Linewidth Measurements Research Articles

1H nuclear magnetic resonance study of distinct interstitial hydrogen dynamics in ZnO

A comprehensive 1H nuclear magnetic resonance (NMR) study has been carried out for hydrogen dynamics in a sol–gel-prepared ZnO system. The temperature-dependent linewidth and chemical shift measurements sensitively reflected the proton motions and changes in the local environment. Besides, two types of interstitial proton (Hi+) motions were distinguished from the spin–spin relaxation time measurements, one of them with an activation energy of 0.16eV and the other with that of 0.33eV depending on the temperature ranges.

Diode laser spectroscopic measurements of gas temperature in a pulsed dielectric barrier discharge using collisional broadening and shift of 1s3−2p2and 1s5−2p7argon transitions

The average gas temperature rise within an argon dielectric barrier discharge operating from 50 to 500 Torr excited by 5 kHz repetition rate fast rise time high voltage pulse has been measured. For these measurements within high pressure discharges, we have employed two novel gas temperature measurement techniques based upon tunable diode laser absorption spectroscopy that take advantage of the nonresonant collision line broadening and collisional frequency shifts from relatively strong argon 1s3-2p2 and 1s5-2p7 transitions from the metastable states. An in situ estimate of collisional broadening coefficients for both transitions have been obtained from 5 to 30 Torr data using an independent estimate of gas temperature from Doppler line width measurements. Our measurements show that the effect of the isolated line assumption inherent within the van der Waals collisional impact approximation limit begins to fail for the 1s3-2p2 and 1s5-2p7 spectral lines when collisional line broadening exceeds ∼23 GHz line separation at gas pressure >300 Torr with gas temperature near ambient. A comparison of gas temperature estimates from both line broadening and peak frequency shift shows that the frequency shift provides a more reliable measurement of gas temperature, indicating that the isolated line assumption holds for collisional peak frequency shifts, even for partially overlapping lines.

Sub-Doppler spectroscopy with an external cavity quantum cascade laser

The linewidth of an external cavity quantum cascade laser is studied as a function of injection current and laser scan rate. The laser linewidth is inferred to be ca. 2.5 MHz from Lamb-dip spectra on a low pressure sample of NO and its variation with injection current is well modeled using literature values for the intrinsic material properties of the lasing medium. The laser linewidth measurements are corroborated by polarization spectroscopy studies as well as by analysis of hyperfine structure and cross-over resonances.

The effect of aluminum substitution on the mechanically induced self-sustaining reaction of molybdenum-silicon powders

The effect of Al concentration on the ignition of mechanically-induced self-sustaining reaction (MSR) in Mo + (2 − x)Si + 2xAl powder mixtures has been investigated. When MoSi2 is prepared by SHS method, Al addition results in the formation of Si-Al eutectic and consequently lowers the ignition temperature. In the case of MSR, replacing brittle Si with ductile Al also affects the activation process. The ignition of MSR was investigated as a function of the Al content in a SPEX 8000 Mixer Mill. The ignition time decreased by 30% between x = 0 and 0.08. At the same time, the grain size increased by about 50% according to XRD linewidth measurements. Comparison of SEM images suggests that Al substitution promotes the formation of agglomerates and lamellar structures, although the differences between the binary Mo-Si and Alcontaining samples are very small. Al substitution encourages the formation of hexagonal Mo(SiAl)2 over the tetragonal form of MoSi2. It also promotes more complete conversion during MSR.

