Some mirrors for infrared lasers are constructed with alternating layers of hafnia and silica. Suppose you want to produce constructive interference from a thin film of hafnia (n = 1.90) on BK-7 glass (n = 1.51) using infrared radiation of wavelength 1.06 μ,m. What is the smallest film thickness that would be appropriate, assuming that the laser beam is oriented at right angles to the film?