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Flexible transparent electrodes, encompassing the combination of optical transparency and electrical conductivity, empower numerous optoelectronic applications. While the main efforts nowadays concentrate on developing wire meshes and conductive oxides, those technologies are still in a quest to find a balance between price, performance, and versatility. Here we propose a new platform, encompassing the advantages of nanophotonic design and roll‐to‐roll large‐scale lithography fabrication tools, granting an ultimate balance between optical, electrical, and mechanical properties. The design is based on an array of silica microspheres deposited on a patterned thin aluminum film attached to a flexible polymer matrix. Microspheres are designed to squeeze 80% light through nanoscale apertures with the aid of the photonic nanojet effect given the light impinges the structure from the top. The photonic structure blocks the transmission for the backpropagation direction thus granting the device with the high 5‐fold level of asymmetry. The patterned layer demonstrates a remarkable 2.8 Ω sq−1 sheet resistance comparable to that of a continuous metal layer. The high conductivity is shown to be maintained after a repeatable application of strain on the flexible electrode. Such remarkable optical, mechanical and electrical properties, makes the demonstrated device an essential component for applications, where such attributes are critically required. [ABSTRACT FROM AUTHOR]

High‐efficient fabrication of well‐ordered nanostructures on flexible substrates is a challenge to surface‐enhanced Raman spectroscopy (SERS) for analytical fingerprinting trace‐detection. In this work, a laser parallel nanofabrication method is reported via incident‐angle‐dependent photonic nanojet ablating Au film on the bottom surface of microsphere‐lens‐array (MLA), for combination with formed dual Au‐nanoholes (MLA/2‐AuNHs) as the flexible SERS substrates. The process parameters, i.e., pulsed laser energy, MLA diameter, Au film thickness, and laser incident angle, are optimized for high finish‐quality of dual‐AuNHs with a diameter of ≈875 nm and a tip gap of ≈90 nm. The SERS substrate demonstrates the limit of detection down to 10−11 M for 4‐nitrobenzenethiol molecules by the multiple optical regulations, including self‐aligned focusing to the hotspots and directional antenna, the strongly localized surface plasmon resonances, and optical whispering‐gallery modes for resonance energy transfer. The flexible PDMS film supporting the rigid MLA holds the SERS performance of MLA/2‐AuNHs with high flexibility. Moreover, the MLA/2‐AuNHs SERS substrate exhibits differential responses to orthogonally polarized excitation, by which the background noises can be eliminated to improve the Raman spectrum. The present work opens new opportunities to fabricate dielectric‐metal flexible SERS substrates by laser parallel nanofabrication via MLA for Raman trace detection. [ABSTRACT FROM AUTHOR]

Although optical microscopy is a widely used technique across various multidisciplinary fields for inspecting small-scale objects, surfaces or organisms, it faces a significant limitation: the lateral resolution of optical microscopes is fundamentally constrained by light diffraction. Dielectric micro-spheres, however, offer a promising solution to this issue as they are capable of significantly enhancing lateral resolution through extraordinary phenomena, such as a photonic nanojet.Building upon the potential of dielectric micro-spheres, this paper introduces a novel approach for fabricating 3D micro-devices designed to enhance lateral resolution in optical microscopy. The proposed 3D micro-device comprises a modified coverslip and a micro-sphere, facilitating easy handling and integration into any existing optical microscope. To manufacture the device, two advanced femtosecond laser techniques are employed: femtosecond laser ablation and multi-photon lithography. Femtosecond laser ablation was employed to create a micro-hole in the coverslip, which allows light to be focused through this aperture. Multi-photon lithography was used to fabricate a micro-sphere with a diameter of 20 µm, along with a cantilever that positions the above the processed micro-hole and connect it with the coverslip. In this context, advanced processing strategies for multi-photon lithography to produce a micro-sphere with superior surface roughness and almost perfect geometry (λ/8) from a Zr-based hybrid photoresist are demonstrated. The performance of the micro-device was evaluated using Mirau-type coherence scanning interferometry in conjunction with white light illumination at a central wavelength of 600 nm and a calibration grid (Λ = 0.28 µm, h > 50 nm). Here, the 3D micro-device proved to be capable of enhancing lateral resolution beyond the limits achievable with conventional lenses or microscope objectives when used in air. Simultaneously, it maintained the high axial resolution characteristic of Mirau-type coherence scanning interferometry. The results and optical properties of the micro-sphere were analyzed and further discussed through simulations.

