The reaction microscope end station (ReMi-ES, aka COLTRIMS) is designed for studying many-particle quantum-dynamics of atoms, molecules and small clusters initiated by their interaction with pulsed, ionizing laser radiation. The instrument permits kinematically complete measurements of photoionization fragments over the full solid angle and with high momentum resolution.
Figure 1: Photo of the ReMi-ES assembled in the thin jet configuration.
The ReMi system (photographed in Figure 1) consists of a bipolar Spectrometer which simultaneously images the momenta of oppositely charged fragments onto two time and position sensitive detectors.
After the photoreaction occurs in the interaction region in the centre of the spectrometer, the charged particles are accelerated by electric fields and move towards the two respective detectors. Each detector consists of a pair of multichannel plates followed by two hexagonal delay line anodes. This combination provides sub-ns temporal and sub-mm spatial resolution with a high multi-hit capability. Two coils in the Helmholtz configuration placed outside the vacuum chambers produce a uniform magnetic field that provides additional confinement to higher energy electrons in order to achieve near unit detection efficiency. Thanks to the high detection efficiency, coincidence type single-particle experiments become feasible when combined with a high-repetition rate laser source. The spectrometer configuration can be adjusted to the specific needs of an experiment. The specifications of the detectors and the spectrometer are demonstrated in Table 2.
The instrument includes a cold particle source derived from a supersonic Gas jet source (Table 3) which can be configured for thin or dense particle beams depending on the type of interaction to be studied. The particle beam intersects the interaction region where it crosses with the optical beam before reaching a Gas dump which effectively removes the beam from the UHV environment of the target chamber. The optical beam is provided by an XUV and/or IR beam. The device includes a back-focusing option but it can also use a collimated beam or a forward focusing geometry provided by the corresponding laser source. In the latter case, online diagnostics of the transmitted optical beam is possible.
The signals from the detectors are conditioned by a set of data acquisition (DAQ) electronics including amplifiers, constant fraction discriminators (CFDs) and time-to-digital converters (TDCs). The data is acquired by a PC running the CoboldPC software package.