Optics, double-focusing

Double-focusing forward geometry ion optics is a combination in which the ESA is placed before the magnet, as shown in Figure 24.5. 

This is a very high-performance instrument in which instrument control resides in a multiprocessor system manager leaving only the analytically important parameters to be defined by the operator. It utilizes a completely new concept of ion optics for double focusing and this gives the instrument unmatched performance. 

Instruments using as analyzer a B,E arrangement are consequently called double-focusing mass spectrometers (see Fig. 2.5). Under these conditions, what are called first-order aberrations are overcome however, further aberrations of the ion optics are still present, due to the fringing fields present either at the magnetic or electrostatic sector levels. To reduce these undesired effects, usually electrostatic lens are placed in the field-free region of the instrument. 

There are two options to increase the flux at the sample for a double focusing optics ... 

Double-resonance Spectroscopy.—A review has been given of double-resonance methods in spectroscopy.378 Attention will be focused here on optically (usually phosphorescence) detected magnetic resonance experiments (ODMR). Microwave-optical double-resonance experiments have been carried out on the spectrum of gaseous N02,379 permitting assignment of the rotational = 0—4 side-bands of the 493 nm band. 

Fig. 2. Schematic diagram of the high-resolution double-focusing mass spectrometer. The insert shows an enlarged view of the ion extraction optics for the high-extraction-efficiency mode. P, pusher electrode C, collision chamber B, electron beam (z direction) S, collision chamber exit slit S2, penetrating field extraction slit S3, grounded slit S4 and Ss, deflector electrodes.

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