Series of CPT Resonances with Multifrequency Pumping by a Diode Laser

For the first time, a series of CPT resonances under the simultaneous exposure of microwave and VHF modulation of the injection current of a diode laser with an external cavity, represented by diffraction gratting, was observed. The frequency spacing between resonances was coincided with half of the VHF modulation frequency. The contribution to pumping in this case comes from pairs of VHF components located in different spectral bands and separated from each other by the frequency of hyperfine splitting of ground state of rubidium-87 atom (about 6.8 GHz). The use of multifrequency pumping will make it possible to reduce the light shifts of the observed CPT resonances due to averaging, and the use of a semiconductor laser with an external cavity opens up the possibility of creating a combined optical and radio frequency standard. The dependences of the CPT parameters of resonances on the intensity of the incident radiation are also studied in this work, and the threshold observed in this case is consistent with the results described in the literature. The dependences of the amplitude of CPT resonances on the deviation of the applied VHF modulation have also been studied. The VHF modulation frequency remained unchanged at 34 MHz (1/200 of the clock transition frequency).