On the battlefield, soldiers must face not only the dangers of high-technology weaponry, but also the risk of chemical and biological warfare. In the event of a biological attack, rapid identification of the organisms used is critical. Two instruments that can efficiently perform sample analyses are under development, thanks to a Defense Advanced Research Projects Agency contract. Under the contract, SRI International, a nonprofit research, technology development and consulting organization, is developing handheld and flow cytometer biodetectors to detect and identify pathogens. Multiple benefits The two instruments employ a diode laser as an illumination source. SRI chose the OPC-A002-980-FC/150 diode laser from Opto Power Corp. for both devices for several reasons: It comes in a small package -- less than a cubic inch in total volume -- is fiber-coupled, offers the power level required for this application and is very efficient. The handheld biodetector, a battery-operated compact unit a bit larger than a video camcorder, will be used by troops trained in biological warfare agent detection. It can be taken into the field along with a sampler, collect fluid samples from the environment and in minutes determine if the sample contains one or more of the pathogens of interest. Airborne pathogens or soil samples have to be put into a liquid solution, typically water. The phosphor flow cytometer, a more complex instrument that probably will be vehicle-mounted, also is designed for field samples, but it works on a different principle than the biodetector. The cytometer will measure about 1 to 2 cubic feet and weigh about 30 lb. It also requires a liquid sample but is designed to work as part of a larger integrated detection system that the US Army is working on. The two devices being constructed currently use simulants and eventually will detect bacteria, viruses and toxins. The incubation period for the biodetector and cytometer is approximately 15 minutes. The team at SRI is working to get the detection probability above 95 percent and the false alarm probability below 1 or 2 percent. David Cooper, program director at SRI, said he finds the Opto Power laser diode very reliable: "We've not had one fail on us. In addition, the OPC laser is electrically very efficient."