unaffected by the electrostatic deflectors. Hence neutral fragments produced in
straight section 1 will be measured in detector 1 (see Fig. 3.1). An advantage of
this detection method is that as all photodissociation channels are measured
simultaneously; a change in dissociation channel with excitation wavelength has
little or no effect on the experiment. Furthermore, as the dissociation can be
monitored over time, kinetic shifts (vide infra) can often be corrected for. Ions,
however, have to live long enough after photoexcitation to take half a turn in the
ring (~50 μs). The detection efficiency is high as the neutrals travel with high
kinetic energies (keV).
2. Neutral products in a Secondary Emission Detector (SED) which can be inserted
after straight section 2 (Fig. 3.3). To quantify the production of neutrals, a
channeltron detector measures accelerated electrons emitted from a glass plate
after neutrals impaction. Laser light, on the other hand, passes through the plate
and can be detected in a power meter. The advantage of using this detector is that
dissociation from short-lived ions can be identified. However, the wavelength
Fig. 3.1 Schematic of ELISA. Deflection within the ring is induced by four parallel-plate
deflectors and two cylindrical deflectors. A microchannel plate (MCP) detector (detector 1) is
located at the end of straight section 1, while a power meter at the end of straight section 2 is used
to measure the laser light intensity. A channeltron detector (detector 2) can measure ionic products
with a higher mass-to-charge ratio than that of the parent when positioned on one side of the parent
beam (as depicted in the figure), or lower if moved to the other side. Pairs of quadrupoles are used
to focus the ion bunch in both horizontal and vertical directions. The pressure in the ring is on the
order of 10
À10 mbar, which sets an upper limit of seconds or hundreds of milliseconds on the
storage time
Fig. 3.2 ElectroSpray Ionisation (ESI) source used at ELISA
3 Experimental Techniques
23
straight section 1 will be measured in detector 1 (see Fig. 3.1). An advantage of
this detection method is that as all photodissociation channels are measured
simultaneously; a change in dissociation channel with excitation wavelength has
little or no effect on the experiment. Furthermore, as the dissociation can be
monitored over time, kinetic shifts (vide infra) can often be corrected for. Ions,
however, have to live long enough after photoexcitation to take half a turn in the
ring (~50 μs). The detection efficiency is high as the neutrals travel with high
kinetic energies (keV).
2. Neutral products in a Secondary Emission Detector (SED) which can be inserted
after straight section 2 (Fig. 3.3). To quantify the production of neutrals, a
channeltron detector measures accelerated electrons emitted from a glass plate
after neutrals impaction. Laser light, on the other hand, passes through the plate
and can be detected in a power meter. The advantage of using this detector is that
dissociation from short-lived ions can be identified. However, the wavelength
Fig. 3.1 Schematic of ELISA. Deflection within the ring is induced by four parallel-plate
deflectors and two cylindrical deflectors. A microchannel plate (MCP) detector (detector 1) is
located at the end of straight section 1, while a power meter at the end of straight section 2 is used
to measure the laser light intensity. A channeltron detector (detector 2) can measure ionic products
with a higher mass-to-charge ratio than that of the parent when positioned on one side of the parent
beam (as depicted in the figure), or lower if moved to the other side. Pairs of quadrupoles are used
to focus the ion bunch in both horizontal and vertical directions. The pressure in the ring is on the
order of 10
À10 mbar, which sets an upper limit of seconds or hundreds of milliseconds on the
storage time
Fig. 3.2 ElectroSpray Ionisation (ESI) source used at ELISA
3 Experimental Techniques
23