The Use of Fabry-Perot Filters for Spectral Scanning

1969 ◽  
Vol 1 (6) ◽  
pp. 293-294
Author(s):  
M. D. Waterworth
Keyword(s):  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Resolving Power ◽  
Doppler Broadening ◽  
Collisional Broadening ◽  
Fabry Perot

In designing a stellar spectrograph, it is pointless to exceed the resolving power necessary to obtain all the information from the spectrum of a star. This is limited mainly by atomic thermal motions, giving rise to the Doppler broadening of spectral lines, by turbulence and rotation of the stellar atmospheres in which the lines are formed, and by collisional broadening.

scholarly journals Quantifying Resolving Power in Astronomical Spectra

2013 ◽  
Vol 30 ◽  
Author(s):  
J. Gordon Robertson
Keyword(s):  
Spectral Line ◽  
Spatial Dimension ◽  
Spectral Lines ◽  
Resolving Power ◽  
Noise Power ◽  
Line Spread Function ◽  
Fabry Perot ◽  
Lorentzian Profile ◽  
Multi Mode ◽  
Line Spread

AbstractThe spectral resolving power R = λ/δλ is a key property of any spectrograph, but its definition is vague because the ‘smallest resolvable wavelength difference’ δλ does not have a consistent definition. Often, the FWHM is used, but this is not consistent when comparing the resolution of instruments with different forms of spectral line-spread function. Here, two methods for calculating resolving power on a consistent scale are given. The first method is based on the principle that two spectral lines are just resolved when the mutual disturbance in fitting the fluxes of the lines reaches a threshold (here equal to that of sinc2 profiles at the Rayleigh criterion). The second criterion assumes that two spectrographs have equal resolving powers if the wavelength error in fitting a narrow spectral line is the same in each case (given equal signal flux and noise power). The two criteria give similar results and give rise to scaling factors that can be applied to bring resolving power calculated using the FWHM on to a consistent scale. The differences among commonly encountered line-spread functions are substantial, with a Lorentzian profile (as produced by an imaging Fabry–Perot interferometer) being a factor of two worse than the boxy profile from a projected circle (as produced by integration across the spatial dimension of a multi-mode fibre) when both have the same FWHM. The projected circle has a larger FWHM than its true resolution, so using FWHM to characterise the resolution of a spectrograph which is fed by multi-mode fibres significantly underestimates its true resolving power if it has small aberrations and a well-sampled profile.

scholarly journals Astro-comb: revolutionizing precision spectroscopy in astrophysics

2008 ◽  
Vol 4 (S253) ◽  
pp. 499-501
Author(s):  
Claire E. Cramer ◽  
Chih-Hao Li ◽  
Andrew J. Benedick ◽  
Alexander G. Glenday ◽  
Franz X. Kärtner ◽  
...  
Keyword(s):  
Doppler Shift ◽  
Extrasolar Planets ◽  
Frequency Comb ◽  
Laser Frequency ◽  
Spectral Lines ◽  
Resolving Power ◽  
Long Term Stability ◽  
Fabry Perot ◽  
Line Spacing ◽  
Wide Line

AbstractSearches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision better than 60cm/s. To find a 1-Earth mass planet in an Earth-like orbit, a precision of 5cm/s is necessary. The combination of a laser frequency comb with a Fabry-Perot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration. Here we report the fabrication of such a filtered laser comb with up to 40 GHz (~1 Angstrom) line spacing, generated from a 1 GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb (astro-comb) is well matched to the resolving power of high-resolution astrophysical spectrographs. The astrocomb should allow a precision as high as 1cm/s in astronomical readial velocity measurements.

scholarly journals The relationship between photometric and spectroscopic oscillation amplitudes from 3D stellar atmosphere simulations

2021 ◽  
Author(s):  
Yixiao Zhou ◽  
Thomas Nordlander ◽  
Luca Casagrande ◽  
Meridith Joyce ◽  
Yaguang Li ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Wavelength Shift ◽  
The Sun ◽  
Theoretical Derivation ◽  
Velocity Amplitude ◽  
Good Agreement

