Caesium hydride (CsH) is a compound of caesium and hydrogen. It was the first substance to be created by light-induced particle formation in metal vapor, and showed promise in early studies of an ion propulsion system using caesium.

The caesium nuclei in CsH can be hyperpolarized through interactions with an optically pumped caesium vapor in a process known as spin-exchange optical pumping (SEOP). SEOP can increase the nuclear magnetic resonance (NMR) signal of caesium nuclei by an order of magnitude.