As a technique for high resolution spectroscopy one-photon and photon—gated persistent spectral hole burning was realized in our organic materials. Hole shape, properties and quantum efficiency of hole formation were investicated. Hole growth dynamics and theory for it were given.
Persistent spectral hole burning (PSHB) was performed for several porphyrin molecules imbedded in polymer hosts and rare-earth ion Sm2+ doped in BaFCl0.5Br0.5 matrix. Power saturation and broadening effects for hole depth and width were observed. The dynamical process of hole formation was measured and explanation by population rate equations was given. Quantum efficiency of photochemical hole burning was investigated. For BaFCl0.5Br0.5:Sm2+ the capacity of data storage was estimated according to the result of multiple hole burning.
Persistent spectral hole-burning (PHB) has been proposed as the essential element of a frequency domain optical storage system1 in which the frequency at which a hole is burned in an inhomogeneously broadened absorption line at low temperatures serves as an additional dimension for the storage of digital information. Essentially all of the mechanisms studied until recently have been single-photon mechanisms, i.e., the photoionduced change leading to hole-burning (writing) for a given center occurs with a certain fixed probability after the absorption of one photon. Such linear, monophotonic processes suffer from the drawback that the act of detecting holes (reading) can also produce changes in the absorption line. Recent modeling studies of the generalized single-photon process2 have shown that thousands to tens of thousands of reads can be obtained from single-photon mechanisms only when the material possesses high quantum efficiency and low absorption cross section. These restrictive requirements do not apply for photon-gated hole-burning mechanisms, i.e., those mechanisms for which hole-burning occurs only in the presence of an additional “gating” light source, because for these mechanisms, reading is performed in the absence of the gating light and is therefore nondestructive.
The persistent spectral hole-burning (PSHB) phenomenon has been known since 1974. It is still an important research area for the study of the intimacy of complex molecular systems in the solid state, revealing high-resolution spectra, photophysics, photochemistry, and dynamics of molecular doped amorphous media, organic as well as inorganic. From another point of view, PSHB allows the engraving of any spectral structures in the inhomogeneous absorption band profile of molecular doped amorphous hosts or ion doped crystals cooled down to liquid helium temperatures. Therefore, a PSHB material is programmable in the spectral domain and consequently it can be transformed in an optical processor capable of achieving user-defined optical functions. Some aspects of both fields are illustrated in the present paper. Concerning the search for efficient PSHB materials, the hole-burning performances and the photophysics of polymer and xerogel based systems are compared. The problem of high-temperature persistent spectral hole-burning materials and the search for new frequency selective photosensitive systems for fast optical pulse processing at 800nm are considered. Regarding the points treated, inorganic hosts based on silicate xerogels or porous glasses have shown the best results. Moreover, by combining inorganic and organic capabilities or by grafting organic species to the host, hybrid xerogels have not yet revealed all possibilities. Also, the interest of two-photon materials for engraving spectral features with near-infrared or infrared light is developed. As an introduction to possible applications of PSHB material, the basics of spectro-temporal holography are remembered and a demonstrative experiment using a naphthalocyanine-doped polymer film is described, proving that the temporal aberration free recompression of ultrashort light pulses is feasible, therefore opening a way for applications in ultrashort light pulse shaping. Aspects for a comparison between cw hole-burning and femtosecond spectro-temporal experiments are considered, and prospects for coherent control of light fields or photochemical processes are also evoked.
We introduce a method of polarization spectroscopy into photon-gated persistent spectral hole burning, which results in considerable improvement in the signal-to-background ratio. Fifty multiple spectral holes burnt into meso-phenyl-tetrabenzoporphyrinato-zinc/aromatic cyanide/poly(methyl methacrylate) were clearly detected by this measurement technique. We developed a simplified model to account for the hole shapes. Background birefringence combined with refractive dispersion is thought to play a key role in the generation of asymmetric line shapes.