Line-narrowing Effects Research Articles

Spectral line shapes of self-broadened P-branch transitions of oxygen B band

We used the Pound–Drever–Hall-locked frequency-stabilized cavity ring-down spectrometer assisted by the optical frequency comb for systematic line-shape study of self-broadened P-branch transitions of the O216B band [b1Σg+(v=1)←X3Σg−(v=0)]. In the line-shape analysis we take into account the line-narrowing effects described by Dicke narrowing or the speed dependence of collisional broadening. The relation between the parameters describing Dicke narrowing with the use of the soft- and hard-collision models is discussed and verified experimentally in the low pressure regime using the multispectrum fitting technique. We report line positions with uncertainties of about 170kHz, the collisional broadening coefficients with 0.45% uncertainties, and line intensities with 0.5% uncertainties. We compare these results to data available in the literature.

Line-narrowing effects in the near-infrared spectrum of water and precision determination of spectroscopic parameters.

A dual laser absorption spectrometer operating at 1.39 μm was employed to acquire high-quality absorption spectra in coincidence with the 44,1 → 44,0 line of the H2 (18)O ν1 + ν3 band, at the temperature of the triple point of water. A rather sophisticated global fitting procedure was developed and used to simultaneously fit spectra across the explored pressure range, roughly between 1 and 4Torr. Adopting the speed-dependent Galatry profile with a hypergeometric dependence of the collisional width and shift on the absorbers' velocity, we could take into account narrowing effects ascribed to collision-induced velocity changes and speed-dependence of relaxation rates. The global approach allowed us to implement and exploit some relevant physical constraints at the aim of reducing significantly statistical correlation issues among free parameters. Consequently, we demonstrated the possibility of determining pressure broadening and shifting parameters with high precision and accuracy, at the level of one part over 10(3). Furthermore, even being in the Doppler regime, it was possible to determine the effective frequency of velocity-changing collisions for self-colliding H2 (18)O molecules.

A review of molecular effects in gas-phase KL X-ray emission

The unique capabilities of resonant inelastic X-ray scattering (RIXS) to provide a deep insight into molecular dynamics following core excitation are reviewed here. Characteristic features of molecular X-ray emission are experimentally observed and theoretically interpreted. Some of our most significant results on molecular dynamics following deep core excitation are presented. In particular, we provide several examples of nuclear dynamics on the femtosecond or subfemtosecond time scale; line-narrowing effects related to the quenching of vibrational structure due to parallelism of intermediate and final state curves; anomalous line dispersion across a resonance, which is due to core-hole lifetime effects; spin–orbit-state populations derived from polarized RIXS experiments. We also show how to connect the RIXS results to the general chemical properties of the investigated systems.

Effects of line-narrowing of amplified spontaneous emission analyzed by a Monte Carlo model

This work focuses on the effects caused by line-narrowing of the amplified spontaneous emission (ASE) encountered in two-photon laser-induced fluorescence (TPLIF) processes. The line-narrowing effects complicate the TPLIF problem significantly, but are important for the quantitative interpretation of the TPLIF measurements. Past models are predominately developed for one-dimensional (1D) problem under ideal conditions. Therefore, this work develops a Monte Carlo (MC) method to robustly and flexibly incorporate non-ideal conditions including arbitrary temporal, spatial, and spectral beam profiles in multi-dimension practical problems. The MC model was the applied to analyze the TPLIF processes, both in 1D and 2D. The results show that the ASE radiation is more effectively amplified when the line-narrowing effects are considered than not. Because the ASE serves as a depopulation mechanism in TPLIF, such enhanced amplification has direct implications to the quantification of signals typically measured in practice. For example, our results show that neglecting the line-narrowing effects can cause significant error in the interpretation of the LIF and ASE signals. These results are hence expected to be useful for the design and analysis of experiments.

