Comb-calibrated solar spectroscopy through a multiplexed single-mode fiber channel
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| License | CC Attribution 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.5446/38801 (DOI) | |
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26
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Field-effect transistorMultiplexCombSolar energyFiberSpectroscopyElectric power distributionParticle physicsPlain bearingVideoTransverse modePorcelainOpticsSchmidt cameraFrequency combHot workingSpectroscopyLaserComputer animation
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CaliberSolar energySunlightHot workingFrequency combFiberLaserAudio frequencySpectrographLightMeeting/Interview
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Audio frequencyLaserAmplitudeClockReference workLaserVideoFrequency combFrequency standardAudio frequencyAtomic clockFunkgerätSpectral lineElectromagnetic spectrumYearComputer animationDiagram
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Audio frequencyAstronomical objectVideoRadial velocityAstronomerFlugbahnFrequency combSpectrographLaserSpectral lineDoppler-VerschiebungMeasurementReference workCaliberAudio frequency
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UniversePlanetStarFrequency combCrystal habitLaserRückstoßScale (map)Brillouin zoneFundamental frequencyMembrane potentialCosmic distance ladderMeeting/Interview
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FiberLaserFuel injectionSpectroscopyAudio frequencyFiberSource (album)Transverse modeFuel injectionLightProfil <Bauelement>AstronomerLaserMeasurementSpectrographSolar energyLichtleitkabelFrequency combHot working
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Transmission towerVakuumphysikSolar energy
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FullingStarSunlightDisc brakePhotosphereSolar energy
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FiberTARGET2FiberTransverse modeStarFuel injectionHose couplingSunlightPower (physics)
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Ladungsgekoppeltes BauelementMeasurementSource (album)SunlightTransmission (mechanics)LightBird vocalizationList of light sourcesLichtleitkabelFiberTransverse modeCombDiagram
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RedshiftAudio frequencySolar energyHelioseismologieMeasurementOrbital periodComputer animationDiagram
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Ladungsgekoppeltes BauelementVideoStellar atmosphereStellar atmosphereNyquist stability criterionSpectral lineDiagram
Transcript: English(auto-generated)
00:05
This work shows how laser frequency combs can be used for solar spectroscopy and how they might be used in future nighttime astronomy. Our method uses a single-mode fiber to feed a solar spectrograph both with sunlight from a solar telescope
00:23
and with calibration light from a laser frequency comb. The spectrum of a laser frequency comb consists of a series of sharp, evenly spaced spectral lines. The laser that generates the frequency comb is stabilized to an accurate radio frequency reference such as an atomic clock.
00:41
The optical frequencies of the lines are then known to an extreme accuracy given by the radio frequency reference. In recent years, laser frequency combs have been established in astronomy as calibrators for astronomical spectrographs. The laser frequency comb provides a highly accurate optical reference
01:00
that allows precise determination of line positions in astronomical spectra. This is used, for example, to measure radial velocities of celestial bodies via Doppler shifts of spectral lines. Frequency combs have an intriguing potential in astronomy. They can be used to search for Earth-like planets
01:23
in the habitable zone of distant stars by looking at the recoil that's imprinted on the star by the orbiting planet. They can be used to observe directly the accelerating expansion of space in the universe
01:43
by looking at distant lasers. And they can be used to look for variations, for possible variations of fundamental constants on cosmological scales. High-precision astronomical spectrographs are connected to their telescopes via optical fibers
02:02
to detach them from telescope guiding. Multimode fibers are typically used for this purpose as it is difficult to inject light from astronomical sources efficiently into single-mode fibers. The beam profile at the output of a multimode fiber however depends on fiber injection and bending
02:20
which translates into uncertainties in spectroscopic measurements. In this work, we demonstrate the use of single-mode fibers for frequency comb-calibrated solar spectroscopy. These fibers support only a single, approximately Gaussian-shaped beam profile independent of the circumstances. This increases the precision and robustness of the measurements.
02:44
We demonstrate our technique at the VTT Solar Telescope located in Tenerife, Canary Islands and run by the Kipahoya Institute for Solar Physics. For our observations, we use the Crotel telescope that is installed in the same building as the VTT.
03:01
This full-disc solar telescope allows feeding the fiber with light averaged over the complete solar disk thus viewing the Sun similar to a distant star. The high optical powers available from the Sun facilitate single-mode fiber coupling because strong coupling losses can be tolerated. However, advanced fiber injection techniques
03:22
are anticipated to enable efficient single-mode fiber coupling of distant stars making our approach interesting even for faint astronomical targets. The comb light and the Sun light are both fed through the same optical fiber. We investigate both temporally separated and simultaneous fiber transmission of the two sources.
03:41
In the latter concept, both light sources simultaneously share the same spatial mode which enables particularly robust measurements. We demonstrate our method by measuring global solar oscillations with a period of five minutes and compare our results to other measurements. The technique is also used to assess the stability of absorption lines from Earth's atmosphere.