Refraction of a narrow probe beam using layered light diodes

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 14–17, June, 1991.     

Nondiffracting narrow light beam with small atmospheric turbulence-influenced propagation

A narrow light beam that propagates in the atmosphere with less disturbance than conventional light beams is introduced. The operating method and features of the newly proposed long-range nondiffracting beam (LRNB) are briefly demonstrated. Some experimental results of the atmospheric propagation of this beam at a distance of 500 m are shown in comparison with a conventional collimated beam and a focused beam. The results and related analyses show that the LRNB is much less influenced by atmospheric turbulence than other beams and suggest that the LRNB can apply to many fields.     

舰船声场的近程分布式声源模型

根据舰船声场的近程分布式声源特性,采用三轴声强测量法建立了模型,提出了提高其精度的方法.     

Modulation instability of light beam propagation near the supercollimation frequency in nonlinear photonic crystals

The modulation instability (MI) of light beam propagation near the supercollimation frequency in nonlinear photonic crystals was investigated. The role of the nonlinear diffraction effect, merged as a result of nonlinear tuning of the equal-frequency contour curvature, in MI is particularly identified. It is found that the nonlinear diffraction effect tends to stimulate or suppress MI depending on the sign of the product of nonlinear diffraction and Kerr effects. Further analysis reveals that the MI and soliton phenomenon may be steered by the tunable supercollimation frequency in nonlinear photonic crystals.     

Internal energy flows and instantaneous field of a monochromatic paraxial light beam

It is known that the orbital angular momentum of a paraxial light beam is related to the rotational features of the instantaneous optical-frequency oscillation pattern within the beam cross section [J. Opt. A 11, 094004 (2009)]. Now this conclusion is generalized: any identifiable directed motion of the instantaneous two-dimensional pattern of the field oscillations ("running" behavior of the instant oscillatory pattern) corresponds to the transverse energy flow in the experimentally observable time-averaged field. The transverse orbital flow density can be treated as a natural geometric and kinematic characteristic of this running behavior.     

Some useful data for narrow beam dosimetry

Organ doses and effective dose have been estimated in the case of an anthropomorphic mathematical model exposed to monoenergetic narrow beams of various types of incident radiation (photons, electrons, protons) and energies. The target organs considered were right eye, thyroid and breast. Calculations have been carried out using the latest version of the Monte Carlo transport code FLUKA. The investigated energy range was extended from 5 MeV to 10 GeV. In the case of photons, incident energies in the region between 30 keV and 1 MeV were also considered. Preliminary results are presented.     

A trap for Cherenkov light from a wide beam of relativistic particles

A system is proposed which makes it possible to trap Cherenkov light from a wide beam of relativistic particles.     

Imaging profiles of light intensity in the near field: applications to phase-shift photolithography

We describe a method of imaging the intensity profiles of light in near-field lithographic experiments directly by using a sensitive photoresist. This technique was applied to a detailed study of the irradiance distribution in the optical near field with contact-mode photolithography carried out by use of elastomeric phase masks. The experimental patterns in the photoresist determined by scanning electron microscopy and atomic force microscopy were compared with the corresponding theoretical profiles of intensity calculated by use of a simple scalar analysis; the two correlate well. This comparison makes it possible to improve the theoretical models of irradiance distribution in the near field. Analysis of the images highlights issues in the experimental design, provides a means for the optimization of this technique, and extends its application to the successful fabrication of test structures with linewidths of ~50 nm.     

Experimental study of the self-deflection of a light beam in a photorefractive crystal exposed to an external alternating electric field

We have experimentally studied the propagation of an intensity-modulated light beam in a Ba₂NaNb₅O₁₅ photorefractive crystal exposed to an external alternating sinusoidal electric field. The dependence of the extent of beam self-focusing on the applied field amplitude is determined. The possibility of soliton formation under such conditions is demonstrated.     

Genetic redundancy strengthens the circadian clock leading to a narrow entrainment range

Circadian clocks are internal timekeepers present in almost all organisms. Driven by a genetic network of highly conserved structure, they generate self-sustained oscillations that entrain to periodic external signals such as the 24 h light–dark cycle. Vertebrates possess multiple, functionally overlapping homologues of the core clock genes. Furthermore, vertebrate clocks entrain to a range of periods three times as narrow as that of other organisms. We asked whether genetic redundancies play a role in governing entrainment properties and analysed locomotor activity rhythms of genetically modified mice lacking one set of clock homologues. Exposing them to non-24 h light–dark cycles, we found that the mutant mice have a wider entrainment range than the wild types. Spectral analysis furthermore revealed nonlinear phenomena of periodically forced self-sustained oscillators for which the entrainment range relates inversely to oscillator amplitude. Using the forced oscillator model to explain the observed differences in entrainment range between mutant and wild-type mice, we sought to quantify the overall oscillator amplitude of their clocks from the activity rhythms and found that mutant mice have weaker circadian clocks than wild types. Our results suggest that genetic redundancy strengthens the circadian clock leading to a narrow entrainment range in vertebrates.     

A study of the cosmic-ray neutron field near interfaces

This study investigated the characteristics of the cosmic-ray neutron field near air/ground and air/water interfaces with an emphasis on the angular distribution. Two sets of high-efficiency neutron detecting systems were used. The first one, called the Bonner Cylinders, was used for measurements of the energy information. The other one, referred to as the eight-channel neutron detector (8CND), was used to characterize the angular information of the neutron field. The measured results were used to normalize and confirm one-dimensional transport calculations for cosmic-ray neutrons below 20 MeV in the air/ground and air/water media. Annual sea level cosmic-ray neutron doses were then determined based on the obtained characteristics of low-energy cosmic-ray neutrons near interfaces and estimated contribution from high-energy neutrons.     

Modeling the diffuse reflectance due to a narrow beam incident on a turbid medium

We present a model for the diffuse reflectance when a continuous beam is incident normally on a half space composed of a uniform scattering and absorbing medium. This model is the result of an asymptotic analysis of the radiative transport equation for strong scattering, weak absorption, and a narrow beam width. Through comparison with the diffuse reflectance computed using the numerical solution of the radiative transport equation, we show that this diffuse reflectance model gives results that are accurate for small source--detector separation distances.     

Mapping of near field light and fabrication of complex nanopatterns by diffraction lithography

We report a single-step lithographic approach for precisely mapping near field light diffraction in photoresist and fabricating complex subwavelength structures. This method relies on the diffraction of UV light from opaque patterns on a photomask, and utilizes the central diffraction maximum (known as the 'Poisson spot' for an opaque disk) and its higher orders. By correlating pattern geometries with the resulting diffraction, we demonstrate that the near field light intensity can be quantified to high precision and is in good agreement with theory. The method is further extended to capture higher order diffraction, which is utilized to fabricate unconventional subwavelength nanostructures with three-dimensional topographies. The simplicity of this process and its capability for light mapping suggest it to be an important tool for near field optical lithography.     

Biomimetic interfaces for high-performance optics in the deep-UV light range

We report an innovative approach for the fabrication of highly light transmissive, antireflective optical interfaces. This is possible due to the discovery that metallic nanoparticles may be used as a lithographic mask to etch nonstraightforward structures into fused silica, which results in a quasihexagonal pattern of hollow, pillar-like protuberances. The far reaching optical performance of these structures is demonstrated by reflection and transmission measurements at oblique angles of incidence over a broad spectral region ranging from deep-ultraviolet to infrared light.