Active wavelength-shifting in atomic resonance filters

Active wavelength-shifting is described as a method to expand the number of wavelengths at which atomic resonance filters operate. Optical pumping and exoergic collisional energy transfer are shown to be powerful wavelength-shifting techniques. Expressions have been derived for internal photon conversion efficiency in limiting cases. They are cast in forms that suggest simple branching ratio model equivalents. The photophysical models yield important insights into methods to obtain good photon conversion for even strongly absorbing levels. The results are applied to atomic resonance filters operating at intense Fraunhofer wavelengths