Progress toward a water-vapor differential absorption lidar (DIAL) using a widely tunable amplified diode laser source

Abstract

Water vapor is one of the most significant constituents of the atmosphere because of its role in cloud formation, precipitation, and interactions with electromagnetic radiation, especially its absorption of longwave infrared radiation. Some details of the role of water vapor and related feedback mechanisms in the Earth system need to be characterized better if local weather, global climate, and the water cycle are to be understood. A Differential Absorption LIDAR (DIAL) with a compact laser diode source may be able to provide boundary-layer water vapor profiles with improved vertical resolution relative to passive remote sensors. While the tradeoff with small DIAL systems is lower vertical resolution relative to large LIDARs, the advantage is that DIAL systems can be built much smaller and more robust at less cost, and consequently are the more ideal choice for creating a multi-point array or satellite-borne system. This paper highlights the progress made at Montana State University towards a water vapor DIAL using a widely tunable amplified external cavity diode laser (ECDL) transmitter. The ECDL is configured in a Littman-Metcalf configuration and was built at Montana State University. It has a continuous wave (cw) output power of 20 mW, a center wavelength of 832 nm, a coarse tuning range of 17 nm, and a continuous tuning range greater than 20 GHz. The ECDL is used to injection seed a tapered amplifier with a cw output power of 500 mW. The spectral characteristics of the ECDL are transferred to the output of the tapered amplifier. The rest of the LIDAR uses commercially available telescopes, filter optics, and detectors. Initial cw and pulsed absorption measurements are presented.

Extending the continuous tuning range of an external-cavity diode laser

“…External-cavity diode lasers (ECDLs) have proven to be useful laboratory tools because of their spectral coverage and tunability. Some of the many applications involving ECDLs include differential absorption lidar, [1][2][3] molecular spectroscopy, 4,5 and sources for stabilized wavelength references. 6 The typical performance of an ECDL when used with a standard Fabry-Perot diode laser as the laser source includes 20 nm of noncontinuous tuning, a linewidth of 200 kHz, and output powers of 20-50 mW.…”

Preliminary Testing of a Water-Vapor Differential Absorption LIDAR (DIAL) Using a Widely Tunable Amplified Diode Laser Source

“…CW measurements were made as an initial test of the system before pulsed measurements were attempted. These early measurements as well as a full description of the ECDL and LIDAR setups are described elsewhere [4]. Results from the pulsed experiments are discussed in detail here.…”