Line-shape study of self-broadened O2transitions measured by Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectroscopy

We present high-sensitivity and high-spectral-resolution line-shape and line-intensity measurements of self-broadened O${}_{2}$ $b{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Sigma}}_{g}^{+}(v=1)\ensuremath{\leftarrow}X{\phantom{\rule{0.16em}{0ex}}}^{3}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}(v=0)$ band transitions measured using the Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectroscopy technique. We give collisional broadening parameters and take into account the line-narrowing effects described by Dicke narrowing or the speed dependence of collisional broadening. We compare line intensities measured with relative uncertainties below 0.4% to data available in the HITRAN spectroscopic database.

New Line Narrowing Effects in the Infrared Collision-Induced Spectra of Molecular Hydrogens in Liquid Neon

The first spectroscopic observation of the relative (solute-solute) diffusion in a fluid environment is reported. New, unusually sharp Q1q(J) lines developing against the diffuse background in the collision-induced fundamental IR bands of hydrogen isotopomers (H2, D2, and HD) dissolved in liquid Ne (T approximately 25 K) are studied as functions of the solute concentration x. In all cases, the Q1q intensity parabolically scales with x, accompanied by a striking narrowing of the line shapes. The narrowing, as revealed by the p-H2 solution studies, is due to a faster growth with x of the sharper solute-solute induced component of the single Q1q(0) line. The latter as well as other observed solute-solute lines are strongly narrowed by fast velocity decorrelations and are signatures of microscopic-scale diffusion. Also, a first observation of the solute-solvent induced J-->J + 4 transitions is reported.

Line narrowing effects and enhanced back scattering from ZnO colloids

The dependence of the fluorescence emission intensity from nano ZnO colloid as a function of incident laser power is investigated. Emission in the near UV region from ZnO particles in diethylene glycol medium is studied using frequency tripled radiations at 355 nm from Nd-YAG laser. The spectrum, which was broad at lower pump intensities, exhibits an increase in the intensity as well as line narrowing above a threshold. The emission occurs in all directions and varies with pumping area. Results indicate the phenomenon of random lasing action due to multiple scattering inside the highly disordered medium. Coherent back scattering experiments confirm multiple scattering and weak localization effects in these samples. These preliminary studies show that colloidal nano ZnO medium is a promising candidate for random lasers.

2H double-quantum MAS NMR spectroscopy as a probe of dynamics on the microsecond timescale in solids

The sidebands observed in the magic angle spinning (MAS) NMR spectrum of a spin I = 1 2H nucleus may be very strongly broadened if motion is present in the solid. The broadening arises from interference between the line-narrowing effects of MAS and the dynamics-driven reorientation of the 2H quadrupole tensor. Here, we show that this motional broadening is absent or much reduced in the corresponding double-quantum MAS NMR spectrum. This observation suggests a new approach to studying dynamics in solids and examples are drawn from 2H MAS NMR of oxalic acid dihydrate, sodium tetrathionate dihydrate, and the synthetic polymer PMMA.

Conformation and mobility of the arabinan and galactan side-chains of pectin

The function of the arabinan and galactan side-chains of pectin remains unknown. We describe 13C NMR experiments designed to yield spectra from the most mobile polymer components of hydrated cell walls isolated from a range of plant species. In pectin-rich cell walls, these corresponded to the pectic side-chains. The arabinan side-chains were in general more mobile than the galactans, but the long galactan side-chains of potato pectin showed high mobility. Due to motional line-narrowing effects these arabinan and galactan chains gave 13C NMR spectra of higher resolution than has previously been observed from ‘solid’ biopolymers. These spectra were similar to those reported for the arabinan and galactan polymers in the solution state, implying time-averaged conformations resembling those found in solution. The mobility of the highly esterified galacturonan in citrus cell walls overlapped with the lower end of the mobility range characteristic of the pectic side-chains. The cellulose-rich cell walls of flax phloem fibres gave spectra of low intensity corresponding to mobile type II arabinogalactans. Cell walls from oat coleoptiles appeared to contain no polymers as mobile as the pectic arabinans and galactans in primary cell walls of the other species examined. These properties of the pectic side-chains suggest a role in interacting with water.

