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Flexibly adjustable depth-of-focus photoacoustic microscopy with spatial light modulation
摘要： Through focusing the excitation laser, optical-resolution photoacoustic microscopy (OR-PAM) is capable of measuring optical absorption properties down to micrometer-scale lateral resolution within biological tissues. The focused Gaussian beam routinely employed in the OR-PAM setups is inadequate for acquiring the volumetric images of biological specimens with thickness from tens micrometers to millimeter without scanning in depth because of the inconsistent lateral resolution along the depth direction due to its short depth of focus (DoF). Here, we integrate a spatial light modulator (SLM) into the optical path of an OR-PAM for realizing the flexibly adjustable DoF. By simply switching the phase patterns assigned onto the SLM interface, three representative illumination beams are produced, including conventional short-DoF Gaussian beam (GB), needle-like Bessel beam (BB), and extended depth-of-focus beam (EDFB). These modulations can be well realized based on the extended Nijboer-Zernike theory. The photoacoustic excitations show variable DoFs ranging from hundreds of micrometers (GB and BB) up to 1.38 mm (EDFB) but a consistent lateral resolution of (cid:2)3.5 lm. The proposed method is confirmed by volumetric imaging of multiple tungsten fibers positioned at different depths.
关键词： spatial light modulation,photoacoustic microscopy,depth-of-focus,extended depth-of-focus beam,Bessel beam,optical-resolution
更新于2025-09-23 15:21:21
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[IEEE 2019 International Conference on Optical MEMS and Nanophotonics (OMN) - Daejeon, Korea (South) (2019.7.28-2019.8.1)] 2019 International Conference on Optical MEMS and Nanophotonics (OMN) - Micro-optical system for depth-controlled Bessel beam arrays
摘要： We present an integrated, compact micro-optical system capable to generate depth-controlled Bessel beams by integrating a miniaturized adaptive liquid crystal ring aperture array with a micro-lens array, a lensacon, which is a combination of a lens and an axicon. We were able to successfully demonstrate a functional system that is able to generate and control Bessel beams.
关键词： micro-lens arrays,Bessel beam,micro-optical system,aspherical lenses,ring aperture,liquid crystal
更新于2025-09-16 10:30:52
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Optimized Chemical Potential Graphene-Based Coding Metasurface Approach for Dynamic Manipulation of Terahertz Wavefront
摘要： In this paper, a new method for the design of pixelated graphene-based coding metasurface is proposed. This method suggests a straightforward approach by utilizing graphene tunable pixels (GTP), which can control the reflection phase in a real-time manner at terahertz (THz) frequencies. The proposed unit cell is composed of four distinct graphene patches in the same layer, which has a chemical potential that obtained by utilizing optimization-based methods. By changing the reflection phase profile across the metasurface, the proposed device can manipulate the reflected wave phase, amplitude, and polarization control in various beamforming applications at THz spectrum for modern information systems, data encryption, and THz communication applications. Chemical potential optimization method in graphene-based coding metasurface is not limited to a specific structure for phase-only metasurface. Indeed it has an exceptional capability for metasurface to manipulate electromagnetic (EM) wave in the half-space and generate converged vortex beam, non-diffractive Bessel beam, and EM bump illusion. The simulation and theoretical results show that the suggested method offers a feasible strategy for multifunctional metasurface applications.
关键词： Bessel beam,Illusion,Chemical potential optimization,Vortex beam,Metasurface,Graphene
更新于2025-09-11 14:15:04
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Optical-trapping of a red Bessel beam controlled by co-propagating green Gaussian beam in azobenzene liquid crystal
摘要： Simultaneous co-propagation of red nondiffracting Bessel beam and green Gaussian beam at milliwatt powers in a photosensitive azobenzene liquid crystal has been studied. The fine displacement of the narrow-width Gaussian beam relative to the Bessel beam central maximum showed the Bessel beam distortion and controlled bending of its core in the direction opposite to the location of green Gaussian beam. After switching off the green beam, the dynamics of restoration of Bessel beam demonstrated the pronounced optical-trapping feature of its central core and transient soliton-like propagation with reduced diameter and increased intensity and propagation depth thus forming a waveguiding channel.
