Narrowing of spectral lines beyond the natural or dephasing line width

Transient excitation and gated or delayed observation provides a narrowing of the inherent line width of the transition. Possible experimental one- and two-photon systems are discussed and the loss of signal with line narrowing is calculated. The general case of lines broadened by dephasing processes is treated. Contact is made with the line narrowing in recent Raman type experiments.     

Relation between the spatial growth rate of a traveling wave and the temporal growth rate of a standing wave

The relation between the spatial growth rate of a traveling wave and the temporal growth rate of the corresponding standing wave is examined. It is shown that, when radiation propagates in a gain medium with a sufficiently narrow gain line and a high amplification coefficient in the line center, the frequency dependences of the spatial and temporal growth rates of the field amplitude can differ significantly. In particular, at a fixed population inversion, the unbounded narrowing of the gain line, which results in an unbounded increase in the spatial growth rate and the narrowing of its frequency profile, is accompanied by neither an unbounded increase in the maximum value of the temporal growth rate nor an unbounded narrowing of the frequency profile of this growth rate.     

Narrowing and rebroadening of amplified spontaneous emission in high gain laser media

A series of recent papers by Allen and Peters on line narrowing in high gain laser media is criticized. New data demonstrating spectral narrowing followed by rebroadening are presented.     

Line narrowing effect on the retrieval of HF and HCl vertical profiles from ground-based FTIR measurements

Collision-induced line narrowing, which has been discovered in the 1950s and investigated thoroughly in the laboratory since then, has yet never been taken into account in the spectroscopic remote sensing of the atmosphere. This work investigates the effect of collision-induced line narrowing onto the retrieval of HCl and HF vertical profiles from ground-based solar absorption FTIR measurements made at the NDSC station of the Jungfraujoch (46.5^°N, 8^°E and 3580 m above see level). The retrievals are performed with the Atmosphit software, recently developed at the Université Libre de Bruxelles. It is presented in this paper for the first time and is validated against the widely used SFIT2 software. The impact of the line narrowing onto the retrieval of HCl and HF vertical profiles is examined relying on careful information content and error budget analyses. We report that the effect is relatively weak for HCl but significant for HF. Confirmation of the need to take the line narrowing into account for the retrieval of vertical profiles from ground-based FTIR spectra is given by comparison with data from the HALOE space borne instrument, rather insensitive to this spectroscopic effect.     

Are the prefactor anomalies in superionic conductors due to 1-D effects?

We have examined both the ionic conductivity and the NMR line narrowing in two channel-structured superionic conductors in the light of Richards' one-dimensional theory. For Li₂Ti₃O₇ the ionic conductivity is not sufficiently anisotropic to explain the observed small NMR prefactor in terms of i-D effects. For β-LiAlSiO₄ the NMR line narrowing in the crossover region does not yield the predicted large change in the activation energy given by the 1-D theory.     

On new complex soliton structures of the nonlinear partial differential equation describing the pulse narrowing nonlinear transmission lines

The present paper studies the pulse narrowing nonlinear transmission lines equation, describing pulse narrowing in the field of communication engineering. More precisely, the pulse narrowing nonlinear transmission line equation is solved analytically using the recently developed techniques viz the modified Kudraysov method, the sine-Gordon equation expansion method and the extended sinh-Gordon equation expansion method. As a result, a wide range of dark, bright, dark–bright, singular or combined singular and optical soliton solutions for the pulse narrowing nonlinear transmission lines equation is formally obtained. All solutions have been verified back into its corresponding equation with the aid of maple package program.     

Application of dynamic line narrowing in resonant optical sensing

We propose a dynamic operational mode and the resulting dynamic line narrowing as a method for enhancing the resolution and the detection limit of high-quality (high-Q) resonant optical sensors. Using a silica microtoroid as an experimental platform, we demonstrate that dynamic line narrowing through the thermo-optic effect can significantly improve the detection limit in both resonant shift and resonance splitting operating modes.     

A contribution to the theory of the exchange narrowing of spectral lines

The intensity distribution of a composite spectral line with exchange narrowing is calculated by integrating a matrix expression derived by Anderson     

Improved line narrowing and wavelength stabilization technique of distributed feedback dye lasers

A new method is described, for the wavelength stabilization and line narrowing of DFB dye lasers, using a dispersive pumping arrangement, where the wavelength shift of pumping light is compensated by a change in the incident beam angle. A predicted relation between pumping wavelength shift and DFB laser wavelength shift is verified experimentally. A twentyfold line narrowing in comparison with pumping linewidth, is realised in a preliminary experiment.     

Effect of diffraction of molecules on collisional line narrowing

A new model of line profile is proposed, which simultaneously takes into account hard and soft (in velocity) collisions leading to collisional line narrowing. It is shown that parameters of collisional narrowing and broadening obtained by processing experimental profiles on the basis of the standard model of hard collisions contain almost no contribution of diffraction scattering of molecules by buffer gas particles. The model proposed for the line profile makes possible a correct comparison of frequencies of the collision integral measured by methods of linear and nonlinear spectroscopy.     

On interpretation of the Dicke effect

It is shown that the Dicke narrowing of the Doppler profile of a spectral line is a purely classical effect, while the recoil is a quantum effect.     

