Atmospheric Turbulence Measurements with the Palomar Testbed Interferometer

Context. The fringe sensor unit (FSU) is the central element of the phase referenced imaging and micro-arcsecond astrometry (PRIMA) dual-feed facility and provides fringe sensing for all observation modes, comprising off-axis fringe tracking, phase referenced imaging, and high-accuracy narrow-angle astrometry. It is installed at the Very Large Telescope Interferometer (VLTI) and successfully served the fringe-tracking loop during the initial commissioning phase. Aims. To maximise sensitivity, speed, and robustness, the FSU is designed to operate in the infrared K-band and to include spatial filtering after beam combination and a very-low-resolution spectrometer without photometric channels. It consists of two identical fringe sensors for dual-star operation in PRIMA astrometric mode. Methods. Unique among interferometric beam combiners, the FSU uses spatial phase modulation in bulk optics to retrieve real-time estimates of fringe phase after spatial filtering. The beam combination design accommodates a laser metrology for pathlength monitoring. An R = 20 spectrometer across the K-band makes the retrieval of the group delay signal possible. The calibration procedure uses the artificial light source of the VLTI laboratory and is based on Fourier transform spectroscopy to remove instrumental effects. Results. The FSU was integrated and aligned at the VLTI in July and August 2008. It yields phase and group delay measurements at sampling rates up to 2 kHz, which are used to drive the fringe-tracking control loop. During the first commissioning runs, the FSU was used to track the fringes of stars with K-band magnitudes as faint as m K = 9.0, using two VLTI auxiliary telescopes (AT) and baselines of up to 96 m. Fringe tracking using two Very Large Telescope (VLT) unit telescopes was demonstrated. Conclusions. The concept of spatial phase-modulation for fringe sensing and tracking in stellar interferometry is demonstrated for the first time with the FSU. During initial commissioning and combining stellar light with two ATs, the FSU showed its ability to improve the VLTI sensitivity in K-band by more than one magnitude towards fainter objects, which is fundamental for achieving the scientific objectives of PRIMA.

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“…the K-band coherence time and outer scale size of the VLTI site, as demonstrated by Linfield et al (2001) for the Palomar testbed interferometer.…”

Section: Residual Opdmentioning

confidence: 89%

The PRIMA fringe sensor unit

Ménardi¹,

Abuter²,

Accardo³

et al. 2009

A&A

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“…above a characteristic scale. In the results of [42] this transition occurs between τ = 10 s and τ = 100 s with D(τ ) reaching a plateau at about 4 × 10 −10 m 2 . With a data rate of 0.01 Hz for DOLL this corresponds to a variance of 2 × 10 −10 m 2 of the fluctuations of DOLL data.…”

Section: Error Sourcesmentioning

confidence: 88%

“…For τ between 10 ms and a few seconds the observed D(τ ) follows a power law with a slope around 1.5. At 10 ms typical values are D(10 ms) ≈ 5 × 10 −14 m 2 [42]. This corresponds to fluctuations with an amplitude of about a third of the 674 nm wavelength of DOLL at 10 ms and to about 6% of the wavelength at 1 ms.…”

Section: Error Sourcesmentioning

confidence: 93%

Quantum physics exploring gravity in the outer solar system: the SAGAS project

et al. 2008

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We summarise the scientific and technological aspects of the Search for Anomalous Gravitation using Atomic Sensors (SAGAS) project, submitted to ESA in June 2007 in response to the Cosmic Vision 2015-2025 call for proposals. The proposed mission aims at flying highly sensitive atomic sensors (optical clock, cold atom accelerometer, optical link) on a Solar System escape trajectory in the 2020 to 2030 time-frame. SAGAS has numerous science objectives in fundamental physics and Solar System science, for example numerous tests of general relativity and the exploration of the Kuiper belt. The combination of highly sensitive atomic sensors and of the laser link well adapted for large distances will allow measurements with unprecedented accuracy and on scales never reached before. We present the proposed mission in some detail, with particular emphasis on the science goals and associated measurements and technologies.

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“…4 has been reported for the power spectral density of the optical path difference induced by the atmosphere turbulence. 25 …”

Section: Effect Of Air Convection On Laser Pointing Stabilitymentioning

confidence: 99%

Air convection noise of pencil-beam interferometer for long trace profiler

et al. 2006

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In this work, we investigate the effect of air convection on laser-beam pointing noise essential for the long trace profiler (LTP). We describe this pointing error with noise power density (NPD) frequency distributions. It is shown that the NPD spectra due to air convection have a very characteristic form. In the range of frequencies from ~0.05 Hz to ~0.5 Hz, the spectra can be modeled with an inverse-power-law function. Depending on the intensity of air convection that is controlled with a resistive heater of 100 to 150 mW along a one-meter-long optical path, the power index lies between 2 and 3 at an overall rms noise of ~0.5 to 1 microradian. The efficiency of suppression of the convection noise by blowing air across the beam optical path is also discussed. Air-blowing leads to a white-noise-like spectrum. Air blowing was applied to the reference channel of an LTP allowing demonstration of the contribution of air convection noise to the LTP reference beam. The ability to change (with the blowing technique presented) the spectral characteristics of the beam pointing noise due to air convection allows one to investigate the contribution of the convection effect, and thus make corrections to the power spectral density spectra measured with the LTP.

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Atmospheric Turbulence Measurements with the Palomar Testbed Interferometer

Cited by 30 publications

References 13 publications

The PRIMA fringe sensor unit

The PRIMA fringe sensor unit

Quantum physics exploring gravity in the outer solar system: the SAGAS project

Air convection noise of pencil-beam interferometer for long trace profiler

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