Two decades of terahertz cross-correlation spectroscopy.

Terahertz cross-correlation spectroscopy enables phase-sensitive measurements without the need for a laser source and, hence, presents a cost-efficient and versatile alternative to common terahertz time-domain spectroscopy approaches. This review article presents the development of this technique over the past two decades as well as applications of this approach. It is completed by a detailed mathematical description proving the irrelevance of the optical phases of the employed pump light modes. Numerical investigations of the resulting signal demonstrate the applicability and are compared to state-of-the-art measurements. Terahertz cross-correlation spectroscopy is a valuable alternative for moderate-demand applications already. Further possible improvements are discussed. [ABSTRACT FROM AUTHOR]