Fluorescence/depolarization LIDAR for mid-range

stand-off detection of biological agents

Z. Mierczyk, K. Kopczynski, M. Zygmunt, J. Wojtanowski, J. Mlynczak, A. Gawlikowski, A. Mlodzianko,

W. Piotrowski, A. Gietka, P. Knysak, T. Drozd, M. Muzal, M. Kaszczuk, R. Ostrowski, M. Jakubaszek

Institute of Optoelectronics Military University of Technology, ul. gen. Sylwestra Kaliskiego 2, 00-908 Warszawa, Poland

LIDAR [1] system for real-time standoff detection of bio-agents is presented and preliminary experimental results are discussed. The detection approach is based on two independent physical phenomena:

- laser induced fluorescence [2], - depolarization resulting from elastic scattering on non-spherical particles [3].

The device includes three laser sources, two receiving telescopes, depolarization component and spectral signature analyzing spectrograph. It was designed to provide the stand-off detection capability at ranges from 200 m up to several kilometers. The system as a whole forms a mobile platform for vehicle or building installation. Additionally, it's combined with a scanning mechanics and advanced software, which enables to conduct the semi-automatic monitoring of a specified space sector.

For fluorescence excitation, 3-rd (355 nm) and 4-th (266 nm) harmonics of Nd:Y AG pulsed lasers are used. They emit short (�6 ns) pulses with the repetition rate of 20 Hz. Collecting optics for fluorescence echo detection and spectral content analysis includes 25 mm diameter f/4 Newton telescope, Czerny Turner spectrograph and 32-channel PMT. Depending on the grating applied, the spectral resolution from 20 nm up to 3 nm per channel can be achieved.

The system is also equipped with an eye-safe (l.5 /-lm) Nd:YAG OPO laser for elastic backscatteringldepolarization detection. The optical echo signal is collected by Cassegrain telescope with aperture diameter of 125 mm. Depolarization detection component based on polarizing beam-splitter serves as the particle-shape analyzer, which is very valuable in case of non-spherical bio-aerosols sensing.

The first experimental results prove high efficiency of standoff detection of fluorescence emission signals. The multichannel detection approach provides the capability which is not limited just to detection of these signals, but also enables to measure their spectral fingerprints. Thus, a discrimination of certain groups of biological species seems to be achievable from standoff position in real time. The main goal for our device is to provide efficient discrimination performance concerning dangerous 1 non-dangerous biological species.

Fig. 1 Picture of the developed LIDAR device (on the left) and the example of fluorescence signature of the biological target collected from standoff position (on the right).

References [1] C. Weitkamp, Lidar Range-Resolved Optical Remote Sensing of the Atmosphere, (Springer, Singapore, 2004).

[2] A. Hoekstra, V. Maltsev, G. Videen, "Optics of biological particles", NATO Science Series 238, 63 (2005). [3] M. Mishchenko, 1. Hovenier, "Depolarization of light backscattered by randomly oriented non-spherical particles", Optics Letters 20, 1356 (1995).