Silica-on-silicon is a major optical integration platform, while the emergent class of the integrated laser-written circuits' platform offers additionally high customizability and flexibility for rapid prototyping. However, the inherent waveguides' low core/cladding refractive index contrast characteristic, compared to other photonic platforms in silicon or silicon nitride, sets serious limitations for on-chip efficient coupling with single photon emitters, like semiconductor nanowires with quantum dots, limiting the applications in quantum computing. A new light coupling scheme proposed here overcomes this limitation, providing means for light coupling >50%. The scheme is based on the incorporation of an optical microsphere between the nanowire and the waveguide, which is properly optimized and arranged in terms of size, refractive index, and the distance of the microsphere between the nanowire and waveguide. Upon suitable design of the optical arrangement, the photonic nanojet emitted by the illuminated microsphere excites efficiently the guided eigenmodes of the input channel waveguide, thus launching light with high-coupling efficiency. The method is tolerant in displacements, misalignments, and imperfections and is fabricationally feasible by the current state of art techniques. The proposed method enables the on-chip multiple single photon emitters' integration, thus allowing for the development of highly customizable and scalable quantum photonic-integrated circuits for quantum computing and communications. [ABSTRACT FROM AUTHOR]

A dielectric microsphere concentrates light into a photonic nanojet (PNJ), and swims towards the near-infrared laser in response to the nanojet-mediated force. In contrast, a Janus particle with an opaque metal layer was thought to be impossible to concentrate light into a stable nanojet. However, the Janus particle may experience optical torque owing to the inhomogeneous composition on both sides even in linearly polarized non-resonant light. Herein, we report on topologically protected PNJ produced by a synthetic Janus particle, and observed the backaction force on the Janus particle. Due to symmetry, the counter-propagating beams can both form PNJ on the respective opposite sides, and pull Janus particles towards respective sources. Furthermore, we unveil that the hysteresis on backaction force with respect to the injection power also exists on synthetic Janus particle compared with their dielectric counterparts. Additionally, the magnitude of the backaction force varies between power increase and decrease stages even with the same laser power. We anticipate that the observation offers great possibilities to pull irregular particles by concentrating light with the particle, and such scheme may be applied for parallel particle manipulation and classification.

Three-dimensional micro- and submicrometer-scale structures exhibit unique functions that cannot be obtained with bulk materials. To create such three-dimensional microstructures with high precision and efficiency, we proposed laser ablation using a photonic nanojet. A photonic nanojet is an optical beam with both a small beam diameter and a large depth of focus, which is obtained by irradiating a dielectric microsphere using a laser beam. In this study, we proposed an in-process depth measurement method to improve the machining accuracy of laser ablation using a photonic nanojet. We focused on the propagation characteristics of the shock waves generated during laser ablation. Shock waves were generated at the deepest point of the machining area and reached the microspheres as the pressure decayed, showing that different machining depths exerted different pressures on the microspheres. The microspheres were displaced by the pressure of the shock wave, and the amount of displacement depended on the pressure. Therefore, microspheres can be used as probes for shock wave detection, and the machining depth can be determined by measuring the displacement of microspheres during photonic nanojet machining. In this study, the displacement of a microsphere was measured simultaneously during photonic nanojet machining using a confocal optical system. From the obtained microsphere vibration data, the effect of the shock wave pressure was extracted, and the displacement of the microsphere due to the shock wave was obtained. When the hole depth varied from 155 to 1121 nm, the displacement of the microspheres varied from 0.58 to 0.03 µm. The experimental results show that the displacement of the microspheres vibrated by the shock wave decreased as the machining depth increased. This was due to an increase in the shock wave propagation distance and a decrease in the pressure of the shock wave as the machining depth increased. In conclusion, in-process depth measurements are possible in laser ablation using a photonic nanojet with a microsphere as a probe to detect shock waves. [ABSTRACT FROM AUTHOR]

Results of numerical simulations of optical radiation focusing by a cluster of identical nanospheres close packed into a spherical volume (a "metaparticle") are presented. Parameters of the focal region (intensity and longitudinal and transverse sizes) formed by metaparticles with different internal structure are calculated. It is shown that the problem of optical radiation focusing by a spherical cluster of nanoparticles can be reduced in certain cases to the problem of light focusing by a homogeneous spherical particle with an effective refractive index derived from the effective medium theory. Moreover, certain spherical cluster topologies make it possible to improve optical focusing in the near-field region, in particular, to increase the peak intensity or enhance its spatial localization. [ABSTRACT FROM AUTHOR]

All naturally found and technologically fabricated solid microparticles possess surface roughness. Upon optical wave scattering from such particles, in addition to its geometric shape, the surface relief becomes an important morphological factor determining the optical properties of the scatterer. We present results of the numerical 3D-simulations of focusing an optical wave with a dielectric microsphere with randomly distributed surface roughness. We address different cases of azimuthally symmetric and asymmetric distortions of the particle surface. We show that the key parameters of the near-field focal region (intensity, longitudinal and transverse dimensions) referred to as a photonic nanojet (PNJ) are sensitive to changes in the microsphere surface texture. Two important PNJ parameters, the peak intensity and the longitudinal length, are subject to more prominent changes. The influence of the optical contrast (relative refractive index) of the microsphere on PNJ parameters is investigated in detail. The possibility of reducing the influence of surface roughness on the near-field focusing strength by microsphere watering (water-uptake) is demonstrated.

