Feasibility analysis of solid immersion lens-based dual-layer near-field recording optics with a numerical aperture of 1.84

A dual-layer near-field recording (NFR) optical system with a high numerical aperture (NA) of 1.84 was designed by appropriate cover and spacing layer selection, using layers with refractive indices of 2.0. The designed aplanatic imaging optics exhibited additional aberrations in the multi-layered stack, mainly due to the air-gap and spacer layer. Given optics designed only to compensate for aberrations caused by a 2-μm-thick cover-layer, a 3-μm-thick spacer layer induces 96.2 mλ_rms and 6.5 mλ_rms of spherical aberration and defocus, respectively. A complete electric field calculation analysis for the inside of the multi-layer stack verified that diffraction-limited spot quality can be ensured on the recording layer with phase-only correction. As the aberration caused by the multi-layered stack cannot be corrected perfectly, due to the high oscillation of the aberration function along the radial direction in the exit pupil, three different types of liquid crystal (LC) electrodes were considered for practical implementation. Of the three phase-correction methods, the approximate linear phase-correction method was the most tolerant of axis decenter from the optical axis, providing acceptable diffraction-limited correction performance.     

Optimizing the optical field distribution of solid immersion lens system by a continuous phase filter

In solid immersion lens (SIL) microscopy systems with high numerical aperture (NA), there always exists the aberration produced by Fresnel effects at the interface between SIL and the sample. This aberration may cause the degradation of the image of sample. We design a continuous phase filter and optimize the optical field distribution of SIL system. The numerical results show that when the continuous phase filter is used, the field distribution of SIL system can be optimized, and the focal depth and intensity of transmitted light can be increased. At the same time, the intensity of side-lobe and the resolution are kept almost unchanged.     

Theoretical study of optical recording with a solid immersion lens illuminated by focused double-ring-shaped radially-polarized beam

Based on the Richards–Wolf vector diffraction theory, the intensity distributions in the recording sample near a solid immersion lens are calculated for two different radially-polarized beams ( and modes). Numerical results show that a double-ring-shaped mode focusing has some excellent features in near-field optical storage, compared with a single-ring-shaped mode focusing. The recording density is markedly improved, the focal depth of the near-field recording system is substantially increased, and a subsurface recording is effectively obtained using the mode focusing.     

Experimental research on the longitudinal field generated by a tightly focused beam

The longitudinal optical field is a peculiar physical phenomenon that is always involved with the domain of near-field optics. Due to its extraordinary properties, it has recently attracted increasing attention in research and application. In this work, the longitudinal fields generated by the evanescent illumination of tightly focused, different polarized hollow beams are investigated. The focused light fields are numerically simulated according to vector diffraction theory, and their vector analysis is also carried out. The longitudinal fields on the focal plane are demonstrated experimentally using tip-enhanced scanning near-field microscopy. The simulation and experimental results show that the tightly focused radially polarized beam is suited to generating a stronger and purer longitudinal optical field at the focus.     

Reflected image of a strongly focused spot

We describe the reflection of a strongly focused beam from an interface between two dielectric media. If the beam is incident from the optically denser medium, the image generated by the reflected light is strongly aberrated. This situation is encountered in high-resolution confocal microscopy and data sampling based on solid immersion lenses and oil immersion objectives. The origin of the observed aberrations lies in the nature of total internal reflection, for which there is a phase shift between incident and reflected waves. This phase shift displaces the apparent reflection point beyond the interface, similarly to the Goos-H?nchen shift.     

固体浸没透镜光存储的信号探测技术

信号探测是固体浸没透镜成为实用存储技术的一个必需的组成部分。对在该项研究中获得的理论和实验成果进行了介绍。总结了针对固体浸没透镜机理的三维矢量理论 ,对影响信号探测的因素 ,例如头盘间距、盘片结构和光的偏振态等进行了讨论。介绍了基于固体浸没透镜光存储中信号探测的新技术和重要的实验结果。     

Optical fiber tip in front of a phase conjugator: focused light spot with inclusion of evanescent field contribution

 Within the framework of electric dipole approximation, the focused light spot produced by a tiny optical fiber tip in front of a phase conjugate mirror is investigated numerically. The fiber tip is the probe of a reflection scanning near field optical microscope and the incident light is guided through the fiber. Intensity distribution of local field is calculated in the half space where the fiber tip locates. Both homogeneous (q _‖≤ω/c ₀) and part of inhomogeneous (ω/c ₀<q _‖≤ωn/c ₀) fields are included in establishing a field propagator (Green’s function) which is employed to calculate the local field distribution. The local field forms at the tip position a diffraction light spot with a finite central value and a finite size, and when the tip-surface distance is sufficient small, the strength and the shape of the light spot become a function of the distance, which is due to the contribution of evanescent field. Fairly good agreements are found with the existing experimental reports. Received: 30 April 1996/Accepted: 19 August 1996     

The validity of high-pass angular spectrum filter in solid immersion lens system

应用矢量方法计算了具有高通角谱滤波器的固体浸没透镜（SIL）系统的焦场分布。数值结果显示，对于径向（角向）偏振输入光，高通角谱滤波器可以减小SIL系统的光斑（暗斑）大小。然而，对于线性偏振输入光，简单的高通角谱滤波器不能够优化SIL系统的光场分布，也不能够改进系统的光存储密度。     

Realization of population inversion in a two-level system by damping field

We propose a new method for reversing the quantum state of a two-level system. From solving the time-dependent Schrödinger equation numerically, we show that by applying a classical decaying oscillatory field the state in a two-level system can be completely reversed if the parameters of the field satisfy certain conditions. The transition probability from one level to the other is calculated for different parameters and its maximum value can reach unity. By using such field with specific oscillatory frequency the Rabi oscillations between two levels in the case of applying a constant field can be suppressed and a stable manipulation of the quantum state can be performed. The estimation of such manipulation by using laser pulse acting on the states of hydrogen atom shows that the population inversion higher than 0.9 may be realized in less than 2 fs.     

