Terahertz Frequency Metrology for Spectroscopic Applications: a Review

Abstract

We provide an overview on terahertz (THz) frequency metrology, starting from the nowadays available continuous wave THz sources, discussing their main features such as tunability, spectral purity, and frequency referencing to the primary frequency standards. A comparison on the achieved results in high-precision molecular spectroscopy is given and discussed, and finally, a special emphasis poses on the future developments of this upcoming field.

A methodology for sorting haploid and diploid corn seed using terahertz time domain spectroscopy and machine learning

“…This method provides a small bandwidth continuous THz wave that is tunable according to the frequencies of the pump lasers. Ferguson and Zhang (2002) and Consolino et al (2017) provide good reviews of modern CW sources and their applications to molecular spectroscopy.…”

QCL-based frequency metrology from the mid-infrared to the THz range: a review

“…The so-called terahertz spectrum, also known as far-IR, conventionally spans the frequency range from 0.1 to 10 THz, corresponding to the wavelength interval from 30to 3000-μm wavelength. Historically, this region is known as "terahertz gap", due to the lack of sufficiently strong and compact sources and sensitive detectors [17]. One of the oldest applications of terahertz radiation is spectroscopy.…”

“…Efficient nonlinear generation of mid-IR and THz radiation with excellent spectral properties, performed since the 1980s of the XXth century, opened the way to metrological research in these spectral regions [16,17]. However, the optical power available for experiments and the complexity of such setups were not suitable for compact and practical applications.…”

Study of glucose concentration influence on blood optical properties in THz frequency range

“…Currently, terahertz time-domain spectroscopy (THz TDS) and imaging techniques are applied in various fields such as astronomy, security screening, communications, genetic engineering, pharmaceutical quality control, medical imaging and biomedical engineering [1][2][3][4].…”