Patent attributes
In a near-field heterodyne spectroscopy system, a near-field generation device receives the output of a pump beam source and is also made to vibrate or move at a frequency f to generate a modulated near-field beam having a near-field component. The outputs of the pump beam source and a probe beam source (optional) as well as the modulated near-field beam are directed to the same point on a sample. At least one of the outputs of the pump beam source and probe beam source is modulated at a frequency Ω. Thus, the reflected beam that results from the interaction with the region illuminated by the modulated near-field beam is modulated at frequencies Ω+f and Ω−f. Because the excitation is near-field, the electric field in the sample is evanescent and ensures a shallow probing depth as well as smaller lateral dimensions beyond diffraction limit.