Highly selective excitation in biomolecular NMR by frequency-switched single-transition cross-polarization.

A new method for selective excitation in biomolecular NMR uses two-fold single-transition cross-polarization between protons and nitrogen-15 or carbon-13 nuclei. Switching the frequencies between the forward and backward transfer steps allows one to select a multiplet pattern that is associated with a single pair of spins in a medium-size protein. The efficiency of the transfer benefits from so-called TROSY line-narrowing effects which arise from interference between relaxation mechanisms.

Line shapes of saturated absorption spectroscopy in optically thick media

The line shapes of saturation spectroscopy in optically thick two-level media are calculated for atomic and molecular transitions. Line narrowing and distortion effects due to propagation are presented. For Doppler-broadened media it is shown that, due to multiphoton processes, the natural linewidth limits the ultimate narrowing that can be reached. Thus, up to ${\ensuremath{\alpha}}_{0}L=20,$ only when the rate-equation approximation is valid subhomogeneous linewidths are expected.

Spectroscopy in Dense Coherent Media: Line Narrowing and Interference Effects

Spectroscopic properties of coherently prepared, optically dense atomic media are studied experimentally and analyzed theoretically. It is shown that in such media the power broadening of the resonances can be substantially reduced. A density-dependent spectral narrowing of the electromagnetically induced transparency (EIT) window and novel, even narrower, resonances superimposed on the EIT line are observed in dense Rb vapor. A nonlinear two-photon spectroscopic technique based on coherent atomic media and combining high resolution with a large signal-to-noise ratio seems feasible.

On the Speed-Dependent Hard Collision Lineshape Models: Application to C2H2Perturbed by Xe

Three infrared absorption lines of the ν5band of C2H2diluted by Xe at pressures ranging from 40 to 300 mbar have been recorded at high resolution near 750 cm−1, using a tunable diode-laser spectrometer. Their lineshapes have been first analyzed by means of models using either the Dicke narrowing effect or the absorber speed-dependent collisional broadening and shifting. None of these models have given satisfactory results over the full pressure range of the perturber. It is shown that a correct treatment must include both line narrowing effects. We have investigated two possibilities of doing so: a convolution between two profiles corresponding to each effect and a noncorrelated and speed-dependent Rautian profile that we have developed here. The latter lineshape model appears to be the most appropriate.

Mapping Molecular Orientation by Solid-State NMR Imaging

A new solid-state NMR imaging experiment is presented which provides high-resolution chemical-shift selective images of abundant nuclei. This experiment employs the line-narrowing effects of the TREV-8 pulse sequence and a constant-time phase-encoding period to achieve spatial resolution. At the end of the phase-encoding period, however, the chemical-shift evolution is reversed and an echo is recorded during the subsequent acquisition period. A 3D data set is acquired which, after processing, results in one 2D image for each point in the chemical-shift spectrum. A single vector passing through all of the images provides a dipolar-decoupled NMR spectrum for any picture element in the image. This method has been applied to monitor the propagation of stress during crack growth in polytetrafluoroethylene.

R-matrix predictions on 4f2 levels and 4fnf Rydberg series of barium with J=4-6

The 4fnf J=4, 5, 6 series of barium have been investigated through a combination of the eigenchannel R-matrix and the multichannel quantum defect theory (MQDT) methods. The energy positions and autoionization widths for the 4f2 levels are predicted. The intermediate 4fnf levels, 5<or=n<or=7, located below the Ba+ 6d5/2 threshold interact strongly with the 7snl and 6dnl Rydberg series, giving rise to 'complex resonance' patterns and line narrowing effects. For the 4fnf J=4 levels with n>or=8, the theoretical results agree with a recent experiment. The investigation of the whole series from their bottom end allows the determination of the entire part of the quantum defects. The strong mixing between the 4f5/2f7/2 and 4f7/2f5/2 series observed for J=4-6 is shown to primarily originate from the large exchange electrostatic interaction.

