THE LHIRES-III SPECTROGRAPH © C2PU, Observatoire de la Cote d’Azur, Université de Nice Sophia-Antipolis Jean-Pierre Rivet CNRS, OCA, Dept. Lagrange [email protected]

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

19/04/23 C2PU-Team, Observatoire de Nice 2

LHIRES = Littrow High RESolution spectrograph

Diffraction by 1 element


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


Incident beam

(wavelength )

Screen

?Non-reflecting

substrate

Reflecting

elements

Collimator

i



Incident beam

(wavelength )

i Screen

?

Collimator



Screen

Collimator

NO LIGHT !

Diffracted beams out of phase :destructive interferences NO LIGHT



Screen

Collimator

LIGHT !

Diffracted beams in phase :constructive interferences MAXIMUM LIGHT



aa

aa

i

Ray

0R

ay 1

Delay of Ray 1 wrt Ray 0 = a sin(i)



aa

aa r

Ray 0

Ray 1

Delay of Ray 1 wrt Ray 0 = a sin(r)



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”



aa

aa r

Ray 0 ’

Ray 1 ’

i

Ray

0R

ay 1

Order k = 0


= 0, whatever

sin(i) + sin(r) = 0

Snell’s law !direction of reflection on the grating’s plane

according to geometric optics

NON DISPERSIVE



aa

aa r

Ray 0 ’

Ray 1 ’

i

Ray

0R

ay 1

Order k ≠ 0


= k .

sin(i) + sin(r) = k . / a

DISPERSIVE

Diffraction pattern (monochr.)


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.)


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


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


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


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


Dispersing element

(grating)

r

i

Collimated input beam

Collimation optics

Dispersed beam

Camera optics

Sensor

Entrance slit

Light from

the telescope

Littrow configuration


i

Littrow condition: r = i

Collimator optics = Camera optics(cost effective configuration)

r

The LHIRES-III


The LHIRES-III


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


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 LHIRES-III


The slit environment


Bending flat mirror Input beam

(from telescope)

Guiding output portInput slit

Output port

focusing optics

Slit environment

The slit environment


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


Calibration lamp housing

Calibration lamp flip button

The Neon spectrum


The diffraction ratings


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


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


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

19/04/23 31

The Hydrogen H line in the solar spectrum (LHIRES-III + 2400 gr/mm)

Sample spectra

19/04/23 32

The Sodium D1 and D2 lines in the solar spectrum (LHIRES-III + 2400 gr/mm)

Sample spectra

19/04/23 33

The Magnesium triplet in the solar spectrum (LHIRES-III + 2400 gr/mm)

Sample spectra

19/04/23 34

The Hydrogen H line in Saturn’s spectrum (LHIRES-III + 2400 gr/mm)The lines are tilted by the planet’s surface rotation (Doppler effect)

Documents

THE LHIRES-III SPECTROGRAPH © C2PU, Observatoire de la Cote d’Azur, Université de Nice Sophia-Antipolis Jean-Pierre Rivet CNRS, OCA, Dept. Lagrange [email protected]