Development of a Spatial Heterodyne Terahertz Raman Spectrometer with Echelle Gratings

This paper introduces an echelle grating spatial heterodyne terahertz Raman spectrometer (E-SHTRS) that combines echelle gratings with spatial heterodyne terahertz Raman spectroscopy technology by replacing the gratings on the interference arms with 36 gr/mm echelle gratings. Echelle gratings are characterized by high diffraction levels and multi-level simultaneous diffraction capability, giving the E-SHTRS higher spectral resolution and a wider detection band range than the conventional spectrometer. The system’s resolution can reach 1.37 cm−1. The spectral detection range of a single level of the proposed system is 701.61 cm−1. A total of nine levels are used in the system, giving a total spectral detection range of 6314 cm−1. Using this system, terahertz Raman spectroscopy of organic acid samples was performed, some food additives and medicines were measured, and a salicylic acid aqueous solution was measured with a minimum measurable concentration of 0.01 mol/L. In addition, the samples were detected over a wide band (10–5131 cm−1) to acquire more complete spectral information. These experiments verify that the E-SHTRS offers good detection performance and has a wide range of possible applications, including a theoretical support role in food safety, biomedicine, environmental protection, and other fields.