Dissipation, decoherence and preparation effects in the spin-boson system

The dynamics of the reduced density matrix of the driven dissipative two-state system is studied for a general diagonal/off-diagonal initial state. We derive exact formal series expressions for the populations and coherences and show that they can be cast into the form of coupled nonconvolutive exact master equations and integral relations. We show that neither the asymptotic distributions, nor the transition temperature between coherent and incoherent motion, nor the dephasing rate and relaxation rate towards the equilibrium state depend on the particular initial state chosen. However, in the underdamped regime, effects of the particular initial preparation, e.g. in an off-diagonal state of the density matrix, strongly affect the transient dynamics. We find that an appropriately tuned external ac-field can slow down decoherence and thus allow preparation effects to persist for longer times than in the absence of driving. Received 23 October 1998 and Received in final form 26 February 1999     

Direct Monitoring of Thickness and Refractive Index of Optical Thin Film Deposited on Fiber End-face

We propose a system for depositing thin films on waveguides which enables low-temperature deposition and precise control of the refractive index and film thickness. It is composed of a conventional ion-beam sputtering (IBS) system and a new system for directly monitoring film characteristics during deposition. We controlled refractive indices over a wide range from 1.52 to 1.97 by moving the sputtering targets (SiO₂ and Si₃N₄) in the IBS system. The refractive index or film thickness was in-situ monitored by observing the optical power reflected from the end-face of a monitoring fiber set in the deposition chamber. Antireflection coating films were successfully deposited on a fiber end-face and a laser diode chip facet with low reflectivity from 0.05 to 0.07%. This deposition system is attractive for constructing highly functional optical devices for future photonic networks.     

Creep deformation measurement using quartz optical fiber

This paper describes an optical system for high temperature creep strain measurement using quartz optical fiber, super long working distance microscope and digital image processing techniques. In this system one end of the quartz optical fibers is arrayed in a small area on the specimen surface and the other end is illuminated by a laser beam. The fiber ends on the specimen surface form the spot array. The small optical spots on the specimen are tracked by a CCD camera and the images are processed by digital image processing software. The diameter of each quartz fiber is 100 μm and the fibers can be arrayed in a small area. The local strains are determined by measuring the variety of relative distance between two spots. Experimental results of local creep strain on the welding joints of 15CrMo and HK40 at 850°C are obtained.     

Four-wave mixing in semiconductor laser amplifiers: Applications for optical communication systems

Four-wave mixing in semiconductor laser amplifiers enables various applications in photonic switching including wavelength conversion, space and time switching, optical phase conjugation, and demultiplexing. Switching times faster than 1 ps are possible.     

Effects of low-LET radiations on CR-39 track detector

The effects of Co-60 gamma-rays and about 25-MeV pulsed electrons have been investigated on CR-39 plastic nuclear track detector. The bulk etch rate was measured as a function of the absorbed dose under three different irradiation conditions; gamma-ray exposure in air at the dose rate of 6 kGy/h, that in vacuum and electron shower in air at 126 kGy/h on average. It was found that the bulk etch rate (V) increased nearly exponentially with the dose (D); V=V₀exp(kD), and the characteristic parameter (k) was 35, 9 and 12 MGy⁻¹, respectively. It is considered that a lack of oxygen in damage formation processes could occur momentarily during a short electron pulse, just similarly to the vacuum effect of reduction in track etch rates in outgassed CR-39 plastic.     

A Ferroelectric Frequency-Doubling Material-Potassium Lithium Niobate

The potassium lithium niobate crystals have been grown up. The shapes of solid-melt interfaces which maintaining the steady growth of the potassium lithium niobate crystals have been described. The optical transmission spectrum of the crystal has been surveyed. The perfected crystals showed good Second Harmonic Generation properties.     

Photoinduced non-linear optical diagnostic of SiNxOy/Si111 interfaces

Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiN_xO_y/Si1 1 1 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm). The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10–50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiN_xO_y films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si1 1 1–SiN_xO_y interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50.     

Single-mode fused coupler for undersea optical transmission systems

A single mode 3 dB fused coupler, to be used as a redundant laser combiner in the submerged repeater of an undersea optical fibre transmission system, is described. The fabrication and package design of the component for this high reliability application is discussed, and the results of a wide range of environmental tests are given.     

Calibration of a stochastic health evolution model using NHIS data

This paper presents and calibrates an individual’s stochastic health evolution model. In this health evolution model, the uncertainty of health incidents is described by a stochastic process with a finite number of possible outcomes. We construct a comprehensive health status index (HSI) to describe an individual’s health status, as well as a health risk factor system (RFS) to classify individuals into different risk groups. Based on the maximum likelihood estimation (MLE) method and the method of nonlinear least squares fitting, model calibration is formulated in terms of two mixed-integer nonlinear optimization problems. Using the National Health Interview Survey (NHIS) data, the model is calibrated for specific risk groups. Longitudinal data from the Health and Retirement Study (HRS) is used to validate the calibrated model, which displays good validation properties. The end goal of this paper is to provide a model and methodology, whose output can serve as a crucial component of decision support for strategic planning of health related financing and risk management.