Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

Abstract

With the ongoing proliferation of terahertz time-domain instrumentation from semiconductor physics into applied spectroscopy over the past decade, measurements at terahertz frequencies (1 THz [ 10 12 Hz [ 33 cm À1) have attracted a sustained growing interest, in particular the investigation of hydrogen-bonding interactions in organic materials. More recently, the availability of Raman spectrometers that are readily able to measure in the equivalent spectral region very close to the elastic scattering background has also grown significantly. This development has led to renewed efforts in performing spectroscopy at the interface between dielectric relaxation phenomena and vibrational spectroscopy. In this review, we briefly outline the underlying technology, the physical phenomena governing the light-matter interaction at terahertz frequencies, recent examples of spectroscopic studies, and the current state of the art in assigning spectral features to vibrational modes based on computational techniques.

Invited Article: An active terahertz polarization converter employing vanadium dioxide and a metal wire grating in total internal reflection geometry

“…[1][2][3][4][5] A key element in the growing interest of the terahertz field has been the continued improvement in the development of robust terahertz sources and detectors, such as the air-plasma techniques pioneered over the last decade, 6,7 which have unlocked ever higher powers and broader spectral ranges. However, there is still a lack of active THz polarization-manipulation components, including THz waveplates and polarizers, that are able to work across wide frequency bands.…”

Boson peak dynamics of glassy glucose studied by integrated terahertz-band spectroscopy

“…Recent researchers have regarded the BP as the broad peak appearing in the imaginary part of the complex dielectric constant ε (ν) in the THz region [44][45][46], although the name of the broad peak has recently been changed to the "VDOS peak" [47]. In order to understand how the BP appears in the IR spectra, we must consider the following relation derived from the linear response theory for disordered materials [48]:…”

Raman Spectroscopy of Pharmaceutical Cocrystals in Nanosized Pores of Mesoporous Silica

“…[18][19][20][21][22][23][24][25] Recent improvements in optical filters make it possible to extract small Raman shifts and directly distinguish intermolecular bonds in addition to intramolecular bonds. 26,27 Moreover, Raman peak deformations in intramolecular bonds reveal the adsorption of molecular crystals on the surfaces, 28,29 which play an important role in cocrystallization in porous materials. By following the Raman peak of the fingerprint band, the transformation of carbamazepine and cocrystallization with nicotinamide has been investigated.…”