Linewidth Narrowing and Power Scaling of Single-Frequency 2.X $\mu{\rm m}$ GaSb-Based Semiconductor Disk Lasers

A study of frequency stability and power scaling of single-mode GaSb-based 2.05-μm semiconductor disk laser (SDL) modules is presented. Single-mode emission and wavelength tuning over a range of 120 nm is accomplished by inserting a birefringent filter into the cavity. In order to evaluate the frequency stability, heterodyne beat-note linewidth measurements are performed for different time scales. Furthermore, a deeper insight in relevant noise mechanisms could be obtained by determining the Allan deviation and the frequency noise spectral density. For reducing the frequency noise, side-of-fringe and Pound-Drever-Hall locking are applied with the cavity length, and for the latter locking scheme also the pump diode current, controlled by the active feedback loop. That way, single-mode operation at a few kHz linewidth up to sampling times >;0.1 are achieved. Operating the SDL in a cavity configuration optimized for higher output powers, up to 1-W output power at a 100-μs sampled linewidth of 20 kHz were obtained when using active stabilization.

Measurement of photoluminescence spectral linewidth of a GaAs quantum well in perpendicular electric fields: Evidence of a crossover from trions to an electron-hole gas

By measuring the photoluminescence linewidth of a GaAs quantum well under perpendicular electric fields, we have traced the variation of the effective radius ${a}^{*}$ of a charged exciton (trion) as a function of electron density. The ${a}^{*}$ increases sharply above a critical density ${n}_{s}=2\ifmmode\times\else\texttimes\fi{}{10}^{14}$ m${}^{\ensuremath{-}2}$, which is consistent with the decrease of the screening length predicted by nonlinear-screening theory. Our analysis shows that the crossover from trions to the two-dimensional electron gas plus hole is generated by Coulomb screening in the high-electron-density regime, eliminating the possible mechanism by the trion localization effect due to the single-electron localization.

FMR linewidth and the crystallization processes in Co-based amorphous microwires

The ferromagnetic resonance (FMR) technique has been used for many years as a tool to characterize the dynamic magnetic properties of bulk, thin film magnetic materials and microwires. Also, the FMR linewidth is associated to the dissipative processes involved on the magnetization dynamics. Such dissipative channels may be separated in two groups: intrinsic and extrinsic ones. While the first one is related mainly to the Landau–Lifshitz (LL) and eddy-currents damping mechanisms, the second one take in to account contributions coming from the inhomogeneities in the sample. Each one of these relaxation processes contributes to the FMR linewidth in a different frequency and/or magnetic field range and they can be separated by an appropriate FMR linewidth measurement. This work presents FMR measurements, obtained by the impedance method, ranging from 100KHz to 1.8GHz, in Joule annealed Co-based amorphous microwires. It is shown that the crystallization process can be followed by the evaluation of the extrinsic magnetization damping terms, specifically analyzing contributions from inhomogeneities to the FMR linewidth. From the fitting of models which consider LL damping term, anisotropy dispersion and magnon scattering to the experimental data, three ranges of annealing temperatures can be distinguished in terms of spin dynamics on the studied samples: annealing temperatures lower than the Curie temperature, a temperature range between the Curie and the crystallization temperature and another temperature range above the crystallization temperature.

The Effect of Polarization Control in Loss-Compensated Recirculating Delayed Self-Heterodyne Interferometry Measurement of Laser Linewidth

In the implementation of the loss-compensated recirculating delayed self-heterodyne interferometry (LC-RDSHI) measurement of laser linewidth, we observe the fluctuations among the different orders of beat spectra, which are not expected according to theoretical analysis and may lead to the distortion of lineshape and inaccurate estimation of the laser linewidth. To explain the observation, we in this paper simplify the polarization model in the recirculating heterodyne ring interferometer containing a polarization controller (PC) and point out the effect of the polarization control in the LC-RDSHI measurement. The simulation result of our model explains well the observed fluctuations.

Improved Frequency Shifting Realization for the Delayed Self-Heterodyne Interferometric Linewidth Measurement

A new implementation of frequency shifting for the delayed self-heterodyne interferometer (DSHI) is proposed in this paper. In order to avoid the costly and complicated acoustic-optic modulator to shift frequency in the DSHI, we propose that a phase modulator can be used instead. The alternative strategy simplifies the complexity of the DSHI setup, as well as reduces the modulation-induced noise by modulating the two arms of DSHI at the same time. Theoretical and experimental analysis show that such a strategy successfully fulfills the frequency shifting function for the DSHI and accurate measurement of a laser’s linewidth and lineshape is realized correspondingly.

