InAsSb/InAsSbP double heterostructure lasers for 3-4 micrometer spectral range

InAsSb/InAsSbP double heterostructure diode lasers for the spectral range of 3-4 microm grown by liquid phase epitaxy have been investigated. The laser tuning was studied as a function of the stripe width. The temperature and current tuning of such lasers was measured. Emission spectra, far-field patterns and wavelength tuning versus current have been studied in the wide current range from threshold, Ith, up to 6Ith at liquid nitrogen temperature. Current wavelength tuning in single-mode lasing has been obtained both towards the shorter wavelengths (up to 4.56 cm-1) and towards the longer wavelengths (up to 0.9 cm-1) at the temperature T=77K. Comparison of the emission properties of the lasers, driven by different types of current pulses showed the same quantum-mechanical nature of current tuning. The theoretical model of this nonlinear optical phenomenon is proposed. The estimated times of current tuning defined mainly by the photon lifetime in the cavity are about 10(-9) to 10(-12) s. The emission line-width was determined to be 20 MHz. Optimal conditions were found for the use of the lasers and were employed for the detection of NH3, CH3Cl, OCS and atmospheric water.     

Frequency tuning of long-wavelength VCSELs

Tuning properties of long-wavelength VCSELs have been studied experimentally, for the first time to our knowledge. Injection current and temperature tuning rates of two VCSELs operating near 1,512 and 1,577 nm have been measured using a Fabry-Perot etalon with free spectral range 0.056 cm(-1). A 100-Hz saw-tooth modulation with depths of modulation of approximately 10% or less was superimposed on a direct injection current (dc bias) to tune lasers in narrow spectral intervals (0.3-1.2 cm(-1)) around a central frequency set by the dc bias. The lasers have been found to be capable of being tuned faster at higher levels of dc bias. The enhancement factors were up to approximately 2 and approximately 3 for the 1,512- and 1,577-nm lasers, respectively, as compared with their tuning rates measured at the levels of the dc bias close to the threshold of lasing. A linear dependence between injection current tuning rates and the levels of dc bias has been observed. Temperature tuning coefficients have been proved to be independent of the laser heat sink temperature and of the dc bias. Frequency tuning curves were approximated with a second-order polynomial. The frequencies of more than 40 absorption lines of CO, CO(2), H(2)O and NH(3) known from spectral databases were compared with the calculated frequencies. The accuracy of the approximation was found to be within 0.2 cm(-1) for spectral intervals up to 38 cm(-1). The dependence of current tuning rates of the VCSELs on dc bias was shown to be taken into account for accurate analysis of absorption line profiles. The results obtained can be used for precise spectroscopic measurements with long-wavelength VCSELs.     

Stabilization, injection and control of quantum cascade lasers, and their application to chemical sensing in the infrared

Quantum cascade lasers (QCLs) are a relatively new type of semiconductor laser operating in the mid- to long-wave infrared. These monopolar multilayered quantum well structures can be fabricated to operate anywhere between 3.5 and 20 microm, which includes the molecular fingerprint region of the infrared. This makes them an ideal choice for infrared chemical sensing, a topic of great interest at present. Frequency stabilization and injection locking increase the utility of QCLs. We present results of locking QCLs to optical cavities, achieving relative linewidths down to 5.6 Hz. We report injection locking of one distributed feedback grating QCL with light from a similar QCL, demonstrating capture ranges of up to +/-500 MHz, and suppression of amplitude modulation by up to 49 dB. We also present various cavity-enhanced chemical sensors employing the frequency stabilization techniques developed, including the resonant sideband technique known as NICE-OHMS. Sensitivities of 9.7 x 10(-11) cm(-1) Hz(-1/2) have been achieved in pure nitrous oxide.     

基于氯化胆碱离子液体的铜电沉积研究（英文）

采用恒电流和恒电位方法,基于含有氯化铜溶液的乙二醇-氯化胆碱或硫脲-氯化胆碱离子液体,室温下在钢阴极上进行了铜的电沉积. 利用扫描电子显微镜和X-射线衍射技术研究了各种实验条件对电沉积的影响以及沉积层的形貌. 结果表明,室温下施加不超过-0.45 V的沉积电位和不超过-4.0 A·m^-2的沉积电流密度,可以同时从氯化胆碱基乙二醇和硫脲离子液体中沉积得到非常光滑、有光泽、致密且具有良好结合力、色泽鲜艳的铜金属涂层. 铜的电沉积阴极电流效率约为97%.     

