Compact way to generate guide star for wavefront sensing in Bessel two-photon microscopy.

Higher-order Bessel-like optical beams can be created through off-axis coupling of light into a multimode fiber. Thanks to the aberration that is inherent in spherical surfaces, through directing the Bessel-like beam comprising multiple concentric rings onto a low-cost lens, we created multiple foci at different depths. Moreover, scanning of the optical fiber with a piezoelectric actuator in the lateral direction, we were able to acquire data from different targets located at different planes. After coupling back into the fiber, the reflected portions of light from different targets could be spatially differentiated and directed to different photo-detection units. The proposed architecture is particularly appealing for laser scanning endoscopy applications, as it does not require additional passive or active optical components for generating Bessel beams (axicons or spatial light modulators), therefore offering both miniaturized realization and high optical transmission. We've further demonstrated the tunability of foci separation via altering fiber-coupling conditions with tilt and translation stages. Overall, the proposed scanning method has paved the way for addressing multiple slices at single lateral scan, thus offering improved speed for imaging or ablation applications.

One of the key trends in laser material processing is the usage of structured laser beams. One such example is the Bessel beam with an elongated focal area and self-healing properties. Higher-order Bessel beams can be formed by axicons, spiral phase plates, or equivalently by the phase masks (holograms). In this work, a demonstration of “optical drill” beams with dynamic intensity distributions resembling the spinning mechanical drill is shown. Bessel beam mixing of two different helicities is achieved by using a Spatial Light Modulator (SLM). Both Bessel beams are formed on the same optical component – the phase mask consisting of two parts. Each part consists of spirals with different winding numbers and different periods that correspond to different step plates and axicons. Such a mask forms the stationary optical drill beam. As the beam propagates the outer and inner parts start to overlap and form the resultant interfering beam. Now, to make it a true drill, it must rotate in time. In our experiment, that is achieved by rotating one part of the combined hologram. This induces an angular offset to the interference and as a result, the orientation of the helical intensity pattern starts to rotate in time. This continuous motion gives the impression of an optical drill. With the beams dynamic properties, it could become a new tool in laser material micromachining, as a mechanical drill was to construction.

.SignificanceTypical light sheet microscopes suffer from artifacts related to the geometry of the light sheet. One main inconvenience is the non-uniform thickness of the light sheet obtained with a Gaussian laser beam.AimWe developed a two-photon light sheet microscope that takes advantage of a thin and long Bessel-Gauss beam illumination to increase the sheet extent without compromising the resolution.ApproachWe use an axicon lens placed directly at the output of an amplified femtosecond laser to produce a long Bessel-Gauss beam on the sample. We studied the dopaminergic system and its projections in a whole cleared mouse brain.ResultsOur light sheet microscope allows an isotropic resolution of in all three axes of the scanned volume while keeping a millimetric-sized field of view, and a fast acquisition rate of up to . With slight modifications to the optical setup, the sheet extent can be increased to 6 mm.ConclusionThe proposed system’s sheet extent and resolution surpass currently available systems, enabling the fast imaging of large specimens.

By mapping traditional amplitude modulation to spatial modulation and employing adaptive optics compensation technique, we propose and experimentally demonstrate a high-speed Bessel beam encoding/decoding free-space optical link through atmospheric turbulence. The Bessel beam encoding/decoding speed is not limited by the conventional slow switching response of a spatial light modulator (SLM) but is fully determined by the modulation rate of an intensity modulator, which easily supports tens of gigabits per second modulation and resultant encoding/decoding. We use an SLM loaded with a pseudorandom phase mask to emulate atmospheric turbulence in the laboratory environment. An adaptive optics closed loop is used to sense the phase distortion of an extra probe Gaussian beam and then compensate the distorted Bessel beams. A 20-Gbit/s Bessel beam encoding/decoding link with adaptive turbulence compensation is demonstrated in the experiment, showing favorable operation performance.

