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.     

Photonic crystalline IR fibers for the spectral range of 2-40 μm

Monocrystals of Ag(1-x)Tl(x)Br(1-x)I(x) and Ag(1-x)Tl(x)Cl(y)I(z)Br(1-y-z) for the spectral range from 2.0 to 40.0 μm with improved photostability were developed and grown. The grown crystals were used for fabrication of single-mode IR fibers. Experimental studies of optical properties of these fibers have confirmed their single-mode operation at CO2 laser wavelength and demonstrated wider mode field for microstructured fiber compared to fibers with conventional double-layered structure.     

A test of a planar spark counter of 500 μm spark gap

A planar spark counter of 500 μm spark gap was tested with cosmic rays. A time resolution of 134 ps was achieved. The test was carried out for several quenching gas pressures. The best performance was obtained at a gas pressure of 4 atm (2.5 atm of argon and 1.5 atm of the quenching gas). The counter efficiency was about 93%. This low pressure permits easy construction of the counter with a thin pressure vessel. Subsequent measurements using ⁶⁰Co γ-ray sources gave a discharged area of about 5 mm in diameter.     

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.     

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.     

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.     

Certification of NIST SRM 1961: 30 μm Diameter Polystyrene Spheres

This report describes the certification of SRM 1961, an NIST Standard Reference Material for particle diameter. It consists of an aqueous suspension of monosize 30 μm diameter polystyrene spheres. The primary technique used optical microscopy; it gave a mean diameter value D¯=29.62±0.04μm and a standard deviation of the size distribution σ_D = 0.21 μm. Over 2000 spheres were measured. The supporting technique used electron microscopy, which yielded D¯=29.68±0.11μm. Ninety spheres were measured.     

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.     

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.     

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).     

Comparison between the Efficiencies of sub-2 μm C(18) Particles Packed in Narrow Bore Columns

The chromatographic performance of two types of core-shell particles and two fully porous particles packed in 2.1 ID × 50 mm columns was investigated. Comparisons of the performances of the EiS-150-C(18) to that of the Kinetex-1.7 μm-C(18), Acquity-BEH-1.7 μm-C(18), and Zorbax-XDB-1.8 μm-C(18) are made and discussed. The physical factors that govern the performance of these columns, such as particle size distribution and column external, total, and particle porosity of the C(18) packing materials were among the prime foci of investigation. The differences in the mass transfer behavior measured using naphtho[2,3-a]pyrene between these columns provides an indication of improved performance of the new EiS-150-C(18) column. The minimum reduced height equivalent to a theoretical plate (HETP) value for the EiS-150-C(18), h(min) = 1.95, was achieved and was comparable to that obtained from the C(18) phases of the Kinetex (h(min) = 2.53), the Acquity (h(min) = 2.26), and the Zorbax (h(min) = 2.57) columns. This study reveals the importance of the dimension of the shell thickness in controlling the performance of columns packed with shell particles in narrow bore columns.     

Performance improvement and analysis of a 1.6 μm continuous-wave modulation laser absorption spectrometer system for CO2 sensing

In a previous study, we developed a 1.6 μm continuous-wave (cw) modulation laser absorption spectrometer system for CO(2) sensing and demonstrated the measurement of small fluctuations in CO(2) corresponding to a precision of 4 parts per million (ppm) with a measurement interval of 32 s. In this paper, we present the process to achieve this highly specific measurement by introducing important points, which have not been shown in the previous study. Following the results of preliminary experiments, we added a function for speckle averaging on the optical antenna unit. We additionally came up with some ideas to avoid the influences of etalon effects and polarization dependence in optical components. Because of the new functions, we realized a calibration precision of 0.006 dB (rms), which corresponds to a CO(2) concentration precision of less than 1 ppm for a 2 km path. We also analyzed the CO(2) sensing performance after the improvements described above. The measured short time fluctuation of the differential absorption optical depth was reasonably close to that calculated using the carrier-to-noise ratio of the received signal.     

