Abstract
Efficient terahertz and photoelectron emission were observed from nano-porous gold (NPG) films deposited on an intrinsic gallium arsenide (GaAs) semiconductor substrate stimulated by femtosecond laser with pulse width of 60 fs. Time-domain THz emission and reflection spectroscopy confirmed that the free charges accelerated by irradiated femtosecond laser pulses transferred from the NPG films into the GaAs substrates. Accordingly, charges accumulation was reduced in the NPG films, resulting in a stronger emission of THz pulse than that from NPG films deposited on SiO2 substrate. Charges injected into the GaAs substrate enforced an observable decrease of the THz refractive index proportional to the intensity of incident light. In comparison, for NPG deposited on glass substrates, laser induced free charges were accumulated in the NPG films, and femtosecond laser pulses irradiating on the NPG films made no changes of the THz refractive index of the glass substrates.
Highlights
Much effort has been devoted to developing compact and efficient terahertz (THz) sources, and especially with the development of ultrafast nonlinear optics and material science, THz technology has enabled intriguing applications in spectroscopy, imaging and sensing
Surface-plasmon excitation on a glass grating coated with 30-nm gold films [13], and metamaterials composed of split-ring resonators (SRRs) in 40-nm gold films [14] were applied to generate efficient THz emission, wherein photoelectron accelerations and optical rectifications were engineered by surface-plasmon structures
We report on experimental demonstration of efficient terahertz emission from nano-porous gold (NPG) films deposited on an intrinsic gallium arsenide (GaAs) substrate with electron mobility of ~5300 cm2/V/s
Summary
Much effort has been devoted to developing compact and efficient terahertz (THz) sources, and especially with the development of ultrafast nonlinear optics and material science, THz technology has enabled intriguing applications in spectroscopy, imaging and sensing. Liquids and gases have been applied to generate broadband and high-energy THz pulses driven by high-intensity ultrafast lasers [1,2,3,4]. Weak THz emission was observed from ultrathin gold films with thickness of 100 nm, as reported by Kadlec’s subsequent work [12]. Based on their investigation, Kadlec suggested that accumulated charges near the metal–glass interface formed electric field opposite to the initial current at the origin of THz generation, which eventually damped optical rectification for THz emission. Photoelectron emissions from the metallic surface are intrinsically not affected and there still exists inhomogeneous charge accumulation on the metallic nano-films
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