This work innovatively designs an all-dielectric metasurface fabricated using 3D printing technology with alumina as the substrate material. This metasurface successfully generates vectorial non-diffracting Bessel beams at a specific frequency of 0.1THz. Initially, through comprehensive simulation analysis of the interaction between the metasurface and the incident beam, it was discovered that the metasurface can precisely manipulate the properties of the transmitted beam based on the polarization state of the incident beam. Specifically, when illuminated by a left-handed circularly polarized (LCP) Gaussian beam, the transmitted beam manifests as a radially polarized Bessel beam. Conversely, under right-handed circularly polarized (RCP) Gaussian beam illumination, the transmitted light transforms into an azimuthally polarized Bessel beam. Building upon the theoretical simulations and considering experimental constraints, further experimental validation was conducted using linearly polarized light, confirming the effectiveness and feasibility of the proposed design. Experimental results demonstrate that the presented all-dielectric alumina metasurface, fabricated via 3D printing, successfully achieves the generation of vector nondiffracting Bessel beams. On one hand, the combination of alumina material and 3D printing technology significantly reduces manufacturing costs, laying a foundation for large scale application. On the other hand, leveraging the high precision of 3D printing ensures the accurate fabrication of the metasurface structure, thereby guaranteeing the high quality and stability of the generated vector beams. This work provides a novel approach for the efficient generation of Bessel beams and is expected to have profound implications in the field of terahertz technology.

We demonstrate how to create non-diffracting vector Bessel beams by implementing a spatial light modulator (SLM) to generate scalar Bessel beams which are then converted into vector fields by the use of an azimuthally-varying birefringent plate, known as a q-plate. The orbital angular momentum (OAM) of these generated beams is measured by performing a modal decomposition on each of the beam’s polarization components. This is achieved by separating the circular polarization components through a polarization grating (PG) before performing the modal decomposition. We investigate both single charged Bessel beams as well as superpositions and the results are in good agreement with theory.

Microtube, with simple and uniform geometry, is one of the basic structures in micro/nano field. We present a method for the fabrication of magnetic drivable microtubes, by direct femtosecond laser writing combined with magnetron sputtering with metal layer. Femtosecond laser beam is modulated into Bessel beam with spatial light modulator (SLM), and then Bessel beam is focused with a high numerical aperture objective. Microtubes are fabricated by scanning focused femtosecond Bessel beam in a sample anchored on a three dimension stage. Followed by magnetron sputtering a nickel layer, the microtubes exhibit supermagnetic property and can be flexibly driven by external magnetic field. In this study, the propagation and high numerical aperture focusing properties of femtosecond Bessel beams are investigated. Microtubes, with well controlled diameter, length and distribution are efficiently fabricated. Rapid steering of nickel coated microtubes along specific route in fluid environment with external magnetic field has been realized. The steering of microtubes can be realized in various fluid environments. This method is flexible, controllable and efficient and the fabricated drivable microtubes have a promising applications in noninvasive surgery, targeted drug delivery, bioimaging or biosensing and microenvironment cleaning.

Materials processing with superposed Bessel beams

Bessel beams, characterized by an extended depth of focus and non-diffracting propagation, have been extensively employed in areas such as laser processing and optical imaging. However, their applications in precision machining are hindered by high-energy sidelobes that cause unintended damage to non-target regions, increasing surface roughness and reducing accuracy. Conventional sidelobe suppression techniques, such as the use of axicons combined with phase plates or annular apertures, generally involve complex setups, exhibit high alignment sensitivity, and are unsuitable for high-power lasers. To address these limitations, we realize a high-damage-threshold metasurface for generating sidelobe-suppressed Bessel beams (SSBB). The design employs a hybrid modulation strategy that integrates a simulated-annealing-optimized binary phase ring with an axicon phase. The metasurface is fabricated in silica glass via femtosecond laser direct writing, where laser-induced birefringent nanopores enable geometrical phase modulation. The prepared metasurface exhibits high threshold characteristics and a conversion efficiency of 96.3%. The metasurface-generated SSBB shows a first sidelobe peak intensity of only 5.2% of the main lobe—representing a 72.3% reduction compared to conventional Bessel beams (18.8%). The generated SSBB demonstrates superior machining quality in the drilling of silica glass. This approach provides an integrated solution to the sidelobe issue in Bessel beams and holds significant potential for advanced manufacturing applications, including semiconductor packaging and cooling hole drilling in aero-engine turbine blades.

