Masaharu Mitsunaga

Time- and frequency-domain hybrid optical memory: 1.6-kbit data storage in Eu3+:Y2SiO5

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 materials long dephasing time and lack of spectral diffusion.

Laser annealing effect on carrier recombination time in CdSXSe 1– X-doped glasses

The carrier recombination time of CdSxSe1–x-doped glasses has been studied in detail by using laser-induced-grating and pump–probe measurements. Decay curves have been found to show strong sharpening as a function of the laser-pulse exposure time. A slow decay of a few nanoseconds in the first stage is quenched during the irradiation, and finally a fast decay as short as 7 psec remains. Simple three-level rate equations, including the valence band, the conduction band, and the intermediate trap level, are proposed to explain the observation that this annealing effect may be parameterized by the conduction-to-trap-level decay time.

Ultralong optical dephasing time in Eu 3+ :Y 2 SiO 5

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.

Nonlinear laser spectroscopy of eu3+: Y2sio5 and its application to time-domain optical memory

Linear- and nonlinear-optical properties of Eu3+:Y2SiO5 have been investigated. All the energy levels of the7F0,1,2,… ground-state manifold and the 5D0,1,2 excited-state manifold were identified, and they were found to be doubly structured because of the two inequivalent optical sites. Two absorption lines of the 7F0–5D0 transition were studied in detail by using nonlinear spectroscopic techniques, photon-echo and stimulated-photon-echo methods. It was found by the photon-echo measurement that the optical dephasing time for one site is extremely long and is excitation-intensity dependent. With the smallest possible intensity we observed the longest ever dephasing time in a solid, 822 μs, or a 387-Hz homogeneous linewidth. From the stimulated-photon-echo measurement, the linewidth was found to be constant over a wide range of time scales, implying the absence of spectral diffusion in this crystal. These quite advantageous properties of this crystal were used for the demonstration of two novel types of time-domain optical data readout: time- and frequency-domain hybrid optical memory and spectrally programmed coherent transients.

Spectrally programmed stimulated photon echo.

A stimulated photon echo has been observed from the artificially modulated inhomogeneous distribution of a medium. A cryogenic Eu (3+):YAlO(3) sample with a quasi-persistent hole lifetime is exposed to a frequency-scanned and intensity-modulated cw laser for multiple hole burning. A coherent burst equivalent to the stimulated photon echo is obtained by triggering this sample by a pulsed laser. We demonstrate further that any desired transient pulse shape can, in principle, be obtained by appropriate frequency-domain programming, which opens the way to a novel type of optical memory.

Time-domain optical data storage by photon echo

Principles and applications of time-domain optical data storage using stimulated photon echo are briefly reviewed. Special emphasis is laid upon the comparison of this memory with holography; both memories use the interference between two optical waves. Some new experimental developments are introduced using samples of europium-ion-doped crystals, one of the most promising candidates in time-domain data storage. Some other topics, such as ultrafast data storage, time-domain data processing, and time- and spatial-image storage using photon echo, are also discussed.

Holographic motion picture by Eu 3+ :Y 2 SiO 5

Real-time recording of a moving object was made with persistent spectral hole burning of a cryogenic Eu(3+):Y(2)SiO(5) crystal. In a basic holographic configuration the ultrastable laser frequency was continuously scanned within the (7)F(0)-(5)D(0) absorption line (typically 200 MHz in 20 s) while the object was in motion, thus permitting the storage and reconstruction of the moving image. The success of this motion picture is attributable to (1) the kilohertz-wide hole width, (2) the quasi-persistent hole lifetime, and (3) the high hole-burning quantum efficiency of this material.

Dressed-atom spectroscopy of cold Cs atoms

Absorption spectra of cold Cs atoms in a magneto-optical trap under the influence of a strong external pump laser field with arbitrary detuning and intensity have been systematically investigated. The spectra featured the Rabi sidebands of each transition, and their behavior was nicely fitted by the dressed-atom theory. A pronounced dispersion-type profile with sub-natural linewidth at the pump frequency may be attributable to the stimulated Raman process by sublevels that are lightshifted and optically pumped by the pump laser.

Degenerate photon echoes: Simultaneous storage of multiple optical data

It is shown that simultaneous and spatially overlapping multiple photon echoes can occur following application of a single optical pulse followed by multiple pairs of counterpropagating pulses in various directions-degenerate photon echoes. This scheme has been experimentally verified in Pr(3+):LaF(3) for the doubly degenerate case. In the small-pulse-area regime, the two echoes are observed to be independent with no cross talk between them. From the viewpoint of transient optical memory, this enables us to store multiple independent optical data in one sample spot and to retrieve any one of them, thereby multiplying the memory capacity of the crystal.

High-resolution spectroscopy of hyperfine Zeeman components of the sodium D_1 line by coherent population trapping

High-resolution spectroscopy of hyperfine Zeeman components in a sodium atomic vapor has been performed by a coherent population trapping (CPT) technique. The measurement features the simple configuration of a single laser source with a frequency-swept double-pass acousto-optic modulator. Well-resolved CPT dip signals in the presence of longitudinal or transverse static magnetic fields can be nicely explained by a theory based on two-photon resonance.