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.     

Linewidth collapse in three-photon exciton-polariton spectra of CsI under pressure

Unusual phenomena occurring under hydrostatic compression in the near-band-edge structure of CsI crystals were examined using the nonlinear optical technique of three-photon excitation. The lowest one-photon allowed transition to the exciton-polariton A of gamma-4 symmetry redshifts, while the one-photon forbidden paraexciton C of gamma-5 symmetry blueshifts to a crossing of energies at 4.4 kbar. During this process, the A level exhibits strong spectral line narrowing by more than a factor of 10, while the C level intensity increases by about the same factor. We believe this is the first reported observation of pressure induced line narrowing of deep UV electronic states in solids.     

Resonant fluorescence line narrowing and gain spectral hole burning in erbium-doped fiber amplifier

Gain spectral hole burning and resonant fluorescence line narrowing have been performed at low temperature in standard aluminosilicate erbium-doped fiber amplifier to demonstrate the nature of the line broadening. Comparison of the hole-width measurements with resonant fluorescent line narrowing data shows a good agreement at 77 K, working temperature for which both experiments are feasible and have been performed simultaneously. The FWHM results reported here compare well with the earlier line profile measurements performed on aluminosilicate glass preform of the same chemical composition as the fiber. The pump power dependences are reported and indicate that they influence both the depth and line width, which may induce a limitation for wavelength division multiplexing techniques in the long-haul transmission regime of telecommunications.     

The mean-size dependence of the exchange narrowing in molecular J-aggregates

The effect of segment-size fluctuations on exchange narrowing in a molecular J-aggregate of site-energy disordered distributions is studied using a one-dimensional Frenkel-exciton model. It is found that the segment-size disorder leads to the width of the absorption spectra deviating from the scaling law, σ^4/3 of the site-energy disordered standard deviation σ, being suitable for the system only with the site-energy disorder. In larger σ, the segment-size disorder has little influence on the linear absorption spectra. With increasing segment mean-length, the absorption line width monotonically increases, and then approaches a saturated value. By comparing a system of larger mean-length segment with a smaller one, both with the same segment-size disorder, it is found that the absorption line width of the former is broadened, and the exchange narrowing effect is reduced. The present result shows that the correlation effect can be partially maintained for the system with larger mean-length segment.     

Diffusion-induced Ramsey narrowing

Diffusion-induced Ramsey narrowing is characterized and identified as a general phenomenon, in which diffusion of coherence in and out of an interaction region such as a laser beam induces spectral narrowing of the associated resonance line shape. Illustrative experiments and an intuitive analytical model are presented for this spectral narrowing effect, which occurs commonly in optically interrogated atomic systems and may also be relevant to quantum dots and other solid-state spin systems.     

Tailored slice selection in solid-state MRI by DANTE under magic-echo line narrowing

We propose a method of slice selection in solid-state MRI by combining DANTE selective excitation with magic-echo (ME) line narrowing. The DANTE RF pulses applied at the ME peaks practically do not interfere with the ME line narrowing in the combined ME DANTE sequence. This allows straightforward tailoring of the slice profile simply by introducing an appropriate modulation, such as a sinc modulation, into the flip angles of the applied DANTE RF pulses. The utility of the method has been demonstrated by preliminary experiments performed on a test sample of adamantane.     

Spectral narrowing of a dye laser oscillation using an intracavity vapor prism

A new method for narrowing the oscillation spectrum of a broad-band dye laser is reported in this paper. The narrowing is achieved by a vapor prism placed inside the laser cavity, which is based on an anomalous dispersion of the atomic vapor so that the narrowing effect occurs only in the vicinity of the absorption line. Using a sodium vapor prism inside a Rhodamine 6G dye laser cavity, an oscillation linewidth less than 0.01 nm was attained at a sodium temperature of 320°C.     

Argon broadening of the CO R(0) and R(7) transitions in the fundamental band at temperatures between 80 and 297 K: comparison between experiment and theory

We present measurements of Ar-broadening parameters for the R(0) and R(7) lines in the fundamental band of ¹³CO at eight temperatures from 80 to 297 K. The broadening parameters are determined by simultaneous least-squares fitting of spectra recorded using a frequency stabilized diode laser spectrometer. The comparison of the broadening parameter values for R(7) derived at room temperature and different pressures from different line profiles shows that an empirical line profile, which takes into account narrowing effects (Dicke narrowing and absorber speed dependence) but neglects any correlation between collisions, is able to describe the observed lines with constant values of the narrowing and broadening parameters over a 10-500 Torr pressure range. Starting from a recent ab initio potential energy surface, theoretical thermally averaged close coupling values of the Ar broadening parameter are calculated for the same temperatures. The comparison between experimental and calculated values shows an overall agreement of 1.5%.     

Motional effects in the EPR-spectrum of Cu-H-centers in ZnO

At low temperatures, the EPR signal of a Cu²⁺ center is observed in ZnO single crystals doped both with copper and hydrogen. A clear effect of line narrowing on the copper hfs-lines is observed at T=16K. It is discussed in the model of a Cu-(OH) complex taking into account the thermally induced reorientation of the center.