Stefan B. Altner

Recording of 6000 holograms by use of spectral hole burning.

Experiments verifying a new method of storing spectral hole-burning holograms, which yields reduced cross talk as compared with standard spectral hole-burning holograms, have been conducted. Results demonstrating the reduced width of this type of hologram in both frequency and the applied electric-field dimension are presented. Analytic solutions for the spectral width and diffraction efficiency of these holograms are presented. Using this exposure technique, we have recorded 6000 holograms in a single spectral hole-burning sample.

Frequency and phase swept holograms in spectral hole-burning materials.

A new hologram type in spectral hole-burning systems is presented. During exposure, the frequency of narrow-band laser light is swept over a spectral range that corresponds to a few homogeneous linewidths of the spectrally selective recording material. Simultaneously the phase of the hologram is adjusted as a function of frequency-the phase sweep function. Because of the phase-reconstructing properties of holography, this recording technique programs the sample as a spectral amplitude and phase filter. We call this hologram type frequency and phase swept (FPS) holograms. Their properties and applications are summarized, and a straightforward theory is presented that describes all the diffraction phenomena observed to date. Thin FPS holograms show strongly asymmetric diffraction into conjugated diffraction orders, which is an unusual behavior for thin transmission holograms. Investigations demonstrate the advantages of FPS holograms with respect to conventional cw recording techniques in freq ncymultiplexed data storage. By choosing appropriate phase sweep functions, various features of holographic data storage can be optimized. Examples for cross-talk reduction, highest diffraction efficiency, and maximal readout stability are demonstrated. The properties of these FPS hologram types are deduced from theoretical considerations and confirmed by experiments.

Data compression in frequency-selective materials using frequency-swept excitation pulses.

We demonstrate the temporal compression of photon echoes in frequency-selective materials by application of frequency-swept excitation pulses. Experimental results in Pr(3+):Y(2)SiO(5) for two- and three-pulse photon echoes are presented and compared with theory. A possible application to temporal reduction of optical data streams is shown.

Power broadening of the spectral hole width in an optically thick sample

Under the assumption of negligible absorption, spectral holes are known to broaden in frequency proportional to the square root of the recording intensity. In this paper the standard expression for power broadening is compared with more general results for the case of non-zero absorption. Analytic results are derived for the upper and lower limits of the hole width, corresponding to the cases of low and high absorption, respectively. These results are compared with numerical solutions, and used to fit experimental data for an optically thick sample of chlorin in PVB, in a temperature range of 450 mK to 3 K. The temperature dependence and zero kelvin value of the dephasing time, T2, are evaluated.

Photon-echo demolition spectroscopy in Eu3+: Pr3+:Nd3+:Y2SiO5

Abstract Photon-echo experiments in a Y 2 SiO 5 crystal codoped with Eu 3+ , Pr 3+ and Nd 3+ were performed with the objective of studying the influence of excited neighboring ions on the rephasing properties of the ions studied by the coherent transient technique. A strong ‘scrambler’ pulse was applied to ions of one species before (or while) a two-pulse photon-echo experiment was carried out on a different species. The dependence of the echo intensity on the ‘scrambler’ wavelength as well as on the time delay between ‘scrambler’ pulse and echo sequence was investigated. Experimental agreement with a simple model has been obtained.

Spectral holeburning and holography VI: Photon echoes from cw spectrally programmed holograms in a Pr3+:Y2SiO5 crystal

Abstract Spectral programming of stimulated photon echoes is presented. The preparation pulses — pulse #1 and #2 of the three pulses of the echo sequence—are substituted by writing a frequency dependent modulation into the inhomogenously broadened absorption line of a persistent spectral holeburning material. A holographic setup is used, and arbitrarily predefined echo signals can be generated. Linear response theory is applied to calculate the required modulation of both the intensity of the write beam and the holographic spatial phase as a function of optical frequency. Experimental results are shown using a Pr 3+ :Y 2 SiO 5 crystal at cryogenic temperatures.

Spectral hole-burning holography in optical memory systems

Experiments verifying a new method of storing spectral hole burning holograms, which yields reduced crosstalk, have been conducted. Results demonstrating the reduced width of this type of hologram in both frequency and applied electric field are presented. Using this technique, 6000 holograms have been recorded in a single spectral hole burning sample.

Data compression in Pr3+:Y2SiO5 by frequency-swept pulses

Abstract Temporal compression of photon echoes in frequency selective materials by application of frequency-swept excitation pulses has been achieved. Experimental results in Pr 3+ :Y 2 SiO 5 for two and three pulse photon echoes are presented and compared to theory. A possible application to temporal reduction of optical data streams is shown.