Title of Paper: High-Power Fiber Sources for In Situ and Remote Detection of Trace Species


Principal Author: Dahv Kliner


Abstract: Rare-earth-doped fiber lasers and amplifiers are finding widespread use in applications requiring compact, rugged optical sources with high beam quality. Single-mode (SM) fiber sources offer the advantages of:


  1. high efficiency (we have demonstrated 39% electrical-to-optical efficiency);


  1. high-gain (~50 dB) and low-threshold operation;


  1. diffraction-limited beam quality that is insensitive to thermal or mechanical fluctuations, optical power level, or aging of the laser system;


  1. continuous tunability;


  1. broad wavelength coverage in the near-IR by selection of various rare-earth dopants;


  1. pumping with low-cost, reliable diode lasers;


  1. room-temperature operation and no significant cooling requirements; and


  1. scalability to high power (>100 W).


We are developing pulsed and cw fiber sources for spectroscopic detection of trace species in the IR and UV spectral regions. Current projects include development of a high-sensitivity instrument for in situ detection of atmospheric SO2 by laser-induced fluorescence and construction of a hand-held imager for stand-off detection of CH4 using backscatter absorption gas imaging. Advances made in the course of this research include:


  1. demonstration of a method to increase the peak and average powers of fiber amplifiers by at least an order of magnitude using multimode fiber, while maintaining the diffraction-limited beam quality characteristic of SM fiber;


  1. development of polarization-maintaining, double-clad, Yb-doped fiber, which allows fabrication of fiber sources that maintain stable, linear polarization;


  1. construction of a compact, packaged, narrow-linewidth (<1 MHz) fiber amplifier with >4 W cw output power;


  1. use of a fiber-pumped OPO based on periodically poled lithium niobate to generate tunable radiation in the 3-micron region; and


  1. frequency-quadrupling of a pulsed fiber source to generate UV radiation with high efficiency.


I will review these developments and will discuss application of fiber sources to in situ and remote detection of trace species throughout the atmosphere.