Single-Photon Recording

Since single-photon recording does not require ultrashort-pulse lasers, conventional semiconductor lasers can be used in the 3D memories. The optics in CD and DVD devices can be easily applied for a recording system of 3D optical memory. 

Two-photon excitation is preferable in 3D optical memory because the crosstalk between two adjacent layers is much reduced. Another advantage of two-photon excitation is reduction in multiple scattering. This reduction occurs because of the use of an illumination beam at infrared wavelength. 

4 RECORDING AND READOUT OPTICS 16.4.1 Single Photon Recording 

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Figure 8.9. Time-resolved fluorescence spectra of 9,10-diphenylanthracene, recorded wi th time-correlated single photon counting, Aa = 360 nm. Parameters gate width and delay time relative to the intensity maximum of the excitation pulse.

The recording of sequential photon pulses for measurements of low levels of electromagnetic radiation as well as the recording of emission decays. The pulses are recorded from electron emission events from some photosensitive layer in conjunction with a photomultiplier system. See also Time-Correlated Single Photon Counting Fluorescence... 

Fig. 28 a Single-photon fluorescence readout of data recorded by single-photon writing scale bar 100 ixm) b intensity profile (the direction is shown hy the arrows) of (a) c two-photon fluorescence readout of data recorded by single-photon writing (scale bar 100 xm) d intensity profile (the direction is shown by the arrows) of (c) e quadratic dependence of up-converted fluorescence of fluorene 17 on the input intensity. The smallest readout pattern achieved in this system was 3.5 xm... 

The most important light detector in photochemistry is the photomultiplier (PM) tube. It is based on the photoelectric effect (section 2.1), but the primary electrons released by light are accelerated over a number of dynodes to produce an avalanche of secondary electrons (Figure 7.24). A single photon can produce a pulse of some 106 electrons at the anode. Each of these pulses lasts about 5 ns, so that when the light intensity is rather high these single pulses combine to form a steady electric current. This current is amplified and displayed on a chart recorder or computer. 

Figure 1. Block diagram of single-photon time-correlation apparatus from Barker and Weston 11 HV, high-voltage supplies L, lamp PI, photomultiplier M, monochromator FURN, furnace C, sample cell LP, light pipe F, interference filter P2, photomultiplier AMP, amplifier DISCI, discriminator D1SC2, discriminator T-S, timer scaler DL, delay line TAC, time-to-amplitude converter BA, biased amplifier MCPHA, multichannel pulse-height analyzer TTY, teletype printer and paper-tape punch REC, strip-chart recorder.

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