Search

Air pressure induced broadening and shift coefficients for methane absorption lines in the 6000–6100 cm–1 region have been measured. The spectra were recorded using Bruker IFS 125 HR spectrometer at room temperature, at the spectral resolution of 0.01 and 0.007 cm–1 and in a wide pressure range of air. The multispectrum fittings with the quadratic speed dependent Voigt profile were performed to retrieve the broadening parameters for CH4 spectral lines. The atmospheric transmission of CH4 calculated by line-by-line method with use of absorption lines parameters from different spectroscopic databases and data obtained in this work was compared.

Lidar is short for light detection and ranging, which is a tool to help measuring some useful information of atmosphere. In the recent years, more and more attention was paid to the research of wind measurement by lidar. Because the accurate wind information can be used not only in weather report, but also the safety guarantee of the airplanes. In this paper, a more detailed signal model of wind measurement lidar is proposed. It includes the laser transmitting part which describes the broadening of the spectral, the laser attenuation in the atmosphere, the backscattering signal and the detected signal. A Voigt profile is used to describe the broadening of the transmitting laser spectral, which is the most common situation that is the convolution of different broadening line shapes. The laser attenuation includes scattering and absorption. We use a Rayleigh scattering model and partially-Correlated quadratic-Velocity-Dependent Hard-Collision (pCqSDHC) model to describe the molecule scattering and absorption. When calculate the particles scattering and absorption, the Gaussian particles model is used to describe the shape of particles. Because of the Doppler Effect occurred between the laser and atmosphere, the wind velocity can be calculated by the backscattering signal. Then, a two parameter Weibull distribution is used to describe the wind filed, so that we can use it to do the future work. After all the description, the signal model of coherent wind measurement lidar is decided. And some of the simulation is given by MATLAB. This signal model can describe the system more accurate and more detailed, so that the following work will be easier and more efficient.

Utilization of Near-Infrared (NIR) spectral features in a muzzle flash will allow for small arms detection using low cost silicon (Si)-based imagers. Detection of a small arms muzzle flash in a particular wavelength region is dependent on the intensity of that emission, the efficiency of source emission transmission through the atmosphere, and the relative intensity of the background scene. The NIR muzzle flash signature exists in the relatively large Si spectral response wavelength region of 300 nm-1100 nm, which allows for use of commercial-off-the-shelf (COTS) Si-based detectors. The alkali metal origin of the NIR spectral features in the 7.62 × 39-mm round muzzle flash is discussed, and the basis for the spectral bandwidth is examined, using a calculated Voigt profile. This report will introduce a model of the 7.62 × 39-mm NIR muzzle flash signature based on predicted source characteristics. Atmospheric limitations based on NIR spectral regions are investigated in relation to the NIR muzzle flash signature. A simple signal-to-clutter ratio (SCR) metric is used to predict sensor performance based on a model of radiance for the source and solar background and pixel registered image subtraction.

Brillouin distributed optical fiber sensing system based on spontaneous Brillouin scattering frequency shift measurement may measure temperature in the optical fiber, due to the dependence of spontaneous Brillouin scattering frequency shift on temperature. In this paper, nonlinear theoretical models of the Brillouin spectrum in the BOTDR temperature sensing system are analyzed. The model parameters are optimized with Levenberg-Marquardt algorithm. By numerical calculation, it is indicated that pseudo-Voigt function can approach approximated the Voigt profile well and quickly.

The ultimate objective of laser speckle flowmetry (and a host of specific implementations such as Laser Speckle Contrast Analysis-LASCA or LSCA, Laser Speckle Spatial Contrast Analysis-LSSCA, Laser Speckle Temporal Contrast Analysis-LSTCA, etc.) is to infer flow velocity from the observed speckle contrast. A proper inversion of this association depends critically on the correct model for the statistical relationship between motion of the scatterers and the resulting spatial and temporal speckle contrast. Many researchers use the Lorentzian model for such a relationship. In fact, the Lorentzian is a homogeneous line profile appropriate only for Brownian motion. In such a case, the dynamics of a single particle are representative of the ensemble. The other extreme is an inhomogeneous (Gaussian) profile which corresponds to a process in which the dynamics are particular to the individual scatterers. The proper model for complex motion such as blood flow is undoubtedly intermediate between these two extremes. One such model for the net effect of these two stochastically independent processes is a Voigt profile. In this paper we explore the quantitative relationship between the statistics of speckle contrast and ordered flow. The study addresses the effects of speckle size relative to that of the pixel, temporal integration time relative to the decorrelation times associated with ordered and un-ordered motion, and the spatio-temporal processing schemes used to quantify speckle contrast.

