Broadband terahertz generation using the semiconductor-metal transition in VO2

Nicholas A Charipar,Heungsoo Kim,Alberto Piqué,Scott A Mathews

doi:10.1063/1.4941042

Nicholas A Charipar, Heungsoo Kim + Show 2 more

Open Access

https://doi.org/10.1063/1.4941042

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Journal: AIP Advances	Publication Date: Jan 1, 2016
Citations: 19	License type: cc-by

Affiliation: United States Naval Research Laboratory

Abstract

We report the design, fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2 (vanadium dioxide). With the appropriate geometry, picosecond electrical pulses are generated by illuminating 120 nm thick VO2 with 280 fs pulses from a femtosecond laser. These ultrafast electrical pulses are used to drive a simple dipole antenna, generating broadband terahertz radiation.

Highlights

Terahertz radiation is defined as the portion of the electromagnetic spectrum from 300 GHz to 3 THz
Fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2
In this work we demonstrate photoconductive VO2 terahertz emitters that exploit the ultrafast semiconductor-metal transition (SMT) in VO2, rather than the nonlinear effects recently reported by Esaulkov et al.[20]

Summary

INTRODUCTION

Terahertz radiation is defined as the portion of the electromagnetic spectrum from 300 GHz to 3 THz. A femtosecond laser pulse alters the conductivity of the material in the gap by creating free charge carriers, where the DC field accelerates these excited carriers This results in an electrical pulse with a fast rising edge; in photoconductive materials, the turn off time is limited by carrier trapping and recombination time. VO2 exhibits a phase change at ≈ 68 oC, during which the crystal lattice changes from a monoclinic-M1 to a rutile R-phase,[12] with a simultaneous large decrease in resistivity This semiconductor-metal transition (SMT) can be induced thermally, electrically, or optically.[13] Optically pumped terahertz probe spectroscopy has been used to measure both the switching time and the time dependent conductivity in VO2.14,15 These measurements indicate that the structural distortion associated with the SMT can occur on time scales less than 100 fs.[16]. In this work we demonstrate photoconductive VO2 terahertz emitters that exploit the ultrafast SMT in VO2, rather than the nonlinear effects recently reported by Esaulkov et al.[20]

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS