Abstract

A cw narrow-linewidth tunable mid-IR coherent source has become a useful tool for trace gas detection since almost all gases exhibit fundamental ro-vibrational absorption lines with high absorption strength in the mid-IR. This particular source is obtained by a difference frequency generation (DFG) technique which is that two near-IR laser pump sources (λ₁, λ₂) are mixed to generate mid-IR (λ₃ = (1/λ₁−1/λ₂)⁻¹) in a quasi-phase-matched (QPM) nonlinear optical crystal such as a periodically poled LiNbO₃ (PPLN) in single-pass geometry. Such spectroscopic source can operate at room temperature with single spatial mode, single frequency and tunable in wide frequency region without mode hop. This paper reports an experimental study of a fiber laser ^l−2 (1064 nm) based mid-IR generation to detect NO₂. This DFG source is applied to NO₂ detection which is of interest in various applications such as combustion, environmental trace gas monitoring. This work reports the demonstration of a fiber laser pumped DFG based mid-IR source for trace gas sensing, and the detection of NO₂ line at ~3.5 μm with a high-resolution DFG spectroscopic source with a PPLN crystal.

© 2002 Optical Society of America