Stop

Stop baths are used in holography in the same way they're used in photography, to cease the action of the developing agent. There are several chemicals used from from running tap water, DI water to acetic acid purchased at the chemist or even vinegar purchased at the grocery store.

From [1] "The use of a stop bath in ordinary photography is common, but when processing holograms certain points should be kept in mind as regards the type of hologram to the be processed. Amplitude holograms and certain types of phase holograms are also normallly fixed before bleaching. It is important to avoid contamination resulting from the use of different processing solutions, which is why careful washing between active baths is necessary. It is also important to maintain a constant temperature of all processing solutions, including all washing baths. If a develoer contains sodium carbonate (like in D-19) which when mixed with the acetic acid stop bath can cause liberation of carbon dioxide, it will result in the emulsion being perforated with a multitude of tiny bubbles."

References

1 - Silver-Halide Recording Materials - H.L. Bjelkhagen ISBN 3-540-56576-0