For optimisation of devices and verification of device simulation models the knowledge of heat dissipation and of free carrier concentration in the device is essential. Non-destructive optical methods based on monitoring of the refractive index, absorption or light emission have previously been developed for investigation of transient temperature or free carrier changes. However, these methods suffer either from small spatial or time resolution. Therefore two testing techniques based on transient interferometric mapping have been developed within this thesis: a two-dimensional multiple-time-instant single-shot technique and a two-beam technique with sub-nanosecond time resolution.