Transient digitizer

Fig. 5.5. The electrical response of piezoelectric polymers under shock loading is studied experimentally by placing the thin PVDF element on the impact surface of a standard target, either the polymer, Kel F, z-cut quartz, or z-cut sapphire. The im-pactor is typically of the same material. The current pulse is recorded on transient digitizers with frequency responses from 250 to 1000 MHz.

Fig. 6. Schematic diagram of the Nottingham apparatus for IR kinetic measurements on solutions. Solid lines represent the light path, broken lines the electrical connections. L = Line tunable CO laser, S = sample cell, F = flash lamp, P = photodiode, D = fast MCT IR detector, T = transient digitizer, O = oscilloscope, and M = microcomputer. Nonfocussing optics were used throughout, and the IR laser beam was heavily attenuated by a variable path cell V, filled with liquid methanol, placed immediately in front of the detector. [Reproduced with permission from Moore et al. (61).]...

Pulse radiolysis was performed using e from a linear accelerator at Osaka University [42 8]. The e has an energy of 28 MeV, single-pulse width of 8 nsec, dose of 0.7 kGy, and a diameter of 0.4 cm. The probe beam for the transient absorption measurement was obtained from a 450-W Xe lamp, sent into the sample solution with a perpendicular intersection of the electron beam, and focused to a monochromator. The output of the monochromator was monitored by a photomultiplier tube (PMT). The signal from the PMT was recorded on a transient digitizer. The temperature of the sample solution was controlled by circulating thermostated aqueous ethanol around the quartz sample cell. Sample solution of M (5 x 10 -10 M) was prepared in a 1 x 1 cm rectangular Suprasil cell. 

The final point of comparison between the two techniques concerns the time required to record the data. A decent time resolution on the signal requires data to be taken at perhaps 100 time points following photolysis, and this is done in a facile manner by use of a transient digitizer, as described for... 

Fig. 13.4 Diabatic field ionization signals for i changing under increasing incident beam intensities. For clarity the successive curves are displaced upward by one scale unit. Data points are taken from the transient digitizer records, and a small sloping background has been subtracted. Full curves are fits to the model of MacAdam et al. (from ref. 8).

FIGURE 6.9 Typical wiring of a photomultiplier. Each of the dynodes, beginning in the photocathode, is linked stepwise by resistors RD of the same value. The photocurrent is read as the voltage drop across the load resistor R with high impedance filter (Rf, Cp) and oscilloscope or transient digitizer (detector). 

Figure 1. Diagram of apparatus for picosecond fluorescence studies using streak camera detection. A laser oscillator B dye cell C output reflector D polarizer E spark gap F KDP pockels cell G polarizer (crossed with D) H clear glass beamsplitter J laser amplifier K pin photodiode L transient digitizer M,N 1054 nm reflectors P 2nd harmonic generator Q 3rd or 4th harmonic generator R spectrograph S streak camera T biplanar photodiode U image...

Laser flash photolysis was performed with a Nd-YAG Laser from Quantel which was frequency doubled with a KDP-Crystal. Samples were excited at 532 nm and the transients formed monitored with a pulsed 250 W Xenon lamp and recorded using a monochromator and an R128 photomultiplier connected with a transient digitizer linked to a PDP11-73 minicomputer. 

The other transient recorders, or perhaps more correctly transient digitizers, capture and store the waveform in a digital form in a computer-type memory. These can be further divided into two classes, those that digitize and write directly into the memory, e.g. the Biomation series of waveform recorders, and those that first write on an intermediate target from which it is then read, digitized and stored, e.g. the Tektronix series of transient digitizers. Although they share some features, the operations of these two types of transient recorder are quite different and they will be discussed separately. 

The second mode is to run the experiment at a fixed magnetic field and sweep the second boxcar gate over time to collect kinetic information. There are two problems with this approach. Eirst, the experiment must be repeated several times with a slow scan rate in order to get satisfactory S/N. To extract the EPR kinetic curve, the experiment is repeated off resonance and the two curves subtracted. Kinetics are more easily obtained using a high-bandwidth transient digitizer instead of a boxcar, and many researchers perform TREPR in this fashion." ° It is important to note here two... 

Samples were irradiated by a 10 ps single or 2 ns electron pulse from a 35 MeV linear accelerator for pulse radiolysis studies (17). The fast response optical detection systems of the pulse radiolysis system for absorption spectroscopy (18) is composed of a very fast response photodiode (R1328U, HTV.), a transient digitizer (R7912, Tektronix), a computer (PDP-11/34) and a display unit. The time resolution is about 70 ps which is determined by the rise time of the transient digitizer. 

Fig. 6-8. Time evolution of the pyrene anion (A ) and triplet pyrene ( A ) of the reaction (6-21) in methanol measured in the absence and presence of a magnetic field of 50 mT. For each wavelength and magnetic field, 8-10 transients were averaged with a transient digitizer (time resolution 0.5 ns). (Reproduced from Ref. [23b] by permission from The American Institute of Physics)...

Fig. 8. Time ranges of various optical detection systems. The dotted line for transient digitizer indicates the highest-performance configurations, the solid line routine ones.

The current waveform on the anode of the photodetector is fed to the input connector of a transient digitizer/digital oscilloscope where it is converted into digital format and read into a PC. The resulting stored data can be processed for spectral/ dynamic content by one of several available commercially available data manipulation software packages. 

There has been a considerable decline in the number of papers which deal with the details of techniques of measurement of fluorescence decay. This is no doubt due to the fact that the alternative methods are now essentially well established. Nevertheless a microcomputerized ultrahigh speed transient digitizer and luminescence lifeline instrument has been described . A very useful multiplexed array fluorometer allows simultaneous fluorescence decay at different emission wavelength using single photon timing array detection . Data collection rates could approach that for a repetitive laser pulse system and the technique could be usefully applied to HPLC or microscopy. The power of this equipment has been exemplified by studies on aminotetraphenylporphyrins at emission wavelengths up to 680 nm. The use and performance of the delta function convolution method for the estimation of fluorescence decay parameters has been... 

The fluorescence decay can be measured with a streak camera, a very fast photomultiplier tube-like Hamamatsu 1294U attached to Tektronix transient digitizer, a box car integrator, or photon counting. 

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