Research On Bio-molecules Based On Terahertz Spectroscopy And Density Functional Theory

Terahertz is known as far-infrared radiation or millimeter wave andsub-millimeter wave. With the development of ultrafast laser technology, a kind ofnew THz pulse laser source which is stable and reliable has been designed to leadthe application of the THz radiation more widely. THz time domain spectroscopyas a coherent and emerging measurement technology， has the advantages of highersignal-to-noise ratio in the range from0to3THz and without low temperaturedetection device. Combined with Fourier transform infrared spectroscopy, thecomplementary advantages of two kinds of technology have been realized. It iswell known that biological molecules has colorful information of vibration androtational transition level on THz spectrum, and the THz radiation has advantagessuch as low energy, strong penetrability, no damage to the structure and activity ofbiological molecules, and so on. THz technology has been widely used in the fieldof non-destructive testing. In this paper, we employ THz time-domain spectroscopyand Fourier transform infrared spectroscopy to measure the spectrum of vitamin,chlorophyll and pine needle samples, and make the theoretical explanations forformation mechanism of fingerprinting.Main content of the paper is as followsFirst, we employed THz time-domain spectroscopy and Fourier transform infraredspectroscopy to study the THz spectrum of L-ascorbic acid, thiamine andchlorophyll samples. Detailed discussions about the absorption spectrum andrefractive index of pure samples, the absorption spectrum of sample which aremixed with dispersing agent polyethylene in various proportions have been made.The results of the study provide an important experimental basis for the preparationand testing of biological samples.Second, we simulated THz absorption spectrum of the L-ascorbic acid, thiamineand chlorophyll molecular by using density function theory (DFT) in quantumchemical analysis software Gaussian. The frequency vibrational spectrum wasobtained under a stable configuration and for comparison with the experimentalspectrum.Third, we studied the absorption spectrum and refractive index of pine needlesamples in different period with THz time-domain spectroscopy, and found therelationship between the intensity of absorption spectrum, refractive index with thechlorophyll content of pine needles samples. Fourth, we design a terahertz coupling circuit in the range from0.9to1.3THz. Inthe specific frequency range, coupling efficiency and sensitivity of detector hasbeen improved. It has certain theoretical significance for the design of THzspectroscopy system in detector.