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.

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 Convective blueshifts in the solar atmosphere

2019 ◽  
Vol 622 ◽  
pp. A34 ◽  
Author(s):  
F. Stief ◽  
J. Löhner-Böttcher ◽  
W. Schmidt ◽  
T. Steinmetz ◽  
R. Holzwarth
Keyword(s):  
Solar Atmosphere ◽  
Frequency Comb ◽  
Solar Spectrum ◽  
Solar Limb ◽  
Laser Frequency ◽  
Disk Center ◽  
Spectral Lines ◽  
Significant Discrepancy ◽  
Convective Motions ◽  
The Absolute

Context. Granular convective motions reach into the lower solar atmosphere, typically causing photospheric spectral lines to exhibit a differential line shift. This Doppler shift to shorter wavelengths is commonly known as convective blueshift. Aims. Spectroscopic high-accuracy measurements provide us with a refined determination of the absolute convective blueshift and its atmospheric distribution from disk center to the solar limb. Methods. We performed systematic observations of the quiet Sun with the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telescope. The solar disk was scanned along the meridian and the equator, from the disk center toward the limb. The solar spectrum around 6173 Å was calibrated with a laser frequency comb on an absolute wavelength scale with an accuracy of a few meters per second. We applied a bisector analysis on the spectral lines to reveal the changes of convective blueshift and line asymmetry at different heliocentric positions. Results. Being a signature for convective motions, the bisector curve of Fe I 6173.3 Å describes a “C”-shape at disk center. When approaching the solar limb, the bisector transforms into a “\”-shape. The analysis of the time- and bisector-averaged line shifts yields three distinct results. Firstly, the center-to-limb variation of Doppler velocities measured with LARS reveals a significant discrepancy (up to 200 m s−1) to the full-disk Dopplergrams of the Helioseismic and Magnetic Imager (HMI). Secondly, we obtained a significant decrease of convective blueshift toward the solar limb. Thirdly, the line-of-sight effect of solar activity, including p-mode oscillations and supergranular flows, leads to a scatter of up to ±100 m s−1 at intermediate heliocentric positions. Conclusions. The accurate observation of the absolute convective blueshift with LARS allows the identification of systematic discrepancy with Doppler velocities measured by HMI. The center-to-limb variation of HMI suffers from an additional blueshift for μ <  0.9 that is incompatible with our results. LARS measurements can be taken as a reference for the correction of systematic errors in the synoptic HMI Dopplergrams.

scholarly journals Optimization of operating modes of the weak absorption spectrometer

2021 ◽  
Vol 2091 (1) ◽  
pp. 012016
Author(s):  
P V Korolenko ◽  
O M Vokhnik
Keyword(s):  
Laser Frequency ◽  
Rate Of Change ◽  
Spectral Lines ◽  
Resolving Power ◽  
High Rate ◽  
Test Substance ◽  
Weak Absorption ◽  
Operating Modes ◽  
Longitudinal Modes ◽  
Absorption Spectrometer

Abstract The possibilities of improving the characteristics of a weak absorption spectrometer consisting of a frequency-tunable laser and an external analytical resonator with the test substance are analyzed. The influence of the scanning speed of the laser frequency on the choice of the spectrometer operating modes that provide the required resolution and the required sensitivity of spectral measurements is considered. Particular attention is paid to assessing the role of the interaction of modes in an analytical cavity on the structure of the recorded spectra. It was found that at a high rate of change in the laser frequency and superposition of fields of longitudinal modes, an improvement in the resolving power is combined with a certain decrease in the sensitivity and accuracy of recording weak spectral lines. It is shown that the optimization of the spectrometer operation modes requires correct accounting of the Q-factor of the analytical resonator and the line width of the probe radiation.

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.

