Resonant Scanning Research Articles

Video-rate two-photon microendoscopy using second harmonic resonance fiber scanning

We present a 2.5-mm-diameter resonant fiber scanning two-photon microendoscope with a 30-mm long forward-viewing rigid probe tip that enables video-rate imaging (20 Hz frame rate) suitable for hand-held imaging of tissues without motion artifacts. Higher-order harmonic oscillation scanning techniques are developed to significantly increase the frame rate compared to prior published fiber scanning microendoscopy designs while maintaining the field-of-view (∼125 µm), the optical resolution (1.2 µm lateral and 10.9 µm axial resolution, full width at half maximum), and the spatial sampling (1250 circumferential pixels per spiral × 20 radial pixels over the diameter; 210 spirals per frame, ∼4 spiral samples per resolvable pixel) compared to a traditional scan using the fundamental resonance. 3D printed mounts were created to reduce the cost and simplify the fabrication for the fiber scanner without compromising performance or stability (<0.3 µm drift over 84 hours). A custom long-wavelength (∼1.08 µm) femtosecond fiber laser is coupled into several meters of fiber to realize a flexible, hand-held device for long-wavelength multiphoton microendoscopy.

Microvascular Regeneration and Perfusion of Partially Decellularized Tracheal Grafts.

A critical barrier to successful tracheal transplantation is poor vascularization. Despite its importance, little is known about microvascular regeneration in tissue-engineered grafts. We have demonstrated that partially decellularized tracheal grafts (PDTG) support neotissue formation including new submucosal microvasculature (CD31+). However, the perfusion of this neovasculature is unknown. In this study, we used a mouse model of tracheal replacement to measure the microvascular regeneration and perfusion of PDTG. PDTG and syngeneic tracheal grafts (STG, surgical control) (n = 5 for each group) were orthotopically transplanted into C5BL/6 J mice. We quantified vascularity of STG and PDTG samples at 1 and 3 months with conventional histology (N = 3 ~ 10/group). At 1, 3, and 6 months, animals were injected with fluorescein isothiocyanate (FITC) tomato lectin into the left ventricle. After perfusion, tracheas were fixed, harvested, mounted, stained for CD31 expression, and imaged with resonant scanning confocal microscopy. Percent CD31+, FITC area was compared between groups and endpoints compared with native trachea. Microvascular intersections were quantified using Sholl analysis. Functional microvasculature was seen in both groups. Although percent vascularization (CD31) in PDTG was restored by 3 months, microvascular pattern in PDTG displayed a unique morphology compared with control. Surgery alone appeared to globally change microvascular pattern and perfusion. PDTG demonstrated equivalent perfusion to surgical control by 6 months. Sholl analysis revealed a reduction of microvessel intersectionality that persisted in PDTG and was not seen in surgical or native controls. PDTG exhibited microvascular regeneration. Perfusion was present in PDTG, improved, and persisted over long-term time points. NA Laryngoscope, 2024.

[formula omitted]: A versatile approach for unsupervised segmentation of calcium imaging data

Recent advances in calcium imaging, including the development of fast and sensitive genetically encoded indicators, high-resolution camera chips for wide-field imaging, and resonant scanning mirrors in laser scanning microscopy, have notably improved the temporal and spatial resolution of functional imaging analysis. Nonetheless, the variability of imaging approaches and brain structures challenges the development of versatile and reliable segmentation methods. Standard techniques, such as manual selection of regions of interest or machine learning solutions, often fall short due to either user bias, non-transferability among systems, or computational demand. To overcome these issues, we developed CalciSeg, a data-driven and reproducible approach for unsupervised functional calcium imaging data segmentation. CalciSeg addresses the challenges associated with brain structure variability and user bias by offering a computationally efficient solution for automatic image segmentation based on two parameters: regions’ size limits and number of refinement iterations. We evaluated CalciSeg efficacy on datasets of varied complexity, different insect species (locusts, bees, and cockroaches), and imaging systems (wide-field, confocal, and multiphoton), showing the robustness and generality of our approach. Finally, the user-friendly nature and open-source availability of CalciSeg facilitate the integration of this algorithm into existing analysis pipelines.

Suppression of Subpixel Jitter in Resonant Scanning Systems With Phase-locked Sampling.

