Heterodyne scanning probe microscopy method for imaging structures on or below the surface of a sample, the method including: applying, using a transducer , an acoustic input signal to the sample; sensing, using a probe including a probe tip in contact with the surface, an acoustic output signal, wherein the acoustic output signal is representative of acoustic waves induced by the acoustic input signal that are measurable at the surface; wherein the acoustic input signal comprises at least a first signal component having a frequency above 1 gigahertz, and wherein for detecting of the acoustic output signal the method comprises a step of: applying a further acoustic input signal to at least one of the probe or the sample for obtaining a mixed acoustic signal, the further acoustic input signal including at least a second signal component having a frequency above 1 gigahertz, wherein the mixed acoustic signal comprises a third signal component having a frequency equal to a difference between the first frequency and the second frequency, wherein the frequency of the third signal component is below 1 gigahertz, wherein the further acoustic input signal is applied by inducing acoustic vibrations in the probe tip of the probe, wherein the step of inducing the acoustic vibrations in the probe tip is performed by using an optical excitation beam incident on the probe tip, the optical excitation beam having a time varying optical power for enabling photo thermal excitation of the probe tip for inducing the acoustic vibrations . applying, using a transducer , an acoustic input signal to the sample; sensing, using a probe including a probe tip in contact with the surface, an acoustic output signal, wherein the acoustic output signal is representative of acoustic waves induced by the acoustic input signal that are measurable at the surface; wherein the acoustic input signal comprises at least a first signal component having a frequency above 1 gigahertz, and wherein for detecting of the acoustic output signal the method comprises a step of: applying a further acoustic input signal to at least one of the probe or the sample for obtaining a mixed acoustic signal, the further acoustic input signal including at least a second signal component having a frequency above 1 gigahertz, wherein the mixed acoustic signal comprises a third signal component having a frequency equal to a difference between the first frequency and the second frequency, wherein the frequency of the third signal component is below 1 gigahertz, wherein the further acoustic input signal is applied by inducing acoustic vibrations in the probe tip of the probe, wherein the step of inducing the acoustic vibrations in the probe tip is performed by using an optical excitation beam incident on the probe tip, the optical excitation beam having a time varying optical power for enabling photo thermal excitation of the probe tip for inducing the acoustic vibrations . applying a further acoustic input signal to at least one of the probe or the sample for obtaining a mixed acoustic signal, the further acoustic input signal including at least a second signal component having a frequency above 1 gigahertz, wherein the mixed acoustic signal comprises a third signal component having a frequency equal to a difference between the first frequency and the second frequency, wherein the frequency of the third signal component is below 1 gigahertz, wherein the further acoustic input signal is applied by inducing acoustic vibrations in the probe tip of the probe, wherein the step of inducing the acoustic vibrations in the probe tip is performed by using an optical excitation beam incident on the probe tip, the optical excitation beam having a time varying optical power for enabling photo thermal excitation of the probe tip for inducing the acoustic vibrations . <EOS>