Beat structure

Containment design details - basic structure, major contents (beat structures), internal safety systems performance data, special features, reactor cavity/sump details, layout elevations and floor plans, fnateriais specifications, design limits, etc. 

Fig. 7.17 Time evolution of the nuclear forward scattering for metallic Ni foil. All measurements except for the upper curve were performed with external magnetic field B = 4 T. The solid lines show the fit. The arrows emphasize stretching of the dynamical beat structure by the applied magnetic field. The data at times below 14.6 ns had to be rescaled (from [34])...

A series of NFS spectra of the spin-crossover complex [Fe(tpa)(NCS)2] were recorded over a wide temperature range [45]. A selection of spectra around the spin-crossover transition temperature is shown in Fig. 9.13. At 133 K, the regular quantum-beat structure reflects the quadrupole splitting from the pure high-spin (HS) phase, and the envelope of the spectrum represents the dynamical beating with a minimum around 200 ns. Below the transition, at 83 K, the QBs appear with lower frequency because of smaller AEq of the low-spin (LS) phase. Here the minima of... 

The inscription of SRGs on polymer films also allows for fabricating diffractive optical elements that require intricate surface structxires. For a review of unconventional methods to fabricate and pattern nanostructures, see Xia et Viswanathan et illustrated several such possibilities, such as the honeycomb pattern shown in Figure 14.28, the e -crate-like structure of Figure 14,29, or the beat structure shown in Figure 14.30. These widely... 

FIG. 14.30 A 3D AFM imqge of dual gratings (beat structure) sequentially written with the Ar+ laser beams at 488 and 514 nm at a fixed writing angle. 

An example for the experimental data obtained approximately 2 mm behind the nozzle is presented in Fig. 6. The coherent anti-Stokes Raman signal S ° (tj,) is plotted versus delay time. The data points extend over 4 orders of magnitude and represent an average of 20 individual measurements. A complicated beating structure and the decay of the signal envelope are readily seen. 

Fig. 3a shows a measurement of the beat structure in the Di-line of cesium. The two hyperfine splitting frequencies of the ground and excited state clearly show up. The fast oscillation corresponds to the splitting of the ground state, while the envelope with the smaller frequency results frran the splitting in the excited state. The difference between the measured and calculated oscillating depths can be explained by the finite pulse duration. 

The Fourier transformed signal in Fig. 3b clearly shows the hyperfine splitting frequencies of the excited state with 1.2 GHz and the ground state with 9.2 GHz. Since the beat structure can be described as an amplitude modulation of the fast oscillation with the excited state split-... 

Fig. 3 a) Measurement of the hyperfine beat structure in the Cs Di-line. b) Fourier spectrum... 

Both measurements show a fast rising beat structure at negative delaytimes. The origin of this signal results from optical coherence generated by the linearly polarized probe pulse and corresponds to a first-order Free-Induction-Decay. An interpretation of this signal is found in ref. [2]. 

A beat structure observed with this experimental arrangement is shown in Fig. 3. Within a delay time of l6 ps clearly resolved oscillations with a period of 1.9 ps are monitored. These beats correspond to the 517 GHz fine structure splitting in the 3p state and represent the fastest quantum-beat signal observed so far. 

The theoretical description of the quantum-beat structure in terms of oscillating population differences between Zeeman substates of different fine structure levels gives very satisfactory explanation for the appearance and form of the observed signal. 

Comparison of measured and calculated signal shows that a very satisfactory explanation of the observed signal form is achieved. The beat structure can be understood in terms of atomic coherence between substates yielding an amplitude modulation of optical coherence. The fast decay is mainly determined by Doppler dephasing, however, is also slightly influenced by the excited state splitting frequency. 

The delayed intensity decays essentially exponentially in time, which implies that there is no additional electric field gradient beyond the electric field gradient from the asymmetry inherent in the surface, that is, the surface is practically perfect and undisturbed. By stepwise increase in the temperature a beat appears at about 45 ns that become more pronounced with the temperature. The highest temperature of the experiment was 870 K in order to avoid destruction of the Fe monolayer by diffusion of Fe into the W substrate. When the temperature is lowered again to 300 K, the beat structure disappears and the original spectrum is recovered, proving that thermally activated defects are responsible for the beat... 

The temporal evolution of the ion signal reveals a clear oscillation. Its period is about 500 fs. The maximum oscillation amplitude is close to the zero of time and it decreases within 5ps, but growing again rather rapidly. The long-time behavior shows a repetition of this behavior similar to beat structures, as known for example in acoustics when two frequencies close to each other are superimposed. As can be seen in Fig. 3.5, a closer look at the zero-of-time gives further information. 

To get further information from these real-time data, Fourier analysis is an appropriate tool. In particular, the origin of the beat structure can be analyzed (see Sect. 3.1.3). 

Quantum dynamical calculations of the pump probe spectra for the two isotopes were performed for delay times up to 40 ps. A comparison of the experimental and theoretical ionization signals as a function of the delay time is presented in Fig. 3.15. In agreement with the experimental data, the short-time dynamics of the theoretical signal show the 500 fs oscillation period of the wave packet prepared in the A state (centered around v = 11) and the long time dynamics reflect the totally different beat structures of the two isotopes. However, the oscillation periods of the pronounced regular beat structure of the isotope (Fig. 3.15 a) and of the weak, irregular... 

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