Abstract We establish a quantitative relationship between photometric and spectroscopic detections of solar-like oscillations using ab initio, three-dimensional (3D), hydrodynamical numerical simulations of stellar atmospheres. We present a theoretical derivation as proof of concept for our method. We perform realistic spectral line formation calculations to quantify the ratio between luminosity and radial velocity amplitude for two case studies: the Sun and the red giant ε Tau. Luminosity amplitudes are computed based on the bolometric flux predicted by 3D simulations with granulation background modelled the same way as asteroseismic observations. Radial velocity amplitudes are determined from the wavelength shift of synthesized spectral lines with methods closely resembling those used in BiSON and SONG observations. Consequently, the theoretical luminosity to radial velocity amplitude ratios are directly comparable with corresponding observations. For the Sun, we predict theoretical ratios of 21.0 and 23.7 ppm/[m s−1] from BiSON and SONG respectively, in good agreement with observations 19.1 and 21.6 ppm/[m s−1]. For ε Tau, we predict K2 and SONG ratios of 48.4 ppm/[m s−1], again in good agreement with observations 42.2 ppm/[m s−1], and much improved over the result from conventional empirical scaling relations which gives 23.2 ppm/[m s−1]. This study thus opens the path towards a quantitative understanding of solar-like oscillations, via detailed modelling of 3D stellar atmospheres.

Understanding the concept of resolving power in the Fabry–Perot interferometer using a digital simulation

2006 ◽  
Vol 27 (5) ◽  
pp. 1111-1119 ◽  
Author(s):  
I Juvells ◽  
A Carnicer ◽  
J Ferré-Borrull ◽  
E Martín-Badosa ◽  
M Montes-Usategui
Keyword(s):  
Digital Simulation ◽  
Resolving Power ◽  
Fabry Perot

THE EFFECT OF COLLISIONS ON THE DOPPLER BROADENING OF SPECTRAL LINES

1967 ◽  
Vol 9 (5) ◽  
pp. 701-716 ◽  
Author(s):  
Sergei G Rautian ◽  
Igor I Sobel'man
Keyword(s):  
Spectral Lines ◽  
Doppler Broadening

Characteristics of the defocused spherical Fabry-Pérot interferometer as a quasi-linear dispersion instrument for high resolution spectroscopy of pulsed laser sources

1968 ◽  
Vol 263 (1140) ◽  
pp. 209-223 ◽  
Keyword(s):  
Laser Beam ◽  
Optical Design ◽  
Pulsed Laser ◽  
Resolving Power ◽  
High Resolution Spectroscopy ◽  
Radius Of Curvature ◽  
Spherical Mirror ◽  
Linear Dispersion ◽  
Fabry Perot ◽  
Very High

Defocused spherical mirror Fabry—Pérot etalons, in which the mirror separation is slightly less than the common radius of curvature, produce a multiple-beam fringe pattern of concentric rings, with quasi-linear spectral dispersion over an appreciable annular region corresponding to two free spectral ranges. The characteristics of these interferograms are discussed in relation to their many advantages for pulsed laser spectroscopy. These advantages include: (i) accuracy of frequency difference measurement; (ii) high illumination of the detector with moderate energy density in the laser beam; (iii) ease of alinement and permanent adjustment of the mirrors leading to the attainment in practice of a very high instrumental finesse (N R values of up to 90 have been achieved); (iv) measurement of degree of spatial coherence of laser beam; (v) ease of matching the interferogram to the spatial resolution of the detector. A simple optical path relation determines the positions of the fringes and the location of the quasilinear dispersion region. The interfering wavefronts, formed by multiple reflexion, have been numerically computed and summed to provide information on the finesse, fringe profiles, contrast and optimum conditions of use of this new, very high resolving power (107 to 108) quasi-linear spectrographic disperser. Constructional details are described and optical design criteria are discussed, together with the various experimental arrangements for employing the instrument. Comparison is made with the equivalent confocal and plane Fabry—Pérot etalons and methods of simultaneously measuring

On the combined Doppler and pressure broadening of nonresonant spectral lines

1988 ◽  
Vol 66 (4) ◽  
pp. 341-348
Author(s):  
M. A. Diaz ◽  
F. Palomares ◽  
J. Veguillas
Keyword(s):  
Kinetic Equation ◽  
Inelastic Collisions ◽  
Spectral Lines ◽  
The Other ◽  
Low Density ◽  
Doppler Broadening ◽  
Equation Approach ◽  
Pressure Broadening ◽  
Debye Relaxation ◽  
Collision Model

