Ultrafast laser-scanning time-stretch imaging at visible wavelengths

• Published in: Light, science & applications Vol. 6; no. 1; p. e16196
• Main Authors: Wu, Jiang-Lai, Xu, Yi-Qing, Xu, Jing-Jiang, Wei, Xiao-Ming, Chan, Antony CS, Tang, Anson HL, Lau, Andy KS, Chung, Bob MF, Cheung Shum, Ho, Lam, Edmund Y, Wong, Kenneth KY, Tsia, Kevin K
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2017; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/624/1075; 639/624/1107; 639/624/1111; Applied and Technical Physics; Atomic; Classical and Continuum Physics; Delay; High speed; High-throughput screening; Imaging; Lasers; Microscopy; Molecular; Optical and Plasma Physics; Optical Devices; Optics; Original; original-article; Photonics; Physics; Physics and Astronomy; Scanning; Scientific imaging; Stretching; Visible spectrum; Wavelength; Wavelengths; pulse stretching; optical time-stretch imaging; ultrafast laser scanning
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2016.196

Optical time-stretch imaging enables the continuous capture of non-repetitive events in real time at a line-scan rate of tens of MHz—a distinct advantage for the ultrafast dynamics monitoring and high-throughput screening that are widely needed in biological microscopy. However, its potential is limited by the technical challenge of achieving significant pulse stretching (that is, high temporal dispersion) and low optical loss, which are the critical factors influencing imaging quality, in the visible spectrum demanded in many of these applications. We present a new pulse-stretching technique, termed free-space angular-chirp-enhanced delay (FACED), with three distinguishing features absent in the prevailing dispersive-fiber-based implementations: (1) it generates substantial, reconfigurable temporal dispersion in free space (>1 ns nm −1 ) with low intrinsic loss (<6 dB) at visible wavelengths; (2) its wavelength-invariant pulse-stretching operation introduces a new paradigm in time-stretch imaging, which can now be implemented both with and without spectral encoding; and (3) pulse stretching in FACED inherently provides an ultrafast all-optical laser-beam scanning mechanism at a line-scan rate of tens of MHz. Using FACED, we demonstrate not only ultrafast laser-scanning time-stretch imaging with superior bright-field image quality compared with previous work but also, for the first time, MHz fluorescence and colorized time-stretch microscopy. Our results show that this technique could enable a wider scope of applications in high-speed and high-throughput biological microscopy that were once out of reach. Pulse stretching: stretching achieved at visible wavelengths A new pulse-stretching technique has enabled ultrafast laser-scanning time-stretch imaging to be achieved in the important visible region. Optical time-stretching is used to realize real-time continuous imaging at ultrahigh frame rates, but current technologies based on dispersive fibers are generally restricted to near-infrared wavelengths. Now, a team at the University of Hong Kong led by Kevin Tsia has overcome this limitation by developing a pulse-stretching technique that they dub free-space angular-chirp-enhanced delay. It has the advantages of generating a large dispersion in free space with low loss and of enabling wavelength-invariant stretching. The researchers demonstrated its potential by realizing ultrafast laser-scanning time-stretch imaging with excellent bright-field image quality. They also used it to achieve megahertz fluorescence and color time-stretch microscopy at the optical wavelength of 700 nm.