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THE purpose of this note is to describe a relatively simple apparatus for measuring the properties of transient optical absorption and emission bands in solids under pulsed irradiation. The equipment is presently being for the electron beam. The electron beam traverses a 28 cm air path between the exit window of the electron accelerator and the titanium Dewar window. The sample is mounted in vacuum on the Dewar cold finger approximately 3 cm behind the Dewar window. Under these conditions a single electron pulse will deposit 1017 eV/cm2 in the sample. This generates an easily detected transient absorption if the analyzing light is internally reflected. In this way the dose per pulse is kept relatively low, and a large number of pulses are possible before the concentration of stable color centers builds up sufficiently to affect the transient response.