Amplitude- versus frequency-modulated pumping light for coherent population trapping resonances at high buffer-gas pressure

Coherent population trapping (CPT) signals can be optimized with amplitude-modulated pumping light. As shown theoretically and experimentally in this paper, the optimum wave forms produce strong CPT signals at both low buffer-gas pressures, where the hyperfine structure (HFS) splitting of the optical absorption lines is well resolved, and also at high buffer-gas pressures, where the HFS is no longer optically resolved due to pressure broadening. On the other hand, CPT resonances from frequency-modulated waves are severely degraded for these high-pressure conditions. High buffer-gas pressures may offer advantages for miniature frequency standards and magnetometers, including suppression of diffusion losses in miniature cells, suppression of light shifts, and less stringent requirements for frequency stability of the pumping light sources.