  Laboratory results of the optical properties of vapor-deposited water ice,
specifically the refractive index and extinction coefficient, are available
mainly for a selective set of wavelengths and a limited number of deposition
temperatures. Experimental limitations are the main reason for the lack of
broadband data, which is unfortunate as these quantities are needed to
interpret and predict astronomical and planetary observations. The goal of this
work is to address these lacking data, using an experimental broadband method
that is capable of rapidly providing reliable water ice data across the entire
UV-visible range. This approach combines the simultaneous use of a
monochromatic HeNe laser and a broadband Xe-arc lamp to record interference
fringes of water ice during deposition at astronomically relevant ice
temperatures. The ice thickness is typically more than 20 $\mu$m. Analyzing the
period and intensity patterns combining both the monochromatic and broadband
interference patterns allows the determination of the wavelength-dependent
refractive index and extinction coefficient. We present accurate refractive
index and extinction coefficient graphs for wavelengths between 250 and 750 nm
and ices deposited between 30 and 160 K. From our data, we find a possible
structural change in the ice in the 110-130 K region that has not been reported
before. We also discuss that the data presented in this paper can be used to
interpret astronomical observations of icy surfaces.
