Few/single molecule detection is of great importance in fields including biomedicine, safety and eco-pollution in relation
to rare and dangerous chemicals. Superhydrophobic surfaces incorporated with the nanoplasmonic structure enable this
device to overcome the diffusion limit of molecules dissolved in water with the concentration down to 10 attomolar. In
this paper demonstrated the fabrication of hydrophobic surfaces using optical lithography/reactive ion etching and its
application to overcome the diffusion limit. Various experiments such as contact angle measurements, SEM,
fluorescence, Raman and FTIR absorption spectroscopy were performed which indicate that utilizing this device it could
be possible to perform the measurements for the sample with extremely low dilution. The major application of this novel
family of devices would be the early detection of tumors or other important pathologies, with incredible advances in
medicine.
We reported the synthesis of silicon nanoparticles with mean size varying from 60 nm to 3 nm, by ultrafast laser
ablation of a silicon target in deionized water. Optical absorption, Raman spectroscopy and Electron microscopy
were performed to characterize the nanoparticles. The crystalline structure of the obtained silicon nanoparticles was
confirmed with Raman spectroscopy combined with High resolution transmission electronic microscopy. The
energy confinement of carriers which is evaluated from optical experiments varies from 90 meV to 440 meV when
the mean nanoparticles size decreases from 60 nm to 3 nm. In particular, the evaluated nanoparticles size from
optical analysis and LCAO theoretical model are found in agreement with Transmission Electron Microscopy and
Raman measurements for the silicon nanoparticles with a size less than 6 nm. Finally, we studied the stability of
silicon nanoparticles with time which demonstrates that the smallest nanoparticle aggregates over time.
Gobind Das, Rosanna La Rocca, Tadepally Lakshmikanth, Francesco Gentile, Rossana Tallerico, Lia Zambetti, James Devitt, Patrizio Candeloro, Francesco De Angelis, Ennio Carbone, Enzo Di Fabrizio
KEYWORDS: FDA class I medical device development, Raman spectroscopy, Molecules, Proteins, Principal component analysis, Molecular spectroscopy, Micro raman spectroscopy, Tumors, Biological research, Deconvolution
Human leukocyte antigen (HLA) class I molecules are formed by three immunoglobulin-like domains (α1, α2, and α3) once folded by peptide and β2-microglobulin show the presence of two α-helix streams and one β-sheet limiting the pocket for the antigenic peptide. The loss of HLA class I expression in tumors and virus-infected cells, on one hand, prevents T cell recognition, while on the other hand, it leads to natural killer (NK) cell mediated cytotoxicity. We propose the possibility of using Raman spectroscopy to measure the relative expression of HLA class I molecules at the single-cell level. Raman spectra are recorded for three cell lines (K562, T2, and T3) and monomers (HLA class I folded, unfolded and peptide+β2-microlobulin refolded) using 830 nm laser line. Our data are consistent with the hypothesis that in the Raman spectra, ranging from 1600 to 1800 cm−1, the intensity variation of cells associated with HLA class I molecules could be measured.
Here we report the design, the fabrication and measurement of a photonic-plasmonic device that is fully compatible
with AFM microscopy and surface enhanced Raman spectroscopy. The physical mechanism exploited is the
adiabatic compression of Surface Plasmon Polaritons which propagate along a silver nanocone generating a very
high electric field at the tip end. A photonic crystal cavity is employed to efficiently couple the external laser
radiation with the nanocone. The reported measurements demonstrate the accumulation of the electric field at the tip
of the nanocone that allow the detection of a few molecules located near the tip end. The estimated Raman
enhancement factor is about 106 with respect to a standard configuration. The present results open a good
perspective for the development of an integrated Raman-AFM microscopy able to perform both topography and
chemical mapping in label free condition with a spatial resolution comparable to the tip end.
This paper reports on the fabrication of reproducible surface enhanced Raman scattering (SERS) device based on
nanoPillar coupled with PC cavity by means of FIB milling and electron beam induced deposition techniques (Device 1):
In addition to this device, another SERS device using e-beam lithography and electroless metal deposition techniques
(Device 2) is fabricated in order to have planar geometry particularly useful for future nanoarray architectures SERS
device. Various measurements have been performed for the monolayer of different materials showing extremely
promising SERS based device. It is revealed that the Rhodamine6G is clearly evidenced in Raman 2D mapping
spectrum, showing a very high enhancement in SERS signal in the order of 1012 (theoretically) with respect to the normal
Raman measurements. We estimate the number of Rhodamine6G molecule detected is about 100-150.
