Measurement of the wavelength modulation indices with selective reflection spect

The wavelength modulation indices are measured based on harmonic amplitude ratio of 4f_(amp)/6f_(amp) (4f_(amp) and 6f_(amp) are the 4- and 6-th harmonic central peak amplitudes correspondingly) with the Doppler-free selective reflection modulation spectroscopy. The experiments for the 6S_(1/2)(F =