1,721,173 research outputs found
Two-Photon Absorption Using Synchrotron Radiation
No full textWe report on the first measurements of two-photon absorption spectroscopy performed using the synchrotron radiation as a tunable vacuum ultraviolet radiation source and the light from a Nd-Yag laser. This new technique opens the possibility of performing non linear spectroscopy in the far ultraviolet region. As an example of application, we present and discuss the two-photon absorption spectra near the fundamental thresholds of KI, KCl and NaCl
Electroreflectance of GaSe: the interpretation of the structure above the edge
No full textThe electroreflectance spectrum of GaSe, measured by Balzarotti et al. (1971) between 3.2 and 4.1 eV, is reanalyzed using more accurate values for the optical constants ε1 and ε2. The previous interpretation cannot be maintained because a lineshape analysis by itself is not sufficient to assign the structure at 3.4eV to an M1 interband transition. Other arguments and further reflectivity measurements suggest this structure to be due to an M0 resonant exciton, with spin—orbit partner at 3.7 eV
A new interpretation of the fundamental exciton region in LiF
No full textWe have reanalyzed LiF optical data between 12 and 15 eV. We show that the conductivity spectrum can be fitted using effective mass theory for excitons with asymmetric Lorentzian lineshapes. We find the band gap is about 14.5 eV. The determination of the effective rydberg is not accurate enough to give the short-range correction to the hydrogenic energy for the n=1 state
Inter-band transition probabilities and photon momentum
No full textThe theory of inter-band transitions is re-examined in the case of finite photon momentumq. New expressions for the joint density of states near critical points are derived. They give Van Hove’s expressions in both the limits of long and short wavelengths. The dispersion relation for the transverse dielectric functionɛ 2T due to inter-band processes is given explicitly and it is compared to that of the longitudinal dielectric functionɛ 2L . It is shown that in the limitq = 0ɛ 2T equalsɛ 2L even for anisotropic media. The possibility of an experimental evidence of the effects caused by a finite photon momentum on the shape of the optical absorption is discussed
High-resolution spectroscopy in the far ultraviolet
No full textThermoreflectance (TR) measurements have extended to the far ultraviolet the high-resolution modulation techniques well established at lower energies. The TR spectrum of gold showed for the first time several new features up to 36 eV. Their interpretation is reanalysed also in view of recent CIS photoemission measurements. The TR spectra of the Rb+4 p core excitons in Rb halides allowed us to resolve at 200 K some structures previously observed only at 8 K, enabling us to determine their temperature dependence. The exciton-phonon interaction is suggested to be responsible for the partial failure of the ligand field model for core excitons. The ionization continuum threshold of the Rb+4 p states is also determined. Finally, TR experiments allowed us to discriminate between different interpretations suggested for the strong electron energy loss peak at the end of the valence band excitations of alkali halides. © 1977 Società Italiana di Fisica
Photodesorption studies of alkali iodides in the fundamental absorption region
No full textThe photon-stimulated desorption yield spectra of alkali atoms and iodine atoms emitted from KI and RbI samples near the absorption threshold from 5 eV to 9 eV are discussed in terms of a three-step model for desorption. According to the photon energy, different transport mechanisms, with different diffusion lengths of the excited states are considered
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