This paper reports the fabrication of two reproducible surface enhanced Raman scattering devices using; a) nanoPillar
coupled with PC cavity by means of FIB milling and electron beam induced deposition techniques (Device 1), and b)
plasmonic gold nanoaggregate structures using electro-plating and e-beam lithography techniques (Device 2). Device 1
consists of photonic crystal cavity as an optical source to couple the incident laser with a metallic tapered nanolens.
Exploiting such approach it is possible to overcome the difficulties related to scattering and diffraction phenomena when
visible laser (514 nm) illuminates nanostructures. The nanostructure is covered with HMDS and is selectively removed
leaving HMDS polymer on nanoPillar only. A clear Raman scattering enhancement has been demonstrated for label-free
detection of molecule in sub-wavelength regime. On the other hand, myoglobin protein is deposited on Device 2 using
drop coating deposition method and is estimated that the substrate is able to detect the myoglobin concentration down to
attomole.
Since the diffraction gratings were invented, their use in various security systems has been exploited. Their big advantage is the low production cost and, in the same time, the difficulty of replicating them. Most of the nowadays security systems are using those gratings to prove their originality. They can be seen on all the CDs, DVDs, most of the major credit cards and even on the wine bottles. In this article we present a new way of making such gratings without changing the production steps but generating an even more difficult to be replicated item. This new way consists not only in changing the grating period so that various false colours can be seen, but also their orientation so that for a complete check of the grating it should be seen under a certain solid angle. In the same time, one can also keep the possibility to change the grating period so this way various colours can be seen for each angle variation. By combining these two techniques (changing period and changing the angle ones) one can indeed create different images for each view angle and thus increasing the security of the object. In the same time, as can be seen, from the fabrication point of view no further complications appear. The production steps are identical, the only difference being the pattern. The resolution of the grating is not increased necessarily so neither from this point of view will complications appear.
We discuss a new technique to generate force gradient in arrays of optical traps. The arrays can be configured in two or three dimensions by means of phase diffractive optical elements displayed on a spatial light modulator. The design of the diffractive optical elements is based on the approach of spherical wave propagation and superposition, which enables to individually control the strength of each optical trap. Computer simulation and experimental results are discussed for two and three dimensional arrays of traps. An example with silica micro-beads trapped with different forces in two different planes is presented to demonstrate the validity of our approach.
Optical tweezers enable non-destructive, contact-free manipulation of ultrasound contrast agent (UCA) microbubbles, which are used in medical imaging for enhancing the echogenicity of the blood pool and to quantify organ perfusion. The understanding of the fundamental dynamics of ultrasound-driven contrast agent microbubbles is a first step for exploiting their acoustical properties and to develop new diagnostic and therapeutic applications. In this respect, optical tweezers can be used to study UCA microbubbles under controlled and repeatable conditions, by positioning them away from interfaces and from neighboring bubbles. In addition, a high-speed imaging system is required to record the dynamics of UCA microbubbles in ultrasound, as their oscillations occur on the nanoseconds timescale.
In this work, we demonstrate the use of an optical tweezers system combined with a high-speed camera capable of 128-frame recordings at up to 25 million frames per second (Mfps), for the study of individual UCA microbubble dynamics as a function of the distance from solid interfaces.
We present and discuss a new experimental setup to perform small angle X-ray scattering and diffraction (SAXSD) of localized liposome colloidal microparticles. A home-built inverted infrared laser tweezers microscope is used to trap, manipulate and aggregate micron-scale liposome particles at single locations inside a 100 microns glass capillary. The micro-focused X-ray and the laser beams are aligned to intersect each other perpendiculary, allowing to associate the X-ray diffraction signal to the micron-sized region of interest inside the capillary. Throughout the laser tweezer setup, using diffractive optical elements implemented on a spatial light modulator, we are able to manipulate small aggregates of colloidal particles (liposomes) and fix them in the optical path of the X-ray beam.
