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Updated: Oct 9, 2025
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Microwave Photonics Systems Based on Whispering-gallery-mode Resonators
Published on: August 5, 2013
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Field-resolved high-order sub-cycle nonlinearities in a terahertz semiconductor laser.
Light, Science & Applications
|December 20, 2021
Summary
Ultrafast two-dimensional spectroscopy reveals sub-cycle electron dynamics in quantum cascade lasers (QCLs). This breakthrough quantifies nonlinear polarization dynamics and short gain recovery times, paving the way for advanced terahertz (THz) applications.
Area of Science:
- Physics
- Quantum Optics
- Terahertz (THz) Science
Background:
- Quantum cascade lasers (QCLs) are promising for advanced terahertz (THz) applications.
- Accessing sub-cycle electron dynamics in operational THz QCLs has been challenging.
- Ultrafast dynamics are crucial for developing intense THz sources and metrology systems.
Purpose of the Study:
- To investigate ultrafast electron dynamics in free-running THz QCLs.
- To characterize nonlinear polarization dynamics and gain recovery times.
- To explore potential applications in THz generation and metrology.
Main Methods:
- Employed high-field THz pulses for ultrafast two-dimensional spectroscopy on a THz QCL.
- Detected incoherent and coherent nonlinearities up to eight-wave mixing.
- Utilized a density-matrix approach to model nonlinearities and ultrafast evolution.
Main Results:
- Observed strong nonlinearities below and above the laser threshold.
- Measured extremely short gain recovery times of 2 ps at the laser threshold.
- Quantified dephasing times between 0.9 and 1.5 ps, revealing nonlinear polarization dynamics.
Conclusions:
- The study provides the first direct measurement of nonlinear polarization dynamics in THz QCLs.
- High-order nonlinearities are enhanced by resonance and lack of absorption losses.
- Findings enable future applications like efficient frequency conversion, mode proliferation, and passive mode locking in THz QCLs.
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