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[Ed . Note: The development of laser communications with submarines is getting increased emphasis as submarines realize their capability for joint operations with surface and air units. The requirement for real-time communications involving large volumes of information, places a premium on this means of communications — if successfully made operational. The information on lasers included here is taken from a paper developed by Dr. David Friewald of the General Dynamics Laser Systems Laboratory, San Diego.]

The right color for satellite or aircraft laser communications through seawater to a submarine, depends upon the laser beam’s penetration of seawater and having a very narrow band filter/receiver on the submarine so as to have a high signal to noise ratio.

The transmitter, according to Figure 1, should best transmit a blue light with an approximate wave length of 4590 Angstroms. This sort of beam, as shown, is least absorbed by seawater and should arrive at a deep submarine with sufficient intensity to convey to the submarine’s receiver a considerable amount of information in a very short period of time.

The  two  main  transmitters which  produce  about 4600  A0   light  beams  are  the  Xe/CI  Raman gas laser which    produces  a  blue beam of 4593  A0 , and the Nd:YAG  doubled  solid  state laser which  produces a blue-green beam at  5320  A0

The    receivers on submarines  are  either the CsABF   (Cesium atomic  resonance filter)  which  accepts  only  a  narrow band  (10  milli  A ) of  blue,  centered  at  4593 A , or the tuned quartz filter/receiver  for the  5320  A  beam which  accepts a    beam about 1 A wide —  about  100 times     wider than     the  Cesium filter/receiver.  However, such actors as atmospheric scattering, variations in seawater, etc., make the blue Raman gas-laser at least 30 times better than the solid-state blue green laser and about 100 times better on the average.

The present satellite laser communication program is consequently baselined for the Raman gas laser transmitter and the Cesium filter for the submarine receiver. This allows for transmission of a blue laser beam at the general area where a submarine might be and the sub can pick up the transmitted communications in real time.

It is desirable to have different colors for the up and down links, and significantly, only one kind of laser beam receiver is needed per submarine.

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