We present and discuss first scattering and diffraction experiments on phospholipid liposomes, at the ID13 microfocus beamline of the European Synchrotron Radiation Facility (ESRF). The results demonstrate that we can push the limit of measurable cluster size close to a single liposome.
We present a unified view regarding the use of diffractive optical elements (DOEs) for microscopy applications a wide
range of electromagnetic spectrum. The unified treatment is realized through the design and fabrication of DOE through
which wave front beam shaping is obtained. In particular we show applications ranging from micromanipulation using
optical tweezers to X-ray differential interference contrast (DIC) microscopy. We report some details on the design and
physical implementation of diffractive elements that beside focusing perform also other optical functions: beam
splitting, beam intensity and phase redistribution or mode conversion. Laser beam splitting is used for multiple trapping
and independent manipulation of spherical micro beads and for direct trapping and manipulation of biological cells with
non-spherical shapes. Another application is the Gauss to Laguerre-Gaussian mode conversion, which allows to trap
and transfer orbital angular momentum of light to micro particles with high refractive index and to trap and manipulate
low index particles. These experiments are performed in an inverted optical microscope coupled with an infrared laser
beam and a spatial light modulator for DOEs implementation. High resolution optics, fabricated by means of e-beam
lithography, are demonstrated to control the intensity and the phase of the sheared beams in X-ray DIC microscopy.
DIC experiments with phase objects reveal a dramatic increase in image contrast compared to bright-field X-ray
microscopy.
We present an experimental system based on the use of a spatial light modulator which enables to perform simultaneously 3D optical manipulation and optical sectioning. This has been achieved by modifying the wave front of the trapping beam with properly diffractive optical elements displayed on a computer controlled spatial light modulator. We demonstrated the capability of the system in two experimental schemes, in a first one we performed a 3D optical scanning of 6 trapped beads by displacing the beads through a fixed imaging plane. In a second one we scan the imaging plane and simultaneously compensate for the movement of the objective in order to keep the trapping plane at a fixed position.
Trapping and manipulation of microscopic objects using fiber optical traps is gaining considerable interest, as these objects can be manipulated inside complex environments, thus removing the limitation of short working distance of the conventional optical tweezers. We show that an axicon like structure built on the tip of a single mode optical fiber produces a focused beam shape with a central hole, implying a very small fraction of the power traveling with rays nearly parallels to the optical axis. Interesting transportation behavior of polystyrene particles using the scattering forces from such an axicon tip fiber was observed. As the distance of the particle from the fiber tip increased, since almost no rays interact with the particle, the scattering forces decreased substantially. Therefore, velocity of the particle at different distances was found to depend much more critically on the particle size in contrast to the beam generated by the bare fiber. While the speed of transport could be increased linearly by increasing the laser power in both axicon tipped fiber and bare fiber, increased speed was observed for particles of larger sizes for both the fiber types. However, the fractional increase in speed for increased size of particles was found to be quite large for axicon tipped fiber as compared to the bare fiber. Use of the observed differences in speed of transportation of microscopic objects could be used to sort them based upon their size.
Since the low index particles are repelled away from the highest intensity point, trapping them optically requires either a rotating Gaussian beam or optical vortex beams focused by a high numerical microscope objective. However, the short working distance of these microscope objectives puts a limit on the depth at which these particles can be manipulated. Here, we show that axicon like structure built on tip of a single mode optical fiber produces a focused beam that is able to trap low index particles. In fact, in addition to transverse trapping inside the dark conical region surrounded by high intensity ring, axial trapping is possible by the balance of scattering force against the buoyancy of the particles. The low-index particle system consisted of an emulsion of water droplets in acetophenone. When the fiber was kept horizontal, the low index spheres moved away along the beam and thus could be transported
by influence of the scattering force. However in the vertical position (or at an angle) of the fiber, the particles could be trapped stably both in transverse and axial directions. Chain of such particles could also be trapped and transported together by translation of the fiber. Using escape force technique, transverse trapping force and thus efficiency for particle in Mie regime was measured. Details of these measurements and theory showed that trapping of Raleigh particle is possible with such axicon-tip fibers. This ability to manipulate low-index spheres inside complex condensed environments using such traps will throw new insights in the understanding of bubble-bubble and bubble-wall interactions, thus probing the physics behind sonoluminescence and exploring new applications in biology and medicine.
