Widely-Tunable Quantum Cascade-Based Sources for the Development of Optical Gas Sensors

Area of Science:

• Optics and Photonics
• Spectroscopy
• Laser Technology

Background:

• Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs) are effective for gas detection due to high sensitivity and selectivity in the mid-infrared region.
• A key limitation of DFB QCLs is their narrow tuning range (~10 cm⁻¹), restricting the analysis of complex molecules with broad absorption spectra and multi-gas sensing capabilities.

Purpose of the Study:

• To overcome the tuning range limitation of DFB QCLs for enhanced gas sensing applications.
• To present novel Quantum Cascade Laser (QCL) based sources with significantly wider tuning ranges.

Main Methods:

• Utilizing a DFB QCL array to achieve wider tuning ranges, demonstrated between 1335-1387 cm⁻¹ and 2190-2220 cm⁻¹.
• Implementing a Fabry-Perot QCL chip in an external-cavity (EC) system to tune across the entire gain curve.
• Employing Intra-Cavity Laser Absorption Spectroscopy (ICLAS) with the EC system, placing the gas sample within the laser resonator.
• Leveraging the QCL compliance voltage technique for gas spectrum retrieval without external detectors.
• Developing a scheme using an EC coherent QCL array.

Main Results:

• Demonstrated tuning ranges of 1335-1387 cm⁻¹ and 2190-2220 cm⁻¹ using DFB QCL arrays.
• External-cavity systems enable tuning over the entire QCL gain curve.
• Intra-cavity laser absorption spectroscopy combined with compliance voltage measurements allows for sensitive gas detection without external detectors.

Conclusions:

• Widely tunable Quantum Cascade Laser (QCL) based sources, including DFB QCL arrays and external-cavity configurations, significantly enhance gas sensing capabilities.
• These advanced QCL sources pave the way for the development of more versatile and effective optical gas sensors for various applications.