  The ARIADNE project is developing innovative optical readout technologies for
two-phase liquid Argon time projection chambers (LArTPCs). Optical readout
presents an exciting alternative to the current paradigm of charge readout.
Optical readout is simple, scalable and cost effective. This paper presents
first demonstration of 3D optical readout of TPC, using CF4 gas as a proof of
principle. Both cosmic rays and an Americium-241 alpha source have been imaged
in 100 mbar CF4. A single-photon sensitive camera was developed by combining a
Timepix3 (TPX3) based camera with an image intensifier. When a pixel of TPX3 is
hit, a packet containing all information about the hit is produced. This packet
contains the x,y coordinates of the pixel, time of arrival (ToA) and time over
threshold (ToT) information. The z position of the hit in the TPC is determined
by combining drift velocity with ToA information. 3D event reconstruction is
performed by combining the pixels x,y location with this calculated z position.
Calorimetry is performed using time over threshold, a measure of the intensity
of the hit.
