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Notes: Zero-phonon hole (ZPH) profiles and hole spectra that span about eight decades of burn fluence are reported for Al-phthalocyanine tetrasulphonate in hyperquenched glassy water (HGW) films at 5.0 K. The profiles of unsaturated zero-phonon holes (low burn fluence stage) are more sharply tipped than a Lorentzian. It is shown that the non-Lorentzian behavior is a natural consequence of the interplay between the three distributions that govern the dispersive kinetics of nonphotochemical hole growth. They are denoted by λ, α, and ω, where λ is the tunnel parameter associated with nonphotochemical hole burning (NPHB) and α is the angle between the transition dipole and the laser polarization. The ω distribution stems from off-resonant absorption of the zero-phonon line (ZPL). The single site absorption spectrum used in the calculations included the ZPL and the phonon sideband. The contribution of a distribution of homogeneous ZPL widths to the non-Lorentzian behavior was assessed and found to be negligible compared to that of the above distributions. The burn fluence dependence of the hole spectra, which include the ZPH, phonon sideband, and antihole structures, leads to new insights on the mechanism of NPHB, ones that necessitate modification of the Shu–Small mechanism [L. Shu and G. J. Small, J. Opt. Soc. Am. B 9, 724 (1992)]. Although that mechanism recognizes the importance of coupling between the intrinsic and extrinsic two-level systems (TLSint,TLSext) of the chromophore/glass system and diffusion of excess free volume triggered by optical excitation, it does not adequately account for the effects of multiple excitations of redshifted (relative to the burn frequency ωB) preburn and antihole sites. The results show that multiple excitations ultimately lead to the entire antihole being blueshifted. A "second channel" of hole burning becomes apparent at sufficiently high burn fluences. A model for this channel based on a distribution of extrinsic multilevel systems is proposed. © 2001 American Institute of Physics.

Notes: Zero-phonon hole (ZPH) growth kinetics data that span six decades of burn fluence are reported for Al-phthalocyanine tetrasulphonate (APT) in hyperquenched glassy water (HGW) at 5.0 K. The kinetics are highly dispersive. The hole growth equation used for analysis of the dispersion incorporates three distributions (λ, α, and ω) where λ is the tunnel parameter associated with nonphotochemical hole burning (NPHB), α is the angle between the transition dipole and the laser polarization and the ω-distribution stems from off-resonant absorption of the zero-phonon line (ZPL). The single site absorption profile used includes the phonon sideband as well as the ZPL. The homogeneous width of the ZPL and shape of the phonon sideband were determined from experiment. Eight models, which include the possible combinations of the above distributions, were used to fit the data. As in previous works the λ-distribution was taken to be a Gaussian peaked at λ=λ0 with a standard deviation of σλ. The results show that the contribution to the dispersive kinetics from the λ-distribution is of primary importance. It provides a good fit to the data over the first three decades of burn fluence (∼80% of the saturated ZPH depth). The intrinsic contributions from the α- and ω-distributions become important for the last ∼20% of the burn. These two distributions by themselves or in combination yielded poor fits to the data. The three distributions in combination (λαω-model) provided a good fit over the first five decades of burn fluence. Importantly, the λ0 and σλ values of 8.3 and 0.95 from the λ-distribution alone are nearly the same as those from the λαω-distribution. The above findings for APT/HGW should be widely applicable since previous studies of other NPHB systems led to σλ values (approximately-greater-than)1. It is emphasized that APT/HGW is an ideal system for hole growth studies because of its very narrow ZPL and weak electron-phonon coupling (S∼0.2) and because it satisfies the homogeneity condition, i.e., all sites are burnable. © 2000 American Institute of Physics.

Notes: A liquid helium cryostat that allows for thermospray deposition of samples in vacuum and subsequent pressure dependent studies up to 150 atm is described. Performance of the cryostat is illustrated by study of the pressure-induced shifts and broadening of holes burned in the lowest energy absorption band of aluminum phthalocyanine tetrasulfonate in hyperquenched glassy water. The hole widths exhibit an unusual dependence upon the pressure at which they are burned and also a linear frequency shift which depends upon the sign of the pressure change. © 1999 American Institute of Physics.

Notes: Laser-induced hole filling and spectral diffusion for the dye aluminum phthalocyanine tetrasulfonate in hyperquenched glassy films of water, ethanol, and methanol are investigated. Burning multiple holes into these films reveals a dependence on the burn direction, which is explained by the asymmetry of the antihole produced in the burning process. Spectral diffusion rates are shown to be dependent on sample annealing at temperatures well below the glass transition temperature, Tg. This is interpreted in terms of a β-relaxation process of the glass and is identified with transport of free volume. © 1999 American Institute of Physics.

Notes: The electronic dephasing (spectral dynamics) and electron–phonon coupling of aluminum phthalocyanine tetrasulphonate (APT) in glassy films of ethanol and methanol were investigated by nonphotochemical hole burning over a broad temperature range, ∼5–100 K. Films formed by hyperquenching (∼106 K s−1) at 4.7 K were studied as well as films that were subsequently annealed at temperatures up to ∼170 K. Results are compared against those for APT in glassy water [Kim et al., J. Phys. Chem. 99, 7300 (1995); Reinot et al., J. Chem. Phys. 104, 793 (1996)]. As in the case of water, the linear coupling is weak with a Huang–Rhys factor S∼0.4 but the mean phonon frequencies for ethanol and methanol of 26 and 17 cm−1 are considerably lower than the 38 cm−1 value for water. These modes are assigned as pseudolocalized with significant amplitude (libration) localized on APT. Below about 8 K, the electronic dephasing/spectral diffusion is dominated by coupling to the tunneling intrinsic two-level systems of the glass. At higher temperatures the electronic dephasing is dominated by the exchange coupling mechanism, which derives from diagonal quadratic electron–phonon coupling. Here, for both ethanol and water, a pseudolocalized mode(s) at ∼50 cm−1 is operative. This frequency corresponds to a peak in the spectral density of the liquids which for water is due to the transverse acoustic mode. The results show that the modes responsible for linear and quadratic coupling are distinctly different. Implications of this for optical coherence loss in liquids are considered. Novel results from annealing experiments are reported and discussed in terms of the complex phase diagrams of ethanol and methanol. Formation of the glass from the supercooled liquid just above the melting point of a crystalline phase leads to a marked reduction (∼10×) in the homogeneous width of the zero-phonon hole at 4.7 K. This is interpreted in terms of a reduction in the density of intrinsic two-level systems due to reduced structural disorder of the glass formed from the supercooled liquid. As in the case of water, the highly efficient hole burning in glassy ethanol and methanol is observed to become highly inefficient upon formation of a crystalline phase as predicted by the Shu–Small mechanism for nonphotochemical hole burning. The close connection between this mechanism and Onsager's inverse snowball effect for solvent dynamics around an instantaneously created point charge or dipole in a liquid is emphasized. © 1997 American Institute of Physics.

Notes: The effects of deuteration on hole burning of aluminum phthalocyanine tetrasulfonate (APT) in glassy films of water is reported. Deuteration has no effect on the zero phonon hole width of the APT electronic transition, but a large effect on the hole burning kinetics. These effects are discussed in terms of the two level systems of glassy water. © 1996 American Institute of Physics.