GB1130565A - Atomic resonance apparatus - Google Patents

Abstract

1,130,565. Automatic frequency control. VARIAN ASSOCIATES. 1 Oct., 1965 [5 Oct., 1964 (2)], No. 8034/68. Divided out of 1,130,563. Heading H3A. In an atomic resonance frequency standard the pumping source has a spectral profile comprising a pair of resonance lines and the ratio of intensities of the lines of the pair of lines is controlled proportionally so that changes in the total intensity of the pumping radiation produces no shift in the frequency of the standard. In the Rb<SP>87</SP> resonance frequency standard shown in Fig. 4, Rb<SP>87</SP> atoms in cavity resonator together with nitrogen buffer gas are pumped through glass wall 3 by two R6<SP>87</SP> lamps 42, 45. Lamp 42 has its parameters adjusted to produce a negative light shift, i.e. its wavelength is centred on the low frequency side of the atomic pumping transition, Fig. 3 (not shown), and lamp 45 is adjusted to produce a positive light shift, i.e. its wavelength is centred on the highfrequency side of the atomic pumping transition. Light from the lamps 42, 45 passes through variable transmission filters 43, 47 and Rb<SP>85</SP> filters 44, 48 respectively before being combined by half-silvered mirror 46 to form a single beam which passes through a variable transmission filter 49 into the cavity 1. In operation the ratio of intensities of the radiation from the lamps 42, 45 is adjusted by filters 43, 47 until a point is reached at which zero light shift is observed when the filter 49 is varied. The light shift is monitored continuously by applying 400 c.p.s. electrical signal from modulator 52 to Kerr cell filter 49 in order to amplitudemodulate the pumping beam. If there is a light shift the output maser frequency is frequency modulated at 400 c.p.s. which modulation is detected by F.M. detector 53 and converted to a low-frequency amplitude-modulated signal. This signal is compared with the modulation signal in phase detector 54 to produce a D.C. error signal which is fed back to one of the fillers 47 for controlling the ratio of the intensities of the light from lamps 42, 45 so as to maintain zero shift. The light beams may not be superimposed but may be applied to the cavity from opposite sides.