We present a new method that allows to fabricate structures with tightly controlled three-dimensional profiles in the 10 nm to 100 μm scale range. This consists of a sequence of lithographic steps such as Electron Beam (EB) or Focused Ion Beam (FIB) lithography, alternated with isotropic wet etching processes performed on a quartz substrate. Morphological characterization by SEM and AFM shows that 3D structures with very accurate shape control and nanometer scale surface roughness can be realized. Quartz templates have been employed as complex system of micromirrors after metal coating of the patterned surface or used as stamps in nanoimprint, hot embossing or casting processes to shape complex plastic elements. Compared to other 3D micro and nanostructuring methods, in which a hard material is directly "sculptured" by energetic beams, our technique requires a much less intensive use of expensive lithographic equipments, for comparable volumes of structured material, resulting in dramatic increase of throughput. Refractive micro-optical elements have been fabricated and characterized in transmission and reflection modes with white and monochromatic light. The elements produce a distribution of sharp focal spots and lines in the three dimensional space, opening the route for applications of image reconstruction based on refractive optics.
We introduce simple double-casting replication methods for high-aspect-ratio microstructures fabricated by deep x-ray lithography using intermediate molds of soft materials. Two types of soft material are investigated. The ability to fabricate polymethylsiloxane (PDMS) molds with well-type structures with aspect ratios up to 35:1 is demonstrated for structure densities below 50%, and the reproduction from this mold of pillar-type polymethyl methacrylate (PMMA) structures with aspect ratios of 20:1 is achieved. Polyvinyl alcohol (PVA), a water soluble polymer, is also tested as a sacrificial intermediate mold and successfully used for the replication of structures with aspect ratios up to 5:1. Double-casting replication methods are described and discussed for their potential improvement.
A strongly focused laser beam through an objective microscope with high NA allows the trapping of dielectric particles
with micrometric sizes. The trapping force is proportional to the power of the laser, the relative refractive index (the ratio
between the refractive index of the particle and the refractive index of the medium surrounding it) and the trapping
geometry (shape of the laser beam, shape of the particle, transmission and reflection coefficients). Numerical models to
evaluate the trapping force can be developed for simple geometrical shapes of the trapped particle. For particles with
complicated shapes the trapping force should be measured experimentally. The goal of this paper is to evaluate a
measurement method based on the equilibrium between the drag force in a fluid with known viscosity and the transversal
trapping force. A particle with a known size is fist trapped in a cell filled with water. After stable trapping, the cell is
shifted with controlled velocities using piezoelectric actuators. If the velocity exceeds a certain threshold, the particle
escapes from the trap. This threshold allows to determine the trapping force. Experimental results obtained with high and
low index particles are presented and discussed.
The features of e m inhomogeneous polarized field, which concern an angular momentum, are considered. It is shown
that the e-m field produced by differently polarized optical beams may carry orbital angular momentum. Such angular
momentum arises in field area with the point of circular polarization (C -point). Superposition of relatively simple
orthogonally polarized beams is considered. Experimental results of particles capturing by such focused beam are
presented. On the other hand, in the vicinity of s -contour (field line with linear polarization) spin angular momentum
vanishes. At the same time such angular momentum appears when superposition of beams with different wave-length is
considered.
In the frame of paraxial approximation, we consider the case of free atoms interacting with an Lagtierre-Gaussian
beam. Using Power-Zienaii-Wooley scheme, we calculate the interaction Hamiltonian in the quadrupole approximation and including center of mass motion of the atomic system. The expression of the center of mass transition
probability is derived in analytic form. The influence of the beam and atomic system parameters on the center
of mass transition probability are discussed.
In this work we present a numerical evaluation of the forces in an optical tweezers system, for metallic nanoparticles in the
Rayleigh regime. Initially a Gaussian beam is described in the scalar approximation, and the forces it can apply on Rayleigh
dielectric and metallic particles are computed within the point-dipole approach. The method is then extended to dielectric
and metallic Rayleigh particles in a Laguerre-Gaussian beam, i.e. a higher order beam that is increasingly used for optical
trapping experiments. We discuss the limits of the approximation for the beam intensity by comparing the numerical results
with the experimental measurements that can be found in literature.
