Video-rate quantitative phase imaging with dynamic acousto-optic defocusing

Various quantitative phase imaging techniques exist capable of characterizing transparent and low-contrast samples without the addition of dyes or fluorescent probes. Among them, the transport of intensity equation (TIE) allows phase retrieval by capturing information from different focal planes without complex inteferometric setups. However, current implementations can be limited in speed or accuracy by the lack of optical systems suitable for fast, reliable, and customizable focal plane selection. Here, we report how combining acousto-optics with pulsed illumination enables accurate and on-demand electronic defocus control suitable for TIE phase imaging at speeds only limited by the camera frame rate. The system exhibits diffraction-limited spatial resolution and high reconstruction fidelity, undistinguishable from traditional mechanical defocusing. We demonstrate its feasibility by measuring different dynamic events at rates as high as 100 phase maps per second. The tunability and ease of implementation of our system can pave the way to democratizing quantitative phase imaging in histopathology, fluid dynamics, and other fields involving thin transparent samples

Enhanced light focusing inside scattering media with shaped ultrasound

Light focusing is the primary enabler of various scientific and industrial processes including laser materials processing and microscopy. However, the scattering of light limits the depth at which current methods can operate inside heterogeneous media such as biological tissue, liquid emulsions, and composite materials. Several approaches have been developed to address this issue, but they typically come at the cost of losing spatial or temporal resolution, or increased invasiveness. Here, we show that ultrasound waves featuring a Bessel-like profile can locally modulate the optical properties of a turbid medium to facilitate light guiding. Supported by wave optics and Monte Carlo simulations, we demonstrate how ultrasound enhances light focusing a factor of 7 compared to conventional methods based on placing optical elements outside the complex medium. Combined with point-by-point scanning, images of samples immersed in turbid media with an optical density up to 15, similar to that of weakly scattering biological tissue, can be reconstructed. The quasi-instantaneous generation of the shaped-ultrasound waves, together with the possibility to use transmission and reflection architectures, can pave the way for the real-time control of light inside living tissue

Simultaneous multiplane confocal microscopy using acoustic tunable lenses

Maximizing the amount of spatiotemporal information retrieved in confocal laser scanning microscopy is crucial to understand fundamental three-dimensional (3D) dynamic processes in life sciences. However, current 3D confocal microscopy is based on an inherently slow stepwise process that consists of acquiring multiple 2D sections at different focal planes by mechanical or optical z-focus translation. Here, we show that by using an acoustically-driven optofluidic lens integrated in a commercial confocal system we can capture an entire 3D image in a single step. Our method is based on continuous axial scanning at speeds as high as 140 kHz combined with fast readout. In this way, one or more focus sweeps are produced on a pixel by pixel basis and the detected photons can be assigned to their corresponding focal plane enabling simultaneous multiplane imaging. We exemplify this method by imaging calibration and biological fluorescence samples. These results open the door to exploring new fundamental processes in science with an unprecedented time resolution

Printability conditions for an all-solid-state laser transfer

Several laser technologies exist capable of adding solid materials to a targeted area of a substrate, including photopolymerization, laser sintering, or laser-induced forward transfer. However, the added material normally undergoes a phase change, causing adverse effects such as shrinkage, stress, or degradation. As recently demonstrated, this issue can be addressed by using laser pulses to mechanically delaminate and eject a disk from a solid film. In this case, the laser plays the role of a catapult, with minimal thermal damage to the transferred disk. Despite proven success in micro-electronics and micro-optics, little is known about the mechanical properties of the film that lead to a crack-free all-solid-state transfer. Here, we present a theoretical and experimental study on the effects that film rigidity, elasticity, and plasticity play on laser catapulting. By combining the thermodynamic equations of the laser-generated propulsion force with the theory of thin plate bending, we derived an analytical model that fully describes the list of events responsible for disk ejection. The model is in good agreement with experiments using elastomers, polymers, and metals. A complete printability map based on the film mechanical parameters is reported, which can help to broaden the family of materials suitable for laser additive manufacturing

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

: Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provide

Three-dimensional particle tracking via tunable color-encoded multiplexing.

We present a novel 3D tracking approach capable of locating single particles with nanometric precision over wide axial ranges. Our method uses a fast acousto-optic liquid lens implemented in a bright field microscope to multiplex light based on color into different and selectable focal planes. By separating the red, green, and blue channels from an image captured with a color camera, information from up to three focal planes can be retrieved. Multiplane information from the particle diffraction rings enables precisely locating and tracking individual objects up to an axial range about 5 times larger than conventional single-plane approaches. We apply our method to the 3D visualization of the well-known coffee-stain phenomenon in evaporating water droplets

Variable optical elements for fast focus control

In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications

Selective fluorescence functionalization of dye-doped polymerized structures fabricated by direct laser writing (DLW) lithography

Spatially- and intensity-selective fluorescence photopolymerized resins are fabricated through a thermally-induced di-aggregation mechanism with applications as optical data storage devices

Acousto-optic systems for advanced microscopy

Acoustic waves in an optical medium cause rapid periodic changes in the refraction index, leading to diffraction effects. Such acoustically controlled diffraction can be used to modulate, deflect, and focus light at microsecond timescales, paving the way for advanced optical microscopy designs that feature unprecedented spatiotemporal resolution. In this article, we review the operational principles, optical properties, and recent applications of acousto-optic (AO) systems for advanced microscopy, including random-access scanning, ultrafast confocal and multiphoton imaging, and fast inertia-free light-sheet microscopy. As AO technology is reaching maturity, designing new microscope architectures that utilize AO elements is more attractive than ever, providing new exciting opportunities in fields as impactful as optical metrology, neuroscience, embryogenesis, and high-content screening

Multiplane Encoded Light-Sheet Microscopy for Enhanced 3D Imaging

Light-sheet microscopes have become the tool of choice for volumetric imaging of large samples. Based on a wide-field acquisition scheme, they are capable of optical sectioning at diffraction-limited resolution and minimal overall photodamage. Unfortunately, traditional architectures are limited in speed because 3D images are collected by either sample translation or synchronized movement of both light-sheet and detection objective lens. A promising solution avoiding slow mechanical movements is to extend the depth-of-field of the microscope and moving only the light-sheet. However, this normally comes at the cost of losing light and contrast, compromising the signal-to-noise ratio of the images. Here, we propose an innovative technique devoted to restoring the quality of the images, while preserving the speed of extended depth-of-field microscopes. It is based on generating a stack of parallel light-sheets using a pair of orthogonal acousto-optic deflectors, enabling the simultaneous illumination of different sample planes. Given the extended depth-of-field, all such planes appear in focus and can be acquired in a superimposed single frame. By applying a single-step inversion algorithm, we can decode a stack of frames into a volumetric image whose signal-to-noise ratio and contrast are greatly enhanced. We provide a detailed theoretical framework of the method and demonstrate its feasibility with volumetric images of kidney cell spheroids