Optical characterization of photopolymers materials: theoretical and experimental examination of primary radical generation

Several studies of the time varying photon absorption effects, which occur during the photo-initiation process in photopolymer materials, have been presented. Three primary mechanisms have been identified: (i) the dye absorption, (ii) recovery, and (iii) bleaching. Based on an analysis of these mechanisms, the production of primary radicals can be physically described and modelled. In free radical photo-polymerization systems, the excited dye molecules induce the production of the primary radicals, R ^?, which is a key factor in determining how much monomer is polymerized. This, in turn, is closely related to the refractive index modulation formed during holographic recording. In this article, by modifying the composition of a polyvinylalcohol/acrylamide based photopolymer material, i.e. excluding any co-initiator, the photo-kinetic behaviour of the material is greatly simplified. In this way, the rate constant of intersystem crossing, k _st, in going from the excited singlet state dye to the excited triple state dye can be determined. k _st is then available to be applied in a full model of the photo-initiation process making it possible to accurately predict the time varying concentration of primary radicals generated during exposure.     

Mechanisms responsible for chemical shifts of core-level binding energies and their relationship to chemical bonding

A comprehensive review of different mechanisms which contribute to the chemical shifts of core-level binding energies, BEs, is made. A principle focus is on showing how the mechanisms can be used to relate the BE shifts to features of the chemical bonding and chemical interactions in the studied system. Several initial state mechanisms are identified; while some are well known, the importance of others has been only recognized fairly recently. A theoretical framework is presented which places the analysis and interpretation of these BE shifts on a firm foundation. A rigorous definition and distinction of initial and final state effects is presented. This definition is applied to show that initial state effects are often the dominant factors for the chemical BE shifts. It is also shown that, in many cases, theoretical approaches involving the use of constrained variations can permit a clear and definitive separation of the contributions of the different mechanisms. Several representative applications to the analysis and interpretation of core-level BE shifts are described which show how the theoretical methods of analysis can be used to identify the mechanisms important for the BE shifts. Often more than one mechanism makes an important contribution to the shifts and it is common that the contributions will be canceling. When all of the relevant mechanisms are taken into account in the analysis of the BE shifts, these shifts do provide valuable information about the chemical bonding and electronic structure of the materials being studied. The mechanisms presented and the theoretical frameworks described provide a unified view of BE chemical shifts.     

Electromagnetically induced transparency in semiconductors via biexciton coherence

We report an experimental demonstration and theoretical analysis of electromagnetically induced transparency in a GaAs quantum well, in which the absorption of an exciton resonance is reduced by more than twentyfold. The destructive quantum interference in this scheme is set up by a control pulse that couples to a resonance of biexcitons. These studies illustrate that many-particle interactions, which are inherent in semiconductors and are often detrimental to quantum coherences, can also be harnessed to manipulate these coherences.     

有机双光子吸收材料的研究进展

本文综述了具有优异双光子吸收/双光子荧光性质的有机功能材料的研究工作和成果。近年来,有机材料凭借其出众的性质、丰富的种类、多重功能性以及快速的非线性光学响应引起国际科学和技术界的极大兴趣。文章介绍了测量材料的非线性光学性质和超快响应的实验方法,它们已被广泛应用于有机材料的研究工作,并且取得了重大的进展。本文描述了对偶极、四极、多枝结构、大环结构以及聚合物等有机材料的非线性光学性质和超快光学响应的研究结果。基于有机材料的迷人性质,具有优异非线性光学性质和超快响应的有机材料将会在很多领域显示出巨大的应用潜力。     

Mechanisms of primary long-lived defect production in pure quartz glasses under electron irradiation

Based on an analysis of the dependences of individual absorption band amplitudes in quartz glasses on the electron beam (EB) fluence, mechanisms of primary defect production in KS-4V, KU-1, and Corning 7980 glasses during their prolonged irradiation by EB pulses are determined.     

Primary ion fluence dependence in time-of-flight SIMS of self-assembled monolayer of alkyl thiol molecules on Au(1 1 1)—Discussion of static limit

The nondestructive nature of static secondary ion mass spectrometry (SIMS) in the context of studies of self-assembled monolayers (SAMs) of organic molecules has been examined by measuring the primary ion fluence dependence of secondary ion signals with two well-known SAMs, C₁₈H₃₇SH on Au(1 1 1) and C₁₈H₃₇PO₃H₂ on freshly cleaved mica. This SIMS analysis is challenging because the bonding nature is delicate and the areal molecular density is less than 10¹⁵ cm⁻². In SIMS, it is prevalently assumed that if the primary ion fluence is confined to not more than 1 × 10¹² cm⁻², all secondary ion signals should not change by more than 10% and the practically defined static condition is satisfied. Our results from time-of-flight SIMS with the common primary ions of Bi₃⁺, Bi⁺ and Ar⁺, indicate that this prevalent static assumption fails for both model SAMs. The SIMS results from the phosphyl case, which have been recently published, consistently display the evidence of bombardment-induced damage. In comparison, the thiol case presented here shows much more complex primary ion fluence dependence of SIMS signals. It is therefore concluded that practical static analysis should use primary ion fluence not more than 1 × 10¹¹ cm⁻² or should simply record and report the effects of primary ion fluence.     

