Tunable frequency converter for terahertz frequency range based on space-time transformation

The analytically realization of electromagnetic wave frequency conversion in a time-varying medium was shown by the two methods. The first method considers the optical analog of the electromagnetic wave redshift in the expanding universe using the transformation optics mathematical approach. The second one describes the transient process of pulse electromagnetic wave interaction with the time-varying medium using method of the second order Volterra integral equation. The frequency conversion was shown for several types of commercial laser wavelengths.