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A near-field optical trapping scheme using plasmonic C-shaped nano-engraving is presented. Utilizing the polarization sensitivity of the C-structure, a mechanism is proposed for dynamically controlling the electric field, the associated trapping force, and the plasmonic heating. Electromagnetic analysis and particle dynamics simulations are performed to verify the viability of the approach. The designed structure is fabricated and experimentally tested. Polarization control of the excitation light is achieved through the use of a half-wave plate. Experimental results are presented that show the functioning implementation of the dynamically adjustable plasmonic tweezers. The dynamic controllability can allow trapping to be maintained with lower field strengths, which reduces photo-thermal effects. Thus, the probability of thermal damage can be reduced when handling sensitive specimens.

The plasmonic response of a nano C-aperture is analyzed using the Vector Field Topology (VFT) visualization technique. The electrical currents that are induced on the metal surfaces when the C-aperture is excited by light is calculated for various wavelengths. The topology of this two-dimensional current density vector is analyzed using VFT. The plasmonic resonance condition is found to coincide with a distinct shift in the topology which leads to increased current circulation. A physical explanation of the phenomenon is discussed. Numerical results are presented to justify the claims. The analyses suggest that VFT can be a powerful tool for studying the physical mechanics of nano-photonic structures.

Typical x-ray detectors have a fundamental trade-off between resolution and quantum efficiency (QE). High quantum efficiency x-ray detection requires a thick conversion medium, but decreases the resolution due to limited pixel aspect ratios for both direct and indirect x-ray detection. We present a method for x-ray detection, holographic x-ray detection, which uses photorefractive materials to create a high resolution and high efficiency detector. The x-ray image is recorded in the volume of the photorefractive material, bypassing the aspect ratio issue of typical x-ray detectors. Holographic x-ray detection operates in three stages: recording an x-ray hologram in a photorefractive crystal, reading the hologram with visible light, and then erasing the hologram using ultraviolet light. We have experimentally demonstrated holographic x-ray detection with a resolution of 208 lp/mm (80% QE at 40 keV), an order of magnitude resolution improvement over commercially available x-ray detectors while maintaining > 80% QE.

This Letter covers the design and implementation of a generalizable system for the precise alignment of X-ray gratings. Next-generation high-energy grating-based Differential Phase Contrast (gDPC) X-ray imaging systems require precise alignment of the X-ray gratings as low as 1 mrad in rotation and 0.5 mm in translation. In this work, we designed holographic fiducial marks, consisting of four reflective Fresnel zone plates, each placed in a separate quadrant of the mark. When illuminated with a collimated laser beam, each mark creates a predefined pattern of four points, which changes quantitatively for any misalignment in each of the three translational and three rotational degrees of freedom. We fabricated the designed fiducial marks using photolithography and etching processes. The experimental system is implemented using a HeNe laser and an optical imaging system, which includes a beam expander, a plate beam splitter, and a CMOS camera, suitable for aligning practical gratings in gDPC X-ray imaging systems. Our experimental results demonstrate the rotational precision capabilities of the reported alignment system down to 0.42 mrad around the optical axis and 0.03 mrad around the axes perpendicular to the optical axis. The translational precision of 83.64 μ m along the optical axis and 1.22 μ m along the axes perpendicular to the optical axis is also demonstrated.This Letter covers the design and implementation of a generalizable system for the precise alignment of X-ray gratings. Next-generation high-energy grating-based Differential Phase Contrast (gDPC) X-ray imaging systems require precise alignment of the X-ray gratings as low as 1 mrad in rotation and 0.5 mm in translation. In this work, we designed holographic fiducial marks, consisting of four reflective Fresnel zone plates, each placed in a separate quadrant of the mark. When illuminated with a collimated laser beam, each mark creates a predefined pattern of four points, which changes quantitatively for any misalignment in each of the three translational and three rotational degrees of freedom. We fabricated the designed fiducial marks using photolithography and etching processes. The experimental system is implemented using a HeNe laser and an optical imaging system, which includes a beam expander, a plate beam splitter, and a CMOS camera, suitable for aligning practical gratings in gDPC X-ray ...

The non-conservative nature of the force field generated by a near-field optical trap is analyzed. A plasmonic C-shaped engraving on a gold film is considered as the trap. The force field is calculated using the Maxwell stress tensor method. The Helmholtz-Hodge decomposition is used to extract the conservative and the non-conservative component of the force. Due to the non-negligible non-conservative component, it is found that the conventional approach of extracting the potential by direct integration of the force is not accurate. Despite the non-conservative nature of the force field, it is found that the statistical properties of a trapped nanoparticle can be estimated from the conservative component of the force field alone. Experimental and numerical results are presented to support the claims.

