On the unique possibility to increase significantly the contrast of dark resonances on D1 line of $\mathrm{^{87}Rb}$

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for D1 line of alkali atoms with nuclear spin $I=3/2$ by bichromatic linearly polarized light (lin$||$lin field) at the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for D1 line of $\mathrm{^{87}Rb}$.