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
ZnSe f/45 linear ADC • Better performing and can be made shorter because of slow beam (100 mm long in this example)
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)
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