Detector oscilloscopes

Direct time-dependent detection is limited by the response time of detectors, which depends on the frequency range, and the electronics used for data acquisition. In the most favourable cases, modem detector/oscilloscope combinations achieve a time resolution of up to 100 ps, but 1 ns is more typical. Again, this reaction has been of fiindamental theoretical interest for a long time [59, 60]. 

The necessary material to perform annual verification of flaw detector is mainly composed of an electronic function generator, an external calibrated attenuator and an oscilloscope. 

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).]...

The rest of the detector signal is noise filtered and amplified by a lock-in amplifier. The output of the lock-in amplifier is monitored by an oscilloscope, and recorded as the laser scans across the gas s absorption line. The result is a spectral profile of the gas absorption, impressed on the depth of the locked resonance dip. This is then analyzed using (5.6) to find an experimental effective absorption path length. 

Hendricks (H5) and Cho (C2, Method No. 1) both measured particle charge by measuring the voltage pulse on an oscilloscope due to the passage of a charged particle through a drift tube detector. The particle mass was... 

At this point it is important to mention that the experimental setup used for luminescence decay-time measurements is similar to that of Figure 1.8, although the light source must be pulsed (alternatively, a pulsed laser can be used) and the detector must be connected to a time-sensitive system, such as an oscilloscope, a multichannel analyzer, or a boxcar integrator (see Chapter 2). 

An oscilloscope and a camera were used to record the output voltage of die crystal detector. The oscilloscope was triggered from the ionization switch probe by the detonation and a dielectric rod waveguide (such as described in Ref 18a) was used as a transmission line between the instrumentation and the sample. The dielectric rod waveguide was expandable and acted as a mode selector to launch a pure mode of transmission in the sample. The location of sample, detonator and ionization switch are shown in Fig 30. The standard rectangular waveguide from the instrumentation shown in Fig 29 was converted to circular waveguide by a transition. A polystyrene rod... 

Zarowin (68) has made use of a multiple-sampling technique in the measurement of decay times. This method uses a periodically pulsed- or chopped-excitation source and a continuously operating photomultiplier detector. The fluorescent signal is displayed on an oscilloscope. The response of the photomultiplier tube must be fast enough to resolve individual photoelectron pulses, and the time density of pulses is then proportional to the light intensity. 

Apparatus. All electrical resistances were measured with an electrolytic conductivity bridge (Leeds and Northrup model 4666) which was constructed according to specifications set forth by Jones (28) and described by Dike (29). The audio-frequency source was a General Radio Co. type 1311-A audio oscillator used with the frequency regulated at 1000 Hz and the output at about 5 V. The detector circuit consisted of a high-gain low-noise tuned amplifier and null detector (General Radio Co. type 1232-A) and an oscilloscope (Heathkit model O-ll) ... 

Motored engine cool flames are discernible with the naked eye only with great difficulty, hence the reliance on detection apparatus for quantitative investigations. The essential features of radiation detection apparatus, such as shown in Figure 1, include a quartz window mounted in the combustion chamber, a photomultiplier radiation detector, and an amplifier-oscilloscope arrangement (107). 

Figure 7.31 Diagram of a ns, kinetic, laser flash photolysis apparatus. F, photolytic laser beam B, continuous analytical beam S, sample cell d, light detector M, monochromator D, photomultiplier 0, oscilloscope with t (time-base trigger) andy (vertical signal) inputs, (b) Point-by-point absorption spectra of chloranil in acetonitrile at 20 ns, 1 [xj after excitation. T corresponds to the absorption by the triplet state, C by the radical anion...

In the nanosecond (ns) time-scale the use of kinetic detection (one absorption or emission wavelength at all times) is much more convenient than spectrographic detection, but the opposite is true for ps flash photolysis because of the response time of electronic detectors. Luminescence kinetics can however be measured by means of a special device known as the streak camera (Figure 8.2). This is somewhat similar to the cathode ray tube of an oscilloscope, but the electron gun is replaced by a transparent photocathode. The electron beam emitted by this photocathode depends on the incident light intensity I(hv). It is accelerated and deflected by the plates d which provide the time-base. The electron beam falls on the phosphor screen where the trace appears like an oscillogram in one dimension, since there is no jy deflection. The thickness of the trace is the measurement of light intensity. 

At balance, the points at d and b on the ac bridge must be equal in magnitude as well as in phase. The simplest method for determining when this condition exists is to use an oscilloscope connected as shown in the figure as the null detector. If precautions are taken to ensure that the excitation and the null signal are electronically isolated, the balance condition is easily, albeit slowly, obtained [16]. 

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). 

Schematically, two main systems can be used to collect 3D fluorescence data (time, wavelength, number of photons, see fig. 1). In a first type of system, light is directed into a monochromator connected to a photomultiplier tube and then to a fast oscilloscope (PM detection). The experimentalist thus collects luminescence decays at various wavelengths. This system is known to be very efficient for luminescence decay acquisition but is very time-consuming for the acquisition of emission spectra. In the second type of system, light is directed to a diode array detector (or CCD camera) and a subsequent electronic detection device (diode detection). The experimentalist collects emission spectra at various delay times (time zero for the pulse entering in the sample). This system is very efficient for emission data acquisition but, on the other hand, time-consuming for luminescence decay acquisitions. From this very schematic description, it appears that a system combining the two types of detections would be the optimum.

Figure 5. Fiber-optic vidicon spectrometer. (1) Nitrous oxide/acetylene flame (2) SIT vidicon detector (3) Fiber-optic input lenses (4) Fiber-optic entrance slit system (5) 0.5-m Czemy-Turner monochromator (6) Optical multichannel analyzer (7) Oscilloscope display.

---