We report what is to our knowledge the first measurement of linear and nonlinear spectroscopic properties for the (7)F(0)-(5)D(0) transition of Eu(3+):Y(2)SiO(5). Two clearly resolved lines at 579.879 and 580.049 nm, stemming from different sites, show dissimilar photoluminescence and hole spectra. In addition, these two sites have different inhomogeneous and homogeneous linewidths, which suggests that the local-field effect is smaller for one site. Specifically, the less affected site exhibits the longest dephasing time (822 micros) of any solid, which corresponds to a homogeneous linewidth of 387 Hz, and this linewidth is found to persist for hours without apparent spectral diffusion.

We propose and demonstrate a novel type of frequency-selective optical memory that writes and reads the data in both the time domain and the frequency domain. Temporal 16-bit data were stored by accumulated-photon-echo bit-by-bit storage at 103 frequency addresses within the inhomogeneous line of the (7)F(0)-(5)D(0) transition of Eu(3+):Y(2)SiO(5), which yields a total memory capacity of 1.6 kbits in a single spot of 240-microm diameter. The keys to the success of this experiment are this material's long dephasing time and lack of spectral diffusion.

No abstract

A stimulated photon-echo study has verified the instantaneous shift (< 1 MHz) and subsequent restoration ( -2 ms) of the transition frequency of an impurity ion in a solid when its neighboring ions are exposed to pulsed optical excitation. Experiments were conducted by monitoring the echo intensity for the 7 Fo-5 Z>o transition of Eu ions in one site of YzSiOs, while exciting the other site. A photon-echo theory taking account of the stochastic frequency recovery is developed to explain the observations. PACS numbers: 78.50.Ec, 42.50.Md A ions and B ions can be the same species, as they are in all the previous cases. The magnitude of the EFS should be random, depending on each A ion, which has its own distribution of the excited B ions around it. It is also important to note that this environmental change is instantaneous but temporary. In fact, sooner or later the original environment is restored when the B ions decay back to the ground state, but experimental verification of this restoration process has not been reported. High-resolution nonlinear laser spectroscopy in solids has been a powerful tool for studying small magnetic or electric interactions between optical centers and their circumstances. In 1987 Liu et al [1] and in 1989 Huang et al. [2,3] used photon-echo experiments to show the existence of a small shift (20 to 300 kHz depending on the excitation intensity) in the optical transition frequency of an impurity ion in a solid, induced by the optical excitation of nearby ions. This excitation-induced frequency shift (EFS), also known as instantaneous spectral diffusion, can only be unveiled by nonlinear spectroscopy because otherwise the EFS would be totally buried within the huge inhomogeneous absorption linewidth ( -GHz). Many recent observations of excitation-intensity-dependent optical dephasing times [1-5] can be well interpreted in terms of the EFS. The physical origin of the EFS is very clear. By optically exciting the surrounding ions (B ions) by an intense pulse, which we now call the scrambler, the two-level system of interest (A ion) experiences a sudden change in the local field (electric or magnetic), and this perturbation shifts the energy levels of the A ion. Of course

We studied the receiver performance of two photoconductive antennas ͑bow tie and dipole antennas͒ fabricated on the same low-temperature-grown GaAs substrate to clarify the effect of the antenna structure and gate pulse intensity on terahertz wave detection. We observed the gate pulse intensity dependence of the temporal profiles of the terahertz waves or terahertz spectra. For both antennas, the sensitivity in the low-frequency regime ͑Ͻ0.5 THz͒ was enhanced compared to that in the high-frequency regime for large gate pulse intensities. This is because the carrier trap time increased due to the saturation of the GaAs defect levels. We also observed that the peak-to-peak amplitude of the terahertz wave detected by one antenna was not always larger than that detected by the other antenna, and the peak-to-peak amplitude of the bow tie antenna was larger ͑smaller͒ than that of the dipole antenna when the gate pulse intensity was high ͑low͒. This was explained by the gate pulse intensity dependence of the frequency-dependent detection sensitivity and also by the resonance frequency of the antenna structure.