Abstract: An actively pumped optical filter includes a vapor cell having a population of electrons with the plurality of energy levels which receives light and transmits light according to a pumping mechanism. A magnetic source is provided for applying a magnetic field to the vapor cell. A first pulsed dye laser applies a first beam of light to the vapor cell causing transitions of the electrons from a first energy level to a second energy level. A second pulsed dye laser is used for measuring the transmission through the vapor cell. A third laser applies a beam of light to the first laser and a beam of light to the second laser. The third laser may be an Nd:YAG laser. Polarizers are disposed before and after the vapor cell and a delay path is provided for delaying the second beam of light before the second beam of light is applied to the laser cell. The delay path is tuned by adjusting the length.