Terahertz spectrometer spectrometers

TPS can be used for the real-time monitoring of polymeric compounding processes as demonstrated by Krumbholz et An industrial hardened terahertz spectrometer was interfaced with a polymer extruder, allowing for real-time measurement of the additive content in molten polymers (Figure 16.3). 

Figure 10.28. Schematic diagram of the first Cologne terahertz spectrometer [58]. 

Figure 10.29. Schematic diagram of the second Cologne terahertz spectrometer [59]. Details of the comer cube mixer, the mixer-multiplier and the far-infrared laser are not included.

Figure 10.30. Block diagram of the high-frequency terahertz spectrometer designed by Amano [63] and used to observe the lowest rotational transition of the CH radical. 

Figure 1.33 Schematic representation ofa terahertz spectrometer. Reproduced with permission from Ref. [82].

The main barrier to the use of free induction decay for FT spectroscopy in the infrared region is the lack of a convenient powerful source of broadband coherent radiation. In addition, the decay times for the coherently excited polarization in the system tend to be very short at higher frequencies. Coherent terahertz spectrometers operating in the far infrared region are now practical because of the success of ultrafast laser technology in generating broadband terahertz pulses. 

Figure 1.21 Schematic of a terahertz spectrometer. (Reproduced from Ref. [81]. Copyright...

Terahertz radiation lies between the microwave and the infrared regions of the electromagnetic spectrum. Terahertz typically ranges from 0.1 x 1012 to 10 x 1012Hz. One THz is equivalent to 300 microns in wavelength, 1 ps in time, 4.1 meV, and 47.6 K. THz radiation bridges the gap between photonic and electronic devices and offers a large expanse of unused, unexplored bandwidth. Historically, the lack of sources and detectors, as well as the perceived lack of need, had contributed to the dearth of activity in THz. For example, the first commercially available THz spectrometer did not arrive until 2000. 

Circular dichroism has been well understood and estabhshed in the ultra-violet, visible, near- and mid-infrared frequency range as an integral part of contemporary biophysics with numerous, excellent, turnkey instruments commercially available. However, there have been no documented measurements of terahertz circular dichroism. We have developed a simple physical model of circular dichroism in the terahertz frequency range, and build upon our broad band absorption spectrometer to explore the terahertz circular dichroism signatures of prototypical proteins in aqueous solutiom... 

A reflective circular polarizer is used to construct the terahertz circular dichroism spectrometer (Error Reference source not found.). The... 

To calibrate and test the terahertz circular dichroism spectrometer, we successfully measured magnetic terahertz circular dichroism in a semiconductor. A Helmholtz coil was fabricated that produced an axial magnetic field, homogeneous in the transverse direction. A doped,... 

Figure 6. Frequency dependent magnetic circular dichroism in InAs measured by our terahertz circular dichroism spectrometer.

As the absorption bands caused by water vapor (its rotational spectrum) are intense throughout the far-infrared region, it is important to purge efficiently the inside of the spectrometer with dried air or nitrogen. Some commercial spectrometers can be evacuated, but usually their sample compartment needs to be purged with dried air or nitrogen. This is commonly needed also in terahertz time-domain spectrometry, which is described in the following section. 

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