Atmospheric Dispersion Correctors

ZnSe linear ADC• 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

Residual dispersion of f/15 ZnSe linear ADC, 60 degree zenith angle

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0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

wavelength (microns)

Res

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isp

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illi

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Series1

ZnSe external transmission

ZnSe f/45 linear ADC

• 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

-20

0

20

40

60

80

100

120

140

160

180

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

wavelength (microns)

Res

idu

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isp

ersi

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(m

illi

arcs

ec)

Series1

Two-glass linear ADC

• 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

-20

0

20

40

60

80

100

120

140

160

180

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

wavelength (microns)

Res

idu

al d

isp

ersi

on

(m

illi

arcs

ec)

Series1

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