We present an improved version of the classical heterodyne interferometer for ultrasound detection, which includes a double phase conjugate mirror (DPCM) in the detection arm. The DPCM performs wave front adaptation to plane wave of the speckled beam scattered by the rough surface of the sample. The performances of the system are analyzed regarding the transmission (~30%) and fidelity (~70%) of the phase conjugation and the response time and etendue of the device. An example of application to the detection of laser generated ultrasound is also presented.