186 ISSN 1063-7850, Technical Physics Letters, 2016, Vol. 42, No. 2, pp. 186–190. © Pleiades Publishing, Ltd., 2016. Original Russian Text © A.A. Baranov, S.V. Ermak, E.A. Sagitov, R.V. Smolin, V.V. Semenov, 2016, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2016, Vol. 42, No. 4, pp. 38–45. Signal Correlation in the Tandem of a Spin Oscillator and Microwave Frequency Discriminator with Laser-Pumped Alkali Atoms A. A. Baranov, S. V. Ermak, E. A. Sagitov, R. V. Smolin, and V. V. Semenov* Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia *e-mail: vladimir_semenov@mail.ru Received September 16, 2015 Abstract—We have studied the influence of low-frequency noise on the stability of resonance frequency of a self-oscillating magnetometer on 87 Rb vapor with simultaneous monitoring of the signal of radio-optical res- onance on the magnetic-field-dependent microwave transition under laser pumping at the D 2 line of the head doublet. The difference of synchronous records of detected signals reduced to the same scale in magnetic field units was processed to determine the Allan variance as a function of the averaging time. The correlation coef- ficient characterizing the coupling of detected signals determined by the pumping rate and intensity of radio fields generated in the region of the absorption chamber. The self-oscillating magnetometer can only operate provided that there is laser tuning to the long-wavelength component of the electric-dipole transition. DOI: 10.1134/S1063785016020218 Long-term stability of the frequency of optically pumped alkali-vapor quantum discriminators used for the creation of magnetometers and frequency stan- dards is known to be determined by technical (flicker) noise related to slow variations of device parameters such as the temperature of the absorption chamber, the pressure of alkali metal vapor, and the intensity and spectral composition of pumping radiation. Anal- ysis of the influence of these variations on the fre- quency stability of a self-oscillating device [1] shows that its nonstationary technical linewidth is deter- mined by the intensity of flicker noises of various ori- gins and is inversely proportional to the frequency of self-sustained oscillations. The integral influence of these noises on the self-oscillating device frequency dynamics does not allow the destabilizing effects of separate flicker-noise components to be determined, which hinders the search for ways to improve the metrological characteristics of a measuring module. Nevertheless, the experience gained in the develop- ment of optically pumped quantum self-oscillating devices suggests that the main destabilizing factor is related to so-called light-induced frequency shifts caused by nonresonant components in the spectrum of pumping radiation. In application to alkali metal vapors under condi- tions of their optical orientation by circularly polarized radiation, the light-induced frequency shift consists of three components [2]: (i) scalar shift Δν 0 , which is the same for all mag- netic sublevels F or F* of the hyperfine structure; (ii) vector shift Δν V caused by the effective mag- netic field induced in the medium by circularly polar- ized pumping radiation (this phenomenon is also known as the Faraday effect); and (iii) tensor shift Δν T related to the alignment of atoms in the ground state, which is dependent on mag- netic quantum number m F . Depending on the sign of the circular polarization of pumping light (i.e., the direction of effective mag- netic field), the scalar and vector components of the light-induced shift will be either added or subtracted, which makes possible their mutual compensation and allows the effect of the pumping source on the fre- quency stability of a quantum discriminator to be sig- nificantly decreased. This Letter presents the results of an investigation of the influence of low-frequency noise on the stabil- ity of resonance frequency of a self-oscillating magne- tometer with simultaneous monitoring of the signal of radio-optical resonance on the magnetic-field-depen- dent microwave transition. In this tandem, it is possi- ble to determine contributions to variations of the observed signal frequency related, on one hand, to variation of the working magnetic field and, on the other hand, to light-induced shifts of resonance fre- quencies of the magnetometer and microwave source. The pumping radiation source was an external-cav- ity laser of DL-100-L type (Toptica) tuned to the D 2 line of the head doublet of 87 Rb atoms. This choice was based on a negligibly small contribution of the