Model-free precision control of 808 nm laser pulses
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.71
Model-free precision control of 808 nm laser pulses Brady T. Simon1, Joshua Dupaty1, Ei Ei Brown2 and Makhin Thitsa1 1
Mercer University, Mercer University Drive, Macon, GA 31207, U.S.A
2
Army Research Laboratory, Powder Mill Rd, Adelphi, MD 20783, U.S.A
ABSTRACT
We propose a method for precision control of the temporal pulse shape in 808 nm emission from Er-doped fluoroindate glasses. Previously, authors have reported the model based controller design, in which the controller varies and controls the pump rate in real time through the pump power. In model-based design, the performance of the resultant controller depends on the accuracy of the mathematical model used to represent the device in the design process. In this paper a more robust control scheme using model-free approach is presented. Specifically, the controller design is independent of the mathematical model and hence any modeling error has no effect on the device performance. This robustness against modeling error is critical for control purposes in optical materials where various up-conversion parameters are unknown or hard to determine with certainty.
INTRODUCTION The near-infrared laser of 808 nm wavelength is increasingly attracting attention in the medical field for applications such as nondestructive multiphoton imaging of living specimens, remotely triggered drug release strategies for cancer treatment as well as laser-induced targeted cancer therapy [1-6]. This particular wavelength is also highly applicable as the infrared light source for military night vision targeting tools and weapons. Moreover, it is a commonly used pump source for producing other popular wavelengths such as diode pumped 532 nm green laser. All such applications require these laser pulses to be precisely controlled. We propose a method for precision control of the temporal pulse shape in 808 nm emission from Er-doped fluoroindate glasses by direct modulation. The need for integrated light sources for integrated photonic infrastructure has recently re-popularized direct modulation methods, which do not require bulky external modulators [7-9].
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Authors have previously reported direct modulation methods, where a feedback control loop is implemented for the precise control of the temporal pulse shape [10-12]. The approach in [12] applied a model-based controller design, in which the controller varies and controls the pump rate in real time through the pump power resulting in chirp-free direct modulation. In model-based design, the performance of the resultant controller depends on the accuracy of the mathematical model used to represent the device in the design process. In this paper a more robust control scheme using model-free approach is presented. Specifi
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