Abstract
Modern sources of THz radiation generate high-intensity pulses allowing to observe nonlinear effects in this spectral range. To describe many nonlinear effects theoretically, it is necessary to know the nonlinear refractive index coefficient of optical materials. The work studies the applicability of the Z-scan method to determine the nonlinear refractive index coefficient in the THz frequency range for few-cycle pulses. We have discussed the correctness of the known Z-scan method for calculating the nonlinear refractive index coefficient for broadband THz radiation regarding number of cycles pulses have. We have demonstrated that the error in determining the nonlinear refractive index coefficient is always greater than 70% for true single-cycle pulses. With the increase in the number of oscillations to the measurement error shows strong dependence on the sample thickness and can vary from 2% to 90% regarding the parameters chosen. The fact that such radiation dispersion length is commensurate with the nonlinear length or even less than the latter results in the discrepancy mentioned. It is demonstrated that the decrease in the sample thickness leads to the reduction of the nonlinear refractive index coefficient determination error, and this error is <2% when the ratio between the sample thickness and the pulse longitudinal spatial size is ≤1. This can relate to the fact that the nonlinear effects in such a thin sample occur faster than the dispersion ones.
Highlights
The study of the terahertz (THz) frequency range of optical radiation is one of the developing and promising scientific fields
It is shown that for non-single-cycle pulses, the Z-scan for broadband THz radiation correlates with the analytics of this method for monochromatic radiation well
Regardless of the central wavelength of the radiation, an increase in the error of n2 measurement with an increase in the sample thickness is observed for pulses with 1.5–3 cycles. n2 measurement error can be as large as 90% in this case
Summary
The study of the terahertz (THz) frequency range of optical radiation is one of the developing and promising scientific fields. There are sources of pulsed THz radiation with energy in a single pulse up to 1 mJ have appeared[10,11], i.e., the peak values of the electric field can reach values up to hundreds of MV/cm[12]. The first works on preliminary experiments estimating n2 coefficient using the Z-scan technique in THz spectral range clearly showed the presence of a significant nonlinear effect[31,32]. The application of the Z-scan method raises several questions since the spectrum of pulsed THz sources is even wider than femtosecond one[33] and its electric field can have few cycles only[34,35]. This work is devoted to the theoretical study of the Z-scan method applicability for evaluating n2 coefficient of isotropic transparent materials in the field of broadband few-cycle THz pulses. The latter has a constanly high value for true single-cycle pulses and depends on the ratio of the sample thickness and spatial size of THz pulse for 1.5–3 cycle ones
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