Resonant scanning is critical to high speed and in vivo imaging in many applications of laser scanning microscopy. However, resonant scanning suffers from well-known image artifacts due to scanner jitter, limiting adoption of high-speed imaging technologies. Here, we introduce a real-time, inexpensive and all electrical method to suppress jitter more than an order of magnitude below the diffraction limit that can be applied to most existing microscope systems with no software changes. By phase-locking imaging to the resonant scanner period, we demonstrate an 86% reduction in pixel jitter, a 15% improvement in point spread function with resonant scanning and show that this approach enables two widely used models of resonant scanners to achieve comparable accuracy to galvanometer scanners running two orders of magnitude slower. Finally, we demonstrate the versatility of this method by retrofitting a commercial two photon microscope and show that this approach enables significant quantitative and qualitative improvements in biological imaging.

Large-volume focus control at 10 MHz refresh rate via fast line-scanning amplitude-encoded scattering-assisted holography

The capability of focus control has been central to optical technologies that require both high temporal and spatial resolutions. However, existing varifocal lens schemes are commonly limited to the response time on the microsecond timescale and share the fundamental trade-off between the response time and the tuning power. Here, we propose an ultrafast holographic focusing method enabled by translating the speed of a fast 1D beam scanner into the speed of the complex wavefront modulation of a relatively slow 2D spatial light modulator. Using a pair of a digital micromirror device and a resonant scanner, we demonstrate an unprecedented refresh rate of focus control of 31 MHz, which is more than 1,000 times faster than the switching rate of a digital micromirror device. We also show that multiple micrometer-sized focal spots can be independently addressed in a range of over 1 MHz within a large volume of 5 mm × 5 mm × 5.5 mm, validating the superior spatiotemporal characteristics of the proposed technique – high temporal and spatial precision, high tuning power, and random accessibility in a three-dimensional space. The demonstrated scheme offers a new route towards three-dimensional light manipulation in the 100 MHz regime.

Symmetry Breaking and Spin-Orbit Coupling for Individual Vacancy-Induced In-Gap States in MoS2 Monolayers.

Spins confined to point defects in atomically thin semiconductors constitute well-defined atomic-scale quantum systems that are being explored as single-photon emitters and spin qubits. Here, we investigate the in-gap electronic structure of individual sulfur vacancies in molybdenum disulfide (MoS2) monolayers using resonant tunneling scanning probe spectroscopy in the Coulomb blockade regime. Spectroscopic mapping of defect wave functions reveals an interplay of local symmetry breaking by a charge-state-dependent Jahn-Teller lattice distortion that, when combined with strong (≃100 meV) spin-orbit coupling, leads to a locking of an unpaired spin-1/2 magnetic moment to the lattice at low temperature, susceptible to lattice strain. Our results provide new insights into the spin and electronic structure of vacancy-induced in-gap states toward their application as electrically and optically addressable quantum systems.

Robust real-time estimation of non-uniform angular velocity and sub-pixel jitter in images captured with resonant scanners.

Images captured with resonant scanners are affected by angular velocity fluctuations that result in image distortion and by poor synchronization between scanning and light detection that creates jitter between image rows. We previously demonstrated that both problems can be mitigated in post-processing by recording the scanner orientation in synchrony with the image capture, followed by data resampling [Opt. Express30, 112 (2022)10.1364/OE.446162]. Here we introduce more robust algorithms for estimation of both angular velocity fluctuation and jitter in the presence of random and deterministic noise. We also show linearization of the scanner oscillation model to reduce calculation times by two orders of magnitude, reaching 65,000 jitter estimations per second when using 2,800 samples per image row, and 500,000 when using only 500 samples, easily supporting real-time generation of jitter-corrected images.

Optimal real-time resonant scanner linearization using filtered Hermite interpolation.

High-speed laser scanning microscopy frequently relies on resonant scanners due to their order of magnitude increase in imaging rate compared to conventional galvanometer scanners. However, the use of a nonlinear scan trajectory introduces distortion that must be corrected. This manuscript derives a new algorithm based on filtered Hermite polynomial interpolation that provides the optimal shot-noise-limited SNR for a fixed number of photons and provides higher spatial accuracy than previous methods. An open-source library is presented using the Intel advanced vector instruction set (AVX) to process up to 32 samples in parallel. Using this approach, I simultaneously demonstrate lower shot noise variance, moderately higher spatial accuracy and greater than 1 gigapixel per second interpolation rate on a desktop CPU.

