Stopped Light at High Storage Efficiency in a ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ Crystal

We demonstrate efficient storage and retrieval of light pulses by electromagnetically induced transparency (EIT) in a ${\mathrm{Pr}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal. Using a ring-type multipass configuration, we increase the optical depth (OD) of the medium up to a factor of 16 towards $\mathrm{OD}\approx 96$. Combining the large optical depth with optimized conditions for EIT, we reach a light storage efficiency of $(76.3\pm 3.5)\%$. In addition, we perform extended systematic measurements of the storage efficiency versus optical depth, control Rabi frequency, and probe pulse duration. The data confirm the theoretically expected behavior of an EIT-driven solid-state memory.

Figure 1

Coupling scheme for three frequency ensembles ${\epsilon }_i$ of ${\mathrm{Pr}}^{3+}$ ions in a ${\mathrm{Y}}_2{\mathrm{SiO}}_5$ host lattice in the inhomogeneous line of the optical transition.

Figure 2

Schematic of the multipass ring geometry for a variable number of passes of the probe beam through the PrYSO memory in a cryostat, with reflective prisms $P_1$, $P_2$, mirrors $M_1$, $M_2$, $M_3$, and two telescope systems in $4f$ configurations. Figure shows the beam path for $N=8$ passes as an example. We neglect all other components of the extended optical and laser setup for the light storage experiment. A lateral shift of prism $P_1$ in $x$ direction changes the spatial distance $\mathrm{\Delta }x$ between two passes, the total number of round-trips is varied by shifting mirror $M_3$ in $z$ direction.

Figure 3

EIT light storage efficiency $\eta$ versus control power $P_c$ and probe pulse duration ${\tau }_p$ of a rectangular pulse for a single pass ($N=1$) (a), and $N=10$ passes (b) of the probe beam. Please note that the parameter ranges of $P_c$ and ${\tau }_p$ in (a) and (b) are quite different. The dotted square in (b) indicates the parameter range of (a).

Figure 4

Iterative procedure for optimizing the temporal probe intensity profile for maximal light storage efficiency. Power of input probe pulses and output signals versus time, for $N=14$ passes, a storage time of $2\mu \mathrm{s}$, and fixed control pulse shape with control power $P_c=170\mathrm{mW}$. For a rectangular probe pulse shape with a duration of ${\tau }_p=33\mu \mathrm{s}$, we start with a storage efficiency of 70.3%. After four iterations the temporal intensity profile of the probe pulse converges to a truncated Gaussian-like shape with a FWHM of $23.5\mu \mathrm{s}$, reaching a storage efficiency of $(76.3\pm 3.5)\%$.

Figure 5

Maximal light storage efficiency $\eta$, experimental data (red solid squares) and theory (black solid line), versus number of passes $N$ (i.e., optical depth OD).