The detectors are very similar in design, based on the successful LaD detector operating on the TWINS mission. The Lyman-α detector LαD is almost identical to LaD on TWINS, and HeD only has a new monochromator unit, which is a reflective grating behind a specially designed collimator baffle. Light enters the instrument through the baffle that defines the field of view and cuts off stray light. Inside, the light is spectrally split by the reflective grating and the 58.4 nm wavelength is directed to the channeltron detector. The pulses from the electrons emitted by the electrode due to the impinging extreme ultraviolet (EUV) photons are amplified and counted by the electronics. LαD is very similar but it features a filter in front of the baffle instead of the reflective grating behind the baffle.
All schematics and numbers are preliminary as of the beginning of Phase A. Additional information about each instrument can be found in the Open Access IMAP Paper.