MEASUREMENTS OF ANISOTROPIC ION TEMPERATURES, NON-THERMAL VELOCITIES, AND DOPPLER SHIFTS IN A CORONAL HOLE

We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived parallel and perpendicular ion temperatures and non-thermal velocities. The perpendicular ion temperature was cooler than off-limb polar coronal hole measurements. The parallel ion temperature was consistent with a uniform temperature of 1.8 +/- 0.2 x 10^{6} K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R_sun. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for the perpendicular non-thermal velocity agree with Alfv\'en wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our parallel non-thermal velocity results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time varying intensity fluctuations. Doppler shift measurements yield outflows of ~5 km s^-1 for ions formed over a broad temperature range. This differs from other studies which found a strong Doppler shift dependence on formation temperature.

A comparative study of 1H and 19F Overhauser DNP in fluorinated benzenes

Hyperpolarization techniques, such as Overhauser dynamic nuclear polarization (DNP), can provide a dramatic increase in the signal obtained from nuclear magnetic resonance experiments and may therefore enable new applications where sensitivity is a limiting factor. In this contribution, studies of the (1)H and (19)F Overhauser dynamic nuclear polarization enhancements at 345 mT are presented for three different aromatic solvents with the TEMPO radical for a range of radical concentrations. Furthermore, nuclear magnetic relaxation dispersion measurements of the same solutions are analyzed, showing contributions from dipolar and scalar coupling modulated by translational diffusion and different coupling efficiency for different solvents and nuclei. Measurements of the electron paramagnetic resonance linewidth are included to support the analysis of the DNP saturation factor for varying radical concentration. The results of our study give an insight into the characteristics of nitroxide radicals as polarizing agents for (19)F Overhauser DNP of aromatic fluorinated solvents. Furthermore, we compare our results with the findings of the extensive research on Overhauser DNP that was conducted in the past for a large variety of other radicals.

The instantaneous linewidth measurement of DFB laser with ultrashort delay

The instantaneous linewidth in the process of tuning is a very important parameter of laser, however only static linewidth in steady state could be obtained by all kinds of measurement at present. So we proposed a method of measuring instantaneous linewidth by time-frequency analysis based on local mean decomposition, and after its validity of extracting the instantaneous phase noise of simulation signal was proved, we set the heterodyne measurement system with ultrashort delay (about 0.5 ns) which came from 10 cm optical path difference. Finally, we not only extracted the time-frequency spectrum of the beat signal’s phase noise power, but also obtained the instantaneous linewidth of distributed-feedback diode laser under the pulse current for the first time so far as we Rnow.

Charge density-dependent coil–globule transition of alkali metal polycarboxylates in aqueous organic solvent mixtures

The effects of polymer charge density on the counterion-specific and solvent-specific coil–globule transition of polycarboxylates were investigated for alkali metal salts of poly(styrene-alt-maleic acid) (PSaltMA) and poly(acrylic acid) (PAA) in aqueous organic solvent mixtures. The order of the transition region, namely, the counterion specificity for the transition in, e.g., aqueous dimethyl sulfoxide (DMSO), was the same for both polyelectrolytes, Na+ > K+ > Cs+ > Li+, while the discrepancy of the transition region between Na+ and Li+ systems was appreciably narrower for PSaltMA (approximately 20 vol%) than that of PAA (approximately 29 vol%). Such diminished counterion specificity for the former was ascribed to the nonuniform charge array. Namely, PSaltMA has two kinds of nearest charge arrays, one is the shorter spacing between the maleic acid carboxyl groups and the other is the longer one via one styrene group. Thus, the former may be favorable for binding of the smaller counterion (i.e., Li+) and the latter for the larger one (Cs+). Such a “size-fitting effect” for the counterion binding was in fact further confirmed with variously neutralized PAAs. For example, the counterion specificity in aqueous DMSO of PAA40 that was neutralized to 40 % was Cs+ > K+ > Na+ > Li+, showing that the largest counterion becomes most favorable in inducing the transition with increasing average charge spacing. In fact, the nuclear magnetic resonance line width measurement for 133Cs suggested that the counterion binding strength of the large counterion for PAA increases with decreasing charge density from 100 to 40 % neutralization.