Sodium-tolerant matrix for matrix-assisted laser desorption/ionization mass spectrometry and post-source decay of oligonucleotides

A mixture of 2',4',6'-trihydroxyacetophenone in acetonitrile and aqueous triammonium citrate solution in a 1:1 molar proportion (0.2 M concentration) was found to be a good matrix for the detection of synthetic oligodeoxynucleotide samples. A high proportion of volatile solvent as well as the high salt content ensure fast co-crystallization of the matrix, co-matrix and analyte molecules. Matrix-assisted laser desorption/ionization (MALDI) mass spectra obtained in negative ion reflectron mode from samples prepared with this protocol show deprotonated molecules [M - H](-), rather than sodium adducts, as the most abundant ions even when up to 50 mM of sodium chloride is present in the sample. The matrix is shown to be effective for low mass modified single nucleotides as well as for longer oligodeoxynucleotides (up to 18mer). Post-source decay (PSD) mass spectra can also be obtained by increasing the laser fluence. Simple sequence information such as the identity and localization of a deleted base or the 5'/3' orientation can then easily be obtained. The calibration method and mass accuracy required are discussed depending on the type of information required.     

pH-sensitive C-ON bond homolysis of alkoxyamines of imidazoline series with multiple ionizable groups as an approach for control of nitroxide mediated polymerization

Recently, a new concept of pH-switchable agents for reversible addition-fragmentation chain transfer (RAFT) polymerization has been introduced by Benaglia et al. (J. Am. Chem. Soc.2009, 131, 6914-6915). In this paper we extended the concept of pH-switchable mediators to nitroxide mediated polymerization (NMP) by employing nitroxides with basic or acidic groups as controlling agents. Four alkoxyamines, the derivatives of 2-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-2-(pyridin-4-yl)-2,5-dihydro-1H-imidazol-1-oxyl and 2-(2-carboxyethyl)-5,5-diethyl-2,4-dimethyl-2,5-dihydro-1H-imidazol-1-oxyl, have been prepared. The influence of pH on alkoxyamine homolysis rate constants (k(d)) and on the nitroxide-alkyl radical recombination rate constants (k(c)) was studied. All alkoxyamines under study as well as the parent nitroxides have several basic groups, which under pH variation can undergo consecutive protonation. It was shown that the k(d) value under basic conditions are significantly (up to 15-fold) higher than in acidic solution at the same temperature, whereas the k(c) value in basic solutions decrease by a factor of 2 only. The efficiency of NMP is known to be dependent on k(d) and k(c), both constants being dependent on the monomer structure; therefore the performance of NMP of different monomers in the controlled mode requires different conditions. It is shown that the pH value crucially affects the polymerization regime, changing it from the controlled to the uncontrolled mode. The controlled regime of NMP of different hydrophilic monomers (sodium 4-styrenesulphonate and acrylamide) in aqueous solution under mild conditions (90 °C) can be achieved using the same alkoxyamine by the variation of the pH value. The chain length of polymers depends on pH value during the polymerization.     

The near-infrared (1.30-1.70 microm) absorption spectrum of methane down to 77 K

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by direct absorption spectroscopy between 1.30 and 1.70 microm (5850-7700 cm(-1)) using a newly developed cryogenic cell and a series of DFB diode lasers. The investigated spectral range includes part of the tetradecad and the full icosad regions for which only very partial theoretical analysis are available. The analysis of the low temperature spectrum will benefit from the reduction of the rotational congestion and from the narrowing by a factor of 2 of the Doppler linewidth allowing the resolution of a number of multiplets. Moreover, the energy value and rotational assignment of the angular momentum J of the lower state of a given transition can be obtained from the temperature variation of its line intensity. This procedure is illustrated in selected spectral regions by a continuous monitoring of the spectrum during the cell cool-down to 77 K, the temperature value being calculated at each instant from the measured Doppler linewidth. A short movie showing the considerable change of a spectrum during cool-down is attached as Supplementary Material. The method applied to a 30 cm(-1) section of the tetradecad spectrum around 6110 cm(-1) has allowed an unambiguous determination of the J values of part of the observed transitions.     