We designed, fabricated, and characterized single C-shaped apertures in an Au film, resonant in the visible regime. Our C-shaped apertures showed transmission enhancement of 13–22 times over a square aperture of the same area and suggest as high as 106 enhancement over square apertures that are designed to produce the same near-field spot size. Spectra from individual apertures demonstrate the ability to tune this resonance over 70nm by scaling the dimensions of the apertures. This shows the C aperture to be a versatile tool for gaining high-resolution, enhanced transmission through single subwavelength apertures at optical wavelengths.

We report abnormally large positive and negative lateral optical beam shifts at a metal–air interface when the surface plasmon resonance of the metal is excited. The optimal thickness for minimal resonant reflection is identified as the critical thickness above which a negative beam displacement is observed. Experimental results show good agreement with theoretical predictions and the large observed bidirectional beam displacements also indicate the existence of forward and backward surface propagating waves at the surface plasmon resonance of the metal.

The transmission and photocurrent of a multiple‐quantum‐well optically addressed spatial light modulator are measured to study the screening dynamics of the internal electric field under uniform illumination. The response is modeled with a numerical device simulator which solves the conventional drift‐diffusion transport equations. Evidence is found for bipolar transport, and the photocurrent response at low internal fields is shown to decay due to the transit time of carriers across the quantum well region. For large internal fields the photocurrent response saturates and the corresponding screening rate is estimated using an analytical device model.

We report the growth of epitaxial SrxBa1−xNb2O6 (SBN) thin films by pulsed laser deposition. The films were grown on (100) MgO substrates with thicknesses in the range 200–400 nm. Rutherford backscattering analysis showed that the films have stoichiometric composition identical to the target material. X‐ray diffraction 2θ scans indicate single crystalline layers with the (001) orientation perpendicular to the substrate plane. Phi scans on the (221) plane, however, reveal that the films have two in‐plane orientations. The unit cell of SBN is rotated in the plane of the film by ±18.4° with respect to the MgO substrate unit cell. This rotation is explained using a model which takes into account both the lattice match and the electrostatic energy within the heteroepitaxial interface.

A new high density integrated‐optical switch design using electrically controlled diffraction gratings formed in the intersection of crossing waveguides is proposed and demonstrated. The gratings are formed, in one implementation, by implanting donor atoms in a periodic pattern. Free carriers from the implanted ions modify the index of refraction resulting in Bragg diffraction between the waveguides. Depletion of the free carriers using a reverse bias voltage switches off the diffraction. High speed switch arrays of 100×100 elements on a single substrate may be feasible. Fabrication and demonstration of a low efficiency proof‐of‐concept switch array in GaAs for use at 1.55 μm are reported. Other designs capable of much higher diffraction efficiencies are described.

In several applications, such as electron beam lithography and X-ray differential phase contrast imaging, there is a need for a free electron source with a current density at least 10 A/cm2 yet can be shaped with a resolution down to 20 nm and pulsed. Additional requirements are that the source must operate in a practical demountable vacuum (>1e-9 Torr) and be reasonably compact. In prior work, a photocathode comprising a film of CsBr on metal film on a sapphire substrate met the requirements except it was bulky because it required a beam (>10 W/cm2) of 257 nm radiation. Here, we describe an approach using a 405 nm laser which is far less bulky. The 405 nm laser, however, is not energetic enough to create color centers in CsBr films. The key to our approach is to bombard the CsBr film with a flood beam of about 1 keV electrons prior to operation. Photoelectron efficiencies in the range of 100–1000 nA/mW were demonstrated with lifetimes exceeding 50 h between electron bombardments. We suspect that the electron bombardment creates intraband color centers whence electrons can be excited by the 405 nm photons into the conduction band and thence into the vacuum.

We demonstrate the all-optical recording of deeply subwavelength data bits in Ge2Sb2Te5 using a near-field scanning optical microscope (NSOM) probe that utilizes a C-aperture fabricated using through membrane focused ion beam milling. Data bits recorded with various optical powers were read out optically by C-aperture NSOM and the physical bit size was measured by atomic force microscopy (AFM). Both optical and AFM measurements were found to be in excellent agreement with simulation. We achieved a minimum physical bit size of 53.5×50.2 nm2 at a wavelength of 980 nm (λ/20) indicating a data density of 223 Gbit/in.2.

A high resolution surface plasmon resonance sensor is proposed and demonstrated by measuring the plasmon resonance enhanced Goos-Hanchen effect at attenuated total internal reflection. The giant Goos-Hanchen shift results from the singular phase retardation at the resonance which leads to the superior sensitivity of the sensor.

We present results of nanosecond laser ablation of silicon over a broad range of laser intensities, investigated by studying the time evolution of the ablation plume ejection, which, as measured by transmission of a probe beam, consists of a fast ejection phase followed by a delayed slow ejection phase. Experimental results indicate that different physical processes dominate at different ablation stages. The laser intensity threshold for the appearance of the slow ejection is ∼30GW∕cm2. The plume kinetics parameters extracted from our experiments agree well with estimations based on blast wave and homogeneous nucleation theories, providing a physical explanation for the observed ablation rate dependence on the laser light intensity.