Lattice lightsheet microscopy (LLSM) featuring three-dimensional recording is improved to manipulate cellular behavior with subcellular resolution through optogenetic activation (optoLLSM). A position-controllable Bessel beam as a stimulation source is integrated into the LLSM to achieve spatiotemporal photoactivation by changing the spatial light modulator (SLM) patterns. Unlike the point-scanning in a confocal microscope, the lattice beams are capable of wide-field optical sectioning for optogenetic activation along the Bessel beam path.We show that the energy power required for optogenetic activations is lower than 1 nW (or 24 mWcm-2) for time-lapses of CRY2olig clustering proteins, and membrane ruffling can be induced at different locations within a cell with subcellular resolution through light-triggered recruitment of phosphoinositide 3-kinase. Moreover, with the epidermal growth factor receptor (EGFR) fused with CRY2olig, we are able to demonstrate guided cell migration using optogenetic stimulation for up to 6 h, where 463 imaging volumes are collected, without noticeable cellular damages.

Arrays of Gaussian vortex, Bessel and Airy beams by computer-generated hologram

Extending the depth of field (DOF) is essential for large-volume imaging in biological research, particularly in thick tissue environments. Bessel beams and their variants are widely used due to their simplicity and have been successfully applied to in vivo imaging. A recent advancement demonstrated the application of droplet Bessel beams (DBBs) for multi-photon microscopy, enabling functional imaging in live mouse brains. However, DBB generation inevitably requires active phase switching devices such as spatial light modulators, which reduce imaging speed and increase system complexity. This study introduces a droplet Bessel beam metalens (DBBM) that passively generates DBBs without phase switching by employing rectangular meta-atoms for orthogonal polarization modulation and X-shaped meta-atoms for amplitude control. Optical simulations identify optimal DBBM parameters that maximize the point spread function (PSF) aspect ratio while minimizing energy leakage into side lobes. Furthermore, the fabricated DBBM produces PSFs consistent with simulations. Imaging simulations based on three-dimensional confocal images of expansion microscopy–treated organoids demonstrated that the DBBM maintains superior performance even in the presence of aberrations. These findings establish the DBBM as a compact and passive solution for extended DOF imaging without the need for beam-shaping devices. Metalens technology is anticipated to have broad applications in real-time volumetric bioimaging and enable simplified optical system designs.

Nondestructive pathology based on three-dimensional (3D) optical microscopy holds promise as a complement to traditional destructive hematoxylin and eosin (H&E) stained slide-based pathology by providing cellular information in high throughput manner. However, conventional techniques provided superficial information only due to shallow imaging depths. Herein, we developed open-top two-photon light sheet microscopy (OT-TP-LSM) for intraoperative 3D pathology. An extended depth of field two-photon excitation light sheet was generated by scanning a nondiffractive Bessel beam, and selective planar imaging was conducted with cameras at 400 frames/s max during the lateral translation of tissue specimens. Intrinsic second harmonic generation was collected for additional extracellular matrix (ECM) visualization. OT-TP-LSM was tested in various human cancer specimens including skin, pancreas, and prostate. High imaging depths were achieved owing to long excitation wavelengths and long wavelength fluorophores. 3D visualization of both cells and ECM enhanced the ability of cancer detection. Furthermore, an unsupervised deep learning network was employed for the style transfer of OT-TP-LSM images to virtual H&E images. The virtual H&E images exhibited comparable histological characteristics to real ones. OT-TP-LSM may have the potential for histopathological examination in surgical and biopsy applications by rapidly providing 3D information.

