Patent ID: 7058110

Claim:
An infrared atomic line filter comprising (A) a metal vapor cell having an optical entrance port and an optical exit port and containing a metal vapor defining a first excited energy state, defining a first resonant frequency, and a second excited energy state and having at least one absorption line, at or near a desired filter wavelength within the infrared spectral range, said absorption line being equal, in energy, to a difference between the second excited state and the first excited state; (B) at least one magnet for imposing on said metal vapor a magnetic field to produce polarization rotation near said at least one absorption line; (C) a first polarizer positioned to block polarized light at a first polarization from entering said vapor cell through said entrance port; (D) a second polarizer oriented perpendicular to said first polarization and located across the path of light exiting said exit port so as to block light exiting said vapor cell that is polarized perpendicular to said first polarization; (E) a pump light source for producing light at said first resonant frequency for pumping said metal vapor from said ground state to said first excited state; wherein said metal vapor under the influence of said magnetic field produces a polarization rotation of light within a narrow spectral band near said absorption line permitting light within this spectral band to pass through said second polarizer whereas all light in a much wider spectral range is not rotated in polarization and is blocked by either the first polarizer or the second polarizer.