1. THE LHIRES-III SPECTROGRAPH
Version 02, 02/09/2015
THE LHIRES-III SPECTROGRAPH
Jean-Pierre Rivet
CNRS, OCA,
Dept. Lagrange
© C2PU, Observatoire de la Cote d’Azur,
Université de Nice Sophia-Antipolis

2. C2PU-Team, Observatoire de Nice
The LHIRES-III
LHIRES = Littrow High RESolution spectrograph
19/09/2018
C2PU-Team, Observatoire de Nice

3. Diffraction by 1 element
Incident beam
assumed parallel
(wavelength )
Reflecting
element
Collimator d
Screen i
~  / d r
Diffracted beam
Non-reflecting
substrate
Maximum in the direction of geometric optics: r = - r
Angular width: ~  / d
19/09/2018
C2PU-Team, Observatoire de Nice

4. Diffraction by “n” elements
Reflecting
elements
Incident beam
(wavelength )
Collimator i
Screen ?
Non-reflecting
substrate
19/09/2018
C2PU-Team, Observatoire de Nice

5. Diffraction by “n” elements
Incident beam
(wavelength ) 
Collimator i
Screen ?
19/09/2018
C2PU-Team, Observatoire de Nice

6. Diffraction by “n” elements
Diffracted beams out of phase :
destructive interferences
 NO LIGHT
Collimator
Screen
NO LIGHT !
19/09/2018
C2PU-Team, Observatoire de Nice

7. Diffraction by “n” elements
Diffracted beams in phase :
constructive interferences
 MAXIMUM LIGHT
Collimator
Screen
LIGHT !
19/09/2018
C2PU-Team, Observatoire de Nice

8. Diffraction by “n” elements
Ray 0
Ray 1
Delay of Ray 1 wrt Ray 0 = a sin(i)
19/09/2018
C2PU-Team, Observatoire de Nice

9. Diffraction by “n” elements
Delay of Ray 1 wrt Ray 0 = a sin(r) r
Ray 0
Ray 1
19/09/2018
C2PU-Team, Observatoire de Nice

10. Diffraction by “n” elements
Total delay of Ray 1 wrt Ray 0 :
 = a sin(i) + a sin(r) a
Condition for
constructive interferences:
 = k .  i
Ray 0
Ray 1 r
Ray 0
integer; called the “order”
Ray 1
19/09/2018
C2PU-Team, Observatoire de Nice

11. Diffraction by “n” elements
Order k = 0 a
Condition for
constructive interferences:
 = 0, whatever  i
Ray 0
Ray 1 r
sin(i) + sin(r) = 0
Ray 0 ’
Snell’s law !
direction of reflection on the grating’s plane
according to geometric optics
NON DISPERSIVE
Ray 1 ’
19/09/2018
C2PU-Team, Observatoire de Nice

12. Diffraction by “n” elements
Order k ≠ 0 a
Condition for
constructive interferences:
 = k .  i
Ray 0
Ray 1 r
sin(i) + sin(r) = k .  / a
Ray 0 ’
Ray 1 ’
DISPERSIVE
19/09/2018
C2PU-Team, Observatoire de Nice

13. Diffraction pattern (monochr.)
Relative intensity
~  / (N.a)
~  / a
Diffraction enveloppe
~  / d
-3 / a
-2 / a
- / a
 / a
2 / a
3 / a
sin(i) + sin(r)
19/09/2018
C2PU-Team, Observatoire de Nice

14. Diffraction pattern (polychr.)
Relative intensity
Order 0:
non dispersive
Order 1:
dispersive
Order 2:
more dispersive
Order 3:
even more dispersive
-3 / a
-2 / a
- / a
 / a
2 / a
3 / a
sin(i) + sin(r)
19/09/2018
C2PU-Team, Observatoire de Nice

15. C2PU-Team, Observatoire de Nice
Blazed gratings
STANDARD GRATING
BLAZED GRATING
Diffraction envelope is maximum when:
r = - i
Diffraction envelope is maximum when:
r = - i
0th order is maximum when:
r = - i
0th order is maximum when:
r = - i
 (blaze angle) i i r r i r
: Normal to the grating
: Normal to the grooves
19/09/2018
C2PU-Team, Observatoire de Nice

