Terahertz Spectroscopy is characterized by the electromagnetic radiation with frequencies in the range from 0.1 to 20 THz (~ 3.3 to 667 cm-1). Due to instrumental limitations, this spectral region was known as the "terahertz gap", and for many years it remained unexplored. The low and high frequency borderlines were limited by electronic and optical devices of generation of radiation, respectively.The energy involved in terahertz radiation is responsible for both vibrational and rotational transitions. Low energy vibrational modes, such as long-range phonon vibrations in crystalline solids and intermolecular modes, are usually located at this spectral region. Thus, important information regarding structural properties of several systems in which intermolecular interactions play an important role can be investigated using terahertz spectroscopy. The study of biomolecules such as proteins, nucleic acids and polysaccharides, along with the discrimination of crystalline forms in pharmaceuticals, are just some of the examples of the potential of this technique.Currently, there are several ways to generate and detect THz radiation. Time- Domain THz Spectrometers (THz-TD), which operate using a Ti:Sapphire laser with 10-100 fs pulses, are certainly the most widespread technology. The incidence of a femtosecond pulse on a photoconductive antenna, usually made of GaAs or ZnTe, yields a THz pulse, which typically ranges from 0.1 to 4.0 THz. Instruments based on the High Speed Asynchronous Optical Sampling Technology employ a pair of Ti:Sapphire oscillators, and yield the best results in terms of signal-to-noise ratio, resolution, sensitivity and rapid data acquisition. Unfortunately, this technology is very expensive, and its operation is far too complex for it to be handled by technicians. Thus, routine analyses are not possible with this kind of equipment. Continuous-wave (CW) THz spectrometers, on the other hand, present both lower cost and operational simplicity. The generation of THz radiation in those instruments is made by photomixing two CW lasers beams on a low temperature grown photoconductive antenna. The frequency of the emitted THz beam is given by wavelength difference between the lasers. Thus, a frequency scan can be made by tuning one of the lasers at selected wavelengths.In this work, the development and evaluation of a THz spectrometer based on CW lasers is proposed, which will present a much lower cost than the THz-TD spectrometer. Analytical methods for determination of sugars and discrimination of different crystalline forms of pharmaceuticals will be evaluated using the proposed instrument. Initially, the methods will be developed employing the THz-TD spectrometer recently installed in the Chemistry Institute at the State University of Campinas (UNICAMP). Once properly evaluated, the analytical methods will be tested with the CW THz spectrometer. If a particular method yields promising results and its application is relevant in terms of demand, the development of the instrument will be directed to such application.
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