Multi-frequency pulses

Gradient pulses can also be used together with multi-frequency pulses to create pseudo-pure states in systems with large number of qubits. An example of that is the case of... 

Fittipaldi M, Garcia-Ruhio I, Trandafir F, Gromov 1, Schweiger A, Bouwen A, Van Doorslaer S. 2008. A multi-frequency pulse EPR and ENDOR approach to study strongly coupled nuclei in frozen solutions of high-spin ferric heme proteins. J Phys Chem B 112 3859-3870. 

Fig. 6.6. Principles of pulse fluorometry and multi-frequency phase-modulation fluorometry.

Fig. 5.3.13 Hadamard encoding and decoding for simultaneous four-slice imaging. The encoding is based on four experiments, A-D. In each experiment, all four slices are excited by a multi-frequency selective pulse. Its phase composition is determined by the rows of the Hadamard matrix H2. The image response is the sum of responses for each individual, frequency selective part of the pulse. Thus, addition and subtraction of the responses to the four experiments separates the information for each slice. This operation is equivalent to Hadamard transformation of the set of image responses. Adapted from [Miil21 with permission from Wiley-Liss. Inc., a division of John-Wiley Sons, Inc.

Hadamard spectroscopic imaging (HSI) is a technique to obtain localized spectroscopic information from n regions of interest in n scans [Boll, Hafl, Goel, Goe2, Goe4, MU14]. It is a straightforward extension of the multi-frequency selective-pulse technique... 

The measured responses to the combinations of multi-frequency selective pulse excitation can be unscrambled for each volume element by transformation with a super-Hadamard matrix. The dimension of this matrix equals the product of the dimensions of the Hadamard matrices used for encoding each space axis. 

Observation of the stereoselective manner of chiral substrates binding to these asymmetric metal-salen complexes was not confined to [VO(l,3)] or chiral epoxides. Recently we showed how asymmetric copper salen complexes, [Cu(l)] and [Cu(4)] (Fig. 1), could also discriminate between chiral amines (R-IS-methylbenzylamine, MBA) as evidenced by multi-frequency CW and pulsed EPR, ENDOR, HYSCORE and DPT [45]. The discrimination of the MBA enantiomers was directly observed by W-band EPR. By simulating the W-band EPR spectra of the individual diastereomeric adduct pairs (i.e. R,R -[Cu(4)]+R-MBA and R,/ -[Cu(4)]-l-5-MBA), accurate spin-Hamiltonian parameters could be extracted for each adduct. The EPR spectmm of the racemic combinations (i.e. ra -[Cu(4)]+rac-MBA) was then simulated using a linear combination of the g/A parameters for the homochiral (R,R -[Cu(4)]+R-MBA) and heterochiral (R,R -[Cu... 

Lunsford [3b] and Hoffman and Nelson [23] first reported the ESR spectra for adsorbed NO molecules. Then, Kasai [4b] revealed that ESR spectra of NO probe molecules are very sensitive to the interaction with metal ions and Lewis acid sites in zeolites. The earlier ESR studies of the NO/zeolite system have been summarized in several review papers [3a, 4a, 8]. A number of ESR studies have been also carried out for NO adsorbed on metal oxides such as MgO and ZnO as reviewed by Che and Giamello [5]. Modern ESR techniques such as pulsed ESR [25-27], ENDOR (Electron Nuclear Double Resonance) [26], and multi-frequency (X-, Q-, and W-band) ESR [28] are especially useful for an unambiguous identification of the ESR magnetic parameters (g, hyperfine A, and quadrupole tensors, etc.) and, consequently, for a detailed characterization of structural changes and motional dynamics involved. Some recent advancements in ESR studies on NO adsorbed on zeolites are presented in this section. 

The second topic is an extension of the first one and was concerned with ESR studies of the Cu(I)-NO complexes. Copper ion exchanged high siliceous zeolites such as ZSM-5 and MCM-22 have been considered as a promising environmental catalyst for the NO decomposition. The Cu(I)-NO complex has attracted special interest because of its important intermediate in the catalytic NO decomposition. Poppl and other scientists have extensively applied multi frequency ESR, pulsed ENDOR and HYSCORE methods to clarify the local structure of Cu(I)-NO adsorption complexes. 

Sub-Bottom-Profiler This system is another multi-frequency acoustic system which is comparable to a seismic monitoring system of low seabed penetration capability. The acoustic emissions are frequency-modulated and the pulse rate is adjustable to suit the local requirements. The echoed signal can be recorded and processed into a display-form similar to the side-scan-sonar. It produces information about the thickness of sedimentation and can plot the contour of the seabed below the sedimentation layer. 

The advances in technology in the last years led to the development and optimization of new ESR methods such as high field/multi-frequency ESR [29-31], double resonance [32, 33], and pulse methods [34-36]. The improvements in resolution brought by these methods have made possible analysis and interpretation of more complex systems and detection and characterization of transient paramagnetic intermediates inaccessible before. 

Astashkin AV, Raitsimring AM, Walker FA. 1999. Two- and four-pulse ESEEM studies of the heme binding center of a low-spin ferriheme protein the importance of a multi-frequency approach. Chem Phys Lett 306( l-2) 9-l 7. 

A detailed structural study has also been made of oxygenated cobalt(II) heme model systems and oxygenated Co(II) corrin complexes. " These used a combination of X-, Q- and W-band CW and pulsed EPR, X- and Q-band ENDOR, X-band HYSCORE and S-band ESEEM to determine the g and A tensors and investigate the proton and nitrogen hyperfine interactions. Both studies are excellent examples of the power of multi-frequency CW and pulsed ESR and ENDOR in determining the full electronic structure of metallo-complexes. 

Typically, pulsed light sources are used for time-domain measurements, but frequency-domain measurements are possible as well, since the pulse rate can be made very constant and usually is in the range used for frequency-domain FLIM measurements (around 80 MHz). An added advantage is that a pulsed signal is very rich in harmonic-content, when compared to a modulated signal coming out of an AOM, or EOM, enabling multi-frequency measurements. 

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