an electrical signal , such as a high current pulse , is applied to a series of two or more conducting strips installed in series in a laser cavity containing either a buffer gas or a vacuum . the strips are separated by small gaps . when the electrical signal is applied to the strips , plasmas are formed in the gap regions . the plasmas are comprised of ions from the strip material . once formed , these plasmas expand hemispherically , cool and recombine to generate radiation . the composition of the plasmas depends on the strip material , the electric field in the gaps , the gap size and the background gas type and pressure .