Compensating field

The geometric compensation by means of a gradiometric coil is realised by placing the SQUID exactly between the two halfs of the coil, in order to detect only the response of the sample. In both cases we could achieve a reduction of the excitation field at the location of the SQUID of up to 1000. Electronic and geometric compensation together leads to an improvement of six orders of magnitude in the dynamic range, compared to a system without excitation field compensation. 

B. Carnahan, S. Day, V. Kouznetsov and A. Tarassov, Development and Applications of a Transverse Field Compensation Ion Mobility Spectrometer, presented at the 4th International Workshop on Ion Mobility Spectrometry, Cambridge, UK, 6-9 August 1995. 

Levitation of Cs atoms in the evanescent field has been demonstrated in Ref. [Hammes 2002], where the the optical dipole potential created by 1 W-laser has been utilized for trapping the atoms far from the surface. The exponential profile of the potential decreases at a half-wave length A/,/w,/2 250 nm. At these distances the optical field compensates for the long-range attraction induced by the electrostatic polarization and the Casimir-Polder potential... 

Fig. 10.9. The Ba spectrum in a high magnetic field with the motional Stark field compensated. The data are obtained in atomic beam experiments, and the relative intensities do not suffer from opacity or saturation effects. Both circular polarisations are separated experimentally, and are found to have the same structure (shown by presenting them as though reflected in the axis) when displaced in energy by the linear Zeeman splitting.

Carnahan, B. Day, S. Konznetsov, V. Tarrasov, A., Development and applications of a traverse field compensation ion mobihty spectrometer, in Fourth International Workshop on Ion Mobility Spectrometry, Cambridge, UK, Jnly 1995. 

Whereas the reflection field compensates for the initial energy spread of the created ions, delayed extrachon can also compensate for the hme spread in ion formahon. In this system the ions formed by MALDI are produced in a weak electrical field, and subsequently extracted by applicahon of a high voltage pulse after a predetermined hme delay of typically a few hundred nanoseconds (50-1000 ns) after a laser pulse. Thus, the inihal desorphon and ion formahon process is separated from the ion accelerahon step and, therefore, the hme window required for ion formahon does not contribute to peak broadening. 

Fig. 9.24. Field compensation method, (a) The unit cell with length a and dipole mcxnent /j,> 0. (b) The modified unit cell with additional fictitious diarges ( = that cancel the dipole moment, (c) The modified unit cells (with n = 0) give the oiigiiial polymer when added together.

This multipole killing (field compensation) may be carried out in several... 

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