IIIT Hyderabad Publications |
|||||||||
|
LASER BEAM COMBINATION TECHNIQUES FOR DIRECTED ENERGY SYSTEMSAuthor: Suman Basak Date: 2020-02-20 Report no: IIIT/TH/2020/15 Advisor:Azeemuddin Syed,Jagannath Nayak AbstractHigh power lasers are attractive sources for several applications. Because of good beam quality at all power level, distributed thermal loading, etc fiber lasers are gaining popularity in Directed Energy applications. There is a continued interest in scaling laser systems up to power levels suitable enough for DE systems. Beam combining systems for high average-power lasers began in the late 1960s and early 1970s. Early systems [1, 2] propagated the beams using heavy-water-cooled copper optics and open beam trains with commercial fans to provide fresh air. They have evolved in the intervening 40- plus years to include highly sophisticated gimbaled control systems with extremely high-reflectance uncooled optics and adaptive optics to compensate for less-than-ideal laser beams and for atmospheric distortions. Due to the limitations put by thermo optic effects gain saturation and scattering noise, laser beams cannot be amplified indefinitely. An alternative approach to building high power lasers is to use arrays of relatively lower power lasers. However, this approach requires that the beams from the array elements be combined to have the propagation characteristics of a single beam. Beam combining of laser arrays with high efficiency and good beam quality for power and radiance (brightness) scaling is a long-standing problem in laser technology. Semiconductor and fiber gain elements have attractive attributes for beam-combined sys- tems because of their ease in building in array formats, their high efficiency, and the ability to get near-diffraction-limited beams from individual elements. Beam brightness at the source is of limited importance when considering realistic DE propagation scenarios in turbulent atmospheres. Incoherent combination of the high-quality beams from fiber lasers can generate directional beams that are getting serious consideration for use as laser DE systems. For spatial beam combination where the laser beams propagate through the atmosphere, the atmo- spheric turbulence, pointing errors like platform jitter and boresight error play an important role in the performance of the combination technique. Different models of atmospheric turbulence have been explored. A functional implementation of the HAP model is shown in this thesis. Several architectures of the beam director for incoherent beam combination has been proposed. In these architectures, each of the beams are focused and targeted at a fixed point in space. Equations for inclined beam is derived using transformation rotation and the beam focusing equations have been modified to model real beams with non-ideal divergence. We have analyzed the criticality of the effect of atmospheric turbulence, beam wander, residual mechanical jitter and boresight error on the intensity and spot-size of incoherently combined laser beams. Full thesis: pdf Centre for VLSI and Embeded Systems Technology |
||||||||
Copyright © 2009 - IIIT Hyderabad. All Rights Reserved. |