We have developed a holographic optical tweezers system based on diffractive optical elements (DOES) implemented
on a liquid crystal spatial light modulator (LC-SLM) able to generate fine positioned traps on the sample. Our own
algorithms and code allows to calculate phase DOES that can transform a single laser beam into an array of independent
traps, each with individually specified characteristics, arranged in arbitrary three-dimensional (3D) geometrical
configurations. Different DOEs can be dynamically projected to the SLM in order to achieve a rearrangement of the
configuration of the trapping spots. Silica or latex micro-beads are trapped in different configurations of spots to
demonstrate the fine control capability on each trap. Our setup is built on a standard video microscope coupled with a
laser source, a spatial light modulator and a three axis nano-positioning system. It allows to obtain 3D multi-trapping
and a fine calibration for the positioning of the traps.
The goal of our study is to develop a setup that combines multi-trapping and manipulation with micro Raman spectroscopy of microns size particles. Multiple trapping, in 2D or 3D (two or three dimensional) configurations, is obtained in an inverted microscope scheme by shaping the trapping beam (1064 nm) with diffractive optical elements implemented on a spatial light modulator (SLM). Manipulation of multiple particles, directly trapped by the beam, can be achieved using the dynamic displaying of the SLM. Indirect trapping and manipulation of the sample can be obtained surrounding it with trapped micro beads that are manipulated by the optical tweezers. Laser light is not directly focused on the sample but is distributed on the beads and therefore the photo-induced damaging of biological samples is reduced. This technique offers also other advantages: the sample can be kept in a stable position during the spectroscopic investigation or can be moved in x-y-z to get spatial resolved information in a scanning mode measurement and the shape of a deformable sample can be changed in a controlled manner during the measurement. Sample's excitation and Raman signal collection are accomplished with a separate laser beam (514.5 nm) in a non-inverted microscope coupled with the spectrometer. Some experimental results showing multi trapping and indirect manipulation of human red blood cells are presented and discussed.
One of the main problems in using oil immersed objectives for optical trapping is due to the reflective index mismatch. While in water immersed lens or in "classical" ones the index mismatch is, at most, because of the propagation from a low-index to a high-index medium so no big aberrations appear, in the oil-immersed ones the aberrations cannot be neglected. Due to the propagation of a focalized beam from a high refraction index medium to a low one, spherical aberrations appear. But the numerical aperture an oil immersed objective can reach is usually above 1.2, so theoretically, the Q-factor can reach higher values. In this paper we confront two different methods of force calculations. The first one is based on Ashkin's (Biophys. J. - Feb. 1992) formulas and uses a ray-tracing approach. Using this approach we can observe the asymmetry of the forces along the optical axis and the high Q-factors values on the orthogonal plane. The second approach is a more rigorous one and is based on wave optics. We analyze the Gaussian beam propagation using the scalar version of the diffraction theory and the formulas of the scattering and gradient forces developed by W.H.Wright &al. (Applied Optics - March 1994). This approach, although more precise in defining the focus shape, is not necessarily more precise in determining the force value. This essentially because of the approximations used in the force formulas. While in the ray-tracing approach, the error can be minimized by changing the sampling period of the beam, in the wave-optics approach this cannot be done. In the same time, in the latter approach, the beam shape can be described better so the accuracy of the simulation improved. To our belief the possibility of using both simulations must be taken into account while in the "resonance" regime and, function of the needs one has, decide which one is to be considered reliable.
Higher-order laser beams were demonstrated to enable optical manipulation of low-index-particles. In this work single-ringed Laguerre-Gaussian beams, obtained by means of phase-only diffractive optical elements, are used to perform manipulation of phospholipid-shelled gas microbubbles in water. Implementation of diffractive optical elements on a programmable spatial light modulator allows to generate also arrays of Laguerre-Gaussian traps. We show manipulation of low-index particles by properly displaying a suitable sequence of diffractive optical elements. Control over the distance between the trapped particles in real time is also demonstrated.
