Terahertz imaging and holography with a high-power free electron laser

In this paper we describe the terahertz imagers which characteristics are adequate for measurement of high power terahertz radiation. Three imaging techniques were employed on the Novosibirsk terahertz free electron laser (NFEL): near-infrared thermograph, thermosensitive visible light interferometer, and "a thermal image plate". All this methods are widely used in experiments with NFEL radiation. As examples, we present here the measurements of laser beam coherence and describe experiments on terahertz holography.