Nonlinear Refraction and Absorption in 4BCMU Planar Waveguides at 1·064 μm Wavelength

Abstract

We have measured the nonlinear refractive index, n ₂, and two-photon absorption coefficient, β, in 4BCMU planar waveguides at 1·064 μm wavelength using picosecond pulses. We use a beam propagation code, with n ₂ and β as fitting parameters, to make numerical comparison with the experimental data. Deduced values from this analysis are n₂ = ? 1·5 × 10^?13 cm²W^?1, confirming the negative sign of the nonlinearity at this wavelength, and β = 0·01 cm MW^?1.     

1mN·m～1N·m扭矩标准装置力臂系统

介绍了新研制的1 mN·m~1 N·m扭矩标准装置的关键部件——力臂系统的设计方案,并对力臂进行了不确定度分析。分析表明:1 N·m扭矩标准机力臂长度的不确定度为4.2×10~(-6)(k=2),完全满足1 N·m扭矩标准机技术指标的要求。     

1mN·m～1N·m扭矩国家基准装置的建立

介绍了项目"1mN·m～1N·m扭矩国家基准装置的建立"的立项背景、基本情况和项目取得的成果及主要创新。该项目采用了多项自主研发的关键技术,成功研制了国内首台基于空气轴承支撑技术的全自动高准确度微小扭矩标准装置,该装置复现的扭矩值范围为1mN·m～1N·m,扭矩值不确定度(k=2)在100mN·m～1N·m范围内小于5×10~(-5);在5mN·m～100mN·m范围内小于1×10~(-4);在1mN·m～5mN·m内小于5×10~(-4)。     

Limits to the hardness testing of films thinner than 1 μm

Our purpose was to determine the following: (i) whether there is a minimum depth or film thickness below which surface effects prevent the measurement of the intrinsic mechanical properties of a film material by microindentation at the nanometre level; (ii) the critical ratio of depth δ to thickness h above which the substrate affects the measurement. Continuous recordings of indentation depth vs. load during loading and unloading were performed on typical bilayers consisting of films harder or softer than their substrate and of various thicknesses. In all cases, at depths greater than 100 nm the measured plasticity was intrinsic to the film material provided that δ/h did not exceed a critical ratio, which was found to be greater than that predicted by macroscopic theories.     

Continuously tunable femtosecond pulses covering 2·1–2·5 μm from an optical parametric oscillator based on RbTiOAsO4

Abstract

The operation of a synchronously pumped femtosecond optical parametric oscillator based on the nonlinear material RbTiOAsO₄ is described. The idler output was continuously tuned from 2·1 to 2·5 μm, the pulses having powers as high as 140 mW and durations as short as 140 fs. Characterization of the pulses was achieved by use of a novel autocorrelator based on an InGaAs photodiode and a LiNbO₃ frequency-doubling crystal, capable of producing high quality interferometric and intensity autocorrelations.     

Pulse shaping fiber laser at 1.5 μm

In this paper we present, for the first time to our knowledge, a new pulse shaping technology (modulation schemes for seed laser) used to mitigate pulse narrowing effect and SBS effect in a high energy Er:Yb codoped fiber master oscillator power amplifier system at 1.5 μm to obtain longer pulse duration and higher energy. An average power of over 1.3 W and a pulse energy of over 0.13 mJ were obtained at 10 kHz repetition rate with a pulse duration of 200 ns and near-diffraction-limited beam quality (M(2)<1.2).     

Measurements of 10·6 μm Radiation Scattered by a Pseudo-random Surface of Rectangular Grooves

Measurements are presented of scattering of CO₂ laser radiation by a phase screen of rectangular grooves whose widths have a predetermined statistical distribution. The scattering statistics are interpreted using Huygens-Fresnel optics. The measurements provide a valuable model of scattering by naturally occurring phenomena.     

