The ESPRI project: astrometric exoplanet search with PRIMA - I. Instrument description and performance of first light observations

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Table 1

Details of the PRIMA metrology system.

Feed		FSUA		FSUB

Input channel^a		IP3	IP1	IP4	IP2
Polarisation		p	s	p	s
Monitored path	(m)	L ₃	L ₁	L ₄	L ₂
δν ^b	(MHz)	+38.65	+38.00	−39.55	−40.00
OPD	(m)	ΔL_A = L₃ − L₁		ΔL_B = L₄ − L₂
Beat frequency	(kHz)	650		450
Diff. delay	(m)	ΔL = ΔL_A − ΔL_B

Constants:
Δν_P^c	(MHz)	78.1
ν _P ^d	(MHz)	227 257 330.6
λ _P ^e	(nm)	1 319.176183

Notes.

^(a)

The input channel (IP) refers to the physical location of the beam at the switchyard level. There are eight input channels at VLTI.

^(b)

Frequency shift relative to the laser frequency ν_P.

^(c)

Frequency shift between both feeds introduced to avoid crosstalk.

^(d)

Calibrated laser frequency.

^(e)

Laser vacuum wavelength.

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