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Updated: Feb 5, 2026
09:23
Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators
Published on: May 30, 2014
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[Trace Moisture Measurement with 5.2 μm Quantum Cascade Laser Based Continuous-Wave Cavity Ring-Down Spectroscopy]
Guang Pu Xue Yu Guang Pu Fen Xi = Guang Pu
|September 21, 2018
Summary
This study demonstrates a new method for detecting trace moisture in high-purity gases using mid-infrared cavity ring-down spectroscopy. The technique achieved a minimum detectable moisture concentration of 24.8 parts per billion by volume (ppbv), crucial for semiconductor manufacturing.
Area of Science:
- Spectroscopy
- Laser Technology
- Gas Analysis
Context:
- Semiconductor manufacturing requires stringent control of trace moisture in high-purity gases, as even parts per billion by volume (ppbv) levels can impact processes.
- Mid-infrared (MIR) spectroscopy offers advantages for trace moisture detection due to abundant and strong water absorption lines.
- Quantum cascade lasers (QCLs) are emerging as powerful, reliable light sources for sensitive spectroscopic measurements.
Purpose:
- To establish and apply a continuous-wave cavity ring-down spectroscopy (CRDS) experimental setup using a 5.2 μm external-cavity tunable QCL for trace moisture detection.
- To optimize the CRDS signal averaging for enhanced sensitivity, determining the optimal number via Allan variance analysis.
- To identify the most suitable spectral line for moisture detection within the 1905–1925 cm⁻¹ range using HITRAN database simulations.
Summary:
- A CRDS system utilizing a 5.2 μm QCL was developed to detect trace moisture in high-purity nitrogen gas.
- Signal averaging optimized to 602 measurements improved sensitivity, and a specific H₂O absorption line at 1918 cm⁻¹ was selected.
- The system achieved a minimum detectable moisture concentration of 24.8 ppbv at 296 K and 1 atm, with results aligning with nominal values.
Impact:
- The developed MIR-CRDS technique demonstrates significant potential for precise trace moisture monitoring in demanding industrial applications.
- This method can be applied to industrial production control, environmental monitoring, and health diagnostics, improving process yields and safety.
- The study highlights the capability of QCL-based CRDS for ultra-sensitive gas analysis, paving the way for advanced detection systems.
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