Calbration of the piezo motion of the VINCI instrument, installed at ESO’s VLT Interferometer
Jeff will present us this wednesday some of his work about piezo calibration.
Abstract:
VINCI was the first interferometric instrument used at the VLTI
astronomical interferometer. It performs single spatial mode interference
using an optical fiber combiner using stellar radiation in the astronomical
"K" band (2-2.4 microns). The fringe packet is scanned over its coherence
length using an external path controlled by a piezoelectric actuator.
Alternate scans are in opposite directions, each over a range of about 100
wavelengths. Although the stellar radiation has a much shorter coherence
length, many technical runs used a laser test source which is therefore
coherent over the entire range of each scan and at a specific wavelength,
and from this the motion of the piezo can be derived in detail.
I will present various results concerning the piezo motion derived in this
manner. In addition to an overall error in its velocity compared to its
nominal value, the results display a linear change in the velocity over the
range of the scan (thus a parabolic error in phase), and also a "kink" in
its motion. These effects are distinct between scans in the up and down
directions. In addition to these results concerning the VINCI piezo
actuator, I will present similar conclusions in regard to the piezo
actuator used in the interferometric experiment currently setup to
demonstrate the NOVA Fringe Tracker (NFT) concept using a He-Ne laser.
Further discussion of the characteristics of piezo actuators, widely used
in such interferometric applications, is invited.