16. C2PU-Team, Observatoire de Nice
Diffraction pattern
Relative intensity
STANDARD GRATING
Order 0:
non dispersive
Order 1:
dispersive
Order 2:
more dispersive
Order 3:
even more dispersive
-3 / a
-2 / a
- / a
 / a
2 / a
3 / a
sin(i) + sin(r)
19/09/2018
C2PU-Team, Observatoire de Nice

17. C2PU-Team, Observatoire de Nice
Diffraction pattern
Relative intensity
BLAZED GRATING
Maximum of
diffraction curve
on order k ≠ 0
Blaze angle  depends on
the central wavelength 0
and order k
-3 / a
-2 / a
- / a
 / a
2 / a
3 / a
sin(i) + sin(r)
19/09/2018
C2PU-Team, Observatoire de Nice

18. Basics on spectrographs
Collimation optics
Light from
the telescope
Collimated input beam i
Entrance slit
Camera optics
Sensor r
Dispersing element
(grating)
Dispersed beam
19/09/2018
C2PU-Team, Observatoire de Nice

19. Littrow configuration
Littrow condition: r = i
Collimator optics = Camera optics
(cost effective configuration) i r
19/09/2018
C2PU-Team, Observatoire de Nice

20. C2PU-Team, Observatoire de Nice
The LHIRES-III
19/09/2018
C2PU-Team, Observatoire de Nice

21. C2PU-Team, Observatoire de Nice
The LHIRES-III
F/12.5 input beam
from the telescope
Micrometric screw
(to tilt the gating)
Guiding camera
Diffraction
blazed grating)
Bending mirror
Collimator / camera
optics
Focuser for the
guiding camera
Slit
environment
Science camera
Bending mirror
19/09/2018
C2PU-Team, Observatoire de Nice

22. C2PU-Team, Observatoire de Nice
The LHIRES-III
Guiding port
F/12.5 input port
Bending mirror
Focuser for the
guiding camera
Slit
environment
Science port
Micrometric screw
(to tilt the gating)
Bending mirror
Diffraction
blazed grating)
Collimator / camera
optics
19/09/2018
C2PU-Team, Observatoire de Nice

23. C2PU-Team, Observatoire de Nice
The LHIRES-III
19/09/2018
C2PU-Team, Observatoire de Nice

24. C2PU-Team, Observatoire de Nice
The slit environment
Input beam
(from telescope)
Bending flat mirror
Output port
focusing optics
Guiding output port
Input slit
Slit environment
19/09/2018
C2PU-Team, Observatoire de Nice

25. MUST HE HANDELED WITH CARE
The slit environment
15 m slit
Active slit
35 m slit
19 m slit
25 m slit
Optically polished component:
MUST HE HANDELED WITH CARE
19/09/2018
C2PU-Team, Observatoire de Nice

26. C2PU-Team, Observatoire de Nice
The calibration lamps
Spectral calibration lamp:
a small glass bulb filled with low pressure gases, producing
strong and well-defined emission lines when an
electric current passes through. Example Neon-Argon.
Goal: determine the pixel-wavelength relationship.
Flat calibration lamp:
A Tungsten filament bulb producing a “black body”
continuous spectrum.
Goal: determine the overall photometric throughput,
pixel by pixel.
Spectral calibration switch
Flat calibration switch
Power supply plug
19/09/2018
C2PU-Team, Observatoire de Nice

27. The Neon-Argon spectrum
19/09/2018
C2PU-Team, Observatoire de Nice

28. The diffraction ratings
Protection frame
Active grating surface
Tilt axis
Available gratings:
150 gr/mm
300 gr/mm
2400 gr/mm
Housing
High precision optical component:
MUST HE HANDELED WITH EXTREME CARE
NO FINGER PRINTS !
19/09/2018
C2PU-Team, Observatoire de Nice

