Interferometria a largo campo:

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Interferometria a largo campo NIRVANA su LBT
R. Ragazzoni, T.M. Herbst, W. Gaessler, D.
Andersen C. Arcidiacono, A. Baruffolo, H.
Baumeister, P. Bizenberger E. Diolaiti, S.
Esposito, J. Farinato, H.W. Rix R-R. Rohloff, A.
Riccardi, P. Salinari, R. Soci E. Vernet-Viard,
W. Xu
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NIRVANA e lo strano acronimo di Near InfraRed
and Visible Adaptive iNterferometry for Astronomy
Lobiettivo e quello di realizzare su di un
campo relativamente grande In termini di Ottica
Adattiva (e mostruoso in temrini di
interferometria) Immagini interferometriche al
fuoco combinato di LBT nel vicino IR e Nella
parte rossa della banda visibile.

• Per riuscire nellintento sono necessarie la
• realizzazione simultanea di un certo numero
• di miracoli (o magie)
• Interferometria di Fizeau
• Entrambi I secondari adattivi
• Co-phasing con I secondari
• I due telescopi coordinati in dettaglio
• Ottica Adattiva MultiConiugata
• Sensori multi-piramide
• Layer Oriented
• CCD a basso RON (?)

Tom Herbst?? Piero Stalinari?? Roberto
Ragazzoni?? Giuseppe Bono??
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Fizeau chi era costui ?
Armand-Hippolyte-Louis-Fizeau (1819- 1896)
Nome lungo e complicato che sia di cattivo
auspicio?
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Milestones in Optical Interferometry
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LBT e davvero un telescopio peculiare e non
appena si comincia a cercare di tradurre in
disegni tecnici le chiacchierate ce se ne accorge
rapidamente sigh..
La maggior parte del Sensore di fronte donda
e sostanzialmente disegnata per un telescopio da
22.4m. Il che e certo interessante dal punto di
vista tecnico perche e un vero banco di prova
per i futuri telescopi della classe 30..100m
(Opticon, OWL) ma richiede specifiche,
tol- leranze, etc un fattore 4..5 piu rigide
che per MAD-VLT, Gemini, etc
Wow!!
Sigh..
22.4m
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Ma perche LBT efatto come LBT ???
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Original Bracewell nulling interferometer
conceptBracewell proposed space infrared
nulling interferometer to detect thermal emission
of giant exo-planets (Nature, 1978)
Target Jupiter in solar system twin at 10
pc, 0.5 arcsec Method two element
interferometer in space, set for destructive
interference for star, constructive for
planet. Spin about line of sight to modulate
planet signal Wavelength 40 mm reqd
element separation 7 m (planet on 1st
constructive peak) planet / star _at_ 40
mm 1/5000 sin2 leak 1/400,000 planet / nulled
star 80
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Fizeau and Michelson interferometry are
fundamentally different. In a Fizeau
interferometer, the focal planes are brought into
coincidence as shown, by division of wavefront.
The interference is detected fringes in the focal
plane images. Provided the exit pupil mirrors the
entrance pupil, every star in the field appears
as an Airy pattern appropriate to the individual
aperture, crossed by Youngs fringes with spacing
set by the baseline (center-to-center). The
central fringe in each star image corresponds to
zero path length, and is achromatic By contrast,
a Michelson interferometer combines the beams by
overlapping the pupils at a semi-transparent
beamsplitter (division of amplitude). There are
no interference fringes formed in the focal
plane, interference appears as a modulation in
star intensity according to optical path
difference. Zero path length corresponds to a
single achromatic fringe on the sky. For normal
photometric bands of width l/Dl 0.1, the field
of view for interferometry is very narrow, with a
width of only 10 fringes.
Disegno originale di Roger Angel
Schematic of Fizeau interferometer
The fundamental advantage of Fizeau
interferometry for optical/infrared
interferometers is its much larger field of view
for wide bandwidths. This means that phase
reference stars can be found within the field,
and fringes stabilized over the field, for long
integrations as for adaptive optics. It also can
be implemented with far fewer warm mirrors, and
hence much lower thermal background.
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Michelson vs. Fizeau

• Aperture piccole rispetto la loro distanza
• Misura fatta sul piano della pupilla
• Si misura la visibilita o contrasto delle
  fringe, che rappresenta un punto nel piano
  coniugato di Fourier delloggetto
• Misure meno immediate, ma baseline generalmente
  uno, due o tre ordini di grandezza superiori alle
  aperture e risoluzioni attualmente uniche.

