  Precision measurements of astrometry and photometry require stringent control
of systematics such as those arising from imperfect correction of sensor
effects. In this work, we develop a parametric method to model the wavelength
dependence of photo-response non-uniformity (PRNU) for a laser annealed
backside-illuminated charge-coupled device. The model accurately reproduces the
PRNU patterns of flat-field images taken at nine wavelengths from 290nm to
950nm, leaving the root mean square (RMS) residuals no more than 0.2% in most
cases. By removing the large-scale non-uniformity in the flat fields, the RMS
residuals are further reduced. This model fitting approach gives more accurate
predictions of the PRNU than cubic-spline interpolation does with fewer free
parameters. It can be applied to make PRNU corrections for individual objects
according to their spectral energy distribution to reduce photometry errors.
