Single frequency lasers have long been the cornerstone of standoff gas detection, particularly in both traditional LIDAR (Light Ranging and Detection), DIAL (Differential Absorption LIDAR), and TDLAS (Tunable Diode Laser Absorption Spectroscopy). More recently as single frequency laser diodes have become more common and less expensive they are being utilized in more localized and industrial gas sensing applications as well. These compact laser absorption gas sensors, which may depend on either passive air flow of vacuum suction, are rapidly replacing the older plasma emission systems, particularly for single species detection.
A large number of the molecules of interest for gas sensing have strong absorption in the near infrared region for example; O2 at 760 nm, NH2 at 1512 nm, H2O at 1392 nm & 1877 nm, CH4 at 1654 nm, and CO2 at 2004 nm. As a result, Eblana Photonics‘ propitiatory Discrete Mode (DM) single frequency laser diode technology is an ideal solution for this application, available in wavelengths from 760 nm up to 2150 nm.
Eblana‘s DM laser technology platform delivers distributed feedback (DFB) laser like performance at a lower price point geared toward higher volume applications. Their strained quantum well InP design provides stable, high performance, single wavelength operation and a wide current tuning range even at sub-mW laser powers.
In DM laser diodes single frequency operation is achieved by introducing index perturbations etched into a few specific locations along the waveguide. This manipulates the Fabry-Pérot cavity loss, resulting in the enchantment of one longitudinal mode and the suppression of all others. As can be seen in the figure below (cutesy of Eblana Photonics‘ white paper “Discrete Mode Laser Diodes with Ultra-Narrow Linewidth Emission“) this results in a single-mode output spectrum with >40dB side-mode suppression ratio (SMSR). To ensure similar performance from a DFB laser with a stable single frequency operation and yield requires asymmetric or low reflectivity coated laser facets, which can induce either modal instability or linewidth broadening.
At RPMC Lasers we are currently offer these lasers in a wide variety of packages including 14-pin butterfly with integrated TEC and optical isolator, a 14-pin butterfly with lens-ended butt-coupled fiber, or a free space package with TEC. They are also available as an OEM module incorporating a built-in driver and TEC controller.