87Rb D1 isoclinic point

In the research presented here, we reconsider the problem of obtaining stable resonant features in linear absorption spectroscopy, which has application to ultraminiature atomic physics where sub-Doppler spectroscopic techniques are not always optimal. In particular, we consider the applicability of isoclinic points for precision atomic spectroscopy. These are defined as "[a] wavelength, wave number, or frequency at which the first derivative of an absorption spectrum of a sample does not change upon a chemical reaction or physical change of the sample," and we demonstrate the existence of isoclinic points in the D-1 spectra of I = 3/2 alkali-metal isotopes, where I is the nuclear spin. We then consider the D-1 isoclinic point of Rb-87 in detail, showing that a slight Rb-85 contamination in real Rb-87 samples should have no significant effect on the frequency stability of the isoclinic point and that optical pumping by a linearly polarized laser should also not affect the isoclinic point's stability (i.e., the isoclinic point is insensitive to laser intensity). Finally, we perform an experiment demonstrating that the Rb-87 D-1 isoclinic point has a temperature shift more than an order of magnitude smaller than that of the most isolated transition in the Rb-87 D-1 spectrum.