Interference Of Evanescent Waves Research Articles

Numerical Simulation Analysis of an Optical Virtual Probe Based on Surface Plasmon Polaritonic Band-gap Structures

A 2D optical virtual probe based on surface plasmon polaritons (SPP) in a band- gap structure with a rectangular proflle is proposed and investigated numerically by means of flnite difierence time domain (FDTD) method. The dependence of the distributions of the con- flned optical flelds on difierent structure parameters is numerically analyzed. The results indicate that with the proper structure design, the full width at half maximal (FWHM) of the conflned beam can keep constant in a certain distance range, and the fleld intensity of the conflned vir- tual probe can be enhanced greatly by SPP. Compared with the optical virtual probe based on interference of evanescent waves, this type of virtual probe has merits of high intensity and high sensitivity, and is likely to promise for the applications in nano-photonics devices based on SPP. DOI: 10.2529/PIERS060903234639

Four beams evanescent waves interference lithography for patterning of two dimensional features

This work presents a theoretical study of using the interference of multiple counter-propagating evanescent waves as a lithography technique to print periodic two dimensional features. The formulation of the three dimensional Cartesian space expression of an evanescent wave is presented. In this work, the evanescent wave is generated by the total internal reflection of a plane wave at the interface between a incident dielectric material and a weakly absorbing transmission medium. The influences of polarization, incident angle and the phase shifting of the incident plane waves on the evanescent wave interference are studied. Numerical simulation results suggest that this technique enables fabrication of periodic two dimensional features with resolution less than one third the wavelength of the irradiation source.

Evanescent wave interference and the total transparency of a warm high-density plasma slab

It is shown that an overcritical density plasma slab can be totally transparent to a p-polarized obliquely incident electromagnetic wave. High transparency is achieved due to the interference of the evanescent waves in the subcritical region. The transmission coefficient has the resonant character due to the excitation of a plasma surface mode (plasmon-polariton). In a warm plasma case, the excitation of the propagating longitudinal (electrostatic) modes becomes possible. It is demonstrated that these longitudinal excitations facilitate the total transparency of an opaque plasma slab creating additional resonances in the transmission property of the system.

Nano-fabrication of surface relief gratings on azo dye films utilizing interference of evanescent waves on prism

Nano-patterns were investigated on azo dye thin films exposed by an interference of evanescent waves propagating on a prism surface. The patterns strongly depended upon polarization of the incident laser beams forming electric field vectors of the evanescent waves in the vicinity of the prism surface. Line structures of surface relief gratings (SRGs) were clearly inscribed by selecting s-polarization of the incident light. The cyclic pattern of the lines was approximately 210 nm that was smaller than a half of the wavelength of the incident laser at 488 nm. Any line patterns were not obtained using p-polarization of the light, but nano-dot patterns were fabricated on azo dye films. This technique based on molecular migration due to evanescent waves is thought to be very useful for nano-device processing and future device applications.

Surface relief subwavelength gratings by means of total internal reflection evanescent wave interference lithography

We present the use of total internal reflection (TIR) evanescent waves for lithography purposes. In particular, we focus our attention on their singular capabilities to nano-structure surface relief gratings and the potentialities for nano-photonic device fabrication. Interference of two (or more) evanescent waves achieves periodic linear (or 2D) surface relief gratings of around 100 nm period depending on the wavelength and materials used. In contrast to common and some newer lithographic techniques, the evanescent wave does not propagate all through the film, allowing fabrication of surface profiles with maximum height features limited to around the wavelength of the exposure. Here, we present an analysis of several structures and profiles for linear gratings—many of which are not achievable with known interference photolithographic techniques—and some experimental results validating the model of evanescent wave lithography proposed. Possible applications in the field of nano-photonic devices are antireflection treatments, polarizers, diffraction gratings, micro- and nano-lens arrays, etc. We also find in the technique a great potential for other nano-technologies, as in the fabrication of field emitter arrays for displays, as templates for self-assembling structures, etc.

Evanescent wave holographic recording in nanosize thick chalcogenide glass films

The results of holographic gratings recording in 29, 15 and 8nm thick As2S3 films are presented in the paper. The method is based on the interference of surface-propagating evanescent waves, created by total internal reflection. The condition for successful recording is the penetration depth of these inhomogeneous waves to be greater than the films thickness. In this case, the film’s refractive index does not affect the total internal reflection (TIR) condition and could be greater than the input glass prism. The experimentally obtained low diffraction efficiencies by this holographic recording technique is due to the very low refractive index modulation, but the good signal-to-noise ratio – better than 50:1 and Bragg-type diffraction are a base for future applications of this grating formation method in nanotechnology.