关键词： spatial soliton,Bessel beam,self-focusing,azobenzene liquid crystal,photo-isomerization
更新于2025-09-11 14:15:04
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Packaged Negative Axicon Optical Fiber Probe and Bessel Beam Interferometry for Refractive Index Measurement of Hazardous Liquid Samples
摘要： In this work, we demonstrate the packaging of an optical fiber negative axicon probe generating Bessel beam and its application in the measurement of refractive index (RI) of hazardous liquids. The negative axicon probe is placed inside cascaded capillary tube capped with a glass coverslip of RI ~1.52 and thickness ~0.15 mm. The packaged probe, connected to a broadband source through an optical circulator, is dipped in different hazardous liquid samples. The reflected light from the air-glass as well as the glass-liquid interface couples to the negative axicon probe and interferes with the reference beam generated at the air-negative axicon interface. The interference spectra recorded in a spectrometer through the circulator are analyzed applying Fast Fourier Transform (FFT). The FFT helps to separate and measure powers reflected from the different interfaces which are used to solve the Fresnel equation for estimating the RI of hazardous liquid samples, such as HCl, H2SO4 solutions. The resolution achieved is 1*10-4 ± 0.0005. The probe can be useful to measure RI of liquid samples remotely and in hazardous environmental condition.
关键词： refractive index,Bessel beam,Negative Axicon,optical fiber,hazardous liquid
更新于2025-09-11 14:15:04
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Vortex-sound diffusers using spiral metasurfaces
摘要： Metamaterials allow the accurate control of the acoustic scattering using subwavelength thickness panels. In this work, we report the scattering of spiral-shaped metasurfaces with practical application to sound diffusers. We analytically, numerically and experimentally show that bipolar spiral-shaped metasurfaces produce broadband non-specular reflection. We observe that the reflected energy can be scattered at higher diffraction orders and, due to the spiral geometry, the phase of the scattering field rotates producing a vortex in the near field. Thus, the specular component at normal incidence vanish. This produces a perfect correlation-scattering coefficient when comparing to a rigid flat reflector of same dimensions. In particular, the scattering of an Archimedes spiral metasurface is presented. We show that the scattering pattern corresponds to a high-order Bessel beam. The use of binary locally reacting surfaces with chiral geometry produce non-specular reflected patterns, allowing the use of these structures use as sound diffusers.
关键词： acoustic scattering,sound diffusers,metamaterials,Bessel beam,spiral-shaped metasurfaces
更新于2025-09-10 09:29:36
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Bessel beam expansion of linear focused ultrasound
摘要： Previous work on scattering by Bessel beams shows that expansion of incident sound fields in term of these beams has application to scattering [P. L. Marston, J. Acoust. Soc. Am. 122, 247–252 (2007)]. In this work, an expression for the expansion coefficients of propagating, axisymmetric, sound fields are derived. In this paper, this expression is applied to a linear focused axisymmetric sound field and is expanded in terms of Bessel beam components. This is done for focused beams radiated from a spherical cap source. A physical optics model is applied to sound propagation close to the source to facilitate the calculation of the Bessel beam expansion coefficients. This type of model is useful for focused scattering [P. L. Marston and D. S. Langley, J. Acoust. Soc. Am. 73, 1464–1475 (1983)]. Once the expansion coefficients are found, the sound field can be evaluated by superposition. The model agrees approximately with Chen, Schwarz, and Parker [J. Acoust. Soc. Am. 94, 2979–2991 (1993)] and O’Neil [J. Acoust. Soc. Am. 21, 516–526 (1949)] on axis and with direct integration of a Kirchhoff integral both on and off axis. This type of expansion will have applications to scattering problems. VC 2018 Acoustical Society of America. https://doi.org/10.1121/1.5080602
关键词： physical optics model,Kirchhoff integral,linear focused ultrasound,scattering,Bessel beam
更新于2025-09-09 09:28:46
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Tunable depth of focus of acoustical pupil masked Soret Zone Plate
摘要： In acoustical lenses both resolution and depth of focus are determined by diffraction and the smaller the lens aperture the worse the resolution and the greater the depth of focus. Diffraction-limited resolution has a Soret Zone Plate, but a long depth of focus has an axicon. Nevertheless, these are two different devices each of which requires its own independent design. In this paper we have shown that the transition from focusing to a diffraction limited spot to a quasi-diffraction free beam can be realized in the same focusing device without changing its topology. It has been shown that using a classical planar Soret Zone Plate lens made of a concentric array of circular aperiodical rings with an amplitude pupil mask placed closely to the surface of lens allows to form a quasi-Bessel beams under specific conditions, part of a diffracted wave collimates, producing an elongated focus. Experiments are performed in water tanks in order to verify the simulation results. Experimental verification shown that the depth of focus of a pupil-masked Soret Zone Plate increases 1.63 times and resolution increases 1.2 times (with minimal beam waist about of 0.67 of wavelength and depth of focus about 5.72 of wavelength). By dynamically controlling the size of the amplitude pupil mask, it is possible to quickly control the depth of focus of an acoustic lens.
关键词： ultrasonic lens,acoustic bessel beam,axicon
更新于2025-09-04 15:30:14