Long-term stability of a Fabry-Perot interferometer used for measurement of stellar Doppler shift

1990 ◽  
Author(s):  
Robert S. McMillan ◽  
Peter H. Smith ◽  
Marcus L. Perry ◽  
T. L. Moore ◽  
William J. Merline
Keyword(s):  
Doppler Shift ◽  
Term Stability ◽  
Long Term Stability ◽  
Fabry Perot

scholarly journals New wavelength calibration for echelle spectrographs using Fabry-Pérot etalons

2019 ◽  
Vol 624 ◽  
pp. A122 ◽  
Author(s):  
F. Cersullo ◽  
A. Coffinet ◽  
B. Chazelas ◽  
C. Lovis ◽  
F. Pepe
Keyword(s):  
Radial Velocity ◽  
Extrasolar Planets ◽  
Frequency Comb ◽  
Emission Lines ◽  
Measurement Scale ◽  
Calibration Source ◽  
Data Set ◽  
Wavelength Calibration ◽  
Fabry Perot ◽  
The Absolute

Context. The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for very-high-precision spectroscopy at the level of δλ/λ <  10−9. Only an accurate wavelength calibration of the spectrograph can guarantee that the aimed precision is achieved over a multi-exposure and multi-epoch data set. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner. Aims. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-Pérot-based calibration source. Methods. On the basis of calibration frames acquired each night since the Fabry-Pérot etalon was installed on HARPS in 2011, we constructed a combined wavelength solution that fits simultaneously the thorium emission lines and the Fabry-Pérot lines. The combined fit was anchored to the absolute thorium wavelengths, which provide the “zero-point” of the spectrograph, while the Fabry-Pérot lines were used to improve the (spectrally) local precision. The obtained wavelength solution was verified for auto-consistency and tested against a solution obtained using the HARPS laser-frequency comb (LFC). Results. The combined thorium+Fabry-Pérot wavelength solution shows significantly better performances compared to the thorium-only calibration. In both cases, the residuals of the LFC line positions to the fitted wavelength solution follow a Gaussian distribution with an rms value of about 14 m s−1 for the combined solution, and twice as large for the thorium-only solution (29 m s−1). Given these positive results, we have applied the new calibrations to scientific frames and tested the radial-velocity residual on three well-known stars: HD 10700, HD 20794, and HD 69830. In all three cases the radial-velocity (RV) scatter could be reduced compared to the measurements using the previous calibration. Conclusions. The richness of the Fabry-Pérot spectrum helps to improve the wavelength calibration using thorium-argon lamps or extending the wavelength domain of LFCs with limited operational range. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.

scholarly journals Controlling and Phase‐Locking a THz Quantum Cascade Laser Frequency Comb by Small Optical Frequency Tuning

2021 ◽  
pp. 2000417
Author(s):  
Luigi Consolino ◽  
Annamaria Campa ◽  
Michele De Regis ◽  
Francesco Cappelli ◽  
Giacomo Scalari ◽  
...  
Keyword(s):  
Quantum Cascade Laser ◽  
Frequency Tuning ◽  
Frequency Comb ◽  
Phase Locking ◽  
Laser Frequency ◽  
Optical Frequency ◽  
Quantum Cascade

Line profile analysis of an astronomical spectrograph with a laser frequency comb

2014 ◽  
Vol 14 (8) ◽  
pp. 1037-1045 ◽  
Author(s):  
Fei Zhao ◽  
Gang Zhao ◽  
Gaspare Lo Curto ◽  
Hui-Juan Wang ◽  
Yu-Juan Liu ◽  
...  
Keyword(s):  
Line Profile ◽  
Profile Analysis ◽  
Frequency Comb ◽  
Laser Frequency ◽  
Line Profile Analysis

scholarly journals Traceability of laser frequency/wavelength calibration through the frequency comb at Inmetro

2016 ◽  
Vol 733 ◽  
pp. 012058 ◽  
Author(s):  
I L M Silva ◽  
I B Couceiro ◽  
M A C Torres ◽  
P A Costa ◽  
H P H Grieneisen
Keyword(s):  
Frequency Comb ◽  
Laser Frequency ◽  
Wavelength Calibration

scholarly journals Self referenced Yb-fiber-laser frequency comb using a dispersion micromanaged tapered holey fiber

2007 ◽  
Vol 15 (19) ◽  
pp. 12161 ◽  
Author(s):  
Parama Pal ◽  
Wayne H. Knox ◽  
Ingmar Hartl ◽  
Martin E. Fermann
Keyword(s):  
Fiber Laser ◽  
Frequency Comb ◽  
Laser Frequency ◽  
Holey Fiber
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