Field Properties of Multiple, Coherently Combined Lasers.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OHIO SCHOOL OF ENGINEERING
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The coherent combination of several, single mode lasers can produce a field similar to that of a mode-locked laser but with more flexibility. The field for a quasi-monochromatic wave is considered a complex, coherence separable random process. The ensemble mean and covariance are determined for the case of a temporally stabilized amplitude and a temporal phase that with the appropriate assumptions is a stationary, gaussian random process. Mean fields are used throughout as the signals of interest. The Huygens-Fresnel principle is used to investigate the field properties in the Fraunhofer region for two cases. The first case is for N beams superimposed with optical axes coincident. With appropriate assumptions, the performance of such a system is determined from the ambiguity function. Range measurement precision is found to be proportional to 1.N cubed x delta f to the 12 power where delta f is the frequency difference between adjacent lasers. Velocity measurement precision is found to be proportional to N cubed x delta f to the 12 power. The second case is for N beams in a linear array. The far field result is a scanning beam that in certain cases can be steered. Aperiodic arrays are considered in an effort to reduce grating lobes. An array of about 1000 lasers is needed for reasonably low side lobes. Some generalized results are presented for the effects of misalignmentt of the lasers. In addition, the effects of the random phases of the lasers are considered, and the time-space dual nature of the results is discussed. Author
- Lasers and Masers
- Statistics and Probability