We present a microsphere-based microsensor that can measure the vibrations of the miniature motor shaft (MMS) in a small space. The microsensor is composed of a stretched fiber and a microsphere with a diameter of 5 μm. When a light source is incident on the microsphere surface, the microsphere induces the phenomenon of photonic nanojet (PNJ), which causes light to pass through the front. The PNJ's full width at half maximum is narrow, surpassing the diffraction limit, enables precise focusing on the MMS surface, and enhances the scattered or reflected light emitted from the MMS surface. With two of the proposed microsensors, the axial and radial vibration of the MMS are measured simultaneously. The performance of the microsensor has been calibrated with a standard vibration source, demonstrating measurement errors of less than 1.5%. The microsensor is expected to be used in a confined space for the vibration measurement of miniature motors in industry. [ABSTRACT FROM AUTHOR]

The focusing of laser radiation with triangular dielectric prisms has been numerically studied using the finite element method implemented in the COMSOL Multiphysics software package. It has been shown that two-dimensional triangular prisms make it possible to focus light in free space into spots smaller than the scalar diffraction limit. For example, a quartz glass prism with a base width of 60 μm and a height of 28.5 μm illuminated by light with a wavelength of 4 μm produces a photonic nanojet with the maximum intensity that exceeds the incident radiation intensity by a factor of 6 and has a full width at half maximum of 0.38 of the focused radiation wavelength. The focal spot size can be decreased by selecting the height of the prism so as to the maximum intensity was located inside it. In particular, a barium titanate prism with a height of 21 μm and a base width of 60 μm forms a focal spot directly behind its apex with a width at half maximum equal to 0.25 of the focused radiation wavelength. It has been shown that the use of a prism weakens the wavelength dependence of the focal spot width as compared with the case of a microcylinder. In particular, for a quartz glass microcylinder 60 μm in diameter, a change in the wavelength from 3 to 5 μm leads to the spot width variation by 0.09 of the focused radiation wavelength, while for a prism, by 0.05 of the focused radiation wavelength on average. [ABSTRACT FROM AUTHOR]

All naturally found and man-made solid microparticles have a rough surface. Upon optical radiation scattering from such particles, in addition to geometric shape, the surface texture becomes an important morphological factor of the scatterer that determines its optical properties. We present the results of numerical FDTD simulation of an optical-wave focusing by a dielectric microsphere with a randomly distributed surface roughness. The cases of azimuthally symmetric and asymmetric distortions of the particle surface are analyzed. It is demonstrated that the key parameters of the near-field focal region (intensity, longitudinal and transverse dimensions, focal distance) referred to as the photonic nanojet (PNJ) turn out to be sensitive to changes in the sphere-surface texture. In the process, two parameters, the peak intensity of the PNJ and its length, experience the largest changes. The influence of the optical contrast (the relative refractive index) of the microsphere that scatters radiation on PNJ characteristics is analyzed, and the possibility of reducing the influence of surface roughness on the quality of the near-field focusing by means of microsphere watering (water-uptake) is demonstrated. [ABSTRACT FROM AUTHOR]

Silica-on-silicon is a major optical integration platform, while the emergent class of the integrated laser-written circuits’ platform offers additionally high customizability and flexibility for rapid prototyping. However, the inherent waveguides’ low core/cladding refractive index contrast characteristic, compared to other photonic platforms in silicon or silicon nitride, sets serious limitations for on-chip efficient coupling with single photon emitters, like semiconductor nanowires with quantum dots, limiting the applications in quantum computing. A new light coupling scheme proposed here overcomes this limitation, providing means for light coupling >50%. The scheme is based on the incorporation of an optical microsphere between the nanowire and the waveguide, which is properly optimized and arranged in terms of size, refractive index, and the distance of the microsphere between the nanowire and waveguide. Upon suitable design of the optical arrangement, the photonic nanojet emitted by the illuminated microsphere excites efficiently the guided eigenmodes of the input channel waveguide, thus launching light with high-coupling efficiency. The method is tolerant in displacements, misalignments, and imperfections and is fabricationally feasible by the current state of art techniques. The proposed method enables the on-chip multiple single photon emitters’ integration, thus allowing for the development of highly customizable and scalable quantum photonic-integrated circuits for quantum computing and communications.

Dielectric microspheres naturally possess unique optical properties by which the light's focus and confinement can be manipulated on a microscale. Combining microspheres and optical or Raman microscopy, super‐resolution imaging beyond the diffraction limit and enhancement of Raman signals are demonstrated to provide abundant spectroscopic information on materials. However, microsphere‐aided super‐resolution scanning photocurrent imaging remains challenging to date. Here, based on the photonic nanojet mechanism, a super‐resolution photocurrent and spectral microscopy equipped with a scanning tip with silica dielectric microspheres are presented. With such microsphere‐aided microscopy, order of magnitude enhancements for single‐point Raman and photoluminescence signals can be achieved, and the spatial resolutions for photocurrent and spectral mapping surpass the best resolution of the original confocal system restricted by the diffraction limit. This versatile system enables correlative super‐resolution spectral and photocurrent imaging, serving as a reliable tool for comprehensively understanding and uncovering the optoelectronic properties of materials. [ABSTRACT FROM AUTHOR]

