instrumentation / Diagnostic Imaging - methods / Equipment and supplies / Evaluation / Exact sciences and technology / Fourier transforms / Fundamental areas of phenomenology (including applications) / General equipment and techniques / High-speed techniques (microsecond to femtosecond) / Humanities and Social Sciences / Image processing / Imaging detectors and sensors / Instruments, apparatus, components and techniques common to several branches of physics and astronomy / Laboratory procedures / Laser Therapy / Lasers / letter / Metrology, measurements and laboratory procedures / Microfluidics / Microspheres / Molecular biology / multidisciplinary / Observations / Optical elements, devices, and systems / Optics / Physics / Real time / Real-time data processing / Science / Science (multidisciplinary) / Sensitivity and Specificity / Shock waves / Time Factors / Water