Time resolved luminescence of solids excited by femtosecond VUV pulses and synchrotron radiation

Abstract

Time-resolved luminescence spectroscopy has been widely used in studies of electronic excitations and their dynamics in insulators. Present paper discusses the potential of vacuum ultraviolet spectroscopy applied for wide band gap crystals using classical synchrotron radiation as well as more recently developed pulsed femtosecond short-wavelength light sources. Optical spectroscopy using novel free electron lasers and laser systems based on higher harmonic generation process allow detailed investigation of the interaction between electronic excitations and behaviour of solids under extreme radiation conditions. Significant changes in the quantum yield and emission decay kinetics as well as surface damage of single crystals were observed for CdWO 4 and CaWO 4 crystals studied in the temperature range of 8-300 K. However, in the range of excitation densities applied, up to~10 12 W/cm 2 , the nature of luminescence centres and their characteristic emission spectra remained similar to those observed at low excitation densities. Time-resolved luminescence spectroscopy has been widely used in studies of electronic excitations and their dynamics in insulators. Present paper discusses the potential of vacuum ultraviolet spectroscopy applied for wide band gap crystals using classical synchrotron radiation as well as more recently developed pulsed femtosecond short-wavelength light sources. Optical spectroscopy using novel free electron lasers and laser systems based on higher harmonic generation process allow detailed investigation of the interaction between electronic excitations and behaviour of solids under extreme radiation conditions. Significant changes in the quantum yield and emission decay kinetics as well as surface damage of single crystals were observed for CdWO 4 and CaWO 4 crystals studied in the temperature range of 8-300 K. However, in the range of excitation densities applied, up to ~10 12 W/cm 2 , the nature of luminescence centres and their characteristic emission spectra remained similar to those observed at low excitation densities. 1 Introduction Storage rings (synchrotrons) are well-established short-wavelength light sources, which are widely exploited for various spectroscopic techniques characterising structural properties as well as electronic excitations of various materials. Synchrotron radiation (SR) has played an important role in the development of luminescence spectroscopy and in the investigation of dynamical processes as reviewed recently by Zimmerer [1]. As a tuneable source, along with its inherent time resolution and high repetition rate (a few MHz) SR allows revealing complicated relaxation processes induced by vacuum ultraviolet (VUV) photons in wide gap materials. The pulse duration of SR is typically ~100 ps and the photon fluxes generated reach ~10 12 photons per second. These are sufficient for spectroscopic purposes, but not for direct observation of effects due to high density of electronic excitations reported for the irradiation by ion beams [2] or by pulsed nanosecond elect...

Utilisation des matériaux luminescents pour la métrologie des faisceaux intenses UVX d'impulsions ultracourtes

“…Ainsi une impulsion VUV peut créer une densité importante d'excitations dans cette épaisseur et l'interaction entre ces excitations électroniques peut alors perturber la linéarité de la réponse luminescente. On constate en effet, voir les récentes études [2,3], que sous l'excitation par des impulsions VUV intenses de durée femtoseconde, la réponse est impérativement non-linéaire ce qui pose le problème de métrologie de ces faisceaux par la technique luminescente. Une solution possible, que nous proposons dans cet article, est basée sur la mesure de l'image de faisceaux avec résolution temporelle et la reconstruction de la distribution de l'intensité initiale en utilisant les connaissances sur la réponse de scintillateur.…”

Applications of intense ultra-short XUV pulses to solid state physics: time-resolved luminescence spectroscopy and radiation damage studies

“…Actually, similar results have been obtained recently in the same crystals, using the FEL VUV-FLASH at DESY, at 25.6 nm and 13.8 nm but a much higher fluence. 13 Since the same or closely related processes can be studied on the different XUV sources, there is a strong interest to develop them as complementary tools, and to promote especially dynamical studies at high fluence which explore comprehensively a large range of parameters.…”

Behaviour of scintillators under XUV free electron laser radiation

“…In the nonlinear regime effects arising from mutual interaction of elementary excitations can be investigated in more detail in comparison with conventional radiation sources as discussed in Ref. [3].…”

“…In the nonlinear regime effects arising from mutual interaction of elementary excitations can be investigated in more detail in comparison with conventional radiation sources as discussed in Ref. [3].Using the BL1 of the FLASH facility of HASYLAB at DESY (Hamburg, Germany) [4], we investigated the response of different scintillation materials based on intrinsic or activator emission to 25.6 and 13.8 nm FEL radiation in single bunch mode with a pulse duration of 25 fs and maximum energy of 30 mJ at 5 Hz repetition rate. By applying a N 2 gas absorber, the incident beam could be attenuated up to two orders of magnitude from the estimated maximum value of 10 12 W/cm 2 .…”