This process is called spectral diffusion (Creemers et al. 1997; Den Hartog et al. 1998a, 1999a, b; Friedrich and Haarer 1986; Koedijk et al. 1996; Littau et al. 1992; Lock et al. 1999; Meijers and Wiersma 1994; Silbey et al. 1996; Wannemacher et al. 1993), and the measured width is the ‘effective’ homogeneous linewidth \( \Upgamma_\hom ^’ \). In a time-dependent hole-burning experiment (see below) INCB028050 chemical structure \( \Upgamma_\hom ^’ \) depends on the delay t d between the burn and probe pulse. Principles
of hole burning In a spectral hole-burning experiment, the inhomogeneously broadened absorption band is irradiated at a given wavelength with a narrow-band laser. Whenever the molecules selleckchem resonant with the laser wavelength undergo a photo-transformation (photophysical or photochemical), a hole is created in the original absorption band (see Fig. 1). The width of the hole, under certain conditions (see below), is then proportional to the homogeneous linewidth. The photoproduct will absorb at a different wavelength, either within the absorption band or outside. Since the laser selects molecules absorbing at a given frequency ν 1, and not molecules in
a specific environment, the correlation between transition energy and environmental parameters is, in general, different for the photoproduct and the original molecule. MK-4827 price As a consequence, the width of the photoproduct band, or antihole, is larger than that of the hole (Völker and Van der Waals 1976; Völker and Macfarlane 1979). The optical resolution that can be reached with HB is 103–105 times higher than that with conventional techniques, which makes HB a powerful
tool for spectroscopy in the MHz range (Völker 1989a, b). Fig. 1 Top: Diagram of an inhomogeneously broadened absorption band with a width Γinh. The homogeneous bands of width Γhom of the individual electronic transitions are hidden under the broad inhomogeneous absorption band. Bottom: Laser-induced spectral hole burned at frequency Sitaxentan ν1. The photoproduct absorbs at a different frequency, here outside the inhomogeneous band (Creemers and Völker 2000) Hole-burning mechanisms can be divided into two categories: persistent HB and transient HB (THB). Within the first category, there is photochemical HB (PHB; De Vries and Wiersma 1976; Friedrich and Haarer 1986, and references therein; Völker and Van der Waals 1976; Völker et al. 1977) and non-photochemical HB (NPHB; Carter and Small 1985; Hayes and Small 1978; Jankowiak and Small 1987, and references therein; Small 1983). The time scales involved in PHB and NPHB at low temperature are usually seconds to hours, whereas THB often lasts only microseconds (μs) or milliseconds (ms). For more details about these HB mechanisms, the reader is referred to Völker (1989a, b).