Recording photo-mode

The idea to use this effect for reversible optical data storage goes back to Todorov [77,78] and Rings-dorf [79], which is now addressed as photo-mode recording. The advantage of photo-mode recording over heat-mode recording lies in superior resolution. 

The DRAW disc which offers the facility to make one recording consists of a plastic substrate such as polycarbonate (PC) or polymethylmethacrylate (PMMA) and a recording layer made in amorphous colourants. The thickness of the recording layer is approximately 30-100 nm. The principle of the optical DRAW disc memory, called heat mode system, is shown in Fig. 1. In this system, microscopic pits in the coloured recording layer of a disc are formed by thermal energy transformed from photo energy of a... 

KeV) on samples with concentrations above 10 (atomic ratio), standard X-ray transmission techniques are used. The incident and transmitted fluxes are typically measured by photo-ionization chambers. In the soft X-ray range (i.e., with hv < 1000 eV), absorption spectra may be efficiently measured by recording core-hole decay products. If we describe the inner-shell photo-ionization process as a two-step process, then in the first step the photon excites a core-hole electron pair, and in the second step the recombination process of the core-hole takes place. There are many channels suitable for core-hole recombination. These channels may produce the emission of photons, electrons, or ions, all of which are collected by special detectors. The recombination channel that is normally used to record bulk XAS spectra of dilute systems is the direct radiative core-hole decay that produces X-ray fluorescence lines. When fluorescence lines have high photon energies, this technique probes the bulk. In Figure 4 a beam line with an apparatus to record absorption spectra in the fluorescence mode is schematically represented. 

The single photon detector - typically an avalanche photo diode (APD) driven in counting mode- detects the arrival of fluorescence photons. The recorded photon trace is finally evaluated according to the chosen FFS method, i.e. the sequence of detection events is numerically processed for yielding information about the investigated sample. 

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