Dual microwave frequency modulation of the VCSEL injection current for a CPT-based atomic clock.

Previously, we have proposed a method to control the emission spectrum of the vertical-cavity surface-emitting laser (VCSEL) with the synchronized modulation of the injection current at single and doubled frequencies. In this work, the above method is used to improve the metrological characteristics of the coherent population trapping (CPT) resonance in 87Rb. The dual-frequency (DF) modulation reduces the carrier power and suppresses the light shift of the resonance frequency, if it is unattainable with the single-frequency modulation. In addition, a higher resonance contrast is achieved by equalizing the powers of the resonant components of the spectrum.

Control of the VCSEL spectrum by dual microwave frequency modulation.

We propose and investigate a method for controlling the spectrum of the vertical-cavity surface-emitting laser by simultaneous modulation of the injection current at single and doubled frequencies. We experimentally demonstrate the ability to control the power asymmetry of the first-order sidebands and to suppress the carrier by the proposed method. These possibilities are beneficial to improve frequency stability of atomic clocks based on the effect of coherent population trapping.

Two-quantum magnetic resonance driven by a comb-like rf field.

We report a new method for excitation of magnetic resonance in an optically aligned atomic ensemble. It employs a comb-like rf field acting on the end sublevels of the Fg=1 state separated by the doubled Zeeman frequency. This approach provides a resonance without substructures associated with the quadratic Zeeman shift. A theoretical explanation of the effect is given in terms of the two-quantum transition |Fg=1,mFg=-1⟩⇆|Fg=1,mFg=1⟩ and is corroborated by an experiment with 87Rb atoms. Possible advantages of the approach and its range of applicability are discussed.