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The interaction between polychromatic fields and atoms is an important subject in quantum optics. Frequency locking for small frequency interval multi-field is usually required in some experiments. In this letter, we experimentally demonstrate a holistic scheme for bichromatic laser frequency stabilization. Compared with traditional saturation absorption methods and complicated frequency shift schemes, offset locking for bichromatic fields is simply achieved using polarization spectroscopy and Doppler effect. Frequency locking with a wide-range asymmetry of the detuning is also shown. Our scheme makes laser spectroscopy experiments with polychromatic fields more convenient.

A simple method based on Sagnac interferometric spectroscopy (SIS) is applied for frequency stabilization of diode lasers. Sagnac interferometric spectra of rubidium vapor are investigated both theoretically and experimentally. The interference signal at the output of the Sagnac interferometer displays a sharp dispersion feature near the atomic resonance. This dispersion curve is used as the feedback error signal to stabilize the laser frequency. Linewidth of a diode laser is stabilized down to 1 MHz by this modulation-free method.

Multi-photon parametric magnetic resonance in a miniature vapor cell is demonstrated. Much more multi-photon magnetic resonance can be observed when the radio frequency field becomes stronger. The linewidth of the n photons magnetic resonance equals that of the first-order resonance divided by n, which means that the uncertainty of the magnetic sublevel is reduced by the factor n. The signal-to-noise ratio can be improved when the low-frequency multi-photon resonance takes place, which finds a possible application in precision magnetic field measurement.