Linewidth Reduction Of Semiconductor Lasers Using Feedback Current Proportional To Terminal Voltage Fluctuations

Scatterometry as a non-imaging indirect optical method in wafer metrology is applicable to lithography masks designed for extreme ultraviolet (EUV) lithography, where light with wavelengths of about 13.5 nm is applied. The main goal is to reconstruct the critical dimensions (CD) of the mask, i.e., profile parameters such as line width, line height, and side-wall angle, from the measured diffracted light pattern and to estimate the associated uncertainties. The numerical simulation of the diffraction process for periodic 2D structures can be realized by the finite element solution of the two-dimensional Helmholtz equation. The inverse problem is expressed as a non-linear operator equation where the operator maps the sought mask parameters to the efficiencies of the diffracted plane wave modes. To solve this operator equation, the deviation of the measured efficiencies from the ones obtained computationally is minimized by a Gauß-Newton type iterative method. In the present paper, the admissibility of rectangular profile models for the evaluations of CD uniformity is studied. More precisely, several sets of typical measurement data are simulated for trapezoidal shaped EUV masks with different mask signatures characterized by various line widths, heights and side-wall angles slightly smaller than 90°. Using these sets, but assuming rectangular structures as the basic profiles of the numerical reconstruction algorithm, approximate line height and width parameters are determined as the critical dimensions of the mask. Finally, the model error due to the simplified shapes is analyzed by checking the deviations of the reconstructed parameters from their nominal values.

This paper includes a detailed study of Raman G peak analysis for metallic Single Wall Carbon Nanotubes. The higher frequency Lorentzian line shape and the lower frequency Breit-Wigner-Fano (BWF) line shape are two most intense features of Raman G peaks. BWF line shape originated from the Phonon-Plasmon coupling to an electronic continuum is an intrinsic property for metallic SWNTs. From different Raman samples it is observed that BWF line shape has a strong relation with the diameter distributions of SWNTs. We established an equation form for both line width and interaction parameter (1/q) components of BWF line shape which is consistent with the theoretical prediction.

The deexcitation γ-ray lines in solar flares result from energetic ions (e.g., protons, α-particles) interacting with the ambient nuclei in the solar atmosphere. The centroid and width of lines contain a wealth of information on the directionality, composition, and spectra of energetic ions as well as properties of the interaction sites. New calculations for the deexcitation γ-ray line shape analysis were done to study the properties of these ions. We calculate the shapes of the most intense deexcitation γ-ray lines in the solar flares, including the 12C 4.439 MeV, 16O 6.129 MeV, 24Mg 1.369 MeV, and 28Si 1.779 MeV lines, and explore the profiles of these line shapes as a function of the accelerated ion’s energy spectra and composition, as well as the heliocentric angle of flare location. The merits of deexcitation γ-ray line shape analysis include (1) only a relatively small number of parameters being required in the fitting process and (2) the characteristics of accelerated ions with joint multi-line shape analysis being well constrained. We conclude that the measurement of the width and centroid of lines is an effective method for determining the properties of flare-accelerated ions.

Vibrational spectra of amorphous polystyrene were determined at room temperature as a function of pressure. A sodium chloride high-pressure cell was used to generate pressures up to 40 kbars. Considerable changes in line shape, line width, and intensity were observed in the spectra. In contrast, the former two changes are absent in crystalline polyethylene. The physical basis of pressure effects on line width, line shape, and intensity of the vibra-tional spectra of amorphous polystyrene is discussed.

Vibrational spectral diffusion denotes the time-dependent fluctuations of a solute's vibrational frequencies due to local environmental dynamics. Vibrational line shapes are weakly sensitive to spectral diffusion, whereas three-pulse vibrational echoes are much more sensitive. We report here on theoretical studies of spectral diffusion of the asymmetric stretch of the azide anion in heavy water. We run a classical molecular dynamics simulation of rigid azide in rigid water, and at every time step we calculate the azide's anharmonic asymmetric stretch frequency using an optimized quantum mechanics/molecular mechanics method developed earlier. This generates a frequency trajectory, which we use to calculate the absorption line shape and integrated three-pulse echo intensity. Our results for both the line width and the integrated echo intensity are in excellent agreement with experiment. Our calculated frequency time-correlation function is in excellent agreement with experiment for long times (greater than 250 fs) but differs considerably from experiment at short times; our theoretical correlation function has a very pronounced oscillation, presumably due to intermolecular azide-water hydrogen-bond stretching dynamics.

The shape and width of the different spectral lines — x-ray, emission, Auger, photoelectron — are all determined by the same fundamental principles, which makes it worthwhile to combine our examination of these questions into a single chapter. We will discuss the various factors involved in line broadening in Sec. 9.1: spontaneous transitions, distortions caused by the equipment, Doppler broadening, etc. A quantity closely related to natural linewidth — the fluorescence yield, which is characteristic of the relative role of a radiation and Auger decay of a state with a vacancy — is the topic of Sec. 9.2. The natural linewidth and fluorescence yield as a function of the nuclear charge, one- and many-electron quantum numbers, and the approximate invariance of these quantities that occurs for some configurations is studied in Sec. 9.3.