A flattened Lorentzian irradiance profile, which was introduced by Brenner in 2003, offers prospects for analytic design of beam shaping optics when transforming a Gaussian beam into a soft-flat-top profile. It is shown that for the flattened Lorentzian profile the output power integral and the ray mapping function are analytic functions. This paper presents a systematic derivation of the flattened Lorentzian profile from the super-Lorentzian profile and exploration of properties of the flattened Lorentzian profile and compares its behavior to the super-Gaussian, flattened Gaussian, and Fermi-Dirac profiles. Details are presented for evaluation of the FL profile normalization, profile matching conditions, ray mapping function, and M 2 .

Extensive measurements and modeling of several two photon absorbing materials are described. These are used to elucidate the relative significance of various relaxation and excitation processes that come into play in nonlinear transmission (NLT) and two photon absorption cross section measurements. A reliable measurement of the one photon absorption cross sections at energies 0.5 to ~1.7 eV below the fundamental transition are presented with Voigt function fits that enable the determination of the Gaussian and Lorentzian line widths. Both a numerical model and an analytical model are developed neither of which use any adjustable parameters in comparing calculated NLT results to data. Both models fit the data relatively well over the full range of the experiment. The analytical model captures the primary causes of the nonlinear absorption in the low intensity regime and demonstrates that the nonlinear transmittance can be estimated as a simple effective three-photon process. The numerical model calculates the spatial and time dependence of three state populations and all of the transitions between these states. This model improves the quality of the nonlinear transmission fit which is due to the inclusion of the ground state absorption. Additionally an observation of a strong, long lived transient which is quenched by oxygen suggests multiphoton ionization is happening at low intensities. Thus the full range of constraints applicable to all measurements of the two photon cross section are presented.

The dislocation densities in HgCdTe films grown on CdZnTe by Liquid Phase Epitaxy (LPE) are calculated based on their effects on the x-ray rocking curves. The dislocation densities derived from three kinds of methods, i.e. FWHM of X-ray double axis diffraction, Williamson-Hall plot and Pseudo- Voigt function, are approximately the same. It is found that the thickness of HgCdTe epilayers about 10 µ m is large enough so that effect of crystallize size on the rocking curves width can be ignored. Because the intrinsic FWHM of HgCdTe and the instrumental function of high resolution X-ray diffraction are neglected in Williamson-Hall plot and Pseudo-Voigt function, the dislocation densities obtained by these methods are a little larger than those derived from the first kind of method. Among three kinds of methods, Pseudo-Voigt function method is the easiest one to fit the rocking curves and calculate the dislocation densities. Keywords: HgCdTe, dislocation density, DAD-FWHM, Williamson-Hall plot, Pseudo-Voigt function

Using a laser-induced fluorescence method a detailed analysis ofthe profiles ofthe '14Cd 326.1 nm line perturbed by allrare gases was performed which revealed departures from the ordinary Voigt profile. These departures are shown to beconsistent with fits ofexperimental profiles to a speed-dependent asymmetric Voigt profile or asymmetric Voigt profile.Keywords: Intensities and shapes of atomic spectral lines, Intensities and shapes of molecular spectral lines and bandsInteratomic and intermolecular potentials and forces, potential energy surfaces for collisions.

A modified simplified rate equation (RE) model of flowing chemical oxygen-iodine laser (COIL), which is adapted to both the condition of homogeneous broadening and inhomogeneous broadening being of importance and the condition of inhomogeneous broadening being predominant, is presented for performance analyses of a COIL. By using the Voigt profile function and the gain-equal-loss approximation, a gain expression has been deduced from the rate equations of upper and lower level laser species. This gain expression is adapted to the conditions of very low gas pressure up to quite high pressure and can deal with the condition of lasing frequency being not equal to the central one of spectral profile. The expressions of output power and extraction efficiency in a flowing COIL can be obtained by solving the coupling equations of the deduced gain expression and the energy equation which expresses the complete transformation of the energy stored in singlet delta state oxygen into laser energy. By using these expressions, the RotoCOIL experiment is simulated, and obtained results agree well with experiment data. Effects of various adjustable parameters on the performances of COIL are also presented.

