Temperature-dependent optical constants of water ice in the near infrared: new results and critical review of the available measurements

The optical constants of water ice have been determined in the near infrared from 4000 to 7000 cmϪ1. Polycrystalline ice films with thickness as great as ϳ1164 ␮m were formed by condensation of water vapor on a cold silicon substrate at temperatures of 166, 176, 186, and 196 K. The transmission of light through the ice films was measured during their growth from 0 to 1164 ␮m over the frequency range of approximately 500 –7000 cmϪ1. The optical constants were extracted by means of simultaneously fitting the calculated transmission spectra of films of varying thickness to their respective measured transmission spectra with an iterative Kramers–Kronig technique. Equations are presented to account for reflection losses at the interfaces when the sample is held in a cell. These equations are used to reanalyze the transmission spectrum of water ice ͑358-␮m sample at 247 K͒ recorded by Ockman in 1957 ͓Philos. Mag. Suppl. 7, 199 ͑1958͔͒. Our imaginary indices for water ice are compared with those of Gosse et al. ͓Appl. Opt. 34, 6582 ͑1995͔͒, Kou et al. ͓Appl. Opt. 32, 3531 ͑1993͔͒, Grundy and Schmitt ͓J. Geophys. Res. 103, 25809 ͑1998͔͒, and Warren ͓Appl. Opt. 23, 1206 ͑1984͔͒, and with the new indices from Ockman’s spectrum. The temperature dependence in the imaginary index of refraction observed by us between 166 and 196 K and that between our data at 196 K and the data of Gosse et al. at 250 K are compared with that predicted by the model of Grundy and Schmitt. On the basis of this comparison a linear interpolation of the imaginary indices of refraction between 196 and 250 K is proposed. We believe that the accuracy of this interpolation is better than 20%.