Determination of refractive indices and absorption coefficients of highly purified N-benzyl-2-methyl-4-nitroaniline crystal in terahertz frequency regime

We have measured the refractive index and absorption coefficient of the N-benzyl-2-methyl-4-nitroaniline crystal using terahertz time-domain spectroscopy. We found that the refractive index had a value between 1.5 and 1.9 in the (100) direction and between 1.9 and 2.3 in the (100) direction. We also found that there were resonances at 1.6 and 3.2 THz in the (100) direction, and 1.3, 2.2, and 3.6 THz in the (001) direction within the observed spectral range between 0 and 5 THz. A Lorentz-type oscillator model is applicable to explain our experimental observations.