Photonic nanojets (PNJs) have been used successfully in super-resolution imaging and optical intensity enhancement benefitting from their sub-wavelength beam waists and high intensity. Herein, we introduce a method to further enhance the intensity of PNJs through adding a mirror. About 4 times enhancement factor can be achieved by appropriately selecting the gap length between the cylinder, which generates the PNJ under a TE polarized plane wave illumination, and the mirror. The intensity distributions of the PNJs can be modulated by changing the gap length. Our simulation shows that the full width at half maximum (FWHM) of the beam waist of the enhanced PNJ can reach less than λ/2nb (nb, the refractive index of the surrounding medium) with the illumination at 638 nm, when the refractive index of the cylinder is carefully chosen. Finally, we demonstrate that the added mirror can also work in TM and circular polarized illuminations. Our results are of interest for various applications in nanoparticle manipulation and optical nonlinear enhancement. [ABSTRACT FROM AUTHOR]

Using a finite-difference time-domain method, it has been shown that focal spots generated when tightly focusing a linearly polarized Gaussian beam by a Fresnel zone plate (FZP) and when focusing a Gaussian beam with an embedded optical vortex by a spiral zone plate (SZP) have different patterns of the intensity and energy flux. The most significant differences are observed when the value of the topological charge (TC) is equal to three. The energy flux has an annular distribution when the Gaussian beam is focused by the FZP, while the SZP produces a field whose patterns of intensity and energy flux have three local maxima. The number of local maxima corresponds to the order of the SZP. At a certain distance from the focus, the petal structure of the intensity (and energy flux) changes to a ring distribution.

Reversible control over the microparticle motion using light excites interesting applications in optofluidics, microswimmers, artificial optical matter, and biomedical engineering. The dielectric microspheres swim towards the near infrared pulsed laser in response to the backaction force mediated by photonic nanojet. Hereby, we report that the backaction force exhibits hysteretic behaviour owing to the distinguishable responses of the temperature rise inside the nanojet and the temperature rise of the liquid ensemble. Accordingly, the magnitude of backaction force at the same laser power varies between power increase and decrease stages. In order to develop multidimensional manipulation tool, we studied the possibility of using lasers with different spatiotemporal profiles to mediate the backaction force, and developed the counterpropagating beam scheme for reversible control of the particle motion directions. We further harness the hysteresis to reverse the direction of backaction force on dielectric particles in presence of a constant force from a counter-propagating beam with broadband supercontinuum spectrum. In contrast to the microsphere caught in the single beam gradient trap, the microsphere encounters augmented Brownian motion at higher balanced power level. The microsphere would eventually escape from the common region of the paired beams, enabling high throughput morphology analysis for cancer cell classification, biopsy, and diagnosis.

In this study, we propose a novel design of triangular mesoscale Janus prisms for the generation of the long photonic hook. Numerical simulations based on the finite-difference time-domain method are used to examine the formation mechanism of the photonic hook. The electric intensity distributions near the micro-prisms are calculated for operation at different refractive indices and spaces of the two triangular micro-prisms. The asymmetric vortices of intensity distributions result in a long photonic hook with a large bending angle. The length and the bending angle of the photonic hook are efficiently modulated by changing the space between the two triangular micro-prisms. Moreover, the narrow width of the photonic hook is achieved beyond the diffraction limit. The triangular Janus micro-prisms have high potential for practical applications in optical tweezers, nanoparticle sorting and manipulation and photonic circuits. [ABSTRACT FROM AUTHOR]

We present a microsphere-based microsensor that can measure the vibrations of the miniature motor shaft (MMS) in a small space. The microsensor is composed of a stretched fiber and a microsphere with a diameter of 5 μm. When a light source is incident on the microsphere surface, the microsphere induces the phenomenon of photonic nanojet (PNJ), which causes light to pass through the front. The PNJ’s full width at half maximum is narrow, surpassing the diffraction limit, enables precise focusing on the MMS surface, and enhances the scattered or reflected light emitted from the MMS surface. With two of the proposed microsensors, the axial and radial vibration of the MMS are measured simultaneously. The performance of the microsensor has been calibrated with a standard vibration source, demonstrating measurement errors of less than 1.5%. The microsensor is expected to be used in a confined space for the vibration measurement of miniature motors in industry.

In this study, acoustic wave scattering in a homogeneous media by an obstacle is examined in the case of plane wave excitation and the formation of acoustic jets is explored. Spectral element method (SEM) is employed for the approximate solution of scattered acoustic waves' calculations. An important finding of the study is the concurrence of whispering gallery modes and acoustic jet in the case of proper adjustment of structural parameters, which has not been reported before in the literature. Furthermore, numerical findings based on SEM calculations show that the main characteristics of acoustic jet can be explored and controlled by changing the targeted parameters. Microscopy and imaging applications utilizing acoustic wave can benefit from the conducted study presented in this manuscript. [ABSTRACT FROM AUTHOR]

Photonic hook (PH) is a new type of non-evanescent light beam with subwavelength curved structures. It has shown promising applications in super-resolution imaging and has the potential to be used in micromachining, optical trapping, etc. PHs are generally produced by illuminating mesoscale asymmetric particles with optical plane waves. In this work, we used the finite-difference time-domain (FDTD) method to investigate the PH phenomenon under point-source illumination. We found that the PHs can be effectively generated from point-source illuminated patchy particles. By changing the background refractive index, particle diameters and the position and coverage ratio of Ag patches, the characteristics of the PHs can be effectively tuned. Moreover, the structure of the intensity distribution of the light field generated from small and large particles can have an opposite bending direction due to the near-field light-matter interaction. [ABSTRACT FROM AUTHOR]

