The invention relates to a gas cell for an atomic sensor, comprising an optical cavity provided with at least one optical window (9) and fillable with a gas. The cell also comprises a sealing cup comprising a cavity mouth, a channel mouth, and a sealing access, as well as a membrane which hermetically closes the sealing access of the sealing cup. The membrane can be plastically deformed by heating so as to hermetically close the cavity mouth and/or the channel mouth, in such a way as to hermetically separate the optical cavity from the gas inflow channel.