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Updated: Feb 12, 2026
10:54
Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters
Published on: July 8, 2013
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Doppler-free spectroscopy with a terahertz quantum-cascade laser.
Optics Express
|April 4, 2018
Summary
We demonstrate Doppler-free saturation spectroscopy of a molecular transition at 3.3 THz using a quantum-cascade laser. This technique achieved a sub-Doppler linewidth of 170 kHz for a HDO rotational transition, showing tolerance to optical feedback.
Area of Science:
- Molecular Spectroscopy
- Quantum Cascade Lasers
- Terahertz (THz) Technology
Background:
- Precise molecular spectroscopy is crucial for various scientific and industrial applications.
- Quantum cascade lasers (QCLs) offer tunable THz emission, enabling new spectroscopic techniques.
- Sub-Doppler spectroscopy resolves narrow spectral lines, improving measurement accuracy.
Purpose of the Study:
- To perform Doppler-free saturation spectroscopy on a molecular transition at 3.3 THz.
- To investigate the linewidth and characteristics of the observed spectral feature.
- To assess the impact of external optical feedback on the spectroscopy.
Main Methods:
- Utilized a quantum-cascade laser source.
- Employed Doppler-free saturation spectroscopy in a collinear pump-probe setup.
- Used an absorption cell containing HDO (heavy water) for the molecular transition.
Main Results:
- Observed a Lamb dip, indicative of sub-Doppler resolution.
- Achieved a narrow linewidth of 170 kHz for a rotational transition of HDO.
- Determined that external optical feedback is tolerable under specific conditions related to the free spectral range of the external cavity.
Conclusions:
- Doppler-free saturation spectroscopy with QCLs is effective for high-resolution THz molecular spectroscopy.
- The observed sub-Doppler linewidth demonstrates the precision of the technique.
- The findings provide guidelines for implementing THz spectroscopy systems with QCLs in the presence of optical feedback.
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