Improving the resolution of a solid immersion lens optical system using a multiphase Fresnel zone plate

We propose a method to improve the resolution of near-field optical system with a solid immersion lens by using a multiphase level Fresnel zone plate. The analyses are based on scalar angular spectrum theory. The results show that the multiphase Fresnel zone plate can not only decrease the spot size but also decrease the sidelobe intensity and enhance greatly the diffractive efficiency compared with annular amplitude filter or binary 2-, 3-, 4-zone phase filter.     

Pupil-plane filtering for improved signal detection in an optical data-storage system incorporating a solid immersion lens

A pupil-plane filtering technique is applied to data-signal detection in an optical data-storage system that uses a solid immersion lens (SIL) and a four-layered phase-change recording medium. We have confirmed by numerical calculations and experiment that the technique improves signal contrast and makes the contrast less sensitive to the gap width between the bottom surface of the SIL and the top surface of the recording medium. Light that is incident upon the objective lens that is used with the SIL is linearly polarized, and the full vectorial feature of the light is considered in the calculations.     

Optical and thermal orientation of localized excitons in solid solutions under resonant excitation in a longitudinal magnetic field

A theoretical and experimental study of the effect of a longitudinal magnetic field on optical orientation and magneto-circular polarization of the luminescence of localized excitons in semiconducting solid solutions is reported. It is shown that recombination takes place through two types of emitting states differing substantially in the degree of anisotropy, g factor, and spin relaxation time. Estimates are made of the g factors, anisotropic and exchange splittings, lifetime, and spin relaxation time of localized states in a CdS_0.96Se_0.04/GaAs solidsolution epitaxial layer. Fiz. Tverd. Tela (St. Petersburg) 40, 900–902 (May 1998)     

Scattering of focused ultrasonic beams by cavities in a solid half-space

The ultrasonic field generated by a point focused acoustic lens placed in a fluid medium adjacent to a solid half-space, containing one or more spherical cavities, is modeled. The semi-analytical distributed point source method (DPSM) is followed for the modeling. This technique properly takes into account the interaction effect between the cavities placed in the focused ultrasonic field, fluid-solid interface and the lens surface. The approximate analytical solution that is available in the literature for the single cavity geometry is very restrictive and cannot handle multiple cavity problems. Finite element solutions for such problems are also prohibitively time consuming at high frequencies. Solution of this problem is necessary to predict when two cavities placed in close proximity inside a solid can be distinguished by an acoustic lens placed outside the solid medium and when such distinction is not possible.     

Propagation of nonlinear longitudinal waves in a solid with regard to the interaction between the strain field and the field of defects

A model of nonlinear longitudinal wave propagation in a solid with quadratic nonlinearity of an elastic continuum exposed to laser impulses is developed in view of the interaction between the strain field and the field of point defects. The influence of the generation and recombination of laser-induced defects on the propagation of an elastic strain wave is analyzed. The existence of a nonlinear elastic shock wave of low intensity is revealed in the system and its structure is studied. The estimations of the depth and velocity of the wave front are performed. The contributions due to the interaction of the strain field and the field of defects to both a linear elastic modulus and the dispersion parameters of a lattice are found.     

Field in focus with a maximum longitudinal electric component

Closed formulas are presented for the field in the lens pupil for which the longitudinal electric component at the focal point is larger than any other focused field with the same power. The full-width-at-half-maximum of the squared amplitude of the maximum longitudinal component is 15% to 30% less than that of the classical Airy spot.     

Ionization wave in a longitudinal RF field

We investigate a stationary one-dimensional ionization wave produced in a cold gas by an alternating electric field of frequency (the field is parallel to the direction of propagation of the wave). Primary attention is given to specific features associated with the existence of a plasma resonance transition region at the front of the wave, where the electric-field amplitude and, therefore, the collisional ionization rate of the gas have a pronounced maximum at low electron-collision frequencies . We investigate analytically and calculate numerically the parameters of the wave, which is described by a nonlinear diffusion equation. It is shown that a made of ultrafast discharge propagation with ionization wave velocity V for /0 can be established in the gas due to resonance effects even if the external electric field has amplitude far below breakdown.Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 10, pp. 991–1000, October, 1995.     

Distribution of the longitudinal component of the magnetic field of prominences from radioastronomical measurements

We present the results of prominence observations at RT-22 CrAO in April, May, and September 1993 at 13.5 mm (intensity and circular polarization) and at 8.2 mm (intensity) wavelengths carried out by circular scanning using the combined scalar horn. On the assumption of thermal cyclotron radiation we have measured the values of the longitudinal component of the magnetic field for 18 prominences. The histogram of the distribution of the longitudinal component indicates the presence of maxima in the vicinity of 8, 15, and 25– 30 G. Our results are compared with the distributions obtained from optical measurements.