4 μm SiC颗粒表面化学镀铜工艺

为了增强微米级SiC陶瓷颗粒与金属基体的结合力,采用化学镀铜法对SiC颗粒表面进行了改性处理,使SiC颗粒在金属基体液中分散更均匀、镀覆更好。通过正交试验法优化了化学镀铜工艺的主要参数,研究了其主要工艺条件对化学镀铜的影响;分别通过JSM7500F,S-3400N扫描电镜(SEM)对微米级SiC颗粒镀铜前后的表观形貌进行了观察分析,利用X射线衍射仪(XRD)对其镀铜前后的组成进行了表征,并测试了镀铜层与SiC颗粒的结合力;同时对比了微米级SiC颗粒镀铜前后对锌基复合材料微观形貌的影响;讨论了镀液中配位剂、pH值、还原剂等对铜镀层的影响。结果表明:随着镀液中配位剂、还原剂含量的增加,单位时间内微米级SiC颗粒表面镀铜层的质量先增加后降低,pH值的升高显著降低了镀铜的诱导时间;可实现微米级SiC颗粒表面化学镀铜层的均匀镀覆,且结合良好。     

AlGaAsSb lasers emitting in the 1.6 μm region

AlGaAsSb lasers with different Al concentrations in the active and confinement regions are fabricated and investigated. The structures lase in the region ∼1.6 μm. The AlGaAsSb solid solution in the active region is a direct-gap material with a small energy separation (∼56 meV) between the direct-gap Γ minimum and the indirect-gap L minimum of the conduction band. The lasers have a single-mode spectrum with a predominant longitudinal mode in the spatial distribution of the emission. The lasers operate at room temperature in a pulsed mode. Pis’ma Zh. Tekh. Fiz. 25, 35–41 (May 26, 1999)     

Analysis and Performance of 2·7 μm Er3+ Fibre Laser Amplifiers and Oscillators

Abstract

A mathematical model is described which estimates the performance of erbium doped fibre lasers and amplifiers at 1·5 μm or at 2·7 μm. The model has shown good agreement with experimental results and has been used to optimize the configuration of new systems. Continuous wave laser action has been demonstrated at λ = 2·7 μm in an Er³⁺ doped multi-mode fluorozirconate fibre laser, pumped by an 800 nm laser diode.     

Subwavelength transmission grating retarders for use at 10.6 μm

Designs are given for gallium-arsenide subwavelength grating retarders operating at 10.6 μm. A design procedure is detailed that takes into account the reflections at all surfaces and that uses numerical optimization to improve the transmittance of the retarders to nearly 100%. It is shown that the homogeneous uniaxial layer model for subwavelength gratings can be used to provide starting points for the Nelder-Mead simplex optimization, obviating the need for stochastic optimization techniques such as simulated annealing. An analysis of the designs with respect to wavelength, angle of incidence, and fabrication tolerances indicates that such grating retarders will perform favorably compared with commercial alternatives.     

Structural transformations induced in amorphous free-standing 55wt.%Cr-45wt.%Ni thin films with 2.5 μs (10.6 μm) and 400 μs (0.69 μm) single laser pulses

Experimental results for the pulse laser irradiation of free-standing 55wt.%Cr-45wt.%Ni amorphous thin films with thicknesses ranging from 15 to 60 nm are reported. Transmission electron micrographs and electron diffraction patterns are presented in order to reveal the laser-induced structural transformations.     

The Interpretation of Phase-Slip and Critical-Velocity Data from the Flow of Superfluid 4He through a 2 μm by 2 μm Aperture

An analysis has been made of phase-slip and critical-velocity data for both the ac and dc flow of superfluid ⁴ He through a 2 m by 2 m aperture in a 0.1-m-thick titanium foil between 0.36 and 2.10 K. Single-2 phase slips were resolvable over the entire range of temperature in the ac flow measurements, carried out between 10 and 20 Hz, making it possible to determine the width of the critical-velocity distribution throughout the temperature range from these measurements. These data have been interpreted in terms of the thermal nucleation of vortex half-rings at the walls of the aperture, involving a velocity- and temperature-dependent energy barrier. The barrier can be modeled with moderate success using an approach close to that of Avenel and Varoquaux and coworkers.     

Light emission at 2 μm from Ho-Tm-Yb doped silicate glasses

The 2.0 μm emission properties and thermal stability of Yb-Tm-Ho triply-doped silicate glass are investigated. The characteristic temperatures, absorption spectrum and fluorescence spectra of the glasses are measured. Intensive emission near 2.0 μm is observed upon excitation at 980 nm and the corresponding mechanisms are discussed. Based on the measured absorption spectra, the absorption and emission cross sections, the Judd-Ofelt parameters and radiative properties are calculated and discussed. The predicted spontaneous transition probability for Ho³⁺:⁵I₇ → ⁵I₈ transition in silicate glass is 58.05 s⁻¹. The results indicate that the energy transfer in Yb³⁺ → Tm³⁺, Yb³⁺ → Ho³⁺, Tm³⁺ → Ho³⁺ is efficient and the Yb-Tm-Ho triply-doped silicate glass is a promising 2.0 μm laser glass material.     