The addition of dielectric transparent microlens in the optical scheme is an effective and at the same time simple and inexpensive way to increase the resolution of a light microscope. For these purposes, spherical and cylindrical microlenses with a diameter of 1–100 μm are usually used. The microlens focuses the light into a narrow beam called a photonic nanojet. An enlarged virtual image is formed, which is captured by the objective of the light microscope. In addition to microscopy, the microlenses are successfully applied to amplify optical signals, increase the trapping force of optical tweezers and are used in microsurgery. This review considers the design and principle of microlens‐assisted microscopes. Taking into account the advantages of the super‐resolution optical methods for research in life science, the examples of the use of the microlenses in biomedical practice are discussed in detail. [ABSTRACT FROM AUTHOR]

The size parameter q = 2πR/λ in spheres with a radius R = (2–3)λ (λ is the radiation wavelength) is on the order of 10. Strong Mie resonances () are observed in these structures; these resonances lead to peculiar optical phenomena, caused by the interference of high-order multipoles and localization of magnetic fields. Examples of such optical phenomena are presented in this review. [ABSTRACT FROM AUTHOR]

Focusing of a linearly polarized laser beam of wavelength 633 nm with two-layer dielectric microcylinders of a circular cross-section and 2-um diameter was simulated using a finite-difference time-domain (FDTD) method, implemented using the FullWAVE software. It was shown that using a cladding whose refractive index (1.8 or 1.9) is higher than that of the core (1.45), it is possible to increase the depth of focus by a factor of 2.57 multiplied by the incident wavelength and shift the focal spot position along the optical axis away from the microcylinder boundary. It was also shown that parameters of the microcylinder could be chosen in such a way that a tighter focal spot was generated, with its full width at half maximum of intensity being 2.27 of the incident wavelength. The intensity at this focus was shown to be 1.4 times higher than that at the focus generated with a homogeneous microcylinder.

A photonic nanojet (PNJ) from a microcavity is a narrow and intense beam of light used to enhance the emerging electric field. Metal nanoparticles (NPs), on the other hand, confine a strong field in their vicinity due to the resonance of the free electrons with the incident field. A hybrid combination of a microcavity with a NP can drastically enhance the output field. In this work, a systematic numerical study of the microcavity-NP system has been carried out to investigate the effect of the shape of the metal NPs on the output field strength. The single and their dimer NPs with different dimer nanogaps with PNJ producing microcavity have been investigated. Splitting of the broad dipole mode of the NP has also been observed. As an application of this study, the surface enhanced Raman spectroscopy factor of the order of 107 has been estimated for nano-cube dimer NP-microcavity hybrid system. [ABSTRACT FROM AUTHOR]

A photonic nanojet (PNJ) is a highly confined light beam that focuses from the shadow side of microparticles. In $46.47\lambda $this work, we propose a PNJ with ultrahigh quality factor formed by dielectric truncated microtoroid. The key properties of PNJ, such as the maximum intensity, the length of PNJ, the full-width at half maximum (FWHM), are studied in detail using finite-difference time-domain (FDTD) analysis. The results show that a PNJ with an enhanced intensity of 55.21 times to the incident light, superlong length of $46.47\lambda $ and subwavelength FWHM of $0.77\lambda $ is formed by semi-microtoroid, thus, an ultrahigh quality factor of 3308.68 is achieved. More importantly, the properties of the PNJ are tunable by changing the truncated proportions of the microtoroid. The structure we proposed has the advantages of compact structure and simple experimental operation, which is expected to apply in many research fields, including optical detection, optical data storage, super-resolution image, nanopattern, nanolithography, and so on.

Using the finite difference method implemented in the COMSOL Multiphysics software package, the focusing of laser radiation by dielectric prisms with a triangular profile was numerically investigated. It was shown that two-dimensional triangular prisms make it possible to focus light in free space into spots with dimensions smaller than the scalar diffraction limit. In particular, a silica glass prism with a base width of 60 μm and a height of 28.5 μm forms a photonic nanojet with a maximum intensity of 6 times the intensity of the incident radiation and a width of FWHM=0.38λ. A prism from barium titanate with a base width of 60 μm and a height of 20 μm allows to obtain a photonic nanojet with the same width (0.38λ) and a maximum intensity 5 times the intensity of the incident radiation. The size of the focal spot can be reduced further if the height of the prism is selected so that the maximum intensity is located inside the material of the prism. For example, a barium titanate prism with a height of 21 μm and a base width of 60 μm forms a focal spot with a width of FWHM=0.25λ.

A photonic nanojet (PNJ) is a high intensity light beam that has beam diameter of sub-micrometers and depth of focus of several micrometers. In order to improve the accuracy and resolution of laser ablation using a PNJ, a shock wave generated in laser ablation was focused on. The shock wave pressure depends on the distance from sample surface and the shape of the surface. Thus, detection of the shock wave makes it possible to estimate the processing state. The confocal system made it possible to detect the shock wave via the vibration of the microsphere. The vibration signals in the time domain were Fourier transformed in the frequency domain. After the laser irradiation, there was a frequency peak that was not seen before the laser irradiation. Therefore, it was demonstrated that the shock wave generated by laser ablation could be detected from the vibration of the microsphere.

