Bioaerosol weapons pose a threat to both troops and civilians. Remote detection of bioaerosols is important for timely deployment of effective countermeasures against these weapons and for triggering other detection systems. In this paper we describe a new approach for remote bioaerosol detection based on an eye-safe spectrally broadband backscatter LIDAR. This technique illuminates a remote cloud using a spectrally broadband laser centred about 1.5 μm. The spectrally backscattered fraction of the broadband illumination beam is detected. Using an inverse Monte Carlo algorithm, the particle size distribution and refractive index of the cloud particles can be determined. In this way threat clouds containing anomalous man-made distributions of particles could be discriminated from normal background clouds. The laser is a custom designed source based on a special non-collinear optical parametric oscillator configuration. The laser produces Q-switched pulses with a maximum spectral bandwidth covering the 1.4 to 1.8 μm region. In practice the spectral region of 1.52 to 1.75 μm is used as this matches an atmospheric transmission window. A comparison of this broadband backscatter LIDAR technique, with the commonly used UV lidar fluorescence technique will be presented. Progress to date and details of a prototype LIDAR system will be described.
High average power sources operating in the 3 to 5 μm mid-infrared waveband are of interest for a wide variety of applications. We present design and performance results for a high-power engineered breadboard mid-IR source based on near-infrared pumped periodically-poled lithium niobate (PPLN) optical parametric oscillator (OPO) technology. The source design utilises a pair of singly-resonant PPLN OPOs pumped by a commercial 40 Watt, Q-switched, diode-pumped Nd:YLF laser. The mid-IR outputs from each OPO are polarisation recombined into a single output beam. A twin OPO design was chosen to minimise the effect of optical absorption, reduce thermal loading within each PPLN crystal and provide additional flexibility by offering the option for dual-wavelength mid-IR operation. An average output power approaching 4 Watts has been obtained with a corresponding slope efficiency of 15%. The mid-infrared beam is 6 times diffraction limited. Laser operation is controlled by a remote PC link and power, spectral and temporal pulse diagnostics are included within the system.