Tunable Acoustic Gradient Lens Research Articles

Plug-and-play adaptive optics for two photon high-speed volumetric imaging

To understand brain functions, it is important to study functional connectivity among stereoscopically distributed neurons. Since the brain is composed of 3D neuron networks, volumetric imaging with high spatiotemporal resolution is highly desirable. Two-photon microscopy (2PM) conveniently offers 3D tissue imaging with sub-micrometer resolution based on its intrinsic optical sectioning and deep penetration capabilities. However, the main challenge lies in the volumetric imaging speed and contrast reduction in deep tissue due to aberration. In this study, we integrate a tunable acoustic gradient lens and a plug-and-play adaptive-optics lens into 2PM. The former provides ∼100 kHz axial scan rate, achieving volumetric imaging rate in 1–10 Hz range, while the latter enhances image contrast by nearly two-fold in deep brain regions via correcting both systematic and sample aberrations. The combination offers a practical approach toward high-speed, high-contrast optical volumetric imaging of brain tissues.

Active Feedback 3D Single-Molecule Tracking

Single molecule tracking has the potential to revolutionize the study of biological systems. However, most current single molecule imaging and tracking methods are limited to two dimensions. Meanwhile, real-time 3D single molecule tracking methods, which use active feedback to "lock-on" to single molecules in solution have until now been limited to observation times of 500 msec or less, greatly limiting their utility. Recently we developed a real-time 3D single particle tracking method known as 3D Dynamic Photon Localization Tracking (3D-DyPLoT). 3D-DyPLoT dynamically scans a focused laser spot in 3D with a tunable acoustic gradient lens and a 2D electro-optic deflector and has demonstrated real-time tracking at high diffusive speeds (up to 20 µm2/s) and low photon count rates 10 kHz. Here we demonstrate that the high tracking speed, sensitivity, and robustness of 3D-DyPLoT make it ideally suited active feedback 3D single molecule tracking. By implementing optimized tracking parameters based on single molecule model simulation, 3D-DyPLoT can continuously track single fluorescent dye molecules for several minutes at a time, two orders of magnitudes longer than previously reported methods. We demonstrate the application of this new single molecule tracking microscopy to track the free, 3D diffusion of DNA, RNA and proteins in solution. With two-color observation channels, 3D-DyPLoT was also applied to observing the transcription of single DNA molecules in solution by monitoring the real-time production of mRNA. This real-time 3D single molecule tracking method promises to be powerful tool for capturing the dynamics of single biomolecules at high speeds and over 3D distances. (Supported by NIH R35GM124868 and NSF 1847899).

Analysis of axial scanning range and magnification variation in wide‐field microscope for measurement using an electrically tunable lens

Inserting an electrically tunable lens (ETL), such as liquid lens or tunable acoustic gradient lens, into a microscope can enable fast axial scanning, autofocusing, and extended depth of field. However, placing the ETL at different positions has different influences on image quality. Specially, in a wide-field microscope for measurement, the magnification has to be constant when introducing an ETL, otherwise it will affect measurement accuracy. To determine the best position of ETL, axial scanning range and magnification variation are quantitatively analyzed and discussed in finite and infinite microscopes through theoretical analysis, optical simulation, and experiment for four configurations: when ETL is placed at the back focal plane of objective, at the conjugate plane of objective's back focal plane between two relay lenses, or behind two relay lenses, and at imaging detector plane. The obtained results are as follows. When ETL is placed at the back focal plane, the system has a large scanning range, but the magnification varies because the back focal plane is inside the objective. When ETL is placed between two relay lenses, the magnification stays constant, but the scanning range is small. When ETL is placed behind two relay lenses, the magnification keeps invariant and the scanning range is large, but ETL and two relay lenses are inside the microscope and the system has to be customized. Finally, when ETL is placed at imaging detector plane, the magnification stays constant, but the scanning range is 0, which means the system has no axial scanning capability. RESEARCH HIGHLIGHTS: An electrically tunable lens (ETL) is introduced into a wide-field microscope for measurement. Axial scanning range and magnification variation are analyzed and discussed. Theoretical analysis, ZEMAX optical simulation and experiments are performed.