R-matrix analysis of positions and widths of perturbed 7sng J=4 series of barium

The positions and autoionization widths of the 7sng J=4 levels of barium have been calculated using various procedures based on the eigenchannel R-matrix method. The calculations perfectly reproduce the experimental data recently obtained for the 7sng 1G4 levels. The localized perturbers of the 7sng series are unambiguously identified. The anomalous behaviour of energy positions and widths of high lying 7sng levels are ascribed to 4f8p levels. Line narrowing effects are predicted for 7sng 3G4 levels near n=17.

1H CRAMPS Based on TREV

Line-narrowing effects of the 1H TREV-8 pulse sequence applied to solids rotating at the magic angle have been examined. Polycrystalline samples of adipic, malonic, and fumaric acids, adamantane, a barley seed, and a pyridine-saturated coal sample were examined. The TREV-based 1H CRAMPS technique is seen to provide reasonably effective line narrowing for both "soft" solids (adamantane) and rigid solids (carboxylic acids), enabling 1H chemical-shift fine structure to be observed. For adamantane, the 1H linewidth is reduced from about 13 kHz (static) to 40 Hz (CRAMPS) at a 840 Hz MAS rate and a pulse spacing (τ) of 7.8 μs. The line-narrowing efficiency increases for larger τ values, but does not approach the efficiency of BR-24. However, unlike the case for BR-24 or other multiple-pulse line-narrowing sequences based on the formation of solid echoes, the line-narrowing efficiency of TREV-8 is sustained for large offsets; this feature, along with a relatively large bandwidth, may be an important factor when the sequence is implemented in 19F CRAMPS and in solid-sample imaging studies. TREV-CRAMPS may also be useful for samples in which the somewhat inferior line-narrowing behavior may be masked by line-broadening effects not based on homonuclear dipolar interactions.

Numerical and experimental investigation on ASE effects in high-power slab amplifiers

A three-dimensional calculation of the amplified spontaneous emission (ASE) is presented that allows rapid determination (with suitable approximation techniques) of the gain-length product (GLP) in high-power slab amplifiers. These calculations include non-saturable absorption, ASE line-narrowing effects, and total internal reflections (TIR) at the pumping surfaces. A parametric study of the slab geometry is presented and compared with experimental results. A good qualitative agreement between theory and experiment is achieved.

Line Narrowing Effects in Kinetics of Dispersive First-Order Reactions

Abstract The onset of thermally induced configurational fluctuations in a polymer near the glass transition can be monitored by the ensemble averaged isomerization reaction of probe molecules subject to a significant sterical hindrance. The decay patterns can be rationalized in terms of a distribution of activation barriers together with a temperature dependent correlation time for the matrix cages. Experimental support is given by data of a spiropyran/PBMA system investigated in the temperature range near Tg.

Spectral line-narrowing and saturation effects in fully resonant nondegenerate four wave mixing

Pentacene doped benzoic acid crystals are used to study the line-narrowing capability of fully resonant four wave mixing for inhomogeneously broadened transitions. Both parametric and nonparametric nonlinear spectroscopies are used to scan the vibronic resonances of excited electronic states while maintaining resonance with a vibrational mode of the ground state and the vibrationless level of the excited state. The observed vibronic transitions correspond to modes that are coupled to the ground state mode. The spectra contain both lines that are narrowed and lines that have the full inhomogeneous width. Narrowing of the vibronic transitions is observed when site selection is performed on the vibrationless electronic transition in both parametric and nonparametric methods. Narrowing of the vibrational resonance is not observed under the same conditions showing that the vibrational and electronic inhomogeneous broadenings are not correlated. The shifts of the line positions and the changes in linewidths and relative intensities were measured across the inhomogeneous linewidth for both methods. The nonlinear signal intensity was also measured as a function of laser intensity. All of the results are consistent with a theoretical description where saturation effects are dominant.