Technical information
Functional Analysis and product
breakdown
We can break down the VEGA instrument into two different
sub-systems:
- The Interface Optics (Acronym: IOP)
- The Spectrograph (Acronym: SPE)
The main functions of the Interface Optics sub-system are to:
- inject the beams coming from CHARA to VEGA
- adjust the pupil location (see Annex A)
- reduce the size of the beams (from 3/4 inches to 5 mm)
- configure the beams at the entrance of the spectrograph (vertical
separation of 10mm)
- provide artificial beams to calibrate and align the instrument
- adjust the optical path difference (the zero OPD plan could be the
same as the visible CHARA combiner one)
Due to the important spectral dispersion of the VEGA instrument, it is
not necessary to correct the chromatic image shift caused by the
atmospheric refraction. In addition, the fact that the main part of the
optical path between the telescopes and the instrument is inside vacuum
tubes allows to avoid the use of a chromatic OPD compensator (see Annex
B).
The main functions of the Spectrograph sub-system are:
- to combine the beams
- to disperse the fringe signal
- to optimize the fringe sampling
- to select the polarization
The following diagram shows the different modules which
compose the sub-systems:
Sub system decomposition of VEGA
The following table summarizes the different functions of
each module:
|
SUB-SYSTEM :
INTERFACE OPTICS (IOP)
|
|
MODULE NAME
|
ACR.
|
COMPOSITION
|
M#
|
FONCTIONS
|
|
Picking Optics
|
PGO
|
Set of 4 periscopes
|
*
|
Injects the beam coming from CHARA into VEGA
Avoids beam vignetting due to the mounts of the optical
elements of the CHARA visible combiner
|
|
Beam Compression
|
BCP
|
Parabolic and spherical mirrors
|
|
Reduces the beam size (0.75 inches → 5 mm)
Adjusts the pupil location
Adjusts the ZOPD
|
|
Beam Configuration
|
BCF
|
Set of 4 flat mirrors
|
|
Configures the beam (with a beam separation of 10 mm)
Puts the beam in a vertical configuration
|
|
Calibration and Alignment Unit
|
CAU
|
Artificial sources (spectral and halogen lamps, laser)
Collimator
Mask
|
*
|
Produces light for internal alignment and for the
co-alignment between the instrument and CHARA
Produces light for the calibration (flat-field,
distortion grid, spectral calibration, …)
|
|
CHARA/Sources Selector
|
CSS
|
Beam splitter
Flat mirror
|
*
|
Feeds the spectrograph with the internal sources or with
the beams coming from CHARA
|
|
SUB-SYSTEM :
SPECTROGRAPH (SPE)
|
|
MODULE NAME
|
ACR.
|
COMPOSITION
|
M#
|
FONCTIONS
|
|
Focusing Optics
|
FOC
|
Parabolic mirror
|
|
Produces an image at the spectrograph slits level
|
|
Slit Module
|
SLM
|
Slits
|
*
|
Selects a part of the image
|
|
Anamorphosis Optics
|
ANO
|
2 cylindrical mirrors
|
|
Optimizes the sampling (ratio 12 between the spectral
and the spatial directions)
|
|
Collimating Optics
|
COL
|
Parabolic mirror
|
|
Collimates the beams
|
|
Polarization Module
|
POL
|
Wallaston prism
λ/4 blades
|
*
|
Allows to separate the 2 polarization directions
|
|
Dispersive Optics
|
DIS
|
3 gratings
|
*
|
Disperses the light
Selects between 3 different spectral resolutions (1700,
5000, 35000)
|
|
Camera Optics
|
DFC
|
Parabolic and flat mirrors
|
|
Produces a dispersed fringes image at the detector level
|
|
Neutral Densities
|
NDN
|
Neutral densities
|
*
|
Attenuates the flux
|
|
Detector
|
DET
|
Detector
|
*
|
Detects the dispersed image
|
#: if *, motorized or remotely controlled module
Functional analysis of the different
subsystems of VEGA.
Implantation
We have studied two possible implantations for the VEGA spectrograph.
The first option was to remove the current CHARA visible table and to
replace it by a larger one able to host the VEGA interface optic. In
fact, this solution is really heavy for CHARA and do not minimize the
number of reflexions for VEGA. We present here the preferred solution
for the location of VEGA.
VEGA implantation in the CHARA focal
laboratory
Details of the Zemax solution for
the optic interface
The optic interface is separated into the pick-up mirrors installed on
the CHARA visible table and a new optical table which will support the
interface optics:
Side view of CHARA Visible Table
Top view of CHARA Visible Table
VEGA pick-up systems inside the CHARA visible table
We add motorized pick-up mirrors (periscopic system) in the CHARA
visible table in order to pass above the mounts of the optical elements
and to send the beams towards the Interface Optic Table.
On the following Figure, we present the current optical design
of the interface optic system.
ZEMAX view of the Interface Optic Table of
VEGA (side view)
ZEMAX view of the Interface Optic Table of
VEGA (top view)
The new optical interface table will support
the Beam Compressors (with compensation of OPD and pupil reimaging
function) and the Beam Configuration modules. At the entrance of the
table, the beams have a diameter of 0.75” and a horizontal separation
of 3”. At the output of the Optic interface table, the four beams are
vertically spaced, with a separation of 10mm and the beam size is 5mm.
This table will also host the VEGA calibration and alignment sources.
The following figure presents different views of the optical system
installed on the interface table:
Optical configuration of the interface
optic. Side view (up), front view (bottom)
as seen from the CHARA beams before the pick-up mirrors.
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