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Abstract Electro‐optic sampling has emerged as a new quantum technique enabling measurements of electric field fluctuations on subcycle time scales. In a second‐order nonlinear material, the fluctuations of a terahertz field are imprinted onto the polarization properties of an ultrashort probe pulse in the near infrared. The statistics of this time‐domain signal are calculated, incorporating the quantum nature of the involved electric fields right from the beginning. A microscopic quantum theory of the electro‐optic process is developed adopting an ensemble of noninteracting three‐level systems as a model for the nonlinear material. It is found that the response of the nonlinear medium can be separated into a conventional part, which is exploited also in sampling of coherent amplitudes, and quantum contributions, which are independent of the state of the terahertz input. Interactions between the three‐level systems which are mediated by terahertz vacuum fluctuations are causing this quantum response. Conditions under which the classical response serves as a good approximation of the electro‐optic process are also determined and how the statistics of the sampled terahertz field can be reconstructed from the electro‐optic signal is demonstrated. In a complementary regime, electro‐optic sampling can serve as a spectroscopic tool to study the pure quantum susceptibilities of matter.
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Efficient on-chip terahertz generation and detection with GaN photoconductive emitters
Abstract Photoconductive emitters for terahertz generation hold promise for highly efficient down-conversion of optical photons because it is not constrained by the Manley-Rowe relation. Existing terahertz photoconductive devices, however, faces limits in efficiency due to the semiconductor properties of commonly used GaAs materials. Here, we demonstrate that large bandgap semiconductor GaN, characterized by its high breakdown electric field, facilitates the highly efficient generation of terahertz waves in a coplanar stripline waveguide. Towards this goal, we investigated the excitonic contribution to the electro-optic response of GaN under static electric field both through experiments and first-principles calculations, revealing a robust excitonic Stark shift. Using this electro-optic effect, we developed a novel ultraviolet pump-probe spectroscopy for in-situ characterization of the terahertz electric field strength generated by the GaN photoconductive emitter. Our findings show that terahertz power scales quadratically with optical excitation power and applied electric field over a broad parameter range. We achieved an optical-to-terahertz conversion efficiency approaching 100% within the 0.03–1 THz bandwidth at the highest bias field (116 kV/cm) in our experiment. Further optimization of GaN-based terahertz generation devices could achieve even greater optical-to-terahertz conversion efficiencies.
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- Award ID(s):
- 2414287
- PAR ID:
- 10609303
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Light: Science & Applications
- Volume:
- 14
- Issue:
- 1
- ISSN:
- 2047-7538
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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