• Aperture confrontabili con la distanza (non e
  sempre vero)
• Misura fatta sul piano focale
• Si misurano vere immagini, ma senza deconvolvere
  non si va molto distanti, a meno che non si
  misuri la visibilita (sigh)
• Sostanzialmente si raccolgono immagini, ma si
  paga la relativa pulizia della PSF con una
  baseline relativamente modesta

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Current Ground-based
Optical Long Baseline Interferometer Projects
 
 
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Esempio di un campo crowded (da una tesi di PhD a
Heidelberg)
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Multiple FoV layer oriented MCAO
Annular 2..6arcmin diameter for ground turbulence
correction central 2arcmin for mid and high
altitude correction. Light from several NGSs is
co-added on the plane conjugated to where the DM
is placed.
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• Several interesting variations
• on the layer-oriented theme
• Ground layer correction is
• achieved through secondary
• adaptive mirror
• Co-addition of the relatively
• bright stars for gnd correction
• is made numerically using
• L3CCD or TI detectors
• Third loop coupling the 2 FoV
• with the gnd layer removed
• Wavefront sensing of the 2
• central FoV is made in the
• combined beam.

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NIRVANA block diagram of the optical path
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NIRVANA aboard LBT
NIRVANA in LBT
The instrument is located in one of the
so-called bent combined focus
IR channel
F/60 Fizeau combined visible focal plane
A top view
MCAO WaveFront Sensor
a few components.
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Top
Side
Rear
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An overall view of NIRVANA
Beam splitting between NIR and VIS is achieved In
parallel beam just After the MCAO correction.
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A couple of details
DMs can be adjusted in their range. equivalent
distance between DMs is not variable but it
grow with the range (e.g. 4-8km 6-11km)
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We adopted a slightly diverging,
quasi-collimator, followed by a parallelyzer
Quasi collimator
Parallelizer
DM2
DM3
Parallelizer
Cryostat optics
With the parallelizers the light appears as
coming from infinity and can interfere properly
Pupil
Metapupil (2)
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Stars enlargers positioner details
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After the stars enlarger each collected star is
splitted into four beams by a pyramid acting as
wavefront sensor
Light from all the 2 FoV but the light Collected
from the Stars enlargers
Different pupil sizes because of different F/ of
the beams, in order to allow for easy disentangle
of the two light beams
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Conceptual layout of pupils arranger
From one Mirror
CCD
CCD
CCD
CCD
CCD
CCD
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Se vi sembra complicato date un occhio a MIDI od
AMBER, ad esempio
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A possible approach for the scientific role of
NIRVANA in LBT

• Even a single 1arcmin is too-large for any
  reasonable camera or 3D spectrograph, if
• the potential resolution in the visible is to
  be exploited!
• Take advantage of the other existing instruments
  aboard LBT
• Maximize the scientific return (i.e. not only
  one scientific goal at once)
• Being modular but ambitious make it more failure
  tolerant and hence more productive
• No compromise to the science because of MCAO
  needs