Monte Carlo Simulation of Secondary Electron Emission from Dielectric Targets

In modern physics we are interested in systems with many degrees of freedom. The Monte Carlo (MC) method gives us a very accurate way to calculate definite integrals of high dimension: it evaluates the integrand at a random sampling of abscissa. MC is also used for evaluating the many physical quantities necessary to the study of the interactions of particle-beams with solid targets. Letting the particles carry out an artificial random walk and taking into account the effect of the single collisions, it is possible to accurately evaluate the diffusion process.Secondary electron emission is a process where primary incident electrons impinging on a surface induce the emission of secondary electrons. The number of secondary electrons emitted divided by the number of the incident electrons is the so-called secondary electron emission yield. The secondary electron emission yield is conventionally measured as the integral of the secondary electron energy distribution in the emitted electron energy range from 0 to 50eV.The problem of the determination of secondary electron emission from solids irradiated by a particle beam is of crucial importance, especially in connection with the analytical techniques that utilize secondary electrons to investigate chemical and compositional properties of solids in the near surface layers. Secondary electrons are used for imaging in scanning electron microscopes, with applications ranging from secondary electron doping contrast in p-n junctions, line-width measurement in critical-dimension scanning electron microscopy, to the study of biological samples.In this work, the main mechanisms of scattering and energy loss of electrons scattered in dielectric materials are briefly treated. The present MC scheme takes into account all the single energy losses suffered by each electron in the secondary electron cascade, and is rather accurate for the calculation of the secondary electron yield and energy distribution as well.

Evidence of plasma polarization shift of Ti He-α resonance line in high density laser produced plasmas

A spectroscopic study of the He-α (1s2 1s0 - ls2p 1p1) line emission (4749.73 eV) from high density plasma was conducted. The plasma was produced by irradiating Ti targets with intense (I ≈ l×l019 W/cm2), 400nm wavelength high contrast, short (45fs) p-polarized laser pulses at an angle of 45°. A line shift up to 3.4+1.0 eV (1.9±0.55 mÅ) was observed in the He-α line. The line width of the resonance line at FWHM was measured to be 12.1±0.6 eV (6.7±0.35 mÅ). For comparison, we looked into the emission of the same spectral line from plasma produced by irradiating the same target with laser pulses of reduced intensities (≈1017 W/cm2): we observed a spectral shift of only 1.8+1.0 eV (0.9+0.55mÅ) and the line-width measures up to 5.8+0.25 eV (2.7+0.35 mÅ). These data provide evidence of plasma polarization shift of the Ti He-α line.

Influence of thermal history on mesoscale ordering in polydomain smectic networks

AbstractDramatic changes in mesoscale ordering and macroscopic mechanical behavior are observed in smectic polydomain networks after annealing at a temperature well above the glass transition temperature but below the clearing temperature. Tensile testing reveals gradual stiffening and loss of extensibility, and X‐ray linewidth measurements confirm that stiffening is initially due to thickening of domains. At long annealing times, a more highly ordered smectic mesophase forms, further stiffening the networks and reducing their extensibility. Increasing the concentration of (flexible) crosslinkers hinders domain growth and suppresses formation of the higher order mesophase, a useful guideline for design of smectic networks that exhibit reduced sensitivity to thermal history. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Utilizing a Water-Soluble Cryptophane with Fast Xenon Exchange Rates for Picomolar Sensitivity NMR Measurements

