Direct imaging of photonic nanojets (original) (raw)
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Optics Express, 2011
Photonic Nanojets are highly localized wave fields emerging directly behind dielectric microspheres; if suitably illuminated. In this contribution we reveal how different illumination conditions can be used to engineer the photonic Nanojets by measuring them in amplitude and phase with a high resolution interference microscope. We investigate how the wavelength, the amplitude distribution of the illumination, its polarization, or a break in symmetry of the axial-symmetric structure and the illumination affect the position, the localization and the shape of the photonic Nanojets. Various fascinating properties are systematically revealed and their implications for possible applications are discussed.
Journal of the Optical Society of America A, 2005
The detailed optics of photonic nanojets generated by normal plane-wave incidence on dielectric cylinders is discussed. These nanojets have a subwavelength beam waist and propagate with little divergence for several wavelengths. A physical explanation for this peculiar behavior is presented. Characteristic dimensions of the nanojets for a large range of physical parameters are calculated.
Integrated Optics: Devices, Materials, and Technologies XV, 2011
We experimentally engineer Nanojets produced by dielectric spheres by varying the illumination and observe the effect with a high-resolution interference microscope (HRIM). Converging and diverging spherical wavefronts and Bessel-Gauss beams are considered. We find that the diverging wavefront pushes Nanojets away from the surface of the sphere without change of the spot size. This allows earning several micrometers of working distance contrary to the Nanojet confined at the sphere's surface. When the radius of curvature of the incident wavefront is greater than about 5 times the sphere size, the Nanojet moves back to the sphere surface like it is found for plane wave incidence. On-axis Bessel-Gauss beam illumination with the central lobe covering the whole sphere leads to the same results as the plane wave case. Off-axis Bessel beam illumination can generate multiple-spot Nanojets. We demonstrate the separation of such spots of about 220 nm at 642 nm. This separation is smaller than the feature sizes defined by the diffraction limit at this wavelength. We discuss briefly applications of engineered Nanojets for nano-lithography and near-field sensing.
Photonic nanojet-induced modes: From physics to applications
2011 13th International Conference on Transparent Optical Networks, 2011
The effects of periodical focusing of light are studied in chains of spheres with diameters varying from 2 µm to 300 µm and with index of refraction varying from 1.3 to 2.5. Experimentally, we show that the coupled focused beams decrease in size along the chain of polystyrene microspheres with index n = 1.59, reaching wavelengthscale dimensions in the case of small beads with 4 < D/λ < 10, where D is the spheres diameter and λ is the wavelength of light. We show that these effects are determined by the existence of so-called photonic nanojetinduced modes with the period approximately equal to the size of two spheres. By using numerical ray tracing we show that in the limit of geometrical optics such effect of "tapering" of optical beams does not exist for spheres with n = 1.59, however it should be very pronounced in a narrow range of indices around n = 1.75. The results can be used for developing various focusing devices for photonics and biomedical optics applications.
Combination of scanning probe technology with photonic nanojets
Scientific reports, 2017
Light focusing through a microbead leads to the formation of a photonic nanojet functional for enhancing the spatial resolution of traditional optical systems. Despite numerous works that prove this phenomenon, a method to appropriately translate the nanojet on top of a region of interest is still missing. Here, by using advanced 3D fabrication techniques we integrated a microbead on an AFM cantilever thus realizing a system to efficiently position nanojets. This fabrication approach is robust and can be exploited in a myriad of applications, ranging from microscopy to Raman spectroscopy. We demonstrate the potential of portable nanojets by imaging different sub-wavelength structures. Thanks to the achieved portability, we were able to perform a detailed optical characterization of the resolution enhancement induced by the microbead, which sheds light into the many contradictory resolution claims present in literature. Our conclusions are strongly supported by rigorous data analysis...
Photonic nanojets produced by microcubes
2015 17th International Conference on Transparent Optical Networks (ICTON), 2015
In this work, we numerically study the focusing of a linearly polarized laser beam of wavelength λ = 633 nm using microcubes of heights 0.4 μm, 0.6 μm, and 0.8 μm and width varying from 0.4 μm to 0.8 μm fabricated of silica (refractive index n = 1.46) on a substrate. The minimal focal spot was obtained for microcube with height of 0.6 μm and width of 0.58 μm. The diameters of photonic nanojet in this case were equal to FWHM min = 0.39λ and FWHM max = 0.67λ.
Photonic nanojets in optical tweezers.pdf
Photonic nanojets have been brought into attention ten years ago for potential application in ultramicroscopy, because of its sub-wavelength resolution that can enhance detection and interaction with matter. For these novel applications under development, the optical trapping of a sphere acts as an ideal framework to employ photonic nanojets. In the present study, we generated nanojets by using a highly focused incident beam, in contrast to traditional plane waves. The method inherits the advantage of optical trapping, especially for intracellular applications, with the microsphere in equilibrium on the beam propagation axis and positioned arbitrarily in space. Moreover, owing to optical scattering forces, when the sphere is in equilibrium, its center shifts with respect to the focal point of the incident beam. However, when the system is in stable equilibrium with a configuration involving optical tweezers, photonic nanojets cannot be formed. To overcome this issue, we employed double optical tweezers in an unorthodox configuration involving two collinear and co-propagating beams, the precise positioning of which would turn on/off the photonic nanojets, thereby improving the applicability of photonic nanojets.
Transverse and longitudinal confinement of photonic nanojets by compound dielectric microspheres
Proceedings of Spie the International Society For Optical Engineering, 2009
We discuss the compound set of two dielectric microspheres to confine light in a three dimensional region of dimensions on the order of the wavelength when the spheres are illuminated by a plane wave. This simple configuration enables the reduction of the longitudinal dimension of so called photonic jets, together with a strong focusing effect. The beam shaped in that way is suitable for applications requiring high longitudinal resolutions and/or strong peak intensities.
Photonic nanojets in optical tweezers
Photonic nanojets have been brought into attention ten years ago for potential application in ultramicroscopy, because of its sub-wavelength resolution that can enhance detection and interaction with matter. For these novel applications under development, the optical trapping of a sphere acts as an ideal framework to employ photonic nanojets. In the present study, we generated nanojets by using a highly focused incident beam, in contrast to traditional plane waves. The method inherits the advantage of optical trapping, especially for intracellular applications, with the microsphere in equilibrium on the beam propagation axis and positioned arbitrarily in space. Moreover, owing to optical scattering forces, when the sphere is in equilibrium, its center shifts with respect to the focal point of the incident beam. However, when the system is in stable equilibrium with a configuration involving optical tweezers, photonic nanojets cannot be formed. To overcome this issue, we employed double optical tweezers in an unorthodox configuration involving two collinear and co-propagating beams, the precise positioning of which would turn on/off the photonic nanojets, thereby improving the applicability of photonic nanojets.
Optics Express, 2007
The two-photon excited fluorescence from a dye solution is enhanced when a small amount of micro-meter sized silica beads are added. This observation is made in the simple scattering regime (inter-sphere distance four times larger than their radius) and is shown to depend on the concentration of the silica spheres. For a solution of rhodamine B, the enhancement can reach more than 30 %. As complementary experiments show that the fluorescence efficiency is unchanged, we argue that the non-linear absorption is enhanced due to focussing of the incident beam in the near-field of the spheres, a situation previously referred to as photonic (nano-)jets . Our calculations indeed show that for the parameters of the spheres studied near-field focussing leads to an intensity concentration close to the sphere surface. We suggest that these photonic jets could be used to enhance other non-linear optical effects.