A waveguide for time-domain integration of THz pulses, comprising two wires extending from an input gap gin to an output gap gout at a tapering angle θ relative to a longitudinal axis, a gap of the waveguide decreasing linearly from the input gap gin to the output gap gout, wherein a size of the output gap is at least one order of magnitude smaller than a central wavelength λTHz in a spectrum of the THz pulses, and a method for time-domain integration of THz pulses, comprising confining input THz pulses in the waveguide.