Remote discrimination of willow, pine and poplar trees and their growing environments by femtosecond filament-induced breakdown spectroscopy

Abstract Tree barks and leaves are increasingly used these days as environmental bioindicators for pollution assessment of their growing environment, but remote discrimination of tree species and their growing environments are rarely reported. Here the analytical potential of femtosecond filament induced breakdown spectroscopy (FIBS) for standoff detection and classification of different tree species and their growing environments is evaluated. A 800 nm, 40 fs Ti:Sapphire laser pulse is focused in air by a 2-m lens to generate a ~10–15 cm long single laser filament. The filament induces the emissions from willow, pine and poplar tree bark samples taken from two different environmental zones, i.e., a national park and a downtown business district (Changchun, China). The emission is detected in the backward direction with the bark samples located 2.5 m away from the detection system. Spectral signals, including molecular bands of CN, C 2 and atomic lines of K, Ca, Mg, Na, Sr, Ba, Al, Fe and Mn are obtained from both smooth inner and rough outer surfaces of the bark samples, which can be used as spectral fingerprints. With the assistance of principal component analysis (PCA), simultaneous differentiation of the three tree species and their growing environments is presented, which shows a strong dependence on the tree species. Our results provide a promising strategy for remote, direct and fast tree species and environmental analysis.