Cuprous Oxide (From Palik II: pp. 880)
ANGSTROMS
NK
   3000.        2.0     1.85
   3500.        2.40    1.44
   4000.        2.80    0.99
   4500.        3.06    0.60
   5000.        3.12    0.35
   5500.        3.10    0.19
   6000.        3.02    0.13
   6500.        2.90    0.10
   7000.        2.83    0.083
   7500.        2.77    0.070
   8000.        2.70    0.060
   8500.        2.66    0.053
   9000.        2.63    0.048
   9500.        2.61    0.043
  10000.        2.60    0.040
  11000.        2.59    0.033
  12000.        2.58    0.027
  13000.        2.57    0.021
  14000.        2.57    0.017
  15000.        2.57    0.013
  20000.        2.56    0.002