Population inversion transient

In the literature there are extensive reports on the observation of amplified spontaneous emission (ASE) of polyfluorene [73-76]. ASE occurs at high excitation intensities when it is possible to create a transient excited state population which is greater than the population of the lower lying state to which it radiatively decays, i.e. forming a population inversion. If there is some feedback mechanism of emitted photons, stimulated emission can build... 

Under this condition, we reach the population inversion necessary between the Tm levels of the transition G4 —> F4 and we observed an increase of the emission intensity at the signal wavelength due to the stimulated emission. Transient positive optical gain around 4 cm" ( 17 dB/cm) has been measured in Tm-Yb codoped oxyfluoride glass ceramic. 

An analysis of the rise and decay times of the Er3+ PL transients under the excitation by rectangular laser pulses was proposed to estimate the relative number of the excited ions in nc-Si/SiO2 Er structures [19]. The population inversion of the ion states due to the energy transfer from excitons in nc-Si could be achieved under strong optical pumping [20]. 

The problem of spin polarization in successive differently coupled spin pairs is approached under very simplifying assumptions. The mixing frequencies Q (defined in /6/) are large compared to the inverse lifetime of the spin pair. Therefore, we can consider time independent relative populations on the eigenstates of each spin pair as well as on any other appropriate basis system. The transition probabilities for the electron transfer step follow the projection of the spin states in the first spin pair onto the spin states of the second pair. (A more rigorous treatment has been performed in the group of J. R. Norris.) A test of our analysis is that it yields the expression for the standard CIDEP result (see e.g. /8/) when the coupling in the second pair is set to zero. Fig. 1 shows a simulation of polarized transient X-band... 

Western countries. However, thioguanine concentrations in this population were higher than in a previous study in 51 Japanese children [172 ]. There was a significant inverse correlation between white blood cell counts and thioguanine concentrations. Two patients had leukopenia with alopecia, and four had transiently increased serum activities of pancreatic enzymes, although no TPMT mutations were confirmed. 

The complementary method to time-resolved measurements is the spectroscopy in the energy domain. Energy-resolved experiments determine the Fourier transform of the exponential decay in the time domain, which yields a Lorentzian for the intrinsic spectral lineshape. As mentioned in Section 3.2.4, photoemission does not permit to separate inelastic and elastic decay processes, which both contribute to the linewidth. Because the energy resolution of inverse photoemission is usually not sufficient for a lineshape analysis, this section is devoted to photoemission of occupied states, providing an additional complementary aspect to the time-resolved measurements of transiently populated unoccupied states by 2-PPF. Occupied (initial) states can also be observed by 2-PPE spectroscopy. Their linewidth is similar to the values obtained in regular photoemission [107]. 

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