Some physical insights for active acoustic structure

Active acoustic structure (AAS) proposed in recent years has been viewed as an encouraging approach to actively control sound radiation from vibrating structures. Much work of AAS has been done on theoretical model, arrangement of the secondary panel and error sensing, and experimental investigation of AAS system, but physical mechanisms is little understanding. In this study, under minimization of the total sound power output, the physical mechanism of noise reduction is investigated by analyzing the sound power output change of primary and secondary structures and the distribution of sound intensity. The results show that there are two kinds of energetic behaviors, which includes the suppression of the sound power radiated by the primary panel and absorption of sound power by the primary and secondary panels.     

Optical limiting characteristics of Dichloridobis(1-ethyl-2, 6-dimethylpyridinium-4-olate-κO) zinc (II)

A newly synthesized metal-organic co-ordination compound Dichloridobis (1-ethyl-2,6-dimethylpyridinium-4-olate-κO) zinc(II) (EDMPZC) is characterized by FTIR to confirm the molecular structure. It crystallizes in the monoclinic system with the centrosymmetric space group C2/c and the unit cell parameters are determined from the single crystal X-ray diffraction analysis. Optical energy band gap is found to be 3.5 eV by UV-Visible absorption studies. The third order nonlinear optical properties were investigated by open-aperture Z-scan measurements using Nd:YAG laser (532 nm, 5 ns). Two-photon absorption and reverse saturable absorption mechanisms at the excitation wavelength are found to cause the observed optical limiting behavior.     

A method for determining iron-containing components of liquor in neurosurgical problems

Results of spectral studies of human liquor aimed at determining the specific features of its composition arising as a result of neurosurgical diseases and during the recovery period are presented. A method for detecting characteristic bands attributed to pathology, which is based on precision measurements of the UV-VIS absorption spectra of liquor and on their subsequent computer analysis is presented. With this method, ironcontaining components of liquor can be qualitatively and quantitatively determined, which is important in solving neurosurgical problems.     

Advances in theoretical and experimental XAFS studies of thermodynamic properties,anharmonic effects and structural determination of fcc crystals

Thermodynamic properties, anharmonic effects and structural determination of fcc crystals have been studied based on the theoretical and experimental Debye–Waller factors presented in terms of cumulant expansion up to the third order, thermal expansion coefficient, X-ray absorption fine structure (XAFS) spectra and their Fourier transform magnitudes. The advances in these studies are performed by the further development of the anharmonic correlated Einstein model primary only for approximating three first XAFS cumulants into the method using that all the considered theoretical and experimental XAFS parameters have been provided based on only the calculated and measured second cumulants. The obtained cumulants describe the anharmonic effects in XAFS contributing to the accurate structural determination. Numerical results for Cu are found to be in good agreement with the experimental values extracted by using the present advanced method and with those obtained by the other measurements.     

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.     

Absorption spectroscopy of cold caesium atoms confined in a magneto-optical trap

Absorption spectra of cold caesium atoms confined in a magneto-optical trap are measured around D_2 line at 852nm with a weak probe beam. Absorption reduction dip due to electromagnetically induced transparency (EIT) effect induced by the cooling/trapping field in a V-type three-level system and a gain peak near the cycling transition are clearly observed. Several mechanisms mixed with EIT effect in a normal V-type three-level system are briefly discussed. A simple theoretical analysis based on a dressed-state model is presented for interpretation of the absorption spectra.     

铷蒸气Λ-型系统中的受激Raman谱与光泵效应

从理论和实验上研究了⁸⁵Rb 原子蒸气D1线系统中的受激Raman现象. 在Λ-型能级系统中, 抽运光对弱探测光的影响有两部分: 受激Raman激发和光泵效应. 在一定的抽运光强度和失谐量条件下, 受激Raman谱表现为增益谱或损耗谱; 以光泵效应导致的吸收谱为背景时, 便分别形成了窄线宽透明窗口或线宽差异很大的吸收双线. 理论模拟和实验结果基本符合. 基于这些研究, 从新的角度阐述了在Λ-型系统中的电磁感应透明和Autler-Townes分裂这两个重要现象与受激Raman谱之间的关系. 关键词： 受激Raman谱 光泵效应 电磁感应透明 吸收双线     

Forward coherent inelastic Mössbauer scattering of synchrotron radiation

A theoretical analysis is presented of the possibilities of satisfying the conditions of phase matching (PM) in the coherent inelastic Mössbauer scattering (CIMS, which is scattering accompanied by the creation or annihilation of phonons) of synchrotron radiation (SR) and the conditions under which the maximum intensity of CIMS obtains are studied. Of the two types of CIMS — 1) participation of phonons in a scattering event only in the stage of absorption or only during re-emission of a photon, and 2) participation of phonons in both stages of scattering — PM is possible only in the first. The process in which phonons participate only at the photon absorption stage leads to efficient conversion of the SR from a wide spectral line into a narrow line, determined by the width of the Mössbauer transition. Photons of this type of CIMS effectively possess a higher penetrating power than the standard Mössbauer radiation, and their spectral distribution is shifted somewhat in the direction of low frequencies.     

