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Interest has recently turned to multibeam CO waveguide lasers1'2 as simple, compact sources of intense infrared light. A multibeam laser is an array of parallel discharge tubes (elements) between common plane mirrors. When the elements of the multibeam laser generate light independently, the intensities of all the beams are summed in the far zone (in the focusing plane), and the size of the focus is determined by the divergence of the beam from an individual element and the overall aperture of the multibeam laser. This circumstance imposes an upper limit on the light intensity at the focus. Another consequence of the independent operation of the elements of a random distribution of the light spectrum and polarization over the output aperture. This random distribution in turn has the consequence that it is not possible to realize the full potential of "focusators,t' which are optical devices of a new type for producing a given intensity distribution in a focus3 There is accordingly considerable interest in operating the various elements coherently, so that the multibeam laser operates as a single spatially coherent source. In this case the far- zone light intensity distribution is the result of an interference of all the beams. According to estimates in Ref. 4, operating all the elements of the multibeam laser of Ref. 2 coherently wifi lead to a maximum light intensity in the far zone about 50 times as high as during independent operation of the elements. It has also been shown that a coherent array of waveguide CO lasers can be used for L1DAR4 to produce short light pulses with a high repetition frequency.4'6 Phase locking of the elements of a multibeam laser will therefore substantially extend the possible range of applications and, in particular, permit an increase in the light intensity at the focus.
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