Patent GB-1148294-A (GB)
Title: Optically transparent cavity resonator and gaseous atomic resonance apparatus using same
IPC: H01S1/06
Filed: 1966-05-02
Abstract: 1,148,294. Electro-physical measurement. VARIAN ASSOCIATES. May 2, 1966 [May 17, 1965], No.19271/66. Heading G1N. [Also in Divisions G6 and H1] In atomic resonance apparatus in which optical radiation is passed through light transmissive side wall portions of the cavity resonator the side wall portions are formed of a plurality of conductive axially spaced ring portions, the spaces between adjacent ring portions defining the light transmissive portion of the cavity. The cavity resonator 1, Figs.1 and (2, 3 not shown) may be used in the maser apparatus of Fig. 5 and comprises a plurality of copper rings 2 spaced apart by di-electric ring-like washers 3, the assembly being held in position by a plurality of tie rods spaced around the circumference of the rings and on which the rings and washers are threaded. The ends of the cavity resonator are closed to r.f. by means of a pair of end walls 7 formed by a spirally wound copper ribbon 8. Output from the cavity is by means of a conductive loop passing through one end of the cavity connected to a coaxial line 12. The cavity is dimensioned to support a TE onm  mode where n is at least 1 and m is at least 4 and tuned by means of connecting a shorted coaxial line to the output line 12 by means of a diode, the voltage across which is varied. The ring portions have a thickness less than twice the spacing between adjacent ring portions and have a radial width greater than twice the axial spacing between adjacent ring portions. In the arrangement of Fig.4 (not shown) the side walls of the cavity are formed by a single helically wound copper ribbon held together by being gripped by a transparent di-electric tube. Maser oscillator. The cavity of Fig. 1 is used in a maser which can be used as a frequency standard or magnetometer, the active medium comprising Rb<SP>87</SP> and a nitrogen buffer gas. The rubidium atoms are pumped by light from a Rb<SP>87</SP> lamp 17 disposed along the side of the cavity 1, the light being reflected on to the cavity by a cylindrical reflector 18 having concave reflector end portions. Rb<SP>85</SP> gas forms a filter. The pumping results in the F=1 sub level of the ground state of the Rb<SP>87</SP> atoms being depopulated by excitation to higher levels from which decay to the F=1, F=2 levels of the ground states occurs, population inversion between the F=2, F=1 levels thus resulting. The cavity resonator is tuned to the ground state transition (F=2, M=0#F=1, M=0) hyperfine transition and with optimum adjustment of polarizing coils 24, pumping light and temperature random micro-wave transitions from the F=2 level to the F=1 level excite the cavity resonator in such a way that the fields of the cavity interact back on the atoms to produce continuous coherent emission. The reflector 18 and cavity may be spherical and the temperature is stabilized by oven 22 and the apparatus has magnetic shields 21. Thallium, sodium, potassium, hydrogen and caesium may be used as the active medium. Magnetometer. If the oscillator operates on a field dependant quantum transition the maser oscillator frequency is a measure of the magnetic field intensity and may be employed as a magnetometer.