The first Microwave Laser is constructed by Towens and Shawlow (1954).
Construction:Beam of ammonia passes through an electrostatic focuser to separate out molecules in the upper quantum state.
Mode of working:Physical separation was accomplished in the first microwave laser by projecting a beam of ammonia molecules through a system of focussing electrodes which generate a quadrupolar cylindrical electrostatic field in the direction of the beam. Molecules in the lower quantum state experience an outward force and rapidly leave the beam, those in the upper quantum state see a radial inward (focussing) force and eventually enter the cavity. When microwave power of the appropriate resonant frequency (24 GigaHertz) is passed through the cavity, amplification occurs due to the population inversion. If the output power emitted is sufficiently large, self-sustained oscillations results and the input beam is no longer required. When it is operating beyond this threshold the internal losses are compensated by a large enough gain and the device behaves like an oscillator.