An explicit spectral function for nonresonant transitions has been derived that includes pressure broadening, Doppler broadening, and diffusional narrowing. This has been accomplished through a kinetic-equation approach. The kinetic equation has been resolved by using an extension of the Bhatnagar–Gross–Krook collision model to inelastic collisions, characterized by two collision frequencies: one associated with elastic collisions and the other associated with inelastic ones. The high- and low-density limits have been discussed, and the standard formula for Debye relaxation has been reproduced. Finally, a discussion concerning the above aspects and their possible extensions has been included as well.

scholarly journals The effect of hyperfine splitting on Stark broadening for three blue-green Cu i lines in laser-induced plasma

2019 ◽  
Vol 488 (4) ◽  
pp. 5594-5603 ◽  
Author(s):  
A M Popov ◽  
N I Sushkov ◽  
S M Zaytsev ◽  
T A Labutin
Keyword(s):  
Hyperfine Splitting ◽  
Stark Effect ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Stark Broadening ◽  
Laser Induced Plasma ◽  
Radiation Sources ◽  
And Shifts ◽  
First Time ◽  
Existing Data

ABSTRACT Stark effect is observed in many natural and artificial plasmas and is of great importance for diagnostic purposes. Since this effect alters profiles of spectral lines, it should be taken into account when assessing chemical composition of radiation sources, including stars. Copper is one of the elements which studies of stellar atmospheres deal with. To this end, UV and visible Cu lines are used. However, there is a lack of agreement between existing data on their Stark parameters. It is therefore of interest to obtain new experimental data on these lines and to compare them to previous results. In this work, we have estimated Stark widths and shifts for three blue-green lines at 5105.54, 5153.24, and 5218.20 Å (corresponding transitions are [3d104p] 2P° → [3d94s2] 2D and [3d104d] 2D → [3d104p] 2P°) observed in a ‘long-spark’ laser-induced plasma. For the first time, we have accurately estimated an impact of hyperfine splitting on the profile shapes of the studied lines taking also into account the isotope shifts. We have shown that both effects considerably influence shift and width of Cu i line at 5105.54 Å, and shifts of Cu i lines at 5153.24 and 5218.20 Å.

scholarly journals The potential of many-line inversions of photospheric spectropolarimetric data in the visible and near UV

2019 ◽  
Vol 622 ◽  
pp. A36 ◽  
Author(s):  
T. L. Riethmüller ◽  
S. K. Solanki
Keyword(s):  
Wavelength Range ◽  
Solar Physics ◽  
Solar Observatory ◽  
Spectral Lines ◽  
Resolving Power ◽  
Short Wavelength Range ◽  
Photon Noise ◽  
Infrared Spectral ◽  
The Many

Our knowledge of the lower solar atmosphere is mainly obtained from spectropolarimetric observations, which are often carried out in the red or infrared spectral range and almost always cover only a single or a few spectral lines. Here we compare the quality of Stokes inversions of only a few spectral lines with many-line inversions. In connection with this, we have also investigated the feasibility of spectropolarimetry in the short-wavelength range, 3000 Å−4300 Å, where the line density but also the photon noise are considerably higher than in the red, so that many-line inversions could be particularly attractive in that wavelength range. This is also timely because this wavelength range will be the focus of a new spectropolarimeter in the third science flight of the balloon-borne solar observatory SUNRISE. For an ensemble of state-of-the-art magneto-hydrodynamical atmospheres we synthesize exemplarily spectral regions around 3140 Å (containing 371 identified spectral lines), around 4080 Å (328 lines), and around 6302 Å (110 lines). The spectral coverage is chosen such that at a spectral resolving power of 150 000 the spectra can be recorded by a 2K × 2K detector. The synthetic Stokes profiles are degraded with a typical photon noise and afterward inverted. The atmospheric parameters of the inversion of noisy profiles are compared with the inversion of noise-free spectra. We find that significantly more information can be obtained from many-line inversions than from a traditionally used inversion of only a few spectral lines. We further find that information on the upper photosphere can be significantly more reliably obtained at short wavelengths. In the mid and lower photosphere, the many-line approach at 4080 Å provides equally good results as the many-line approach at 6302 Å for the magnetic field strength and the line-of-sight (LOS) velocity, while the temperature determination is even more precise by a factor of three. We conclude from our results that many-line spectropolarimetry should be the preferred option in the future, and in particular at short wavelengths it offers a high potential in solar physics.

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