Measurement of the Thickness of Deposited Magnesium Fluoride Films by Evanescent-wave Fluorescence: A Critical Test of the General TIRAF Theory

Abstract

We have recently developed a quantitative theory describing the stimulation of fluorescence by an evanescent wave, with a view to the precise measurement of thin films by otherwise conventional light microscope photometry. In our set-up, total internal reflection of a focused laser beam occurs at a glass/water interface and the presence of the evanescent wave is reported by a fluorescent dye dissolved in the water. For convenience, we refer to the method as TIRAF (total internal reflection aqueous fluorescence). We have tested our general TIRAF theory critically by using glass/MgF₂/fluorescein layers such that the evanescent wave established in the glass/MgF₂ interface is, in part, separated from the aqueous fluorescein phase by an accurately and independently measured thickness of deposited MgF₂ film. We show that fluorescence measurements on areas as small as 30 µm² allow precise determination of film thicknesses in the range 2–160 nm for two different decay constants of the evanescent wave.     

A novel CO2 refrigeration system achieved by CO2 solid–gas two-phase fluid and its basic study on system performance

In this report, a new CO₂ refrigeration system is introduced, which can achieve a refrigeration capability below the CO₂ triple point of ?56.6 °C. The proposed CO₂ refrigeration system consists of two thermodynamic cycles arranged in cascade, where one is a CO₂ trans-critical cycle and another is a trans-triple-point cycle. An experimental set-up is constructed and tested in order to obtain a basic knowledge about this CO₂ system. Based on the measured data, it is concluded that the built CO₂ refrigeration system can operate continuously and stably, although dry ice particles exist in the closed CO₂ loops. An average COP (a ratio of cooling energy to the compressor power consumption) is measured at 2.45 in the present experiment range for the low-pressure system of the experimental set-up. In addition, the influence of the condensation temperature on the refrigeration cycle is investigated and more studies are needed for the future optimization work.     

Piezo- and electrooptics phenomena in high temperature superconducting films

Optically-induced linear electrooptics and elastooptics effects were discovered in high temperature superconducting Hg_0.85Pb_0.18Ba_0.13CuO_4+δ (Hg-1201) (T_c=112 K) single crystalline films deposited on the LiNbO₃ surface. Investigations were done by picosecond fast-resolved set-up. The set-up allowed to perform simultaneous measurements of birefirngence in regime of external fields with precision up to the 10⁻⁷. It was shown that below the superconducting critical temperature both piezooptic and linear electrooptics coefficients are substantially changed and show tremendous sensitivity to the appearance of superconductivity.     

Measuring the photon background in the LHC experimental environment

Background benchmarking measurements were performed in an experimental set-up comparable to the shielding of ATLAS, a general purpose experiment at the Large Hadron Collider (LHC). The absolute yield and energy measurements of photons emanating from the final stages of the hadronic showers in the shielding were performed with a Be₄Ge₃O₁₂ (BGO) detector. Detailed simulations of the set-up were done using the FLUKA code. Comparison between measurements and simulations show that they agree within 20%.     

Interferometric Measurement of Holographic Lenslets

Abstract

A holographic optical element can either be characterized by the wave aberrations or by the point spread function or alternatively by the modulation transfer function. Here we propose the measurement of the wave aberrations with the help of a Twyman-Green interferometer adapted to the requirements for testing holographic optical elements. The evaluation of the interferograms is done with the phase-shifting technique. The resulting wave aberrations are expressed by Zernike coefficients. In addition to this evaluation, the point spread function and the modulation transfer function are calculated from the wave aberrations. The set-up, the evaluation method and also exemplary results of a tested holographic optical element are presented.     

Acoustic wave propagation in Laves-phase compounds

We have studied the acoustic wave propagation in the hexagonal structured materials TiCr₂, ZrCr₂ and HfCr₂. In this paper, we have calculated the orientation dependence of three types of acoustic wave velocity and Debye average velocity using second order elastic constants. The six second order elastic constants are calculated for these materials at 300 K using Lenard-Jones Potential. An anomalous behaviour in orientation dependent acoustic wave velocity is obtained which is due to the combined effect of elastic constants and density. These velocity data are important for their structural information and to differentiate them from third group nitrides.     

High pressure effect on MoS<Subscript>2</Subscript> and MoSe<Subscript>2</Subscript> single crystals grown by CVT method

Single crystals of MoS₂ and MoSe₂ were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS₂ and MoSe₂ do not undergo any structural transitions under pressure.     

Interferometric fidelity of self-pumped phase conjugation in BaTiO3 and a four-wave mixing set-up with Bi12SiO20 using nanosecond pulses

Abstract

The fidelity of a self-pumped phase conjugating mirror (SPPCM) in the so-called cat configuration is studied with an interferometric method for a cobalt-doped barium titanate crystal (BaTiO₃:Co) under pulse illumination (8 ns, 532 nm). With this SPPCM a phase conjugating four-wave mixing set-up using the sillenite-type crystal Bi₁₂SiO₂₀ (BSO) was realized. It is shown that the fidelity of both phase conjugating processes under pulse illumination nearly reaches the fidelity of continuous-wave experiments.     

A new approach for estimation of Poisson’s ratio of porous powder compacts

A new correlation between Poisson’s ratio (ν) and ultrasonic longitudinal wave velocity (V _L) has been established and the resulting correlation has been shown to agree well with experimental data on ν versus V _L for a variety of porous powder compacts. Further, it has been demonstrated that ultrasonic longitudinal wave velocity can be used to estimate the elastic properties of sintered powder compacts.     

RCM predictive maintenance of railway systems based on unobserved components models

Turnouts are probably the most important infrastructure elements of the railway system because of its effect on the system safety, reliability and quality of the service. In this paper, a predictive maintenance system in point mechanism, called RCM², has been implemented for increasing the quality service. RCM² is based on the integration of the two other types of maintenance techniques, namely Reliability Centred Maintenance (RCM₁) and Remote Condition Monitoring (RCM₂). The core of the system consists of an Unobserved Components model set-up in a State Space framework, in which the unknown elements of the system are estimated by Maximum Likelihood. The detection of faults in the system is based on the correlation estimate between a curve free from faults (that is, continuously updated as new curves are incorporated in the data base) with the current curve data. If the correlation falls far from one, a fault is at hand. The detection system is tested on a set of 476 experiments carried out by the Universities of Sheffield and Castilla-La Mancha.