Main amplifier

All broadband spectra were amplified by a low-noise preamplifier with a dynamic range > 1,000, and a broadband main amplifier. The amplified time-domain signal is digitized by a 20 MHz, 9 bit Bruker ADC with 128 K words of buffer memory, and Fourier transformed by a Bruker array processor (128 K word FFT in 8 sec). 

Figure 4.47 Typical electronic circuit for the measurement of electron-electron coincidences with two spectrometers (SP1, SP2) placed at the positions 0 , and 5, , respectively. The pre- and main amplifiers are together represented by a triangle. The delay retards the signal from SP1, thus providing a STOP of the time-to-digital converter (TDC) if this time measuring device has been initiated by a START signal from a time-correlated event registered in SP2. The output of the TDC, i.e., the number of time-correlated events as function of the correlation time is stored in a histogramming memory (HIS. MEM.) which then is read out by a computer (COMP.).

Fig. 14.6. Three-dimensional view of the Teramobile. (L) Laser system Ti Sa oscillator and its Nd YAG pump laser LI), stretcher (L2), regenerative amplifier, multipass preamplifier (L3) and their Nd YAG pump laser (LJ,) Multipass main amplifier (L5) pumped by two Nd YAG units (L6) Compressor (L7). (5), Beam expanding system (C), Power supplies D), Lidar detection system [14]...

A wide variety of counting systems has been developed for various purposes. Equipment is often built as NIM (Nuclear Instrument Module standard) or CAMAC (Computer Automated Measurement And Control standard) modules, which fit into standard bins (or crates) containing power supplies and some inter-module connections. Cable connectors are also largely standardized. This facilitates combinations of bias supplies, amplifiers, discriminators, SCAs, ADCs, counters, and other circuitry to fit any need as well as their connection to computers. Some non-standard units, e.g. portable instruments, have their own power supply, main amplifier, counter or rate-meter, etc. 

Fig. 9.34 Output performance of the main amplifier with a repetition rate of 100 Hz output pulse energy and optical-to-optical efficiency, as a function of the diode pump energy, at an input seed pulse energy of 2.4 mJ. Reproduced with pmmission from [261]. Copyright 2009, Elsevita ...

After collection, the pulse-height spectra were analyzed with the MCA software supplied by Spectrum Techniques. Peak centroid channel, fiill-width-at-half-maximum (FWHM) and net and gross peak areas were obtained. The gain setting of the shaping main amplifier was also recorded for each test. 

A typical AE detection system commercially available is illustrates in Fig. 2.8. AE waves are detected by AE sensor, which converts dynamic motions at the surface of a material into electrical signals. Because AE signals are weak, they are normally amplified by two amplifiers of a preamplifier and a main amplifier. The signal-to-noise ratio of equipments shall be low, and the amplifiers often provide more than 1000 times gain. Lately, it is set to normally 100 times or so. As discussed above, the bandpass filter is successfully employed to eliminate the noises. In engineering materials, the band width from several kHz to several 100 kHz or 1 MHz is recommended in the measurement. 

AE signals are normally amplified both by a pre-amplifier and by a main-amplifier, and are filtered. The gain of the amplifier is given in dB (decibels), which means the ratio between input voltage Vj and output voltage Vo as. 

A measurement system consists, as given in Fig. 2.8, of AE sensor, amplifier, and filter. Total amplification by the pre-amplifier and the main amplifier is usually set from 60 dB to 90 dB. To decrease the noises, a band-pass filter between several kHz and 1 MHz is mostly desirable. The noises should be lower than 20 pV as input voltage after detected by AE sensors. 

Galvanostat, Fig. 2 Galvanostat concept using Galvanostat, Fig. 4 Galvanostat with main amplifier... 

Fig. 2 Potentiostat system with main amplifier (MA), impedance buffer IE), and two independent optional current detection systems current-to-voltage converter (CVC) and differential amplifier (DA)...

This circuit is most often used, but some disadvantages must be respected. The CVC must be able to deliver at least the same (large) currents as the main amplifier, and virtual ground is not necessarily guaranteed for fast changing or noisy signals. 

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