The use of diffractive optical elements (DOEs) for multiple trapping of dielectric micro-spheres immersed in a fluid has been demonstrated recently. When the DOEs are implemented on a spatial light modulator (SLM), the trapped particles can be independently moved by changing the configuration of the DOE. In this paper we demonstrate phase DOEs implemented on an optical addressable SLM to move an array of trapped particles in a volume of about 20x20x6 μm. Experimental results show the usefulness of this technique for particle micromanipulation in biology.
Since the first demonstrations of optical trapping, both theoretical and experimental parts of this technique evolved. With all this, the main problem when trapping in the Mie regime is due to the limited numerical aperture a microscope objective has. In literature one finds characterizations of “classical” microscope lens or, at most, water immersed ones. In this paper we are analysing the forces generated in an optical tweezers setup using oil immersed microscope objective and having as entrapped particles water-immersed silica beads. Using such a set-up, we can take advantage of the numerical aperture an oil-immersed objective can reach. This numerical aperture can have a value as high as 1.4. From Roosen's 1 and Ashkin's 2 formulas, we calculated the forces involved in our experiment. We observed that the entrapping range on the optical path axis is larger and asymmetric. This generates the possibility to build optical catapult and optical tweezers in the same time, changing only the distance from the sample to the entrapment point. One of the disadvantages of optical trapping in these conditions is that the focus point and the entrapment one can be different. This fact generates the need of using a second microscope for inspecting the entrapped particle so the optical setup is more complicated. To our belief, this set-up for optical tweezers can have big advantages in the field of optical trapping mainly due to the not so strict trapping spatial conditions.
Trapping and manipulation of microparticles using optical tweezers is usually performed within a sample cell formed by two parallel microscope cover slides. In this paper we discuss and demonstrate trapping and manipulation conditions when the cell has more complex configurations like microchannels or capillary tubes. The microchannels are fabricated on the surface of the cover slide by means of lithographic techniques. Experimental results of trapping and micromanipulation for silica microspheres and biological samples immersed in water show the usefulness of our study for microfluidics and biological applications.
It is shown that the polarization singularities of vector field are connected with the presence or absence of the angular momentum of electromagnetic field. In the vicinity of C-point the orbital angular momentum is observed. Direction of influence of such orbital angular momentum is defined by the sign of topological charge of vibration phase in this area. Spin angular momentum of a field vanishes on the s-contour. At the same time similar momentum appears if the resulting field is formed by the waves with different wavelengths.
Although optical tweezers have been a valuable research tool since their invention in the 1980s, they have remained limited for many years to trapping only one particle per laser beam. One of the most exciting developments in optical tweezers in recent years has been the creation of two- and three-dimensional arrays of optical traps by using diffractive optical elements (DOEs). We have developed our own algorithms and codes to design phase DOEs that can transform a single laser beam into an array of independent traps, each with individually specified characteristics, arranged in various geometrical configurations. The DOEs were fabricated by means of e-beam lithography in PMMA and recently were implemented in computer addressed liquid crystal spatial modulators. This allows us to control the configuration of the optical tweezers almost in real time. Experimental results presented in this paper show trapping and manipulation of multiple silica micro-spheres immersed in water. The trapped particles are moved independently along the x-y-z directions and rotated along circular trajectories with different angular velocities.
In this paper we report results obtained in the design and fabrication of diffractive optical elements (DOEs) with minimum feature size down to tens of nanometers by the use of e-beam and x-ray lithography. The DOEs are patterned using e-beam lithography and replicated by x-ray lithography. Since in our days there is an increased interest for extreme ultraviolet and x-ray microscopy our work has been focused toward the fabrication of DOEs mainly for these applications. Different types of zone plates (ZPs) were fabricated for x-ray beam focusing: high resolution ZPs for high resolution beam focusing, multilevel phase ZPs to increase the diffraction efficiency in the desired order and high aspect ratio ZPs for hard x-rays. Recently we have extended the concept of the ZPs to a more general category of DOEs which beside simple focusing can perform new optical functions in the range of x-rays. In particular, the intensity of the beam after the DOE can be distributed with almost complete freedom. We have designed and fabricated DOEs that focus the beam in an array of spots disposed either in plane or along the optical axis. This type of DOEs has been tested successfully in x-ray differential interference contrast microscopy. The possibility to introduce a specified phase shift between the generated spots is demonstrated in this paper by preliminary results obtained from computer simulations and experiments performed in visible light.
