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Pulse Code Modulation of CO2 TEA Laser Pulse,
ARMY ELECTRONICS RESEARCH AND DEVELOPMENT COMMAND FORT BELVOIR VA NIGHT VISION AND ELECTRO-OPTICS LABS
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The CO2 TEA laser pulse is characterized by a gain-switched spike followed by a slow decaying tail. As a ranging waveform, the tail with its slow fall time does not contribute to the devices accuracy in ranging measurements. Elimination of this tail, with resulting increased energy in the spike, by optimization of the gas ratios, has been sought after. On the other hand, utilization of the entire pulse to include the tail, leads to the concept of multifunctional applications such as range finding and Cooperative Battlefield Identification Friend or Foe CBIFF. Application of CBIFF requirements would utilize the modulated tail by transferring coded telegrams to the target being interrogated. The tail portion of the CO2 TEA laser waveform is approximately 2 to 4 microsec long. Depending on the achievable bandwidths for the modulator and receiver system, 10 to 100 bits of information can possibly be transmitted on a single CO2 TEA laser pulse. A number of applications besides CBIFF can be explored including communication between two vehicles, data transmission, and precision ranging to name a few. In this report, the CO2 TEA laser pulse tail is electro-optically EO modulated with a polarization sensitive switch capable of 5 MHz repetition rate and 100 nanosecond pulsewidths. With this capability, three operational modes can be realized namely, 1 pulse shapingsharpening of the gain-switched spike for precision ranging, 2 information transfer via modulation of tail, or 3 combining 1 and 2 on the same laser pulse. Mode no. 2 has been demonstrated and will be presented in this report. Author
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