Abstract
An all diode-laser-based micropulse differential absorption lidar (DIAL) laser transmitter for tropospheric water vapor and aerosol profiling is presented. The micropulse DIAL (MPD) transmitter utilizes two continuous wave (cw) external cavity diode lasers (ECDL) to seed an actively pulsed, overdriven tapered semiconductor optical amplifier (TSOA). The MPD laser produces up to 7 watts of peak power over a 1 µs pulse duration (7 µJ) and a 10 kHz pulse repetition frequency. Spectral switching between the online and offline seed lasers is achieved on a 1Hz basis using a fiber optic switch to allow for more accurate sampling of the atmospheric volume between the online and offline laser shots. The high laser spectral purity of greater than 0.9996 coupled with the broad tunability of the laser transmitter will allow for accurate measurements of tropospheric water vapor in a wide range of geographic locations under varying atmospheric conditions. This paper describes the design and performance characteristics of a third generation MPD laser transmitter with enhanced laser performance over the previous generation DIAL system.
Highlights
Water vapor is the most dominant and variable green house gas in the Earth's atmosphere and plays a key role in driving long term climate change, atmospheric chemistry and transport, and high impact weather systems [1]
To overcome the near field ocular hazards associated with typical solid state Differential Absorption Lidar (DIAL) transmitters as well as to satisfy the lower maximum permissible exposure (MPE) requirements in the visible-NIR part of the spectrum, an alternative approach known as the micropulse lidar (MPL) technique can be used [11]
The MPL technique minimizes the ocular hazard by beam expansion of the output of a high pulse repetition frequency (PRF) and low pulse energy laser transmitter ranging from 1 to 20 kHz, and 1-100 μJ, respectively
Summary
Water vapor is the most dominant and variable green house gas in the Earth's atmosphere and plays a key role in driving long term climate change, atmospheric chemistry and transport, and high impact weather systems [1]. Accurate measurements of atmospheric water vapor using the DIAL technique requires a robust laser transmitter capable of accessing appropriate strength absorption lines shown in Fig. 1 with minimal sensitivity to changes in temperature and pressure while simultaneously operating with high spectral purity [2, 3]. Another key requirement for accurate retrievals of water vapor profiles is to achieve sufficient laser average power in order to reach satisfactory signal to noise ratios (SNR) with integration periods that fall below the typical lifetimes of tropospheric and boundary layer processes [4].
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