Diffractive optical elements (DOE’s) can be used to manipulate the amplitude, the phase and the polarization of light beams. They can operate over a wide range of wavelength from UV to x-ray radiation. Interest in DOE’s has grown rapidly in recent years since they are smaller and lower in size and weight than conventional optical elements and in addition allow optical functions impossible to reach with other refractive or reflective optical elements. In this paper we report results obtained in DOE’s design and fabrication at the LILIT Nanolithography beam line developed at the national laboratory TASC-INFM. Among the design methods we have used, the phase retrieval iterative algorithm approach is presented in more detail here. There are also presented aspects involved in the fabrication of high-resolution zone plates for focusing soft x-rays. The fabrication process is based on e-beam lithography and etching techniques similar to those used in the microelectronic technology, allowing structures sized down to few tens of nanometers. Experimental results are presented for some applications of our DOE’s: laser beam shaping, optical tweezers array generation and x-ray microscopy.
The present research work is devoted to the realization of an efficient fiber-waveguide optical coupling between single-mode fiber and rectangular waveguide. The outcomimg laser beam exiting from the fiber has a gaussian transversal field distribution. On the contrary, the single-mode waveguide has an asymmetric transversal field distribution in X and Y-axis. To transform the outcoming circular laser beam onto a rectangular, size adjusted, spot we have used a multilevel diffractive phase element fabricated directly on the top of the fiber by means of nanolitography. The diffractive phase element is calculated to focus and reshape the gaussian symmetric beam exiting a single-mode fiber into a desired asymmetric intensity distribution at the waveguide input plane. Phase modulation is obtained by multilevel profiling a polymeric material coated on the top of the fiber by means of a specific fabrications process including e-beam lithography and chemical etching. Experimental results obtained for fiber-waveguide coupling with a 20 microns diameter diffractive element are also presented.
In this paper we compare two techniques to design diffractive gratings with periods close to the wavelength of the illumination beam. The first method, based on the Rayleigh method, is faster and allows good result if grating period is more than 1.2 bigger than the wavelength. The second method, known as Fourier Modal Method, is more precise but also requires a longer calculation time. Results obtained from the computer simulations and experiments are presented for gratings with 0.750μm and 1.5μm period illuminated by a collimated wave with 0.633μm wavelength.
A novel method to design diffractive optical elements, based on the spherical wave propagation and superposition, is presented in this paper. Underlying theory, practical considerations, results and limitations of this method are presented based on computer simulation experiments. Diffraction patterns produced by such diffractive optical elements are shown for binary intensity objects described either by the Cartesian coordinates of their non-zero points or by image format files. The method by itself stands as an effective method to calculate phase diffractive elements for free space optical interconnection between an array of point sources and an array of point detectors, but is shown to be also useful to generate binary intensity objects. The optimization of the phase function which describes the phase diffractive element is also demonstrated by means of a micro-genetic algorithm.
In our days, there is an increased interest for extreme ultraviolet and x-ray microscopy, which is mainly due to the availability of nearly ideal optical sources for diffractive optics. Synchrotrons of the latest generation and free electron lasers (in the near future) are sources that can produce x-ray beams with low divergence, whose wavelength can be tuned over a range of several keV and whose spectrum can be monochromatised within a band pass Δλ/λ< 10-4. In this paper we present the design, fabrication and use of novel diffractive optical elements that, beyond simple focusing, can perform new optical functions in the range of soft X-rays: multi-focusing in single or multiple focal planes and beam shaping of a generic monochromatic beam into a desired continuous geometrical pattern. The design is based on scalar diffraction approaches using iterative or direct algorithms to calculate the optical function. Diffractive optical elements with 100x100 microns size and 100 nanometers resolution have been fabricated using e-beam lithography and their optical functions have been tested in differential interference contrast microscopy. We suggest their use also in mask-less lithography and chemical vapor deposition induced by extreme ultraviolet and x-ray radiation.