In this study, we propose a novel design of triangular mesoscale Janus prisms for the generation of the long photonic hook. Numerical simulations based on the finite-difference time-domain method are used to examine the formation mechanism of the photonic hook. The electric intensity distributions near the micro-prisms are calculated for operation at different refractive indices and spaces of the two triangular micro-prisms. The asymmetric vortices of intensity distributions result in a long photonic hook with a large bending angle. The length and the bending angle of the photonic hook are efficiently modulated by changing the space between the two triangular micro-prisms. Moreover, the narrow width of the photonic hook is achieved beyond the diffraction limit. The triangular Janus micro-prisms have high potential for practical applications in optical tweezers, nanoparticle sorting and manipulation and photonic circuits.

We report on the effects associated with photonic nanojet (PNJ) formation under illumination of a metallic spherical particle with a focused light beam with polarization singularity. Owing to radial polarization, the strongly focused beam generates the on-axis localized structure of intensity in the shadow area of the metal scatterer of different sizes, from the Rayleigh particle to microbeads. Significant amplification factor, small transverse size, and zero magnetic component on the axis and longitudinal polarization of the electric field are the distinctive features of such structures.

Photonic hook (PH) is a new type of non-evanescent light beam with subwavelength curved structures. It has shown promising applications in super-resolution imaging and has the potential to be used in micromachining, optical trapping, etc. PHs are generally produced by illuminating mesoscale asymmetric particles with optical plane waves. In this work, we used the finite-difference time-domain (FDTD) method to investigate the PH phenomenon under point-source illumination. We found that the PHs can be effectively generated from point-source illuminated patchy particles. By changing the background refractive index, particle diameters and the position and coverage ratio of Ag patches, the characteristics of the PHs can be effectively tuned. Moreover, the structure of the intensity distribution of the light field generated from small and large particles can have an opposite bending direction due to the near-field light-matter interaction.

In this study, acoustic wave scattering in a homogeneous media by an obstacle is examined in the case of plane wave excitation and the formation of acoustic jets is explored. Spectral element method (SEM) is employed for the approximate solution of scattered acoustic waves’ calculations. An important finding of the study is the concurrence of whispering gallery modes and acoustic jet in the case of proper adjustment of structural parameters, which has not been reported before in the literature. Furthermore, numerical findings based on SEM calculations show that the main characteristics of acoustic jet can be explored and controlled by changing the targeted parameters. Microscopy and imaging applications utilizing acoustic wave can benefit from the conducted study presented in this manuscript.

The photonic nanojet (PNJ) produced by a vector Bessel beam irradiating a dielectric spheroidal particle is investigated using the Discrete Dipole Approximation. The influence of the beam center, beam order, beam polarization type, and half cone angle of the vector Bessel beam on the characteristics of PNJ is analyzed. Several characteristics of PNJ including maximum intensity, the focal length, the effective length, and full width at half maximum are considered. The results show that the characteristics of the PNJ can be controlled by changing the four parameters of the Bessel beam. We think it will help to enhance the application of Bessel beams in generating PNJ and provide new properties to generate PNJ.

In the recent period of the miniaturization of devices, there has been a high demand for high-resolution, flexible, and fast machining technique to accommodate high production volumes. Conventional laser machining with a focused laser beam has been widely used to fabricate small devices for various applications. However, this process is limited by the optical diffraction limit of the laser beam. Therefore, the photonic nanojet (PNJ) machining technique is a promising solution to tackle this problem. This technique is based on the near-field focusing of light waves with a high-energy laser power below the surface of an irradiated dielectric microsphere. We introduce water as a medium in the proposed PNJ machining technique so that the pattern could be fabricated more efficiently, faster, and with better quality. We evaluate the characteristics of the generated PNJ in water; further, we estimate the PNJ machining results numerically using the FDTD method and confirm them experimentally. To the best of our knowledge, this is the first ever to do so. All the holes obtained from the PNJ machining experiment were consistently in the sub-micrometer order and below the optical diffraction limit value of the constructed setup. [ABSTRACT FROM AUTHOR]

Spatial resolution of conventional optics, which is necessary for nondestructive trapping of microobjects, is limited by diffraction to a value equal to half of the radiation wavelength. Despite this limitation, use of optical methods is one of the main directions in biological and biomedical researches because only these methods have a minimal impact on living organisms. The rapid advance in this area is largely owing to the development of new optical technologies and the considerable advance in mesoscale photonics, which has allowed researchers to develop techniques for controlling structured beams for optical traps. In this work, we consider some recent trends in the field of optical manipulation based on mesoscale dielectric particles. [ABSTRACT FROM AUTHOR]

