Abstract
The refractive indices of ordinary and extraordinary waves (no and ne) of congruent LiNbO3 (CLN) in the terahertz (THz) band are measured at different temperatures. Extended Cauchy equations are proposed to describe the temperature- and frequency-dependent refractive indices. With less than 0.5% deviation, both no and ne can be obtained accurately. The values of no and ne are ~7 and ~5.4, respectively, which are much larger than those in the visible band. The extremely high birefringence (~1.6) may lead to some interesting applications of linear, electro-optic, and nonlinear optical effects of CLN. As an example, true zero-order THz waveplates (WPs) could be obtained with considerable low loss based on thin CLN wafers. The working frequency can be tuned by changing the environmental temperature. Moreover, wide bandwidth achromatic THz WPs were also achievable by stacking four CLN wafers together with precise orientation control.
Highlights
Terahertz (THz) waves, having frequencies between those of microwaves and infrared light, typically are defined as electromagnetic waves in the frequency band of 0.1–10 THz
As a result of the increasingly important applications of THz waves, some impressive attempts to generate THz sources have been carried out using difference frequency generation, optical rectification, and photoconductive antennas [3,4,5,6]
The result may represent the most accurate refractive index equation of congruent LiNbO3 (CLN) in the THz band because the largest deviation is less than 0.5%
Summary
Terahertz (THz) waves, having frequencies between those of microwaves and infrared light, typically are defined as electromagnetic waves in the frequency band of 0.1–10 THz. X. Kärtner, “Temperature dependent refractive index and absorption coefficient of congruent lithium niobate crystals in the terahertz range,” Opt. Express 23(23), 29729– 29737 (2015). The results were able to be well fitted by temperature- and frequency-dependent extended Cauchy equations.
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