Jianglai Wu

Ultrafast laser-scanning time-stretch imaging at visible wavelengths

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.

Multi-MHz laser-scanning single-cell fluorescence microscopy by spatiotemporally encoded virtual source array

Apart from the spatial resolution enhancement, scaling of temporal resolution, equivalently the imaging throughput, of fluorescence microscopy is of equal importance in advancing cell biology and clinical diagnostics. Yet, this attribute has mostly been overlooked because of the inherent speed limitation of existing imaging strategies. To address the challenge, we employ an all-optical laser-scanning mechanism, enabled by an array of reconfigurable spatiotemporally-encoded virtual sources, to demonstrate ultrafast fluorescence microscopy at line-scan rate as high as 8 MHz. We show that this technique enables high-throughput single-cell microfluidic fluorescence imaging at 75,000 cells/second and high-speed cellular 2D dynamical imaging at 3,000 frames per second, outperforming the state-of-the-art high-speed cameras and the gold-standard laser scanning strategies. Together with its wide compatibility to the existing imaging modalities, this technology could empower new forms of high-throughput and high-speed biological fluorescence microscopy that was once challenged.

A high-throughput all-optical laser-scanning imaging flow cytometer with biomolecular specificity and subcellular resolution

Image-based cellular assay advances approaches to dissect complex cellular characteristics through direct visualization of cellular functional structures. However, available technologies face a common challenge, especially when it comes to the unmet need for unraveling population heterogeneity at single-cell precision: higher imaging resolution (and thus content) comes at the expense of lower throughput, or vice versa. To overcome this challenge, a new type of imaging flow cytometer based upon an all-optical ultrafast laser-scanning imaging technique, called free-space angular-chirp-enhanced delay (FACED) is reported. It enables an imaging throughput (>20 000 cells s-1 ) 1 to 2 orders of magnitude higher than the camera-based imaging flow cytometers. It also has 2 critical advantages over optical time-stretch imaging flow cytometry, which achieves a similar throughput: (1) it is widely compatible to the repertoire of biochemical contrast agents, favoring biomolecular-specific cellular assay and (2) it enables high-throughput visualization of functional morphology of individual cells with subcellular resolution. These capabilities enable multiparametric single-cell image analysis which reveals cellular heterogeneity, for example, in the cell-death processes demonstrated in this work-the information generally masked in non-imaging flow cytometry. Therefore, this platform empowers not only efficient large-scale single-cell measurements, but also detailed mechanistic analysis of complex cellular processes.

Ultrafast, laser-scanning time-stretch microscopy with visible light

We demonstrate ultrafast time-stretch microscopy in, to the best of our knowledge, the shortest wavelength regimes, i.e. 532 nm. This is enabled by a new all-optical ultrahigh-speed laser-scanning technique called free-space angular-chirpenhanced delay (FACED) that achieves a line-scan rate as high as 20 MHz. In contrast to the predominant fiber-based implementation, time-stretch imaging based on FACED allows wavelength-independent and low-loss operations, and more intriguingly reconfigurable all-optical laser-scanning rate. Using this technique, we present high-resolution single-cell images captured in an ultrafast microfluidic flow (1.5m/s). This could unleash numerous cell and tissue imaging applications, e.g. high-throughput image flow cytometry and whole-slide imaging.

Optical time-stretch microscopy enabled by free-space angular-chirp-enhanced delay (Conference Presentation)

Optical time-stretch microscopy enables cellular images captured at tens of MHz line-scan rate and becomes a potential tool for ultrafast dynamics monitoring and high throughput screening in scientific and biomedical applications. In time-stretch microscopy, to achieve the fast line-scan rate, optical fibers are used as the pulse-stretching device that maps the spectrum of a light pulse to a temporal waveform for fast digitization. Consequently, existing time-stretch microscopy is limited to work at telecom windows (e.g. 1550 nm) where optical fiber has significant pulse-stretching and small loss. This limitation circumscribes the potential application of time-stretch microscopy. Here we present a new optical time-stretch imaging modality by exploiting a novel pulse-stretching technique, free-space angular-chirp-enhanced delay (FACED), which has three benefits: (1) Pulse-stretching in FACED generates substantial, reconfigurable temporal dispersion in free-space with low intrinsic loss at visible wavelengths; (2) Pulse-stretching in FACED inherently provides an ultrafast all-optical laser-beam scanning mechanism for time-stretch imaging. (3) Pulse-stretching in FACED can be wavelength-invariant, which enables time-stretch microscopy implemented without spectral-encoding. Using FACED, we demonstrate optical time-stretch microscopy with visible light (~700 nm). Compared to the prior work, bright-field time-stretch images captured show superior contrast and resolution, and can be effectively colorized to generate color time-stretch images. More prominently, accessing the visible spectrum regime, we demonstrate that FACED enables ultrafast fluorescence time-stretch microscopy. Our results suggest FACED could unleash a wider scope of applications that were once forbidden with the fiber based time-stretch imaging techniques.

Ultrafast laser scanning cellular microscopy by spatiotemporally encoded virtual sources

We report a new type of all-optical ultrafast laser-scanning microscopy( (at a line-scan rate of 20 MHz) based on a phenomenon called free-space angular-chirp-enhanced delay (FACED). It results in the generation of a reconfigurable array of spatiotemporally encoded virtual pulsed sources, which acts as a scanning laser beam. We demonstrate its application in high-throughput multivariate image-based single-cell analysis (10,000 cells/sec).

Active, large-scale tuning of optical dispersion by free-space angular-chirp-enhanced delay (FACED)

We report a new technique, coined free-space angular-chirp-enhanced delay (FACED), to generate large-scale, wavelength-insensitive, actively tunable optical dispersion, at least 3 orders-of-magnitude larger in dispersion than the current techniques.