Fabrication of surface relief gratings on azo dye thin films utilizing an interference of evanescent waves

Fabrication of surface relief gratings (SRGs) on azo dye thin films has been investigated utilizing an interference of evanescent waves. SRGs of approximately 210 nm were inscribed on the photoisomerized azo dye films, that were smaller than a half wavelength of an incidence laser of 488.0 nm. The films were set on a right-angled triangular prism surface and were in the interference of evanescent waves of totally reflected laser beams at the prism surface. The interference at the surface was performed using a laser beam through the one side of the isosceles and the returned beam at the other side of the isosceles where a mirror was set. The SRG patterns of azo dye films due to trans–cis transition of the dyes were observed in situ using an atomic force microscope above the prism surface.

Direct Measurement of Evanescent Wave Interference with aScanning Near-field Optical Microscope

Evanescent wave interference is studied theoretically andexperimentally. The interference patterns were directly measured with ascanning near-field optical microscope. The acquired image of theinterference pattern is clear and has better contrast than that previously acquiredwith a photon-scanning tunnelling microscope or laser-trapped particles. The spatial period of the interference fringes is 180 nm, whichagrees with the theoretical value. The results indicate that the probeof the scanning near-field optical microscope has a resolution beyond100 nm. The relation between the evanescent field intensity and thedistance is also measured. When the separation between the probe and theinterface is up to 180 nm, the intensity can decrease to 1/e of the maximum.

Numerical simulation analysis of a near-field optical virtual probe

A near-field optical virtual probe based on the principle of near-field evanescent wave interference can be used in optical data storage, nanolithography, near-field optical imaging, and optical manipulation. This letter gives the numerical simulation results of the optical distribution of a near-field virtual probe and analyzes the dependence of the virtual probe’s on the aperture, the polarization, etc. The simulation results reveal that the transmission efficiency is higher than that of a nanoaperture metal-coated fiber probe. The size of the virtual probe is constant when the distance between the lens and recording media increases within a certain range so that the critical nanoseparation control in near-field system can be relaxed.

A virtual optical probe based on evanescent wave interference

A virtual probe is a novel immaterial tip based on the near-field evanescent wave interference and small aperture diffraction, which can be used in near-field high-density optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation of nano-scale specimen, etc. In this paper, the formation mechanism of the virtual probe is analysed, the evanescent wave interference discussed theoretically and the sidelobe suppression by small aperture is simulated by the three-dimensional finite-difference time-domain method. The simulation results of the optical distribution of the near-field virtual probe reveal that the transmission efficiency of the virtual probe is 102-104 times higher than that of the nano-aperture metal-coated fibre probe widely used in near-field optical systems. The full width at half maximum of the peak, in other words, the size of virtual probe, is constant whatever the distance in a certain range so that the critical nano-separation control in the near-field system can be relaxed. We give an example of the application of the virtual probe in ultrahigh-density optical data storage.

Depolarization of evanescent waves scattered by laser-trapped gold particles: Effect of particle size

Depolarization of evanescent waves scattered by laser-trapped gold particles of 0.1, 0.5 and 2 μm in diameter is experimentally characterized in order to reveal its dependence on the size of particles. It is found that the degree of polarization of scattered evanescent waves decreases with the size of gold particles, which is contrary to that previously observed for dielectric particles. This feature becomes advantageous in particle-trapped near-field microscopy since less depolarized photons carry more information of a sample. With the help of polarization gating, this property is demonstrated in images of the evanescent wave interference pattern as well as the surface of a glass prism.

Dependence of strength and depolarization of scattered evanescent waves on the size of laser-trapped dielectric particles

Scattered evanescent waves are characterized experimentally with laser-trapped dielectric particles of different sizes in order to improve image quality in particle-trapped near-field scanning microscopy. It is found that although the strength of scattered evanescent waves increases monotonically with the size of a laser-trapped particle, image contrast of an evanescent wave interference pattern exhibits a maximum value for an intermediate-sized particle. In addition, it is found that the degree of polarization of scattered evanescent waves increases with the size of a laser-trapped particle. The depolarization effect is more significant for s polarized light than p polarized light for a large-sized particle, while this tendency reverses for a particle of small size.

Effect of depolarization of scattered evanescent waves on particle-trapped near-field scanning optical microscopy

The degree of polarization of the scattered evanescent wave is measured with a laser-trapped particle for different incident angles. It is found that depolarization under s polarized beam illumination is stronger than that under p polarized beam illumination. As a result, the contrast of the evanescent wave interference pattern imaged in a particle-trapped near-field scanning optical microscope is improved approximately by a factor of 3 with a parallel analyzer under s polarized beam illumination. The phase shift of scattered evanescent waves under s and p polarized beam illumination is determined from the measured evanescent wave interference pattern.