The effect of the translational nonequilibrium on performance modeling of flowing chemical oxygen-iodine lasers (COIL) is emphasized in this paper. The spectral line broadening (SLB) model is a basic factor for predicting the performances of flowing COIL. The Voigt profile function is a well-known SLB model and is usually utilized. In the case of gas pressure in laser cavity less than 5 torr, a low pressure limit expression of the Voigt profile function is used. These two SLB models imply that ail lasing particles can interact with monochromatic laser radiation. Basically, the inhomogeneous broadening effects are not considered in these two SLB models and they cannot predict the spectral content. The latter requires consideration of finite translational relaxation rate. Unfortunately, it is rather difficult to solve simultaneously the Navier-Stokes (NS) equations and the conservation equations of the number of lasing particles per unit volume and per unit frequency interval. In the operating condition of flowing COIL, it is possible to obtain a perturbational solution of the conservational equations for lasing particles and deduce a new relation between the gain and the optical intensity, i.e., a new gain-saturation relation. By coupling the gain-saturation relation with other governing equations (such as the NS equations, chemical reaction equations and the optical model of gain-equal-loss), We have numerically calculated the performances of flowing COIL. The present results are compared with those obtained by the common rate-equation (RE) model, in which the Voigt profile function and its low pressure limit expression are used. The difference of different model's results is great. For instance, in the case of lasing frequency coinciding with the central frequency of line profile and very low gas pressure, the gain-saturation relation of the present model is quite different with that of the RE model.

A new gain saturation model of chemical oxygen-iodine laser (COIL) is deduced from the conservational equations of population number of upper and lower lasing levels. The present model is compared with both the Voigt profile function (VPF) model and its low-pressure limit model, and the differences between different models are pointed out. These differences are of use to the optimization of COILS' adjustable parameters.

The absorption of laser radiation on various atmospheric paths have been estimated basing on the data on spectral composition of HF, DF, and iodine lasers radiation and on the atmospheric molecular absorption coefficient. Applications of these lasers to atmospheric transmission problems require the information on the attenuation characteristics of the atmosphere at each of the lasing frequencies. Calculations have been made of the monochromatic transmission of HF and DF laser radiation for nonhomogeneous atmospheric slant paths. Aerosol extinction, continuum molecular absorption, and line absorption are included in the computations. An approximate Voigt profile has been used to express mixed Doppler-Lorentz line broadening. HF P 2 (8) and DF P 2 (8) lines are chosen among the presently operational cw chemical lasers for detailed studies.

Author developed a line-by-line atmospheric transmission model based on the Fourier transformed Voigt function. The Voigt function is presented in an integrated form, and direct computation of the function profiles involves a high computational cost because of its numerical characteristics which introduces slow numerical convergency at some area. Many investigations were performed using the polynomial- fitting-to-the-function method to reduce this computation cost. Author introduced a Fourier transformed Voigt function, and developed a line-by-line transmission model for multiple species and lines. In this model, all line-by- line calculations are done in the numerical space which will be Fourier transformed to the wavenumber space a the end of a process. The developed algorithm uses no approximation method for line shape calculation, and has no limitations for the wavenumber resolution and the wavenumber range. Furthermore, the algorithm represents randomly positioned absorption lines by the uniform method and requires no line shapes mapping into the wavenumber space. The model indicates a straight forward implementation procedure of the high-resolution radiation/transmission calculation with huge absorption liens. Author implemented the model on a parallel computing environment and verified that the model calculation performance can be expanded with increasing the number of computing nodes.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This work reports on the analysis of the near-UV and visible absorption spectrum of water vapor. Obtained by combining a high- resolution FT spectrometer and a long path White multiple- reflection cell. A large number of water vapor lines belonging to highly excited vibrational levels are identified. Most of these lines have not been observed previously and do not appear in the spectroscopic databases HITRAN and GEISA, widely used for atmospheric calculations. All identified lines are fitted with a Voigt profile using the WSPECTRA program and their cross section and self-broadening parameters at 291 K are determined. A particular attention is give to the integrate cross section over the total spectral range investigated, in order to estimate the contribution of the weak UV-visible water vapor absorption lines to the earth's radiation balance. Preliminary measurements of cross section in the 20000-16000 cm-1 spectral range are also presented.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