Multifocus optical-resolution photoacoustic microscope using ultrafast axial scanning of single laser pulse

A tunable acoustic gradient (TAG) lens has been introduced in the fast axial scanning in optical imaging. However, it still needs additional imaging time for depth scanning. In this study, we split a single laser pulse into three sub-pulses and introduce them into three fibers with different lengths. The sub-pulses out of the fibers were combined thereafter. We then obtained a pulse train with a time interval of 120 ns. By controlling the fire time of the pulse train and the driving signal of the TAG lens, we can receive three focal spots in one A line data acquisition using a single input laser pulse. The depth of focus (DoF) of the system was measured to be 360 μm, which is three times of that of previous systems without the sacrifice of time resolution. A mouse ear and mouse cerebral vasculature were imaged in-vivo to demonstrate the feasibility of the extended DoF of our system.

Robust real-time 3D single-particle tracking using a dynamically moving laser spot.

Real-time three-dimensional (3D) single-particle tracking uses optical feedback to lock on to freely diffusing nanoscale fluorescent particles, permitting precise 3D localization and continuous spectroscopic interrogation. Here we describe a new method of real-time 3D single-particle tracking wherein a diffraction-limited laser spot is dynamically swept through the detection volume in three dimensions using a two-dimensional (2D) electro-optic deflector and a tunable acoustic gradient lens. This optimized method, called 3D dynamic photon localization tracking (3D-DyPLoT), enables high-speed real-time tracking of single silica-coated non-blinking quantum dots (∼30 nm diameter) with diffusive speeds exceeding 10 μm2/s at count rates as low as 10kHz, as well as YFP-labeled virus-like particles. The large effective detection area (1 μm×1 μm×4 μm) allows the system to easily pick up fast-moving particles, while still demonstrating high localization precision (σx=6.6 nm, σy=8.7 nm, and σz=15.6 nm). Overall, 3D-DyPLoT provides a fast and robust method for real-time 3D tracking of fast and lowly emitting particles, based on a single excitation and detection pathway, paving the way to more widespread application to relevant biological problems.

Fast axial-scanning photoacoustic microscopy using tunable acoustic gradient lens.

An optical-resolution photoacoustic microscope (OR-PAM) with capability of fast axial-scanning was developed by using a tunable acoustic gradient (TAG) lens. The TAG lens was designed to continuously changing the focal plane of OR-PAM by modulating its refractive power with fast-changing ultrasonic standing wave. The performance was shown by imaging a carbon fiber. We achieved a DoF of about 750 μm. The head of a zebrafish was also imaged to further demonstrate the feasibility of our method.

TAG Lens: Revolutionizing Optical Microscopy With Ultra-High Speed Variable Focus

The Tunable Acoustic Gradient Lens, or TAG Lens, is a revolutionary innovation that uses sound waves in liquid to provide the fastest variable focus lens in the field of adaptive optics. Capable of scanning a wide range of focal lengths in microseconds, the TAG lens is orders of magnitude faster than other liquid lenses, optical membrane or mechanical scanning approaches presently available on the market [1]. The award-winning TAG Lens functions by using a piezoelectric element at the boundary of a cylindrical cavity to excite high frequency acoustic pressure waves in a confined liquid. The corresponding oscillations in liquid density create an index of refraction profile like that of a simple aspherical lens (Figure 1). However, unlike static devices that rely on the deformation of a surface or interface, the TAG Lens is a tunable gradient index of refraction (GRIN) lens that does not require any mechanical motion or redistribution of liquid to change its optical properties, allowing it to modulate focal length at very high speeds (70kHz to 1 MHz). Furthermore, the aspheric nature of the index of refraction profile results in a tunable lens with little to no spherical aberration, making it an ideal candidate for high-speed, high-precision applications [2].

High-speed varifocal imaging with a tunable acoustic gradient index of refraction lens

Fluidic lenses allow for varifocal optical elements, but current approaches are limited by the speed at which focal length can be changed. Here we demonstrate the use of a tunable acoustic gradient (TAG) index of refraction lens as a fast varifocal element. The optical power of the TAG lens varies continuously, allowing for rapid selection and modification of the effective focal length at time scales of 1 mus and shorter. The wavefront curvature applied to the incident light is experimentally quantified as a function of time, and single-frame imaging is demonstrated. Results indicate that the TAG lens can successfully be employed to perform high-rate imaging at multiple locations.