Abstract
The values of the nonlinear refractive index coefficient for various materials in the terahertz frequency range exceed the ones in both visible and NIR ranges by several orders of magnitude. This allows to create nonlinear switches, modulators, systems requiring lower control energies in the terahertz frequency range. We report the direct measurement of the nonlinear refractive index coefficient of liquid water by using the Z-scan method with broadband pulsed THz beam. Our experimental result shows that nonlinear refractive index coefficient in water is positive and can be as large as 7×10-10 cm2/W in the THz frequency range, which exceeds the values for the visible and NIR ranges by 6 orders of magnitude. To estimate n2, we use the theoretical model that takes into account ionic vibrational contribution to the third-order susceptibility. We show that the origins of the nonlinearity observed are the anharmonicity of molecular vibrations.
Highlights
Terahertz (THz) frequency range is finding more and more applications in different fields of fundamental research [1] and a variety of everyday applications such as nondestructive spectroscopy [2] and imaging [3], communications [4, 5] and ultrafast control [6] as well as biomedicine [7]
We present the direct measurement of water nonlinear refractive index coefficient for broadband pulsed THz radiation with the conventional Z-scan method
In conclusion we have experimentally demonstrated the possibility of direct measurement of the nonlinear refractive index coefficient n2 of water in the THz frequency range
Summary
Terahertz (THz) frequency range is finding more and more applications in different fields of fundamental research [1] and a variety of everyday applications such as nondestructive spectroscopy [2] and imaging [3], communications [4, 5] and ultrafast control [6] as well as biomedicine [7]. In the first report of such kind of measurements [19] silicon was tested by use of the open aperture Z-scan technique It was predicted theoretically [20] that nonlinear refractive index coefficient for various materials in the THz frequency range exceeds the ones in both visible and NIR ranges by several orders of magnitude. This fact was proven experimentally by the Z-scan method [21, 22]. We present the direct measurement of water nonlinear refractive index coefficient for broadband pulsed THz radiation with the conventional Z-scan method. We demonstrate that the nonlinear refractive index exceeds its visible and NIR ranges’ values by 6 orders of magnitude [25,26,27,28]
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