An ultrahigh-Q isotropically sensitive optical filter employing atomic resonance transitions

A new resonance principle in optical filters has been utilized to simultaneously permit realization of wide field-of-view (∼2π sr) and very narrow acceptance bandwidths, approaching 0.01 Å. A light signal is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, resulting in a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filter. The outer and inner bandpass filters have no common transmission band, resulting in complete blockage of all optical signals (background noise) that are not resonantly shifted in wavelength by the intervening atomic vapor. This ’’resonance filter’’ principle is experimentally verified, and system parameters are discussed for filters utilizing potassium, rubidium, or cesium vapor at nine wavelengths between 420 and 532 nm.