Hyperpolarized (129)Xe chemical exchange saturation transfer ((129)Xe Hyper-CEST) NMR is a powerful technique for the ultrasensitive, indirect detection of Xe host molecules (e.g., cryptophane-A). Irradiation at the appropriate Xe-cryptophane resonant radio frequency results in relaxation of the bound hyperpolarized (129)Xe and rapid accumulation of depolarized (129)Xe in bulk solution. The cryptophane effectively "catalyzes" this process by providing a unique molecular environment for spin depolarization to occur, while allowing xenon exchange with the bulk solution during the hyperpolarized lifetime (T(1) ≈ 1 min). Following this scheme, a triacetic acid cryptophane-A derivative (TAAC) was indirectly detected at 1.4 picomolar concentration at 320 K in aqueous solution, which is the record for a single-unit xenon host. To investigate this sensitivity enhancement, the xenon binding kinetics of TAAC in water was studied by NMR exchange lifetime measurement. At 297 K, k(on) ≈ 1.5 × 10(6) M(-1) s(-1) and k(off) = 45 s(-1), which represent the fastest Xe association and dissociation rates measured for a high-affinity, water-soluble xenon host molecule near rt. NMR line width measurements provided similar exchange rates at rt, which we assign to solvent-Xe exchange in TAAC. At 320 K, k(off) was estimated to be 1.1 × 10(3) s(-1). In Hyper-CEST NMR experiments, the rate of (129)Xe depolarization achieved by 14 pM TAAC in the presence of radio frequency (RF) pulses was calculated to be 0.17 μM·s(-1). On a per cryptophane basis, this equates to 1.2 × 10(4)(129)Xe atoms s(-1) (or 4.6 × 10(4) Xe atoms s(-1), all Xe isotopes), which is more than an order of magnitude faster than k(off), the directly measurable Xe-TAAC exchange rate. This compels us to consider multiple Xe exchange processes for cryptophane-mediated bulk (129)Xe depolarization, which provide at least 10(7)-fold sensitivity enhancements over directly detected hyperpolarized (129)Xe NMR signals.

Sub-Nanometer Line Width and Line Profile Measurement Using STEM Images with Metal Coating

The novel method of sub-nanometer uncertainty for the line width and line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement. In accordance with the proposed method, the traceability and reference metrology of line width measurements are established using Si lattice structures. The interface of SiO2-Air is defined using image intensity of STEM image after metal coating. The edge positions of the Si line from top to bottom are detected. Then, the pixel size of the images is evaluated using 2D Fourier analysis for Si lattice structures. Using the proposed method, the line profile and line width of 50 nm are measured with expanded uncertainty less than 0.3 nm.

Measurement of the intrinsic linewidth of terahertz quantum cascade lasers using a near-infrared frequency comb

We report the measurement of the frequency noise power spectral density of a quantum cascade laser emitting at 2.5THz. The technique is based on heterodyning the laser emission frequency with a harmonic of the repetition rate of a near-infrared laser comb. This generates a beatnote in the radio frequency range that is demodulated using a tracking oscillator allowing measurement of the frequency noise. We find that the latter is strongly affected by the level of optical feedback, and obtain an intrinsic linewidth of ~230Hz, for an output power of 2mW.

Measurement of intrinsic Brillouin linewidth of fibers based on stimulated Brillouin scattering slow light

Intrinsic Brillouin linewidth is one of the essential parameters to optimize the gain spectrum of stimulated Brillouin scattering (SBS). A novel method for the measurement of the intrinsic Brillouin line-width based on SBS slow light is proposed and demonstrated. In this method, an implicit model based on the transient SBS theory is developed, and a data processing method is designed to obtain the value of the intrinsic Brillouin linewidth from the model. The measured results show that the method is effective for studying SBS slow light.