Relation between the Spectrum of a Laser and Coherent Population Trapping Resonances under Multifrequency Excitation

The paper presents the results of studying the coherent population trapping (CPT) resonances observed in a cell with 87Rb vapor with addition of a buffer gas under multifrequency excitation by radiation from an external cavity diode laser (ECDL). The laser diode injection current is modulated simultaneously by microwave (MW) and very high-frequency (VHF) signals. It has been revealed that, for a certain band of VHF modulation frequencies, the amplitude of a CPT resonance is proportional to the product of the electrical field strengths of the spectral components contributing to resonance excitation. The proposed model of calculating the resonance amplitude is in good agreement with experimental data.