Abstract
Attenuation of ultrashort THz pulses poses a significant technological challenge due to the broadband nature of such light pulses. Several methods exist for this purpose, including crossed wire grid polarizers, high refractive index, high resistivity silicon wafers, and ultrathin metal films. In this review, we discuss the operational principles of these methods, and highlight some of the advantages and potential pitfalls of the methods. We describe the limits of high-frequency operation of wire grid polarizers, relevant for contemporary ultra-broadband THz sources in air photonics. We discuss the effects of multiple reflections and interference in sequences of silicon wafers for attenuation, and finally discuss the potential of using ultrathin metallic films for broadband attenuation.
Highlights
Technological developments in the past years has made it possible to use commercial table-top femtosecond laser systems to generate intense, ultrashort THz pulses in the 0.1–5-THz range with focused field strengths in the megavolt/centimeter range, and pulse energies from microjoules towards millijoules and beyond from inorganic and organic nonlinear crystals [1,2,3]
We describe the limits of high-frequency operation of wire grid polarizers, relevant for contemporary ultra-broadband THz sources in air photonics
A pair of freestanding wire grid polarizers can perform this task as long as the THz signal has its spectral components within the high extinction range of the wire grids, when wavelength is much larger than the wire spacing
Summary
Technological developments in the past years has made it possible to use commercial table-top femtosecond laser systems to generate intense, ultrashort THz pulses in the 0.1–5-THz range with focused field strengths in the megavolt/centimeter range, and pulse energies from microjoules towards millijoules and beyond from inorganic and organic nonlinear crystals [1,2,3] Such coherent THz pulses are used to investigate nonlinear interactions between strong, ultrafast THz fields and virtually all material types, including a few examples of studies of dielectrics [4,5,6], semiconductors, metals [7, 8], magnetic materials [9], 2D materials [10], liquids [11, 12], and gases [13]. An alternative method for broadband, high-fidelity attenuation of THz signals is to make use of reflection losses from a sequence of high-index dielectrics such as high-resistivity silicon (HR Si) [18, 19] In this case, internal substrate reflections will play a major role in the transmission properties. We show that for frequencies well below the inverse scattering time of the free electrons in the metal, films with thicknesses in the nanometer range offer broadband and relatively uniform attenuation of broadband THz beams
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