Microsphere-assisted microscopy serves as an effective super-resolution technique in biological observations and nanostructure detections, and optical trapping is widely used for the manipulation of small particles like microspheres. In this study, we focus on the selection of microsphere types for the combination of the optical trapping and the super-resolution microsphere-assisted microscopy, by considering the optical trapping performances and the super-resolution imaging ability of index-different microspheres in water simultaneously. Finally, the polystyrene (PS) sphere and the melamine formaldehyde (MF) sphere have been selected from four typical index-different microspheres normally used in microsphere-assisted microscopy. In experiments, the optically trapped PS/MF microsphere in water has been used to achieve super-resolution imaging of a 139 nm line-width silicon nanostructure grating under white light illumination. The image quality and the magnification factor are affected by the refractive index contrast between the microspheres and the immersion medium, and the difference of image quality is partly explained by the photonic nanojet. This work guides us in selecting proper microspheres, and also provides a label-free super-resolution imaging technique in many research fields. [ABSTRACT FROM AUTHOR]

A new method for enhancing the Raman scattering signal has emerged recently, based on dielectric enhancement. Especially promising is the dielectric method based on microspheres and photonic nanojet. In this paper, geometrical aspects and the influence of the incident beam parameters on Raman enhancement by silica microspheres were systematically investigated in three steps: by characterizing the incident beam using knife‐edge method, performing horizontal and vertical Raman mapping imaging, and analyzing the results using ray transfer matrix analysis. Maps show a distinct enhancement (hotspot) area caused by the microsphere photonic nanojet and lens effect compared to a plain silicon substrate. Enhancement value on maps was the highest (5.7×) for 0.50 numerical aperture objective, when the incident beam size matched the microsphere diameter, and the focus of the incident beam was below the top of the sphere, so that the output beam focus was at the microsphere–substrate contact area. This geometrical configuration was confirmed as ideal by performing simple ray transfer matrix analysis. The ideal ranges of incident and output beam parameters match with the measured hotspot area. This three‐step process and the usage of vertical Raman mapping have been, for the best of our knowledge, performed for the first time in such configuration. This research introduces a new way of investigating microsphere‐assisted Raman enhancement, offers different approach to microsphere optics research, and improves current knowledge of the influence of the incident beam on the enhancement. [ABSTRACT FROM AUTHOR]

In this paper, synthetically using refraction, diffraction, and interference effects to achieve free manipulation of the focused optical field, we firstly present a photonic nanojet (PNJ) generated by a micropyramid, which is combined with multilayer thin films. The theory of total internal reflection (TIR) was creatively used to design the base angle of the micropyramid, and the size parameters and material properties of the microstructure were deduced via the expected optical field distribution. The as-designed bilayer micropyramid array was fabricated by using the single-point diamond turning (SPDT) technique, nanoimprint lithography (NIL), and proportional inductively coupled plasma (ICP) etching. After the investigation, the results of optical field measurement were highly consistent with those of the numerical simulation, and they were both within the theoretical calculation range. The bilayer micropyramid array PNJ enhanced the interference effect of incident and scattered fields; thus, the intensity of the focused light field reached 33.8-times that of the initial light, and the range of the focused light field was extended to 10.08λ. Moreover, the full width at half maximum (FWHM) of the focal spot achieved was 0.6λ, which was close to the diffraction limit.

The photonic nanojet is a non-resonance focusing phenomenon with high intensity and narrow spot that can serve as a powerful biosensor for in vivo detection of red blood cells, micro-organisms, and tumor cells in blood. In this study, we first demonstrated photonic nanojet modulation by utilizing a spider-silk-based metal–dielectric dome microlens. A cellar spider was employed in extracting the silk fiber, which possesses a liquid-collecting ability to form a dielectric dome microlens. The metal casing on the surface of the dielectric dome was coated by using a glancing angle deposition technique. Due to the nature of surface plasmon polaritons, the characteristics of photonic nanojets are strongly modulated by different metal casings. Numerical and experimental results showed that the intensity of the photonic nanojet was increased by a factor of three for the gold-coated dome microlens due to surface plasmon resonance. The spider-silk-based metal-dielectric dome microlens could be used to scan a biological target for large-area imaging with a conventional optical microscope.

A photonic nanojet (PNJ) is a fine light beam generated from a dielectric microsphere or microcylinder illuminated by a laser and has been applied to nanometer scale measurement and machining. In this study, we attempt to control the PNJ intensity distribution flexibly by adjusting the intensity distribution of two incident laser beams: a Gaussian beam and a radially polarized beam. Then, finite-difference time-domain simulations demonstrated that a large PNJ beam diameter (1.08 λ) could be obtained by Gaussian beam with a small beam radius, whereas a small PNJ beam diameter (0.34 λ) could be obtained by radially polarized beam. Moreover, PNJ with isotropic intensity distribution can be obtained as well as a small PNJ beam diameter by a radially polarized beam incidence to a microsphere. • Incident intensity distribution can control photonic nanojet intensity distribution. • Focusing characteristics of microsphere depend on the incident position of light. • Larger PNJ beam diameter can be obtained by Gaussian beam incidence. • Smaller PNJ beam diameter can be obtained by radially polarized beam incidence. [ABSTRACT FROM AUTHOR]