An alternate empirical relationship for the optical absorption edges of certain ferroelectric materials

No theoretical justification has been found for the empirical relationship which has been used previously to describe the optical absorption edges of BaTiO₃ and KTaO₃. In this communication, another, equally valid, empirical relationship is presented that describes both the absorption edges of these materials and new data on gadolinium molybdate.     

Velocity diffusion studied by Hanle effect and saturated absorption

A technique has been developed to detect the Hanle effect on the absorption of the probe beam, in a saturated absorption experiment. The theoretical shape and the experimental verification, on the neon 6328 Å line, are presented here. Since this technique selects a narrow band in the atomic velocity distribution, the Hanle effect curve is sensitive to velocity changing processes which do not destroy alignment: the existence of these processes is demonstrated.     

Laser-driven switching dynamics in phase change materials investigated by time-resolved X-ray absorption spectroscopy

Time-dependent X-ray absorption spectroscopy at the Ge L₃ edge is used to study the optical switching dynamics of epitaxial phase change materials grown on Si(111) membranes. Small differences between the static absorption spectra of the crystalline and laser-amorphized phase of GeTe are observed. Furthermore, a new approach for pump-probe studies on phase change materials is presented. However, no time-dependent change in the X-ray absorption > 0.1% has been detected so far. This is mainly attributed to sample deterioration at 3 kHz pump-probe rates.     

Analysis of the tuning and operation of reflection resonator EPR spectrometers

This paper investigates basic characteristics of the electron paramagnetic resonance (EPR) signal obtained from spectrometers employing reflection resonators. General equations are presented which reveal the phase and amplitude dependence on instrumental parameters of both components of the continuous wave (CW) EPR signal (absorption and dispersion). New phase vector diagrams derived from these general equations are presented for the analysis of the EPR response. The dependence of the phase and absolute value of the CW EPR signal on the local oscillator (LO) phase and on resonator offset and coupling is presented and analyzed. The EPR spectrometer tuning procedures for both balanced and unbalanced heterodyne receivers are analyzed in detail using the new phase diagrams. Extraneous signals at the RF input of the microwave receiver (resulting from circulator leakage and reflections in the resonator transmission line) have been taken into account and analyzed. It is shown that a final tuning condition that corresponds to an extremum of the receiver output as a function of the resonator frequency is necessary and sufficient for the acquisition of pure absorption signal. This condition is universal: it applies to all spectrometer configurations in all frequency ranges. High Frequency EPR spectrometer (130 GHz) data are used to generate experimental phase diagrams that illustrate the theoretical concepts presented in the paper. Conditions are presented under which the absorption signal can be measured with complete suppression of the dispersion, independent of the mutual frequency offset between the microwave source and the EPR sample resonator. Equations describing the approximate relationship between changes of the resonator properties (Q-factor and frequency) and paramagnetic susceptibility are derived and analyzed.     

Absorption line profile recovery based on residual amplitude modulation and first harmonic integration methods in photoacoustic gas sensing

Two methods for recovery of gas absorption line profiles are presented in this paper using photoacoustic spectroscopy and tunable diode laser spectroscopy (TDLS) with wavelength modulation (WM). A theoretical analysis based on Fourier coefficients is given in order to describe the various components that arise under simultaneous intensity and frequency modulation. The first method makes use of the residual amplitude modulation (RAM) signal which is always present in current modulation of distributed feedback (DFB) tunable diode lasers. The second method involves integration of a near-pure first harmonic derivative signal, separated from other distorting components by appropriate choice of the lock-in detection phase in the case of low modulation index. Good agreement is obtained with both methods between the experimental results and the theoretical simulation for the P17 absorption line of acetylene at 1535.39 nm but the second method gives a much improved accuracy and signal-to-noise ratio in lineshape recovery with photoacoustic spectroscopy.     

Structure-dependent behaviors of diode-triggered silicon controlled rectifier under electrostatic discharge stress

The comprehensive understanding of the structure-dependent electrostatic discharge behaviors in a conventional diode-triggered silicon controlled rectifier(DTSCR) is presented in this paper. Combined with the device simulation, a mathematical model is built to get a more in-depth insight into this phenomenon. The theoretical studies are verified by the transmission-line-pulsing(TLP) test results of the modified DTSCR structure, which is realized in a 65-nm complementary metal–oxide–semiconductor(CMOS) process. The detailed analysis of the physical mechanism is used to provide predictions as the DTSCR-based protection scheme is required. In addition, a method is also presented to achieve the tradeoff between the leakage and trigger voltage in DTSCR.