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Bias-Modulated Nanoscale Terahertz Linear and Nonlinear Spectroscopy

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Technical Report,01 Aug 2018,30 Apr 2019

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Brown University Providence United States

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Major Goals In the last few years, imaging below the diffraction limit has become one of the most active topics in the field of terahertz science. A key development that has enabled these results is the use of a metal tip, such as the tip in an atomic force microscope AFM. This tip can be held in close proximity perhaps 10 nm to a sample surface, and illuminated from the far field with terahertz radiation. The scattering of light off this tip-sample junction is sensitive to the dielectric properties of the region of the sample directly underneath the tip, so nanoscale dielectric information can be extracted from the signal. We have recently broadened the scope of this technique to include nonlinear terahertz spectroscopy in the near field. Instead of illuminating the tip with a terahertz signal, we use a near-infrared 800 nm femtosecond pulse as the illumination source, and measure the THz radiation generated by the sample, in the vicinity of the AFM tip. Laser THz emission microscopy LTEM is a well-known and powerful tool for ultrafast spectroscopy. Our new results have translated this nonlinear technique into the nanoscale, as a complementary tool to our existing THz scattering microscope. Here, we propose an exploratory project under the Short-Term Innovative Research STIR program, to develop a potentially transformative advance for these existing nanoscopy tools. We will investigate the use of a DC bias applied to the AFM tip as a means for modulating the samples properties on the nanoscale. A large static DC field can have several different effects on the photophysics of condensed matter systems. In semiconductors, DC fields can induce carrier depletion as a field effect, or carrier multiplication through avalanche charge generation. In addition, a static electric field can cause a non-resonant modification of a samples dielectric function through the DC Kerr effect.

Subject Categories:

  • Atomic and Molecular Physics and Spectroscopy
  • Optics
  • Atomic and Molecular Physics and Spectroscopy
  • Optics

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