A microwave frequency comb (MFC) is produced when a mode-locked ultrafast laser is focused on the tunneling junction of a scanning tunneling microscope (STM). The MFC consists of hundreds of measureable harmonics at integer multiples of the pulse repetition frequency of the laser, which are superimposed on the DC tunneling current. In Scanning Frequency Comb Microscopy (SFCM) the tip and/or sample electrode of the STM is moved vertically and laterally so that the power in the MFC may be measured at one or more locations on the surface of the sample and, from the power, carrier density, and other characteristics, of the sample may be calculated. SFCM is non-destructive of the sample. While many systems are possible to practice SFCM, a preferred apparatus is disclosed.