LIBS is based on atomic emission from plasma formed by laser ablation and excitation. It offers non-contacting and nearly non-destructive elemental analysis, but limited analytical accuracy. An empirical power- law calibration curve is usually required. From our work and from recent work by Gornushkin et al. this arises from self-absorption. Assuming Local Thermal Equilibrium (LTE), irradiance is found from integrals over the Voigt profile, which we compute using the complex error function. Calibration curves show a break between linear and power-law regions, with a square-root dependence at high concentrations. Irradiance depends on width of the Lorentz (pressure broadened) component, and the simple Boltzmann temperature dependence is modified. Gornushkin et al extended calibration curves into the linear region, obtaining the Voigt parameter, but more typically this region is inaccessible. Self- absorption theory should provide improved temperature measurement in the power-law region and, although absolute concentration determination requires the Lorentz width, its known temperature and pressure dependence should reduce the ad-hoc nature of calibration curves.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The influence of speed-changing self-similar collisions on the spectral lien shape is considered in terms of the classical Fourier integral theory. The self-similar mechanism of interference of scalar perturbations for phase shifts of an atomic oscillator is developed. The motion of a radiating dipole in a perturbed gas is examined in the framework of the self-similar diffusion model. A general formula for the correlation function, which allows for a combined effect of speed-dependent Doppler and pressure broadening, is derived. In the Doppler regime this formula yield the self-similar Galatry profile and in the case when speed-changing collisions are neglected it leads to the self-similar Voigt profile. In the limiting case when the self-similar character of collisions is omitted these profiles become identical to the Galatry profile and Voigt profile respectively. It is shown that self-similar collisions are of important in a low and high pressure region for far IR and radio lines. In general case spectral profiles broadened by the self-similar collision mechanism are asymmetric, the line shape depends on a type of the interference of scalar perturbations. In the Doppler regime self-similar collisions give rise to the additional spectral line Dicke-narrowing.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Precise molecular spectra obtained by Tunable Diode Laser Spectrometers were fitted by Voigt profile using routine development. All line parameters (transition frequencies, line intensities, Lorentzian and Gaussian parameters) were obtained from this fitting. Different effects limiting TDLS precision such as laser noises, detector non-ideality, zero absorption and zero transmission levels determination, etc., were considered. Results are presented in analytical form showing error dependence upon various experimental parameters. The results were tested through computer modeling and compared with the obtained experimental results. Some procedures were proposed to minimize the influence of main error sources.

Broadening of the hydrogen fluoride R4 ((nu) equals 0 - 2) absorption line by N2 measured with 1.3 micrometers diode laser was studied. Line parameters (Doppler and Lorentzian half widths, line strength) have been extracted by the least-squares fitting with Voigt function. The spectrum of frequency fluctuations was modeled and its parameters were determined. The line parameters have been improved by taking into account the influence of the diode laser frequency fluctuations.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A diode laser spectrometer has been used for high accuracy line profile measurements in the 1.7-2.4 micron region. Measured lineshapes have been least-squares fitted by Voigt profile with flating Gaussian component. Gaussian component pressure dependence resulting from the Dicke narrowing effect is observed. Line intensities, self-induced broadenings, and shifts of five water vapor lines near 5475/cm are also presented.

We have directly measured a comparably large isotope shifts in the CdI (10p3P°0,1,2- 16s3S1) line by a convenient method of detecting the absorption spectra using a 780 nm band GaAlAs laser diode. The estimated isotope shifts from the measurement were about 2 GHz be-tween the adjacent isotope spectra. Because the presently measured line involves a s-electron transition, such a large isotope shift should be acceptable from the spectroscopic viewpoint. Applying the numerical simulation using Voigt profile to the measured absorption profile, we have also estimated the pressure broadening factors in this spectral line. In addition, we also measured and simulated another absorption spectra of the 782.64 nm CdII (9d2D5/2-5p"2P°3/2) line and the results have confirmed the validity of our estimations.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.