IR spectroscopic analysis of polymorphism in C13H14N4O

IR analysis is used here to investigate the changes in N-N, N-H, CO modes of thermally treated diphenyl carbazide (DPC) during the variation of temperature from room temperature up to ≈160°C. Polymorphism in DPC compound has been studied here by detecting the changes in some IR spectroscopic parameters (e.g., mode shift, band contour) during the elevation of temperature. Also, DSC, X-ray, NMR and atomic mass spectra are used as confirming tools for what is obtained by IR. All of the vibrations of DPC were found to be due to ionic fundamentals 3311 cm(-1), 3097 cm(-1), 3052 cm(-1), 1677 cm(-1), 1602 cm(-1), 1492 cm(-1), 1306 cm(-1), 1252 cm(-1), 887 cm(-1) and 755 cm(-1). The results revealed for the first time that the thermally treated DPC traverse four different phase transformations at 50°C, 90°C, 125°C and 140°C. The crystal structure was found to be amorphous, monoclinic, tetragonal, orthorhombic and amorphous within a temperature range (30°C-160°C). X-ray diffraction patterns support the results obtained by IR and DSC.     

A high current density DC magnetohydrodynamic (MHD) micropump

This paper describes the working principle of a DC magnetohydrodynamic (MHD) micropump that can be operated at high DC current densities (J) in 75-microm-deep microfluidic channels without introducing gas bubbles into the pumping channel. The main design feature for current generation is a micromachined frit-like structure that connects the pumping channel to side reservoirs, where platinum electrodes are located. Current densities up to 4000 A m(-2) could be obtained without noticeable Joule heating in the system. The pump performance was studied as a function of current density and magnetic field intensity, as well as buffer ionic strength and pH. Bead velocities of up to 1 mm s(-1) (0.5 microL min(-1)) were observed in buffered solutions using a 0.4 T NdFeB permanent magnet, at an applied current density of 4000 A m(-2). This pump is intended for transport of electrolyte solutions having a relatively high ionic strength (0.5-1 M) in a DC magnetic field environment. The application of this pump for the study of biological samples in a miniaturized total analysis system (microTAS) with integrated NMR detection is foreseen. In the 7 T NMR environment, a minimum 16-fold increase in volumetric flow rate for a given applied current density is expected.     

Tunable optically pumped lead-chalcogenide mid-infrared emitters on Si-substrates

Two types of novel lead-chalcogenide mid-IR emitters grown by molecular beam epitaxy (MBE) on Si or BaF(2) substrates are described:PbSe/PbEuSe edge emitting double heterostructure (DH) and quantum well (QW) lasers are pumped optically with low-cost III-V laser-diodes. They emit in the 3-6 microm range with powers up to 200 mW. Tuning is performed by temperature change and/or mechanically if bars with slightly tapered composition are used. A "wavelength transformer", a PbSe/PbEuSe active resonant cavity with top and bottom Bragg mirror transforms the incoming 0.8 microm pump radiation to e.g. 4.2 microm wavelength. It operates at room temperature, width and value of the emission line is determined by design.     

Critical evaluation of a handheld Raman spectrometer with near infrared (785nm) excitation for field identification of minerals

Handheld Raman spectrometers (Ahura First Defender XL, Inspector Raman DeltaNu) permit the recording of acceptable and good quality spectra of a large majority of minerals outdoors and on outcrops. Raman spectra of minerals in the current study were obtained using instruments equipped with 785 nm diode lasers. Repetitive measurements carried out under an identical instrumental setup confirmed the reliability of the tested Raman spectrometers. Raman bands are found at correct wavenumber positions within ±3 cm(-1) compared to reference values in the literature. Taking into account several limitations such as the spatial resolution and problems with metallic and black and green minerals handheld Raman spectrometers equipped with 785 nm diode lasers can be applied successfully for the detection of minerals from the majority of classes of the mineralogical system. For the detection of biomarkers and biomolecules using Raman spectroscopy, e.g. for exobiological applications, the near infrared excitation can be considered as a preferred excitation. Areas of potential applications of the actual instruments include all kind of common geoscience work outdoors. Modified Raman systems can be proposed for studies of superficial or subsurface targets for Mars or Lunar investigations.     

