A fiberoptic sensor for electric fieldstrength measurements was developed. This sensor allows to measure even high electric fields in a contactless way, therefore nearly undisturbing the phenomenon to be measured. The basic idea is to rotate the polarization plane of linearly polarized light in an optically active medium (linear electrooptic effect). Further advantages of this method are: high bandwidth near the GHz-region, high local resolution because of small size, no electromagnetic pulse disturbance, useable in high field regions, where electrical methods fail, even in rigid environments. The fiberoptic sensor together with the detector system, which comprises a streakcamera with an image processing system, allows the analog data aquisition and -transmission of about 40 time synchronised signals at one shot using fiberoptics. The application and results of the new diagnostic in the case of the Pseudo Spark Chamber, where classical electric measurements fail, will be presented. The Pseudo Spark1 is a hollow cathode, low pressure gas discharge system, in a special rotational symmetric geometrie. It is situated on the left hand side of the Paschen curve by about 20 Pa hydrogen. During the dicharge there is observed a well pinched electron beam as well as an ion beam; also various kinds of X-ray emission can be detected. The applications of this systems are in Pulse Power technology, lithography, as well as high power switching and material processing.