FIR response of intrinsic Josephson junctions

We present experiments on the far infrared response of intrinsic Josephson junctions in Bi2Sr2CaCu2O8+x (BSCCO), We detected first order Shapiro steps on resistive branches in a frequency range between 584 GHz and 2.5 THz, Du e to the very low power coupled into the junctions the suppression of the c ritical current was only weak With increasing number of junctions in the re sistive state a higher amplitude of the Shapiro steps was measured, As the frequencies are well above the plasma frequency of our junctions, the steps are expected to be stable at any power level. To verify this, step heights were studied at various power levels as a function of frequency. The imped ance matching of the system improved considerably when several junctions ha ve switched into the resistive state.