Analog delay lines

Figure 8 Schematic of the optical system used to perform the Raman FID and echo experiments. P = Polarizer (D)BS = (dichroic) beamsplitter MD = manual delay line SD = computer-scanned delay line CSA = charge sensitive amplifier CH = chopper PH = pinhole S = sample F = bandpass and neutral density filters PD = photodiode A/D = analog-to-digital converter PC = computer PMT = photomultiplier X/2 = half-wave plate. (From Ref. 6.)...

Figure 19. Sketch of the polarization analog of the Hong-Ou-Mandel interferometer pump pulse at the frequency o)p generates in the nonlinear crystal NLC downconverted photons at the frequencies coi and a>2 They propagate through a delay line of the length / and are detected at the detectors D4 and DB BS denotes a beamsplitter, Aa and As are analyzers, F4 and Fs are frequency filters, and C means a coincidence device.

Before we can understand any experiment more complicated than a simple spectrum, we need to develop some theoretical tools to help us describe a large population of spins and how they respond to RF pulses and delays. The vector model uses a magnetic vector to represent one peak (one NMR line) in the spectrum. The vector model is easy to understand but because it represents a quantum phenomenon in terms of classical physics, it can describe only the simpler NMR experiments. It is important to realize that the vector model is just a convenient way of picturing the NMR phenomenon in our minds and is not really an accurate description of what is going on. As human beings, however, we need a physical picture in our minds and the vector model provides it by analogy to macroscopic objects. 

Figure 6e, f show the experimentally relevant case in which a mixture of mechanisms occurs, i. e., E 0 and Wetu 0- The parameters have been chosen such that under steady-state excitation conditions 40% of the upconversion is generated by GSA/ESA, and 60% by GSA/ETU. Panel e shows that following a short pulse the properties of both panels a and c can be identified. Specifically, a nonzero N2 is observed at time = 0, but a delayed maximum and a long decay time are also observed. This provides a way to identify intensity involving both GSA/ESA and GSA/ETU contributions. This transient curve is triexponential, involving the decay of the GSA/ESA population, and the rise and decay of the GSA/ETU population (dashed lines). The analogous square-wave transient is shown in Fig. 6f. Termination of the square pulse leads to a simple biexponential decay curve, with a fast component corresponding to the natural decay rate of the upper state, and a slow component corresponding to twice the decay rate of the intermediate state (dashed lines). Again, a small deviation from pure biexponential behavior is observed at short times due to the effect of k2- The relative contributions of each mechanism, in this case 40 60, can be determined from the decay curve as shown in Fig. 6f. This information can be introduced directly into Eq. (10) for data simulation.

By analogy to the optical absorptions A to E (see Fig. 5) the kinetical generation sequence of the diradical oligomers I to III obtained upon UV-irradiation of the monomer crystals is shown in Fig. 11 Only the ESR line I is formed without any delay. The curves are calculated using the kinetic model described below. In this model the ESR line I corresponds to the DR dimer molecule, II to the DR trimer molecule, etc. 

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