Site-selective nitrogen isotopic ratio measurement of nitrous oxide using 2 microm diode lasers

We demonstrate a high-precision measurement of the isotopomer abundance ratio 14N(15)N(16)O/15N(14)N(16)O/14N(14)N(16)O (approximately 0.37/0.37/100) using three wavelength-modulated 2 microm diode lasers combined with a multipass cell which provides different optical pathlengths of 100 and 1 m to compensate the large abundance difference. A set of absorption lines for which the absorbances have almost the same temperature dependence are selected so that the effect of a change in gas temperature is minimized. The test experiment using pure nearly natural-abundance N(2)O samples showed that the site-selective 15N/14N ratios can be measured relative to a reference material with a precision of +/-3 x 10(-4) (+/-0.3 per thousand) in approximately 2 h.     

The ground electronic state of KCs studied by Fourier transform spectroscopy

We present here the first analysis of laser induced fluorescence (LIF) of the KCs molecule obtaining highly accurate data and perform a direct potential construction for the X (1)Sigma(+) ground state in a wide range of internuclear distances. KCs molecules were produced by heating a mixture of K and Cs metals in a heat pipe at a temperature of about 270 degrees C. KCs fluorescence was induced by different laser sources: the 454.5, 457.9, 465.8, and 472.7 nm lines of an Ar(+) laser, a dye laser with Rhodamine 6G dye (excitation at around 16 870 cm(-1)), and 850 and 980 nm diode lasers (11 500-11 900 and 10 200-10 450 cm(-1) tuning ranges, respectively). The LIF to the ground state was recorded by a Bruker IFS-125HR Fourier transform spectrometer with a spectral resolution of 0.03 cm(-1). Particularly, by applying the 850 nm laser diode we were able to observe LIF progressions to very high vibrational levels of the ground state close to the dissociation limit. The present data field contains 7226 term values for the ground state X (1)Sigma(+) and covers a range from v(")=0 to 97 with J(") varying from 12 to 209. More than 10 000 fluorescence lines were used to fit the ground state potential energy curve via the inverted perturbation approach procedure. The present empirical potential extends up to approximately 12.6 A and covers more than 99% of the potential well depth, it describes most of the spectral lines with an accuracy of about 0.003 cm(-1) and yields a dissociation energy of 4069.3+/-1.5 cm(-1) for the ground state X (1)Sigma(+). First observations of the triplet ground state a (3)Sigma(+) of KCs are presented, and preliminary values of few main molecular constants could be derived.     

Construction and evaluation of a flow-through cell adapted to a commercial static mercury drop electrode (SMDE) to study the adsorption of Cd(II) and Pb(II) on vermiculite

This paper describes the construction and application of a robust flow-through cell for use with the capillary of a commercial static mercury drop electrode. Linearity of peak current was observed up to 0.50 mumol l(-1) for Cd(II) or Pb(II) in anodic stripping voltammetry experiments performed under continuous flow during the deposition step, using 120 s of deposition time and flow rate of 4.0 ml min(-1). Under these conditions the limits of detection for Cd(II) and Pb(II) were 13 and 17 nmol l(-1), respectively. An analytical throughput of 20 analyses per h was possible using 10 s for cleaning the cell between two samples and including the time needed for the potential scan, which was performed with the flow stopped, using the differential pulse mode for current sampling. The linear dynamic range can be extended up to 5 mumol l(-1) for both cations if the deposition time is decreased to 30 s, a condition in which the sampling throughput is 35 analyses per h. The proposed manifold was used to study the adsorption rates of Cd(II) and Pb(II) onto vermiculite at different pHs, allowing one to perform high sensitivity measurements at high sampling frequency, using low cost instrumentation.     

