Experiments are described in which a dilute ruby crystal is found to emit spontaneously a short pulse of light, the photon echo, at a time $\ensuremath{\approx}{\ensuremath{\tau}}_{s}$ after irradiation by two successive ruby-laser pulses separated by ${\ensuremath{\tau}}_{s}$. The phenomenon is explained in terms of a macroscopic oscillating electric dipole moment, which is momentarily reformed at the time the photon echo is observed. The analysis predicts the echo polarization as well as the propagation direction relative to the input pulses. A necessary condition for obtaining echoes in ruby is the application of a moderate magnetic field close to the optic axis of the crystal, and a simple model based on ${\mathrm{Cr}}^{3+}$ -Al interactions is offered to account for this magnetic-field behavior. The relaxation time of the echo is found to exceed 250 nsec at 4.2\ifmmode^\circ\else\textdegree\fi{}K but to be less than 70 nsec at 14\ifmmode^\circ\else\textdegree\fi{}K, and is thought to be due to phonon-induced transitions in the excited $^{2}E(\overline{E})$ level. Multiple echo formation is also described.Experiments are described in which a dilute ruby crystal is found to emit spontaneously a short pulse of light, the photon echo, at a time $\ensuremath{\approx}{\ensuremath{\tau}}_{s}$ after irradiation by two successive ruby-laser pulses separated by ${\ensuremath{\tau}}_{s}$. The phenomenon is explained in terms of a macroscopic oscillating electric dipole moment, which is momentarily reformed at the time the photon echo is observed. The analysis predicts the echo polarization as well as the propagation direction relative to the input pulses. A necessary condition for obtaining echoes in ruby is the application of a moderate magnetic field close to the optic axis of the crystal, and a simple model based on ${\mathrm{Cr}}^{3+}$-Al interactions is offered to account for this magnetic-field behavior. The relaxation time of the echo is found to exceed 250 nsec at 4.2\ifmmode^\circ\else\textdegree\fi{}K but to be less than 70 nsec at 14\ifmmode^\circ\else\textdegree\fi{}K, and is thought to be due to phonon-induced transitions in the excited $^{2}E(\overline{E})$ level. Multiple echo formation is also described.

Physical ReviewJan 7, 1966689 citations

Observation of ultraslow light propagation in a ruby crystal at room temperature

Bao-Hua Fan, Yundong Zhang, Ping Yuan

We have observed slow light propagation with a group velocity as slow as 27.52±0.05m/s in a ruby crystal at room temperature. The Gaussian-like pulse signal, which was gained by modulating beam at 514.5nm, was injected into a ruby crystal. The spectral hole effect, attributed to high laser power density, leads to the induced refractive index steep rising. According as this rising, the group velocity of pulse propagation in the ruby becomes very slowly. The experiment result shows that the velocity of pulse propagation depends on the modulation frequency, laser power, the position of crystal and the profile of signal waveform. At the same condition the Gaussian-like pulse obtains much slower velocity than sinusoidal signal.We have observed slow light propagation with a group velocity as slow as 27.52±0.05m/s in a ruby crystal at room temperature. The Gaussian-like pulse signal, which was gained by modulating beam at 514.5nm, was injected into a ruby crystal. The spectral hole effect, attributed to high laser power density, leads to the induced refractive index steep rising. According as this rising, the group velocity of pulse propagation in the ruby becomes very slowly. The experiment result shows that the velocity of pulse propagation depends on the modulation frequency, laser power, the position of crystal and the profile of signal waveform. At the same condition the Gaussian-like pulse obtains much slower velocity than sinusoidal signal.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEJan 28, 20053 citations

{\mathrm{Cr}}^{3+}

-Al interactions is offered to account for this magnetic-field behavior. The relaxation time of the echo is found to exceed 250 nsec at 4.2\ifmmode^\circ\else\textdegree\fi{}K but to be less than 70 nsec at 14\ifmmode^\circ\else\textdegree\fi{}K, and is thought to be due to phonon-induced transitions in the excited

^{2}E(\overline{E})

level. Multiple echo formation is also described.