Transcript Near IR ADC design

Atmospheric Dispersion
Correctors
ZnSe linear ADC
Residual dispersion of f/15 ZnSe linear ADC,
60 degree zenith angle
180
160
Residual dispersion (milliarcsec)
• Plots are for 60° zenith angle
• < 10 mas residual dispersion
for λ=0.9-2.5μ
• ZnSe transmission starts
rolling off at 0.7 μ (external
transmission shown; losses in
flat region are almost entirely
due to Fresnel reflection)
• <40nm rms for λ=0.9-2.5μ
• ~160 mm long, but could be
made shorter if necessary
• Availability larger than 4.5-5”
would be problematic right
now, but II-VI’s new plant
comes online in the next few
months
140
120
100
Series1
80
60
40
20
0
-20
0.6
0.8
1
1.2
1.4
1.6
1.8
wavelength (microns)
2
2.2
2.4
ZnSe external transmission
ZnSe f/45 linear ADC
180
160
Residual dispersion (milliarcsec)
• Better performing and
can be made shorter
because of slow
beam (100 mm long
in this example)
Residual dispersion of f/15 ZnSe linear ADC,
60 degree zenith angle
140
120
100
80
Series1
60
40
20
0
0.6
0.8
1
1.2
1.4
1.6
1.8
-20
wavelength (microns)
2
2.2
2.4
Two-glass linear ADC
180
160
Residual dispersion (milliarcsec)
• Generally better
correction over wider
band, but at cost of
transmission (extra
surfaces and perhaps
transmission loss in
visible and/or K-band,
depending on glasses
chosen)
Residual dispersion of f/15 S-NPH2/S-BAL42 linear ADC,
60 degree zenith angle
140
120
100
80
Series1
60
40
20
0
0.6
0.8
1
1.2
1.4
1.6
1.8
-20
wavelength (microns)
2
2.2
2.4
S-NPH2 / S-BAL42 transmission
(excludes coating losses)
Visible light (0.7-0.9) f/45 linear
ADC
• Not started, but narrow band, small field,
and slow beam should make this not very
hard.
Summary
• All linear ADC’s should be possible in 200mm or
less length
• Linear ADC’s over 0.9-2.4 μ (at f/15 or f/45) are
straightforward with single glass
• Linear ADC’s over 0.7-0.9 μ possible with one
glass with rolloff at 0.7 μ, or with two glasses
(perhaps with rolloff at K-band); other glass
choices should be investigated
• Linear ADC over 0.7-0.9 μ not started, but
should be straightforward