Means increasing population of selected energy level of masers

Claim 1

IN A MASER HAVING A CHAMBER, SAID CHAMBER BEING TRANSPARENT TO ELECTROMAGNETIC WAVES, A MATERIAL IN SAID CHAMBER HAVING ATOMS WHICH ARE SUSCEPTIBLE TO THE ABSORPTION OF ENERGY OF A PREDETERMINED FREQUENCY AND CAPABLE OF SUSTAINING A POPULATION INVERSION, AT LEAST TWO PAIRS OF DIAMETRICALLY OPPOSED REFLECTORS FACING THE INTERIOR OF SAID CHAMBER AND FORMING AT LEAST TWO PARTLY COINCIDENT RESONANT CAVITIES WHEREIN A PUMPING TRANSITION TAKES PLACE TO GENERATE A POPULATION INVERSION AND STIMULATED EMISSION, ONE OF SAID REFLECTORS OF ONE OF SAID PAIRS BEING A PARTIAL REFLECTOR AND BEING PARTIALLY TRANSPARENT TO THE SAID STIMULATED EMISSION RESULTING FROM SAID POPULATION INVERSION, THE CAVITY SPACING OF THE OTHER PAIR OF REFLECTORS BEING SELECTIVELY RESONANT TO RADIATION FORMED FROM A TRANSITION FROM AN UPPER LEVEL EXCITED STATE TO AN UPPER LEVEL OF THE SAID POPULATION INVERSION, AND MEANS PROVIDING A SOURCE OF ENERGY FOR ENERGIZING SAID MASER MATERIAL.