Efficiency of EEG-Guided Adaptive Neurostimulation Increases with the Optimization of the Parameters of Preliminary Resonant Scanning

Efficiency of EEG-Guided Adaptive Neurostimulation Increases with the Optimization of the Parameters of Preliminary Resonant Scanning

Low Power Compact 3D-Constructed AlScN Piezoelectric MEMS Mirrors for Various Scanning Strategies.

In this paper, the newly developed 3D-constructed AlScN piezoelectric MEMS mirror is presented. This paper describes the structure and driving mechanism of the proposed mirror device, covering its driving characteristics in both quasi-static and resonant scan modes. Particularly, this paper deals with various achievable scan patterns including 1D line scan and 2D area scan capabilities and driving methods to realize each scanning strategy. Bidirectional quasi-static actuation along horizontal, vertical, and diagonal scanning directions was experimentally characterized and even under a low voltage level of ±20 V, a total optical scan angle of 10.4° was achieved. In addition, 1D line scanning methods using both resonant and non-resonant frequencies were included and a total optical scan angle of 14° was obtained with 100 mVpp under out-of-phase actuation condition. Furthermore, 2D scan patterns including Lissajous, circular and spiral, and raster scans were realized. Diverse scan patterns were realized with the presented AlScN-based MEMS mirror device even under a low level of applied voltage. Further experiments using high voltage up to ±120 V to achieve an enhanced quasi-static scan angle of more than 20° are ongoing to ensure repeatability. This multi-functional MEMS mirror possesses the potential to implement multiple scanning strategies suitable for various application purposes.

Results of the Application of Direct-search Mobile Technology in the Exploration Blocks of Shakal and Halabja (Kurdistan)

Using experimental studies of mobile exploration technology, which includes modified methods of frequency-resonance processing, decoding of satellite and photographic images, vertical electron resonant scanning of the geological section, and the method of integral assessment of oil and gas content, the authors identified the potential of large prospecting blocks and licensed areas within the Shakal and Halabja blocks in Kurdistan. In the Shakal exploration area, the authors received oil responses from 3 intervals: 1) 2771-2794 m, 2) 2795.3-2815.45 m, and 3) 2834.40-2854 m in limestone sections. In Halabja exploration area, oil responses were obtained from 12 intervals: 1) 297-311.5 m, 2) 328-330 m, 3) 1190-1260 m, 4) 2018-2020 m, 5) 2059-2061 m, 6) 2132-2133 m, 7) 2192-2201 m, 8) 2249-2276 m, 9) 2307-2310 m, 10) 2317-2321 m, 11) 2326-2329 m and 12) 3310-3340 m. These results suggest that the proposed alternative exploration model can provide a more direct means of assessing the hydrocarbon potential of large exploratory areas, even before other geophysical investigations provide detailed information on possible targets.

Double spiral resonant MEMS scanning for ultra-high-speed miniaturized optical microscopy

Micro–electro–mechanical systems (MEMS)-based optical scanners play a vital role in the development of miniaturized optical imaging modalities. However, there is a longstanding challenge to balance the temporal resolution, field of view (FOV), and systematic fidelity. Here, we propose a double spiral scanning mechanism to enable high-frequency resonant scanning of MEMS scanners without sacrificing imaging quality, and offer a versatile imaging interface for applications in different scenarios. This arrangement, demonstrated by photoacoustic endoscopy, shows that the imaging rate and FOV can be improved by more than 60 and two times, respectively. The proposed method is general to address the limitations of MEMS-based scanning microscopies and can be adapted for various miniaturized imaging modalities, such as endoscopy, intraoperative image-guided surgery, and wearable devices.

Efficiency of EEG-Guided Adaptive Neurostimulation Increases with the Optimization of the Parameters of Preliminary Resonant Scanning