Fast-response p-i-n photodiodes for 0.9–2.4 μm wavelength range

Fast-response, uncooled p-i-n photodiodes with a long-wavelength spectral sensitivity boundary at λ = 2.4 μm have been created on the basis of GaSb/GaInAsSb/GaAlAsSb heterostructures. A low doping level (10¹⁴–10¹⁵ cm^?3) in the active layer ensured a low capacitance of the photodiode structure (below 1 pF at a sensitive area diameter of 100 μm) and a record small response time (on a level of 100–150 ps). The photodiode pass band reaches up to 2 GHz. The proposed devices are characterized by a small dark current level (500–1000 nA at a reverse bias voltage of 1–3 V) and a detection ability reaching 9 × 10¹⁰ cm Hz^1/2 W^?1 in a spectral interval of maximum sensitivity within 1.9–2.2 μm.     

3He NMR with a 100 μm Planar Nb Coil

A superconducting 100 m planar coil has been tested for low field cw NMR. The nine-turn 5 nH coil is connected via a planar 1:8 step-up transformer to an external parallel capacitor and resonated at 0.8 MHz to give a Q of 350. The tank circuit voltage is measured with a liquid He temperature GaAs MESFET preamplifier. Test experiments have been conducted by immersing the Si chip with the planar pick-up coil in liquid and solid ³ He to measure their cw NMR absorptions in the temperature range 0.05 – 0.5 K.     

Studies of the critical velocity of superfluid4he in a 2 μm by 2 μm aperture in a thin foil at various frequencies

Measurements of the critical velocity behavior of oscillatory superfluid⁴He flow through a 2 m by 2 m square aperture in a 0.1 m thick titanium foil are being made at temperatures between 0.36 K and 2.1 K and at pressures of less than 0.4 bar at various frequencies between 50 Hz and 1000 Hz. The purpose of this work is to study a micron-size aperture for possible frequency-dependent deviations from the critical velocity behavior seen in submicron-size apertures. Preliminary results show a nearly linear decrease of critical velocity with increasing temperature that is similar to the temperature dependences seen in smaller apertures and that is approximately independent of frequency. However, at frequencies above 500 Hz, a region appears at the lowest temperatures in which supercritical behavior is dominated by large energy-loss events requiring a number of half-cycles for completion, a region that extends up to 1.1 K at 970 Hz.     

Certification of NIST SRM 1962: 3 μm Diameter Polystyrene Spheres

This report describes the certification of SRM 1962, a NIST Standard Reference Material for particle diameter. It consists of an aqueous suspension of monosize 3 (μm polystyrene spheres. Two calibration techniques were used: optical microscopy and electron microscopy. The first one gave a mean diameter of D¯=2.977±0.011 μm and a standard deviation of the size distribution σ_D = 0.020 μm, based on measurement of 4600 spheres. The second technique gave D¯=2.990±0.009 μm, based on measurement of 120 spheres. The reported value covering the two results is D¯=2.983 μm with a maximum uncertainly of 0.016 μm, with σ_D=0.020 μm.     

1.3 μm Emission from Nd3+-doped Tellurite Glass Fiber

1 wt pct Nd2O3-doped tellurite bulk glass and fiber with the same composition of 75TeO2-15ZnO-5Na2O-5Li2O (molfraction, %) were fabricated. Judd-Ofelt analysis was carried out for the bulk. The emission from the 4F3/2→4I13/2 transition in fiber is at 1.33 μm wavelength with a spectral bandwidth of 55 nm, which is similar to that in bulk. In the case of the fiber, the lifetime of 4F3/2 level is 164μs, and the quantum efficiency is ～100%. The figure-of-merit for gain (σoT0) for Nd3 -doped tellurite glass is about 2.8×10-24 cm2.s, which is quite comparable with that in Nd3 -doped fluoroaluminate glasses, and is an order of magnitude larger than pr3 -doped fluoride glasses.     

A multiwire secondary emission beam profile monitor with 20 μm resolution

A 20 μm resolution multiwire beam profile monitor has been designed for the Fermilab antiproton source. The monitor consists of closely packed wires operating by secondary emission (SEM).