Optical oscilloscope

The summation over all sampled time intervals At gives the total signal 

The spectral response of the system depends on that of the first photocathode and reaches from 350 to 850 urn for the visible version and from 400 to 1550 fim for the extended infrared version. The time resolution is better than 10 ps and the sampling rate can be selected up to 2 MHz. The limitation is given by the time jitter which was stated to be less than 20 ps. 

There are several excellent and more detailed presentations of special instruments and spectroscopic techniques, such as spectrometers, interferometry, and Fourier spectroscopy. Besides the references given in the various sections, several series on optics [4.2], optical engineering [4.1], advanced optical techniques [4.151] and the monographs [4.4-6,150-152] may help to give more extensive information about special problems. Useful practical hints can be found in the handbook [4.153]. 

Problem 4.1. Calculate the spectral resolution of a grating spectrometer with an entrance slit width of 10 /xm, focal lengths fj = f2 = 2 m of the mirrors Mj and Mj, and a grating with 1800 grooves/mm. What is the useful minimum slit width if the size of the grating is 100x100 mm  

Problem 4.2. The spectrometer in Problem 4.1 shall be used in first order for a wavelength range around 500 nm. What is the optimum blaze angle, if the geometry of the spectrometer allows an angle of incidence a about 20  

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The total eost of a TCSPC oseilloseope system is no higher than that of an optical oscilloscope consisting of a fast photodiode and a fast oscilloscope. However, the sensitivity is many orders of magnitude greater. Moreover, the detection area of a PMT is much larger than that of an ultrafast photodiode, so alignment is no longer an issue. 

Figure 4.25. Experimental configuration for optical pyrometry of shock temperatures induced in transparent minerals. Upon impact of projectile with driver plate, a shock wave is driven into the driver plate and then into the sample. Optical radiation from the sample is detected via six lens/interference filter channels and an array of six photodiodes. Signals from photodiode circuits are recorded on oscilloscopes operating in single sweep model. (After Ahrens et al. (1982).)...

The main categories of electrical/optical ceramics are as follows phosphors for TV, radar and oscilloscope screens voltage-dependent and thermally sensitive resistors dielectrics, including ferroelectrics piezoelectric materials, again including ferroelectrics pyroelectric ceramics electro-optic ceramics and magnetic ceramics. 

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).]...

A photoelectric technique has been devised whereby the position of the deton front in an expl can be measured. The light from the deton front is transmitted by a small-diameter optical fiber to the cathode of a photomultiplier tube where the light pulse is converted to an electrical pulse. Additional pulses may be generated by other fibers located elsewhere in the expl. All of the pulses may be recorded on an oscilloscope. The usefulness of the technique has been demonstrated by the measurement of the transmission times of detonators, the propagation velocities-of expl columns, the timing of expl systems, the vels... 

Any pulse can be described both in the time domain and in the frequency domain. In the time domain a signal may be oscillatory. The time domain behaviour is what is seen on an oscilloscope screen, because an oscilloscope is essentially an instrument for displaying a signal as a function of time. But a varying signal may also be described in terms of the components of each frequency present. This is a frequency domain description and is what is displayed by a spectrum analyser, just as an optical spectrum indicates the amount of each frequency (or wavelength) in a source of light. These two descriptions are related by a Fourier transform (Bracewell 1978), which may be written... 

Phosphors for cathode-ray tubes, television screens, monitor screens, radar screens, and oscilloscopes are tested under electron excitation. Electron energy and density should be similar to the conditions of the tube in which the screen will be used. The phosphors are sedimented or brushed onto light-permeable screens and coated with an evaporated aluminum coating to dissipate charge. The luminescence brightness and color of the emitted light are measured with optical instruments such as photomultipliers or spectrophotometers. 

With the photographic flash lamp the light pulse has a duration of several microseconds at best. The Q-switched pulsed laser provides pulses some thousand times faster, and the kinetic detection technique remains similar since photomultiplier tubes and oscilloscopes operate adequately on this time-scale. The situation is different with the spectrographic technique electronic delay units must be replaced by optical delay lines, a technique used mostly in picosecond spectroscopy. This is discussed in Chapter 8. 

Recently, a similar technique has been used (40) to demonstrate the conversion of the neutral H atoms (G 0.5) to e aq. Figure 3 shows an oscilloscope trace obtained with 2.4 X 10 2 M OH at 5780 A., optical path = 80 cm. (no H2). (See (45) for details about the technique.) The initial small increase in optical density is caused by the Reaction 7. This increase is very small, because Gh — 0.2 Ge. The results agree with those obtained with 0.1 M H2, but we did not make any quantitative analysis. 

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