Femtosecond hole burning storage by two-photon absorption

Summary form only given. Spectral hole burning (SHB) is a promising technique for optical recording of information with a potential to store in excess of 10/sup 4/-10/sup 5/ bits per /spl lambda//sup 3/ volume (Moerner, 1988). Highest storage capacity is achieved when frequency- or time-domain addressing is combined with addressing in three spatial dimensions by using a bulk SHB medium. However, so far both bit-by-bit and holographic SHB storage experiments were restricted to two spatial dimensions. This is because focusing a laser beam to a small volume inside the SHB medium is hindered by one-photon absorption in SHB material layers. We propose that this problem may be overcome by burning holes via two-photon absorption (TPA) (Demtro/spl uml/der, 1982; Takeda et al, 2000). TPA has been used earlier for conventional spectrally nonselective recording in photo-chromic materials by focusing two perpendicularly directed laser beams (with photon energies /spl planck//spl omega//sub 1/ and /spl planck//spl omega//sub 2/) on to one spot (Parthenopoulos and Rentzepis, Science, vol. 245, pp. 843-845, 1989). Since the sample is transparent for each beam separately, TPA occurs only at the beam intersection point. In this paper, we investigate frequency-selective SHB by TPA in organic dye-doped polymers at low temperature. In our experiments, the SHB medium is essentially transparent for the writing beams, which allows unrestricted penetration and focusing in the depth of the sample.