the lhires-iii spectrograph © c2pu, observatoire de la cote d’azur, université de nice...
TRANSCRIPT
THE THE LHIRES-IIILHIRES-III
SPECTROGRAPHSPECTROGRAPH
© C2PU, Observatoire de la Cote d’Azur,
Université de Nice Sophia-Antipolis
Jean-Pierre RivetCNRS, OCA,Dept. [email protected]
The LHIRES-III
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LHIRES = Littrow High RESolution spectrograph
Diffraction by 1 element
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Incident beam
assumed parallel
(wavelength )
Diffracted beam
Collimator
Screen
~ / d
d
Non-reflecting
substrate • Maximum in the direction of geometric optics: r = - r • Angular width: ~ / d
i
r
Reflecting
element
Diffraction by “n” elements
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Incident beam
(wavelength )
Screen
?Non-reflecting
substrate
Reflecting
elements
Collimator
i
Diffraction by “n” elements
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Incident beam
(wavelength )
i Screen
?
Collimator
Diffraction by “n” elements
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Screen
Collimator
NO LIGHT !
Diffracted beams out of phase :destructive interferences NO LIGHT
Diffraction by “n” elements
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Screen
Collimator
LIGHT !
Diffracted beams in phase :constructive interferences MAXIMUM LIGHT
Diffraction by “n” elements
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aa
aa
i
Ray
0R
ay 1
Delay of Ray 1 wrt Ray 0 = a sin(i)
Diffraction by “n” elements
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aa
aa r
Ray 0
Ray 1
Delay of Ray 1 wrt Ray 0 = a sin(r)
Diffraction by “n” elements
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aa
aa r
Ray 0
Ray 1
i
Ray
0R
ay 1
Total delay of Ray 1 wrt Ray 0 : = a sin(i) + a sin(r)
Condition for constructive interferences:
= k .
integer; called the “order”
Diffraction by “n” elements
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aa
aa r
Ray 0 ’
Ray 1 ’
i
Ray
0R
ay 1
Order k = 0
Condition for constructive interferences:
= 0, whatever
sin(i) + sin(r) = 0
Snell’s law !direction of reflection on the grating’s plane
according to geometric optics
NON DISPERSIVE
Diffraction by “n” elements
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aa
aa r
Ray 0 ’
Ray 1 ’
i
Ray
0R
ay 1
Order k ≠ 0
Condition for constructive interferences:
= k .
sin(i) + sin(r) = k . / a
DISPERSIVE
Diffraction pattern (monochr.)
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sin(i) + sin(r) 0
Relative intensity
a aaa
N
d
~ / (N.a)
~ / a
~ / d
Diffraction enveloppe
/ a 2 / a 3 / a- / a-2 / a-3 / a
Diffraction pattern (polychr.)
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sin(i) + sin(r) 0
Relative intensity
/ a 2 / a 3 / a- / a-2 / a-3 / a
Order 0:
non dispersive
Order 1:
dispersive
Order 2:
more dispersive
Order 3:
even more dispersive
Blazed gratings
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ri
Diffraction envelope is maximum when:
r = - i
0th order is maximum when:
r = - i
r
i
Diffraction envelope is maximum when:
r = - i
0th order is maximum when:
r = - i
: Normal to the grating
: Normal to the grooves
r
(blaze angle)
i
STANDARD GRATING BLAZED GRATING
Diffraction pattern
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sin(i) + sin(r) 0
Relative intensity
/ a 2 / a 3 / a- / a-2 / a-3 / a
Order 0:
non dispersive
Order 1:
dispersive
Order 2:
more dispersive
Order 3:
even more dispersive
STANDARD GRATING
Diffraction pattern
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sin(i) + sin(r) 0
Relative intensity
/ a 2 / a 3 / a- / a-2 / a-3 / a
Maximum of
diffraction curve
on order k ≠ 0
BLAZED GRATING
Blaze angle depends on the central wavelength 0
and order k
Basics on spectrographs
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Dispersing element
(grating)
r
i
Collimated input beam
Collimation optics
Dispersed beam
Camera optics
Sensor
Entrance slit
Light from
the telescope
Littrow configuration
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i
Littrow condition: r = i
Collimator optics = Camera optics(cost effective configuration)
r
The LHIRES-III
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Micrometric screw
(to tilt the gating)
Diffraction
blazed grating)
Collimator / camera
optics
Bending mirror
Science camera
Guiding camera
Focuser for the
guiding camera
Slit
environment
Bending mirror
F/12.5 input beam
from the telescope
The LHIRES-III
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Micrometric screw
(to tilt the gating)
Diffraction
blazed grating)
Collimator / camera
optics
Bending mirror
Science port
Guiding port
Focuser for the
guiding cameraSlit
environment
Bending mirror
F/12.5 input port
The slit environment
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Bending flat mirror Input beam
(from telescope)
Guiding output portInput slit
Output port
focusing optics
Slit environment
The slit environment
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15 m slit
19 m slit
Active slit
25 m slit
35 m slit
Optically polished component: MUST HE HANDELED WITH CARE
The calibration lamp
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Calibration lamp housing
Calibration lamp flip button
The diffraction ratings
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Protection frame
Active grating surface
Housing
Tilt axis
High precision optical component: MUST HE HANDELED WITH EXTREME CARE
NO FINGER PRINTS !
Available gratings:• 150 gr/mm• 300 gr/mm•2400 gr/mm
The micrometric screw
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Fixed tilt axis
Active grating surface
0
510
15
20
2530354045
Last visible
mark: 23.5
Drum tick mark
in front of the
fixed index : 34
How to read the micrometric screw :
Fixed index
Value = 23.5+0.34 = 23.84
Micrometric screw
Half-integer
tick marksInteger
tick marks
Configurations
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Available slits:•15 microns•19 microns•23 microns•35 microns
15 m 19 m 23 m 35 m
150 gr/mm 834 731 644 465
300 gr/mm 1673 1466 1293 932
2400 gr/mm 18900 16500 14600 10500
Slit
Grating
Spectral resolution @ 589nm
Available gratings:• 150 gr/mm• 300 gr/mm•2400 gr/mm
Sample spectra
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The Sodium D1 and D2 lines in the solar spectrum (LHIRES-III + 2400 gr/mm)