29. C2PU-Team, Observatoire de Nice
The micrometric screw
How to read the
micrometric screw :
Micrometric screw
Value = = 23.84
Drum tick mark
in front of the
fixed index : 34 45 40 35 30 25
Last visible
mark: 23.5 20
Fixed index 15
Active grating surface 10
Half-integer
tick marks
Integer
tick marks 5
Fixed tilt axis
19/09/2018
C2PU-Team, Observatoire de Nice

30. C2PU-Team, Observatoire de Nice
Configurations
Available gratings:
150 gr/mm
300 gr/mm
2400 gr/mm
Available slits:
15 microns
19 microns
23 microns
35 microns
Spectral 589nm
15 m
19 m
23 m
35 m
150 gr/mm
1179
931
769
505
300 gr/mm
2365
1867
1543
1014
2400 gr/mm
26644
21034
17376
11419
Slit
Grating
19/09/2018
C2PU-Team, Observatoire de Nice

31. Spectral range, spectral scale
Spectral range accessible around 589 nm
on a single image, and spectral scale.
Science camera: SBIG ST402
Grating
Spectral range
Spectral scale
150 gr/mm
230 nm
0.30 nm/pix
300 gr/mm
110 nm
0.15 nm/pix
2400 gr/mm
10 nm
0.013 nm/pix
19/09/2018
C2PU-Team, Observatoire de Nice

32. The Hydrogen H line in the solar spectrum (LHIRES-III + 2400 gr/mm)
Sample spectra
The Hydrogen H line in the solar spectrum (LHIRES-III gr/mm)
19/09/2018

33. Sample spectra
The Sodium D1 and D2 lines in the solar spectrum (LHIRES-III gr/mm)
19/09/2018

34. The Magnesium triplet in the solar spectrum (LHIRES-III + 2400 gr/mm)
Sample spectra
The Magnesium triplet in the solar spectrum (LHIRES-III gr/mm)
19/09/2018

35. Sample spectra
The Hydrogen H line in Saturn’s spectrum (LHIRES-III gr/mm)
The lines are tilted by the planet’s surface rotation (Doppler effect)
19/09/2018

36. Methodology Observing session = Observing run = + observing run 1
+ ...
+ bias images
+ dark images
Observing run =
A self-contained set of spectral images with
THE SAME CONFIGURATION and THE SAME SCIENCE TARGET.
It should include:
+ Flat field spectral images (Tungsten bulb)
+ Calibration spectral images (Ne-Ar discharge tube)
+ Reference star spectral images (with known spectrum)
+ Science star spectral images (with known spectrum) +
19/09/2018

37. Methodology Rules for a good observing sessions:
Organize the session so as to minimize the grating changes.
Maintain the log file (see template) accurately, including UT timestamps before and after any group of similar frames, and before and after any hardware change (grating, micrometer).
Minimal working group: two persons (one person for log file and one for telescope/camera operation).
Do flat field and spectral calibration frames before any group of science frames (reference star or target).
Do reference star spectra only if absolute spectro-photometric calibration is needed.
Groups of science frames should not last more than 10 minutes.
Don’t forget to specify the type of frame (Flat, Callib, Science) to the acquisition software (it can’t guess).
19/09/2018

38. Observing log FILE HEADER: 19/09/2018 LHIRES-III OBSERVING LOG
Date : 2017/02/15
Observers : Jean DUPONT, Michel DUPOND.
Telescope : (OCA)
Instrument : LHIRES-IIIa
Science camera: SBIG ST402 FW
Guiding camera: iNova PLB-Mx
OBSERVING RUN NUMBER .
OBSERVING RUN NUMBER
19/09/2018

39. Observing log OBSERVING RUNS: 19/09/2018
OBSERVING RUN NUMBER
Target : Jupiter
Reference star : Vega
Grating : 150 tr/mm
Micrometer : 03.16mm
Central wavelength : 656.3nm
Telescope on target: 22:30:00 UT
22:30:30 UT
05 Tungsten flat frames Exp=0001s000
22:30:50 UT
05 Argon-Neon calibration frames. Exp=0000s100
22:31:00 UT
10 science frames on Ref. star Exp=0000s500
22:32:00 UT
22:32:30 UT
22:33:10 UT
10 science frames on target Exp=0000s500 .
22:35:50 UT
19/09/2018