The development and improvement of closed-loop methods for non-invasive brain stimulation is an actual and rapidly developing area of neuroscience. An innovative version of this approach, in which a person is presented with audiovisual therapeutic stimulation, automatically modulated by the rhythmic components of his electroencephalogram (EEG), is EEG-guided adaptive neurostimulation. The present study aims to experimentally test the assumption that the effectiveness of EEG-guided adaptive neurostimulation can be increased by optimizing the parameters of preliminary resonance scanning, which consists of LED photostimulation with stepwise increasing frequency in the range of θ-, α-, and β EEG-rhythms. In order to test this assumption, we compared the effects of two types of resonance scanning, which differ in the step length of the gradually increasing frequency of LED photostimulation. The experiments involved two equal groups of university students in a state of exam stress. Before EEG-guided adaptive stimulation, one of the groups underwent resonance scanning with a short (3 s), and the other with a long (6 s) step of a gradual increase in the frequency of photostimulation. Changes in the EEG and psychophysiological parameters were analyzed under the influence of combined (resonance scanning plus EEG-guided adaptive neurostimulation) interventions relative to the initial level. It was found that only with a short (3 s) step of increasing the frequency of photostimulation, significant increases in the power of EEG-rhythms are observed, accompanied by significant changes in subjective indicators – a decrease in the number of errors in the word recognition test, a decrease in the level of emotional maladaptation, and an increase in well-being scores. The revealed positive effects are already observed after single therapeutic procedures due to the optimal conditions for the involvement of the resonant and integration mechanisms of the brain and the mechanisms of neuroplasticity in the processes of normalization of body functions. The developed combined approach to neurostimulation after additional experimental studies can be used in a wide range of rehabilitation procedures.

Design and Characterization of a Frequency- and Amplitude-Controlled CMOS MEMS Resonant Scanning Mirror

Design and Characterization of a Frequency- and Amplitude-Controlled CMOS MEMS Resonant Scanning Mirror

Multi-neuronal recording in unrestrained animals with all acousto-optic random-access line-scanning two-photon microscopy.

To understand how neural activity encodes and coordinates behavior, it is desirable to record multi-neuronal activity in freely behaving animals. Imaging in unrestrained animals is challenging, especially for those, like larval Drosophila melanogaster, whose brains are deformed by body motion. A previously demonstrated two-photon tracking microscope recorded from individual neurons in freely crawling Drosophila larvae but faced limits in multi-neuronal recording. Here we demonstrate a new tracking microscope using acousto-optic deflectors (AODs) and an acoustic GRIN lens (TAG lens) to achieve axially resonant 2D random access scanning, sampling along arbitrarily located axial lines at a line rate of 70 kHz. With a tracking latency of 0.1 ms, this microscope recorded activities of various neurons in moving larval Drosophila CNS and VNC including premotor neurons, bilateral visual interneurons, and descending command neurons. This technique can be applied to the existing two-photon microscope to allow for fast 3D tracking and scanning.

Miniature fiber scanning probe for flexible forward-view photoacoustic endoscopy

Forward-view photoacoustic (PA) endoscopy (PAE) is promising for achieving noninvasive biopsy in narrow areas of internal organs. However, current schemes that scan the proximal end of fiber bundles' core-by-cores would cause limited spatial sampling confined by the number of cores, which result in lower lateral resolution at smaller probe size. In this paper, a flexible forward-view PAE probe based on a resonant fiber scanner with a diameter of 5 mm was developed, which compactly integrated a piezoelectric (PZT) bender, a fiber cantilever, a lens, an ultrasound transducer, and a coupler inside. Phantom imaging was conducted to evaluate the performance of the flexible forward-view PAE, exhibiting a lateral resolution of 15.6 μm in a field-of-view of approximately 3 mm diameter and the imaging speed is 0.5 frames per second. In vivo imaging shows the clear vascular network of the rat gastrointestinal wall, which demonstrates the feasibility of resonant fiber scanners for photoacoustic endoscopic imaging, and indicates its potential for application as minimally invasive tools in the clinical evaluation of gastrointestinal lesions.

Structural Design and Experimental Studies of Resonant Fiber Optic Scanner Driven by Co-Fired Multilayer Piezoelectric Ceramics.

Piezo-driven resonant fiber optic scanners are gaining more and more attention due to their simple structure, weak electromagnetic radiation, and non-friction loss. Conventional piezo-driven resonant fiber optic scanners typically use quadrature piezoelectric tubes (piezo tubes) operating in 31-mode with high drive voltage and low excitation efficiency. In order to solve the abovementioned problem, a resonant fiber scanner driven by co-fired multilayer piezoelectric ceramics (CMPCs) is proposed in which four CMPCs drive a cantilevered fiber optic in the first-order bending mode to achieve efficient and fast space-filling scanning. In this paper, the cantilever beam vibration model with base displacement excitation was derived to provide a theoretical basis for the design of the fiber optic scanner. The finite element method was used to guide the dynamic design of the scanner. Finally, the dynamics characteristics and scanning trajectory of the prepared scanner prototype were tested and compared with the theoretical and simulation calculation results. Experimental results showed that the scanner can achieve three types of space-filling scanning: spiral, Lissajous, and propeller. Compared with the structure using piezo tubes, the designed scanner achieved the same scanning range with smaller axial dimensions, lower drive voltage, and higher efficiency. The scanner can achieve a free end displacement of 10 mm in both horizontal and vertical directions under a sinusoidal excitation signal of 50 Vp-p and 200 Hz. The theoretical, simulation and experimental results validate the feasibility of the proposed scanner structure and provide new ideas for the design of resonant fiber optic scanners.