Highlights • 3-d scattering simulations show particles emit electromagnetic energy pulses. • Simple 2-d models are constructed to explore pulse phenomenology. • Simulations show internal travelling wave packets, often with near-surface amplitude maximum. • Packets emit pulses when they coalesce or encounter surface regions of high curvature. • "wave packets" are connected to a deep, highly structured time-evolving internal field. Abstract During the decay phase of the interaction of a femto-second Gaussian pulse with a single spherical particle, the presence of quasi-periodic short oscillatory bursts of electromagnetic energy at points in the near field outside the particle have been observed in three-dimensional simulations. Analogous behavior can be very easy produced and understood in simple one-dimensional scattering calculations. In two dimensions the situation immediately becomes more complicated and interesting. Here we discuss results from two-dimensional pseudo-spectral time-domain simulations of scattering from circular, elliptical, and hexagonal particles with the real index of refraction m = 1.3. Our focus is on how energy initially trapped within a particle after interaction with an incident Gaussian pulse is released over time, and we show two kinds of events that can result in "bursts" of energy release from the particles: (i) the coalescence of counter-propagating wave-packet-like electromagnetic field structures that have maximum amplitude near the surface of the particle, and (ii) encounters of individual packets with surface regions of high curvature. The coalescence events in the circular case show the dynamical origin of a two-dimensional form of "photonic nanojet." The two-dimensional simulations make clear the reason for quasi-periodic intermittent bursts at fixed near-field points outside the particle. Examination of field evolution shows that distinct near-surface internal field maxima, ostensibly the "source" of the emission bursts, are in fact inter-connected by caustic-like internal field structures that extend throughout the particle and have complex time evolution. The revealed intricacy of these connections suggests that understanding the origins of pulsed emissions in three dimensions, even for simple particle geometries, may be quite challenging. [ABSTRACT FROM AUTHOR]

The results of theoretical studies of spatially localized near-field light structures (photonic nanojets) formed when laser radiation is scattered on a meta-surface having the form of an ordered single-layer assembly of dielectric microparticles (spheres, cones) embedded in a transparent matrix (silicone film) are presented. The behavior of the main parameters of the localized light structures (length, width, and peak intensity) under the effects of light fields of neighboring microparticles is thoroughly analyzed by using computational electrodynamics to solve Maxwell's equations with the finite-difference time-domain method (FDTD). It is ascertained that the main factors which affect the parameters of photonic nanojets under study are the spatial orientation of the microcones and the depth of their immersion in the silicone matrix. It is shown that several spatial configurations of the microassembly of the cones allow the creation of an ensemble of photonic nanojets with specific parameters, which are unattainable for isolated microcones. Ordered clusters of spherical particles have an advantage in terms of a comprehensive assessment of the parameters of photonic nanojets. [ABSTRACT FROM AUTHOR]

The effect of photonic nanojets (PNJ) in the scattering near field nearby the surface of dielectric axisymmetric microparticles (hemisphere, axicon, and combined particles) under optical illumination is theoretically considered. Key PNJ parameters (length, width, and peak intensity) are calculated using the discrete-dipole approximation; the dependence of these parameters on the geometric shape of microparticles is analyzed. We show that the use of a special type of combined transparent particle, which consists of an axicon and two attached hemispheres, can produce ultralocalized light fluxes with a peak intensity which considerably exceeds the corresponding values for simple particles (hemisphere and axicon). [ABSTRACT FROM AUTHOR]

The photonic nanojet phenomenon is commonly used both to increase the resolution of optical microscopes and to trap nanoparticles. However, such photonic nanojets are not applicable to an entire class of objects. Here we present a new type of photonic nanojet in reflection mode with the possibility to control the modulation of the photonic nanojet by a standing wave. In contrast to the known kinds of reflective photonic nanojets, the reported one occurs when the aluminum oxide hemisphere is located at a certain distance from the substrate. Under illumination, the hemisphere generates a primary photonic nanojet directed to the substrate. After reflection, the primary nanojet acts as an illumination source for the hemisphere, leading to the formation of a new reflective photonic nanojet. We show that the distance between the hemisphere and substrate affects the phase of both incident and reflected radiation, and due to constructive interference, the modulation of the reflective photonic nanojet by a standing wave can be significantly reduced. The results obtained contribute to the understanding of the processes of photonic nanojet formation in reflection mode and open new pathways for designing functional optical devices.

Near-field focusing of an optical wave by nanoparticle clusters aggregated into a globule (a "metaparticle") is considered for different nanoparticle concentration, size and optical properties. Our numerical simulations show that the self-assembly of spherical nanoparticles into a globular photonic structure can also produce the focal regions of enhanced optical intensity existing in the spatial form of a photonic nanojet (PNJ). A detailed study of all significant PNJ parameters depending on the cluster topology and optical properties of the nanostructure filling is carried out. We determine the conditions when it is possible conditional substitution the nanoparticle cluster by a homogeneous microsphere with the same geometrical dimensions but with some effective refractive index. Besides, we show that in some cases the globular nanosphere clusters is able to produce a PNJ with improved parameters, particularly, with higher spatial localization and increased intensity. [ABSTRACT FROM AUTHOR]