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Updated: Jun 26, 2026

Multiplex Chemical Imaging Based on Broadband Stimulated Raman Scattering Microscopy
Published on: July 25, 2022
Intersubband gain-induced dispersion.
Wolfgang Parz1, Thomas Müller, Juraj Darmo
1Institute for Photonics, Vienna University of Technology, Vienna, Austria. wolfgang.parz@tuwien.ac.at
We precisely measured the optical properties of a mid-infrared quantum cascade laser. This revealed significant group-velocity dispersion, impacting pulse formation and enabling active region temperature monitoring.
Area of Science:
- Optics and Photonics
- Semiconductor Lasers
Background:
- Quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
- Understanding their optical properties is key to optimizing performance.
- Accurate characterization of the gain medium is essential for laser design.
Purpose of the Study:
- To precisely determine the effective refractive index and extinction coefficient of a mid-infrared QCL gain medium.
- To investigate the group velocity dispersion (GVD) and its impact on laser dynamics.
- To measure the active region temperature and its dependence on operational parameters.
Main Methods:
- Utilizing time-resolved transmission spectroscopy.
- Iterative retrieval of optical constants (refractive index, extinction coefficient).
- Exploiting the thermo-optic effect for temperature measurements.
Main Results:
- Achieved high accuracy (+/-7x10(-3)) in retrieving optical constants over a broad spectral range.
- Observed a 3% slowdown in group velocity.
- Discovered significant, sign-changing induced group-velocity dispersion near the gain maximum.
- Demonstrated a linear relationship between active region temperature and current/duty cycle.
Conclusions:
- The retrieved optical properties provide critical data for mid-infrared QCL design.
- The observed GVD has significant implications for self-pulse formation dynamics in QCLs.
- The thermo-optic method offers a reliable way to monitor active region temperature.
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