<sec> With the development of laser technology, the application scope of nondiffracting beams, such as Bessel beams, Mathieu beams, cosine beams, and parabolic beams, which remain invariant along their propagation, continues to expand. During its propagation, the main lobes of these beams tend to bend towards off-axis position, which is called self-accelerating (or self-bending) property. A Bessel-like beam with self-acceleration can realize the propagation of the main lobe along a curved trajectory while maintaining the non-diffraction. Because of the above property, Bessel-like beams have been utilized in various areas such as guiding particles along arbitrarily curved trajectories, self-accelerating beams in nonlinear medium, plasma guidance, and laser-assisted guiding of electric discharges around objects. </sec><sec> In this paper, we propose a method of bending the trajectory of Bessel-like beams by using a magnetic fluid deformable mirror (MFDM) instead of traditional spatial light modulator (SLM) and Pancharatnam-Berry (PB) phase manipulation. The MFDM provides a method without pixelation, where all parameters can be rapidly modified for fine-tuning. Furthermore, compared with the conventional deformable mirror, the MFDM has the advantages of a continuous and smooth mirror surface, large shape deformation, low manufacture cost, easy extension, and large inter-actuator stroke. Therefore, it is easy for the MFDM to generate the ideal shape of an axicon. Firstly, according to geometric analysis, the asymmetrical mirror profile to produce a self-accelerating Bessel-like optical beam is proposed. The proposed mirror profile can be used to compensate for the difference in optical path length for each annular slice of the axicon. If a collimated Gaussian beam is incident on the mirror combining the axicon and the asymmetrical mirror profiles, which can obtain Bessel-like beams with arbitrarily curved trajectories. Secondly, the resultant of the self-accelerating Bessel-like beams along parabolic trajectories is validated by the simulation in MATLAB. Finally, a prototype of MFDM consisting of the dual-layer arrays of miniature electromagnetic coils, a Maxwell coil and the magnetic fluid filled in a circular container is fabricated for the experiment. The experimental results show that the Bessel-like beams propagate along the parabolic trajectories, with the MFDM used, and the accuracy of the curved trajectories is verified. The proposed method in this paper opens a new experimental way to the study of Bessel-like beam; the theoretical approach can also be generalized mathematically for other non-paraxial beam propagation. </sec>

.SignificanceIn mesoscopic imaging research in neuroscience, achieving high spatial resolution optical imaging across the entire field of view (FOV) remains critical. This directly determines whether researchers can precisely analyze the large-scale dynamic activities of neural circuits at the single-cell or even subcellular level. Consistent optical quality throughout the entire imaging FOV is essential to accurately capture the spatiotemporal patterns of neural activity across brain regions, thereby providing a powerful tool for understanding the circuit mechanisms underlying cognition, behavior, and disease at cellular and subcellular resolution in vivo.AimThis study aims to develop a technology that extends the imaging FOV in a two-photon mesoscope while enhancing the optical quality across the entire FOV in vivo. The key point is to establish a robust method that can significantly extend the FOV beyond what the micro/mesoscope objective had been originally designed for, yet maintain the original resolution specifications. As such, the value of the method also extends beyond improving just one mesoscope, which we use as a demo in this study.ApproachThis study introduces an innovative approach that combines block scanning with adaptive optical (AO) correction through a bioinspired honeycomb-based cellular multipoint adaptive technology (CMAT) to achieve mesoscopic two-photon imaging. This system enables unprecedented large-FOV, high-resolution imaging by dividing an imaging area into subregions, each pre-optimized with deformable mirror (DM) compensation while applying real-time dynamic wavefront correction during scanning. Furthermore, we have designed multiple user-defined sub-region scanning functions. Each sub-region automatically loads the aberration correction compensation values from the nearest reference point relative to its center, thereby ensuring optimal optical performance for every individual sub-region. The robustness of this technology has been systematically verified across multiple neural circuit observation scenarios using transgenic mouse models, demonstrating its capability for reliable single-cell resolution imaging across extensive brain regions.ResultsComprehensive evaluation using standard samples and transgenic mouse models demonstrated that the CMAT significantly enhances the imaging performance of the two-photon mesoscope. This technique extends the effective two-photon imaging FOV from to while markedly improving the optical quality in the peripheral regions. High resolution was maintained at (lateral) and (axial) in the central area, with edge regions achieving improved resolutions of (lateral) and (axial). Quantitative analysis confirmed that multipoint AO not only enhances image contrast and optical resolution but also substantially increases the signal-to-noise ratio (SNR) in imaging. This work delivers a pivotal technical advance for large-scale functional imaging of neural circuits.ConclusionCMAT significantly extends the effective FOV and enhances the optical quality of the two-photon mesoscope system.