Optical source in microwave impedance microscopy

A system for atomic force microscopy in which a sharp electrode tip of an flexing probe cantilever is positioned closely adjacent a sample being probed for its electrical characteristics. An optical beam irradiates a portion of the sample surrounding the probe tips and is modulated at a radio or lower modulation frequency. In one embodiment, a reference microwave signal is incident to the electrode tip. Microwave circuitry receives a microwave signal from the probe tip, which may be the reflection of the incident signal. Electronic circuitry processes the received signal with reference to the modulation frequency to produce one or more demodulated signals indicative of the electronic or atomic properties of the sample. Alternatively, the optical beam is pulsed and the demodulated signal is analyzed for its temporal characteristics. The beam may non-linearly produce the microwave signal. Two source lasers may have optical frequencies differing by the microwave frequency.