Tilted Wave Laser diode emitters represent a promising approach for high power laser diodes. These devices, manufactured by VI Systems, are broad area devices that make use of an effective large vertical cavity to reduces the overall power density delaying the onset of thermal rollover and COD effects. A challenge of the TWL approach is a dual-beam emission, each single-mode in the vertical dimension. This paper addresses resent efforts to efficiently coherently beam combine these two beams into one single-mode beam having what is quite likely world class brightness, power, and conversion efficiency for a broad area diode array.
For many years optical designers have been intuitively aware of the value and potential that an inhomogeneous refractive index distribution can bring to the manufacture of precision optical instruments. Even so, designers have been cautious when considering lens designs with inhomogeneous glass, partly because of design difficulties, but mostly because of the need for controlled and reliable materials. In this paper we demonstrate the feasibility of graded index lenses by addressing the index control requirements that are needed for a diffraction limited lens. We chose for our analysis a rather stressing case: an F/1.5 plano-convex singlet. A general analytic expression for the index of refraction is developed for a perfect axial gradient lens (single color, on axis). Index errors were then added to the perfect index and the lens evaluated for wavefront quality. We found that index errors on the order of 1.6x10-3 rms produced aberrations of 0.04 waves rms, which is within the bounds of a diffraction limited lens. LightPath now routinely fabricates glass with much less index variation, making feasible the fabrication of repeatable diffraction limited lenses with inhomogeneous glass.
This paper describes the differential phase experiment (DPE) which formed a major part of the ABLE ACE suite of experiments conducted by the Air Force. The work described covers the rationale for the experiment, the basic experimental concept, the analysis of the differential phase, the optical and software design analysis, a discussion of the polarization scrambling characteristics of the optics, calibration of the equipment and a presentation of some of the major results of the data reduction effort to date. The DPE was a propagation experiment conducted between two aircraft flying at an altitude of 40,000 feet whose purpose was to measure the phase difference between two beams propagating at slightly different angels through the atmosphere. A four bin polarization interferometer was used to measure the differential phase. Due to the high level of scintillation that was presented branch points were present in the phase function. Rytov theory, wave optics simulation and the experimental measurements are in general agreement. Self consistency checks that were performed on the data indicate a high level of confidence in the results. Values of Cn2 that are consistent with the measurements of the differential phase agree with simultaneous scintillometer measurement taken long the same path in levels of turbulence where the scintillometer is not saturated. These differential phase based Cn2 estimates do not appear to saturate as is typical of scintillometer measurements and appear to extend the range over which high levels of Cn2 can be estimated. In addition the differential phase and anisoplanatic Strehl computed from the data is consistent with Rytov theory and wave optics simulations.
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