Interpulse stimulation Fourier-transform coherent anti-Stokes Raman spectroscopy

Exploiting the time-resolving ability of ultrafast pulses, Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) stands out among the coherent Raman spectroscopic techniques for providing high-speed vibrational spectra with high spectral resolution, high Raman intensity, and immunity to nonresonant background. However, the impulsive stimulation nature of FT-CARS imposes heavy demands on the laser source and makes it inherently difficult to monitor high-frequency vibrations. Here, a novel FT-CARS strategy to our knowledge based on interpulse stimulation is proposed to provide more flexible measuring wavenumber region and lighten the requirement on ultrafast pulses. The mechanism of this technique is analyzed theoretically, and simulation is performed to show an orders-of-magnitude improvement of Raman intensity in the high-wavenumber region by the method. Experimentally, an ytterbium-doped fiber laser and photonic crystal fiber-based solitons are employed to provide two ∼ 100 - fs pulses as the pump and Stokes, respectively, and to perform interpulse stimulation FT-CARS without sophisticated dispersion control devices. The high-wavenumber region and upper-part fingerprint region measurements are demonstrated as examples of flexible measurement. Combined with other rapid scanning techniques, such as resonant scanners or a dual-comb scheme, this interpulse stimulation FT-CARS promises to make the fascinating FT-CARS available for any desired wavenumber region, covering many more realistic scenarios for biomedical, pathological, and environmental research.

On the design of piezoelectric actuator for 1D MEMS scanning mirror applications

This study presents the design, implementation, and characterization of 1D resonant type micro-electro-mechanical-systems (MEMS) piezoelectric scanning mirrors with different actuator designs to investigate their influences on the figure of merits (FoMs) for automotive light detection and ranging application. The MEMS scanning mirrors are driven by lead zirconate titanate (PZT) thin film in this study owing to its outstanding piezoelectric properties. Three different beam-type piezoelectric actuators are designed, including the reference meander straight-beam actuator design, and the proposed meander curved-beam and straight-curved tapered beam actuator designs. Simulations show the scan angle enhancement for two proposed designs, yet the resonant scanning frequency of meander curved-beam design dropped to below the 2 kHz requirement. To evaluate the designs, scanning mirrors with two proposed actuators are fabricated and tested. Measurements show that the resonant frequencies for the two proposed MEMS scanning mirrors are 1735 Hz and 2578 Hz, respectively. Two proposed designs respectively have the maximum optical angles of 48.1° and 50.6° at the 20 Vpp driving voltage. Due to the much higher stress on the beam structure induced by the misalignment of PZT film, the actuator could not reach the predicted scanning angle of near 80°. In comparison of the two proposed designs, the straight-curved tapered beam actuator design could enhance the FoM for about 56%. In summary, the performances of piezoelectric MEMS scanning mirror can be improved by varying the designs of length and shape of actuator, and the distribution of PZT film on the suspended actuator is also a critical design concern.

Design and development of 1D torsional spring resonant scanner

This paper presents the design and dynamic response of a proposed non- Micro-Electro Mechanical Systems (MEMS) 1D torsional spring resonant scanner. The torsional spring was selected as the compliant structure of the device, and it was fabricated using aluminum with dimensions of 49 x 3.50 x 0.18 mm (L x W x T). An Analysis of Variance (ANOVA) test was performed to determine the difference in mean between the operating resonant frequency and the three types of materials, which are aluminum, stainless steel, and carbon steel. The device operates at a resonant frequency of 80.65 Hz, yielding a maximum scanning angle of 58.06 ˚. Hysteresis was observed from the frequency response chart of the system. By comparing the resonant frequency of the experimental results with the dynamic analysis of this device, the percentage error of the resonant frequency and optical scanning angle was found to be 6.67% and 16.84%, respectively.