Coherent population trapping in a crystalline solid at room temperature

Observation of coherent population trapping (CPT) at ground-state Zeeman sublevels of ${\mathrm{Cr}}^{3+}$ ion in ruby at room temperature is reported. A mechanism of CPT, not owing to optical pumping, is revealed in a situation when the optical pulse duration is shorter than the population decay time from the excited optical state.

Figure 1

Temporal evolution of the upper optical state population under pulsed excitation according to Eq. (1). The inset shows the model of a three-level atomic medium interacting with a light pulse.

Figure 2

Energy levels of ${\mathrm{Cr}}^{3+}$-ion. Optical transitions allowed for $\sigma$-polarization of light propagating in a $c$ direction with $\mathbf{B}\perp c$ are indicated by arrows connecting the corresponding energy levels accompanied by the corresponding matrix element. For $R_1$-line the upper (lower) sign stands for ${\sigma }^{+}\left({\sigma }^{-}\right)$-polarizations respectively while for $R_2$-line the first and second number corresponds to ${\sigma }^{+}\left({\sigma }^{-}\right)$ [11].

Figure 3

CPT resonances in a zero magnetic field: (a) trace for the $R_1$ line and (b) trace for the $R_2$ line. Narrow peaks are shown in detail in the insets. See the text for details.

Figure 4

CPT resonances with a mode-locked laser: (a) trace for the $R_1$ line and (b) trace for the $R_2$ line. See the text for details.