Quad quantum cascade laser spectrometer with dual gas cells for the simultaneous analysis of mainstream and sidestream cigarette smoke

A compact, fast response, infrared spectrometer using four pulsed quantum cascade (QC) lasers has been applied to the analysis of gases in mainstream (MS) and sidestream (SS) cigarette smoke. QC lasers have many advantages over the traditional lead-salt tunable diode lasers, including near room temperature operation with thermoelectric cooling and single mode operation with improved long-term stability. The new instrument uses two 36 m, 0.3 l multiple pass absorption gas cells to obtain a time response of 0.1s for the MS smoke system and 0.4s for the SS smoke system. The concentrations of ammonia, ethylene, nitric oxide, and carbon dioxide for three different reference cigarettes were measured simultaneously in MS and SS smoke. A data rate of 20Hz provides sufficient resolution to determine the concentration profiles during each 2s puff in the MS smoke. Concentration profiles before, during and after the puffs also have been observed for these smoke constituents in SS smoke. Also, simultaneous measurements of CO(2) from a non-dispersive infrared (NDIR) analyzer are obtained for both MS and SS smoke. In addition, during this work, nitrous oxide was detected in both the MS and SS smoke for all reference cigarettes studied.     

Molecular dynamics simulations of a chemical reaction; conditions for local equilibrium in a temperature gradient

We have examined a simple chemical reaction in a temperature gradient; 2F <==> F2. A mechanical model was used, based on Stillinger and Weber's 2- and 3-body potentials. Equilibrium and non-equilibrium molecular dynamics simulations showed that the chemical reaction is in local thermodynamic as well as in local chemical equilibrium (delta(r)G = 0) in the supercritical fluid, for temperature gradients up to 10(12) K m(-1). The reaction is thus diffusion-controlled. The velocity distributions of both components were everywhere close to being Maxwellian. The peak distributions were shifted slightly up or down from the average velocity of all particles. The shift depended on the magnitude of the temperature gradient. The results support the assumption that the entropy production of the reacting mixture can be written as a product sum of fluxes and forces. The temperature gradient promotes interdiffusion of components in the stationary state, a small reaction rate and an accumulation of the molecule in the cold region and the atom in the hot region.     

C2H2分子(X1∑g+,ν2”=1,J”)态mj定向布居及光学AC Stark效应

利用相干受激Ｒａｍａｎ抽运,选择性地激发Ｃ２Ｈ２分子单一振转态。在Ｒａｍａｎ泵浦与探测激光不同偏振条件下,获得紫外探测激光诱导的Ａ＾￣＾１Ｊ（Ｖ′３＝１）←－＾￣Ｚ＾２Σ＾＋ｇ,ｖ′２＝１,ｊ″）荧光增益光谱,从而研究了Ｃ２Ｈ２分子单一振转态的光学ＡＣ Ｓｔａｒｋ效应和ｍｊ的定向分布Ａ０＾（１）,利用Ｓｔａｒｋ线型加宽数值模型,从理论上计算得到的Ｒａｍａｎ线型与实验结果进行比较。     

NO3-+Cl2→ClONO2+Cl-反应势能面和势能阱

采用密度泛函理论B3LYP方法和6-311+G(d)基组, 计算构建离子-分子气相反应NO3-+Cl2→ClONO2+Cl-的三维势能面. 三维反应势能面证明该反应没有过渡态和势能垒, 但是存在一个深达-55.0 kJ/mol的势能阱(以氯气分子和硝酸根离子相隔无穷远为参量). 在势能阱底部, 有个化合物(O2NOClCl)- 称为势阱化合物, 依赖于势能阱而稳定存在. 理论红外光谱预测低温红外光谱能检测该势阱化合物. 低温条件下, 该反应由热力学控制, 反应产物是势阱化合物(O2NOClCl)-. 当温度升高, 该反应由动力学控制, 势阱化合物(O2NOClCl)-不稳定, 发生分解反应, 重新生成NO3-和Cl2. 研究结果可用来解释低温时ClONO2与Cl-气相反应不能产生Cl2的原因.