The shape of a collision-broadened spectral line depends on the assumptions made about the collision processes involved. If the collision cross section varies inversely as the relative speed of the colliding molecules, the half-width to the half-power points and to the points of steepest slope should be 1/27T1' and 1/(2";3)7T1' respectively, where l' is the mean interval between line-broadening collisions. It is shown that, in a gas of "hard-sphere" molecules, the shape of the line is modified and the above half-widths are reduced by' 6·4 and 9·7% respectively. While it is not suggested that gas molecules behave entirely as hard spheres, it is suggested that some deviations from the Van Vleck-Weisskopf-Lorentz shape may occur, and that it may be possible to detect these deviations experimentally

The fundamental formula of the EPR lineshape of field-swept spectra has been modified for the case of a broad homogeneous line. As a consequence, a new formula has been obtained for the derivative of the absorption. For the case of an inhomogeneous line, the original formula of Pilbrow holds, these formulae lay the basis for the determination of the number of spins by integration of the experimental EPR spectrum. The Pilbrow lineshape theory is then combined with the standard results for a Kramers ion having an effective spin 1/2, an anisotropic g tensor and no hyperfine interaction. The assumption is made that the linewidth in frequency units σν is independent of the orientation. This assumption completes the model specifying the line position, intensity, shape and width for any given orientation. The model thus enables one to simulate a powder EPR spectrum and its derivative knowing the principal values of the g tensor and the linewidth σν. The simulation entails a double integration over the spherical coordinates of the magnetic field in the frame of the principal axis of the g tensor. The number of sampling points for numerical integration is determined as a function of gx, gy, gz and σν. Experimentally the EPR spectrum of a coordination compound of trivalent uranium in powder form, U3(BH4)9(dcc)2, in which there are two kinds of uranium sites, has been recorded at 10.5 K in X-band. The least-squares fit between the observed and simulated spectra has been achieved using the optimisation software BSOLVE, and excellent agreement was reached with a Laplace–Gauss lineshape. The adjusted parameters for the two uraniums were confirmed by an independent fit based on the least absolute values criterion. Based on the final parameters, the EPR spectrum predicted at higher frequencies is better resolved, whereas the actual resolution of the spectrum at 16 GHz is no better. Finally, the effective magnetic moment is predicted to be slightly above 2.

Raman spectroscopy with CW lasers in the visible, near-IR, and near-UV is one of the most precise techniques to investigate low frequency elementary excitations in solids. It is particularly suitable for determining quasiparticle renormalizations due to small perturbations. The technique will be illustrated with examples for conventional semiconductors (effects of isotropic mass changes and fluctuations on phonon frequencies and line widths, effect of doping on same parameters) and high-Tc superconductors (effect of superconducting gaps on phonons frequencies and line widths, effect of crystal field transitions of the rare earth atoms on phonon frequencies and line shapes).© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Raman spectroscopy with cw lasers in the visible, near ir and near uv is one of the most precise techniques to investigate low frequency elementary excitations in solids. It is particularly suitable for determining quasiparticle renormalizations due to small perturbations. The technique will be illustrated with examples for conventional semiconductors (effects of isotopic mass changes and fluctuations on phonon frequencies and line widths, effect of doping on same parameters) and high-Tc superconductors (effect of superconducting gaps on phonon frequencies and line widths, effect of crystal field transitions of the rare earth atoms on phonon frequencies and line shapes).

Mesure directe par resonance magnetique nucleaire de la distribution du champ magnetique dans un supraconducteur de deuxieme espece

The effect of dislocation dipoles on the broadening of a NMR line is studied. The shape of the satellite line is determined. The line width is obtained as a function of the dipole concentration, the dipole length and the relative orientation of the dipole and the external constant magnetic field. The shape of the central line is also determined. The shape function of the central line is presented for certain relative orientations of the dipole and the magnetic field.

Aiming at the problem of easy breakage and low tensile performance during the preparation of flexible conductive lines on the fabric surface, numerical simulation methods are used to establish a medium-scale three-dimensional (3D) model of the knitted fabric-based conductive line. The influence of the shape and width of the conductive line on the tensile properties is studied, and the deformation and fracture processes of knitted fabrics and conductive lines under different stretching directions (horizontal, vertical, and shear) are clarified. The results show that the optimal geometric shape of the conductive line is horseshoe shape, the width of the conductive line is inversely proportional to the tensile performance, the crack section of the conductive line is straight when stretched horizontally, and the cross-section of the crack is sawtooth when stretched vertically, the initial stage of the crack section during shear stretching is the same as that of horizontal stretching, and the later crack development is irregular.

Optical frequency stabilisation and linewidth reduction by the current feedback technique were studied with a multi-electrode DFB laser. In the current feedback technique, phase rotation in the feedback loop, particularly induced by a laser, is the fundamental problem. This problem was resolved by using multielectrode DFB lasers without phase inversion. We simultaneously succeeded in optical frequency stabilisation and linewidth reduction with only one feedback electrical circuit. Optical frequency drift and spectral line-width were reduced to 1/14 and 1/126, respectively, of those in the free-running state. The minimum spectral linewidth obtained was 95 kHz.

The absorption spectrum of water vapor has been studied quantitatively with a resolution of approximately 0.12 cm−1 between 475–692 cm−1. Several methods of extracting the intensity and line-width parameters from the measurements on 19 well-resolved lines are compared and discussed. The intensities show deviations from those calculated for a rigid asymmetric rotor, which are attributed to effects of centrifugal stretching. Half-widths are presented for H2O–H2O, H2O–N2, H2O–CO2, and H2O–He broadening at 80°C and for H2O-air at 24°C.