Measurement of the complex refractive index of liquids and biological substances in the terahertz range at the NovoFEL facility

Terahertz ellipsometric measurement system has been commissioned with the Novosibirsk free electron laser being a source of monochromatic radiation. The highest precision of {ψ, Δ} ellipsometric parameters have been achieved for the THz range (0.3° for ψ, 0.01 for cos(Δ)). Complex refractive index of various liquids has been measured in the THz range using the ellipsometer with a silicon-prism internal reflection system. Since the characterization of biologically important highly absorbing substances is one of the important applications for the THz ellipsometry, the measurement technique has been optimized both theoretically and experimentally for water solutions. Precision of the measurement of the absolute values of the real and imaginary parts of the refractive index (n, k) equal to 0.01 is achieved experimentally.