  The bubble-assisted Liquid Hole Multiplier (LHM) is a novel concept for the
combined detection of ionization electrons and scintillation photons in
noble-liquid time projection chambers. It consists of a perforated electrode
immersed in the noble liquid, with heating wires generating a stable bubble
underneath. Radiation-inducted ionization electrons in the liquid drift into
the electrode's holes and cross the liquid-vapor interface into the bubble
where they induce electroluminescence (EL). The top surface of the electrode is
optionally coated with a CsI photocathode; radiation-induced UV-scintillation
photons extract photoelectrons that induce EL in a similar way. EL-photons
recorded with an array of photosensors, e.g. SiPMs, provide event localization.
We present the basic principles of the LHM and summarize the results obtained
in LXe and LAr.
