Behind the biprism the partial waves overlap
and interfere with each other. The interference pattern
has a period of several 100 nm and is oriented parallel to
the biprism in the x-direction. It is magnified by an
electrostatic quadrupole lens to fit the detectors resolution
of about 100 lm. The image rotator, a magnetic coil,
allows to rotate the interferogram to correct possible
misalignments. The interference pattern is detected by a
MCP-detector with a delay line anode. It is able to operate
at background gas pressures up to about 104 mbar. Above
that level the risk of destruction of the MCPs due to electric
discharges is high.