Atmospheric CO2 measurements with a 2 μm airborne laser absorption spectrometer employing coherent detection

We report airborne measurements of CO(2) column abundance conducted during two 2009 campaigns using a 2.05 μm laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO(2) column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO(2) measurements from low Earth orbit pertinent to the NASA Active Sensing of CO(2) Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO(2) 2 μm band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO(2). The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign.     

Specific Heat Near the Superfluid Transition of a 0.9869 μm 4He Film

We report measurements of the specific heat of ⁴He near the superfluid transition while confined between silicon wafers at 0.9869 m separation. These data are analyzed to check on the behavior expected from correlation-length scaling. Comparison is also made with other data for planar confinement, as well as data for cylindrical confinement. These represent different lower-dimensional crossovers. We find that the present data scale very well above the bulk transition temperature, and in the region immediately below it. Near the specific heat maximum however, the data for planar confinement do not collapse on a universal curve. We compare these results with specific theoretical scaling functions. In particular we find that on the normal side, and for large enough values of the scaling variable, one can describe the data well using the concept of the surface specific heat. The locus of the data in this region agrees well with the most recent theoretical calculations.     

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。     

Fabrication of light absorbing TiO2 μ-donuts

TiO₂ µ-donuts were fabricated on glass and silicon by sol-gel technique using a mask of PMMA nanopillars created by removing PS from a spin-coated composite polymer of PS and PMMA. X-ray diffraction confirmed the anatase TiO₂ phase. X-ray photoelectron spectra showed signals from Ti 2p_3/2 at 458.8 eV and O 1s at 530.4 eV confirming presence of TiO₂. The heights and diameters of the TiO₂ µ-donuts are ~ 353 nm and ~ 2.8 µm, respectively as revealed by atomic force microscopy. UV-vis absorption spectra of TiO₂ µ-donuts showed an unusual light absorption at ~ 524 nm making its potential use in solar-cell applications.     

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)     

Liquid argon ionization drift chamber with coordinate resolution of σx ∼ 20 μm

Estimates of the spatial resolution of a liquid argon ionization drift chamber are presented in the paper. The results obtained exhibit a possibility to construct a simple coordinate detector with a spatial resolution of σ_x = 20 μm and a two-track separation better than 1 mm, while good energy resolution characteristics for the LA detector are being conserved. The calculations were performed for an ionization cylindrical chamber with the cathode and anode diameter 4 cm and 0.1 mm, respectively. The fluctuations of ionization losses in thin samples and the noise jitter after shaping were taken into account in the analysis.     

Ultra-broadband,coherent mid-IR supercontinuum expanding from 1.5 to 12.2 μm in new design of AsSe2 photonic crystal fibre

We propose a new design of AsSe₂ photonic crystal fibre (PCF) with all-normal dispersion, nearly zero flat-top used to generate an ultra-broadband supercontinuum spanning from 1.5 to 12.2 μm. Simulated results show that, when we use only 1 mm of AsSe₂ PCF, a broadband mid-infrared supercontinuum with the specrum extent from 1.5 to 12.2 μm is obtained with a very low input energy of E = 1.3 nJ at the wavelength of 3.5 μm and pulse duration of 100 fs. We study the temporel and spectral impact of optical wave breaking in the development of the continuum. The influence of the fibre length, the input energy and the full width at half maximum is investigated. Compared to previous research works, we have obtained the broadest, coherent supercontinuum, which could be applicable in biomolecular sensing, cancer diagnostics, infrared spectroscopy and free space communication.     

Emission Regimes of 1.06 μm Spectral Bandwidth Two-Sectional Lasers with Quantum Dot Based Active Layer

We have investigated two-sectional semiconductor lasers with an active region comprising five layers of InGaAs quantum dots, emitting in the spectral range near 1.06 μm. Regimes of passive mode-locking, passive Q-switching, and mode-locking with pulse modulated amplitude are realized. The transition conditions between generation regimes are investigated. The frequency tuning range with current increase in the Q-switched regime exceeds more than 4 times. The duration of the mode-locked pulses was 2 ps at the pulse repetition rate of 44.3 GHz.