High-transmission two-crystal acousto-optic monochromator

A two-crystal high-transmission acousto-optic monochromator is developed and studied. The transmittance of the monochromator can substantially be increased and the scheme can be simplified using the reflection from a face of the acousto-optic cell as a separating polarizer. The intervals of parameters of acousto-optic interaction (angles and wavelengths) that correspond to high efficiency of the monochromator are found. Characteristics of two high-transmission monochromators with different parameters of the acousto-optic interaction are determined.     

High-transmission planar x-ray waveguides

We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.     

Ultrahigh light transmission through a C-shaped nanoaperture

Optical resolution beyond the diffraction limit can be achieved by use of a metallic nanoaperture in a near-field optical system. Conventional nanoapertures have very low power throughput. Using a numerical finite-difference time domain method, we discovered a unique C-shaped aperture that provides approximately 3 orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of approximately 0.1 lambda. Microwave experiments at 6 GHz quantitatively confirmed the simulated transmission enhancement. The high transmission of the C-aperture--or one of the related shapes--is linked to both a propagation mode in the aperture and local surface plasmons.     

Characterization of x-shaped nanoaperture antenna arrays operating in mid-infrared regime

The characterization of x-shaped antenna arrays operating in the mid-infrared is proposed. An equivalent circuit model for the resonant characteristic of the x-shaped nanoaperture antenna arrays is also included. In order to understand the resonance behavior of the structure, a detailed study of the field-enhancement capabilities and light transmission characteristics of the structure is proposed. In the experimental studies, the transmission characteristics of the periodic x-apertures are analyzed by varying the geometrical dimensions. Consequently, it is observed that the periodic subwavelength x-apertures show extremely high near-field optical resolution and enhanced transmission compared with the other nm-sized apertures.     

High-transmission spectrograph with a large range of simultaneously measured energies of charged particles

Computer simulation has been performed for a high-transmission electrostatic spectrograph, and charged particle energies in the range E_max/E_min = 25 and 50 have been measured simultaneously. The spectrograph has been designed in the form of two coaxial cylinders with plane endface electrodes; the cylinder of a larger diameter has been cut into fragments with a potential that varies according to a linear law. For this device, the geometric and electrical parameters that ensures a beam that focuses in the entire range of recorded energies with the energy resolution interval (0.4–1.1)% are determined in the regime when the object under investigation is placed outside the field.     

Raman scattering and fluorescence emission in a single nanoaperture: Optimizing the local intensity enhancement

We investigate the potential of a single subwavelength aperture milled in an aluminium film to enhance the local electromagnetic field. We compare the Raman scattering of unadsorbed chlorobenzene molecules and the fluorescence emission of Cyanine-5 dyes, having the same excitation and collection setup for both experiments. For the optimal nanoaperture diameter, we report a clear enhancement factor of about 5 of the Raman scattering intensity per unit volume. Since Raman scattering probes the molecular vibrational levels and avoids the resonant pumping of a real excited state, the observed Raman enhancement is disconnected from the effects of the molecular energy levels alteration previously reported for fluorescent dyes. The observations are similar for both Raman and fluorescence experiments, and stand in good agreement with numerical electromagnetic computations of the excitation intensity inside the nanoaperture.     

High-transmission waveguide with a small radius of curvature at a bend fabricated by use of a circular photonic crystal

A bent photonic crystal waveguide was fabricated by use of a lattice pattern of a circular photonic crystal that allowed high transmission for a broad band of wavelengths with a small radius of curvature at a bend. The waveguide was fabricated by use of alumina rods with a diameter of 3 mm. Windows of high transmission as a result of waveguiding were observed near 9 and 15 GHz. By measurement of the relative wave intensity [E]2 along the line defects, the propagation losses in the straight and the bent sections were estimated at 9.3 GHz to be 0.04 and 0.03 dB/mm, respectively.     

Large enhancement and uniform distribution of optical near field through combining periodic bowtie nanoantenna with rectangular nanoaperture array

We present a novel (to the best of our knowledge) composite nanostructure composed of bowtie nanoantennas (BNAs) and rectangular nanoapertures, which provides a new way to improve the ability of the nanostructure to enhance the optical near field and obtain uniform near-field distribution in the z direction. It is specifically engineered to not only confine the incident light in the nanoscale but also to generate large localized near-field enhancement about 25 times larger than that of solitary BNAs. It also shows a more uniform near-field distribution in the z direction than that of solitary BNAs. The mechanisms of the large enhancement and the uniform near field are also discussed.