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A modified Z-scan method was used to achieve polarization-resolved measurement of nonlinear properties of undoped bulk GaP excited by a femtosecond laser at 1040 nm. The optical Kerr nonlinearities of ⟨100⟩-, ⟨110⟩- and ⟨111⟩-cut GaP slabs were characterized experimentally at room temperature. The open aperture Z-scan curves demonstrate that three-photon absorption in GaP dominates the nonlinear absorption processes under the experimental conditions. In addition, experimental results show that both three-photon absorption and Kerr nonlinearity of undoped GaP possess the same anisotropy and crystal orientation dependence.

Abstract:We introduce a novel method for retrieving the phase from a spectral shearing interferogram, based on wavelet-transform technique. We demonstrate with both theoretical and experimental data that this technique provides an alternative and reliable technique for phase retrieval, particularly for highly structured pulse spectra.

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We report a simple, broadband and high-absorbance coating for terahertz radiometry. The spectral properties of this coating in THz region were characterized with a home-made terahertz time-domain spectrometer. The measured spectral reflectance is less than 0.3% ranging from 0.2 THz to 0.5 THz and less than 0.1% ranging from 0.5 THz to 2.0 THz. We assembled a terahertz radiometer with this coating as absorber, and discussed its heat transfer in comparison with that of a carbon nanotube array radiometer. This coating is highly absorptive both in terahertz region and in visible light; therefore, the responsivity of this radiometer is easily traceable to National Laser Power Standards. This coating is easily fabricated. It is useful in traceability of terahertz sources and detectors to the SI units.