In this contribution, we present a novel technique for converting the specimens phase information into strong image contrast, the differential interference contrast x-ray microscopy (X-DIC). In the used setup, X-DIC operation was accomplished by a zone plate doublet (ZPD), i. e. two zone plates on both sides of the same substrate, laterally shifted by about one outermost zone width. In order to be able to manufacture such ZPDs, new e-beam and nanofabrication techniques have been developed. Once a ZPD has been successfully produced, it is - despite almost all other phase sensitive methods - as easy to use as a single zone plate, without any alignment difficulty or further requirements to the coherence of the illumination. The tremendous contrast enhancement was demonstrated at the microscopy beamline ID2 at ESRF in Grenoble for test objects and biological samples. It could also be shown that ZPDs allows for full field X-DIC imaging as well as for DIC scanning transmission x-ray microscopy. Though the first experiments were carried out at 4 keV photon energy, X-DIC can be adapted to any photon energy where ZPDs with appropriate parameters can be designed and manufactured.
A new experimental station for soft x-ray microscopy is under construction at BACH beamline, at Elettra Synchrotron Radiation Facility (Italy). This station will be devoted both to scanning transmission x-ray microscopy (STXM) and photoemission microscopy (SPEM), with spatial resolution of about 50 nm. A Fresnel Zone Plate (FZP) will provide the micro-focusing of the beam delivered by the monochromator of BACH. The photon beam features are high resolving power (30000-5000 in the 40-1500 eV range), high flux (more than 1011 photons/s after the exit slit) and the possibility to select the light polarization. The experimental chamber will host several photon and electron detectors which should provide spatially resolved information of the bulk and surface composition. The expected acquisition times are of the order of the seconds for STXM and less than 1 minute for SPEM. The branch line hosting this station will start from the exit slit of the BACH monochromator. A toroidal mirror will focus the exit slit-spot on a pinhole which will be the source for the following FZP. With a 10x10 micrometers 2 pinhole it will be possible to obtain a spot of about 50x50 nm2 with enough flux (from 108 to 109 ph/sec) to perform microscopic experiments with polarized radiation. In this paper we present the optical scheme of the instrument as well as the foreseen performances in terms of resolution and flux.
Some considerations on the design of computer generated phase elements applied to the intensity redistribution of Gaussian light beams are presented in this paper. The computer generated phase elements are designed using an iterative transform algorithm for Fresnel domain. Parameters which influence the performances of these algorithms and the computation time are discussed. Results obtained by computer simulations are presented for three different Gaussian beam shaping (flat-top, 2 shifted gaussians, acronym.)
High resolution and high efficiency Zone Plate for X-rays in the energy range of 300 eV and 12 KeV fabricated by means of electron beam and X-ray lithography are presented. Regarding the high resolution regime zone plate with 40 nm outermost zone and thickness of 0.2 micrometer are shown. For high efficiency performances, multilevel zone plate and continuous profile were fabricated to provide an increase of efficiency at the first diffraction order and to suppress higher ones. The combination of the two lithography allows a powerful design flexibility at several energy regimes.
Fresnel zone plates (ZP) have gained popularity as the optics of choice for advanced microfocusing applications. The main virtues of ZP are high resolution, high efficieny, low background, coherence preservation, and ample working distance. Zone plates are also unique because they are a normal incidence x-ray optics, which are much easier to align and use compared to other grazing incidence optics. We will report here recent progress that has drastically enhanced the performance of ZPs in 1) higher spatial resolution, 2) higher focusing efficiency, and 3) extension to higher energies. With the new developments, zone plates have proven to be one of the best microfocusing optics for monochromatic x-ray beams.
An optical VanderLugt correlator for real time recognition of bytes at 1.55 micrometers is presented. The discrimination results with phase only filter are shown.
Lithographic techniques for fabrication of hard x-ray Fresnel zone plates are discussed. Practical results achieved at the Center for X-ray Lithography of the University of Wisconsin- Madison are presented. Fabrication technology includes replication of an e-beam written master mask into a thick photoresist by synchrotron radiation x-ray lithography, and subsequent electroplating of a metal zone plate structure using photoresist pattern as a mold.
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