PrimeFocus LUCIFER MODS
Cover the 2arcmin diameter FoV with different
devices in order to collect all the possible
data from the full FoV
Built a camera with a strong undersampling, but
still useful (gnd correction gives
0.1..0.2 images!) also to center stars for pure
MCAO purposes.
Pick-up for AO reference and science
instruments coexists in the same focal plane
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Prime Focus
25arcmin seeing-limited
Deep Imagers
Integral Field Units
Multi Slit
..turning from drawings to reality
Roberto Ragazzoni
Science with NIRVANA, Firenze (Italy) - 25
February 2002
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As any respectable project we made wonderful
(much better then reality, as usual) simulations
Strehl variation in the central 1 can be as low
as a few percent.
The overall Strehl is maybe Modest but sky
coverages are in the range 10..30 for NGP see
also Marchetti et al. 4839-68
Simulations are made with real asterisms
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Why we believe (erroneously??) to have an unique
opportunity with NIRVANA aboard LBT???
Secondary Adaptive Mirror (one DM, aimed to
remove the ground turbulence, the worst one) is
embedded in the telescope
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Pyramid WaveFront sensor should achieve gains of
the order of 1..2mags (proven in the lab,
positive preliminary checking at TNG see Ghedina
et al. 4839-105)
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Layer-oriented WaveFront Sensing is more
effective and capable of using several faint
stars than conventional MCAO (wavefront sensing
proven in the lab, first test bed on VLT see
Farinato et al. 4839-71)
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We do not rely on lasers (at the expense of a
limited sky-coverage)
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Riepilogo delle opportunita per strumenti
scientifici

• Post-sensore di fronte donda (stile AFOSC,
  quello che non piace a Sergio), ad es. La
  patrol-camera (pazialmente oscurati dagli stars
  enlargers).
• Attorno ad FP60, ovvero nel ramo visibile
  (600..1000nm) di NIRVANA (con preghiera di non
  oscurare gli star enlargers)
• Nel canale IR, dove esiste gia un disegno per
  una camera IR con privision fino ad un 4kx4k, con
  campionamento di Nyquist per il modo
  interferometrico
• Ricordate che Strehl5..15 nel visibile e
  30..50 in NIR, e che il throughput e
  dellordine di pochi percento!

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Competitori

• In linea di principio come interferometro
  multiconiugato non ci sono competitori, ma il
  guadagno e 3x e su un asse solo, a spese di
  throughput narrow scientific case???
• Come MCAO il vero competitore e Gemini, dove
  hanno scommesso su 5 stelle laser
• In prospettiva post-MAD-VLT allESO potrebbe
  essere un competitore!

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Partner soldi

• Max Planck Heidelberg (2MEur attraverso AvH 5
  persone, laboratorio, 2 DMs, WFC, etc)
• Colonia (forschung telefunken di Andreas Eckart,
  il conservatore a sei sigma)
• INAF (?) tramite minacce a mano armata da parte
  di Piero Stalinari (il rivoluzionario a sei
  sigma)
• Bonn ??? (Gerard Weigelt, per ora solo contatti)
• In questo momento non esiste un MoU tra Italia e
  Germania su LBT.

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Solo pura razza germanica (I)
Tedesco della Sassonia Canadese
Tedesco del Baden-Wuttenberg Italiano
Tedesco della Renania Americana
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Solo pura razza Germanica (II)
Non preoccupatevi I soldi del contribuente tedesc
o sono spesi al meglio!
Peter Bizenberg PI of Omega2000, il primo fuoco
criogenico per il 3.5m di Calar Alto un vero
competitore di Giallo, ed uno dei pochi veri
tedeschi del NIRVANA team
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Tempi

• Stiamo convergendo per una Design Review in stile
  intermedio tra LBT () e ESO (growl) da scrivere
  entro fine Novembre e da tenersi Gen-Feb 2003
• Sfumata lopzione di andare in prima luce con un
  arm solo in modalita MCAO. Devono esserci
  entrambi gli specchi!
• Trasporto in Mt. Graham dopo estensivi test in
  Europa (errare e umano ma perseverare e
  diabolico)
• Non prima dellinizio 2006

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Conclusions

• NIRVANA is in a design phase.
• Most of optomechanics is challenging it is a
  24m, after all
• RT-WFC and ICS are being analyzed 3000dof for
  actuation
• and 200 dof for setup, but largely divided
  into almost separate
• block thanks to the layer-oriented approach.
• A realistic schedule can follow only after these
  analysis but our
• goal is to have the instrument in the lab in
  late 2005.

Thanks are due to the Alexander von Humboldt
foundation that made possible my 3 10-7 Hz
oscillation between Firenze and Heidelberg,
allowing me to make noise on both sides of this
project!