Ultrashort-Pulse Matter Interactions Using Compact Fiber CPA Technology.

ultrafast pulse;fiber laser;Electrical Engineering;Engineering;Electrical Engineering

Haines, Michael K.Winful, Herbert Graves ;

University of Michigan

关键词: ultrafast pulse;    fiber laser;    Electrical Engineering;    Engineering;    Electrical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/120656/mkhaines_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Chirped pulse amplification (CPA) was a breakthrough that allowed for high energy ultrashort pulses, leading to many technological and scientific discoveries. Many CPA systems relied on bulky, alignment-sensitive diffraction-grating based pulse stretchers and compressors, making them impractical for industrial applications. Chirped Bragg gratings (CBGs) have recently been demonstrated as compact, monolithic, and robust pulse stretchers and compressors, and so they are more practical for industrial applications. This thesis explores two key properties of CBGs: reciprocity and thermal loading. The CBG would appear to be reciprocal by nature, where one configuration would stretch a bandwidth-limited pulse and the reverse configuration would recompress the pulse back to the bandwidth-limited duration. However, this reciprocity property is not absolute, and under certain conditions recompressed pulses acquire significant temporal distortions. We explored and defined proper CBG design requirements to minimize these temporal distortions. Furthermore, we explored the performance of chirped volume Bragg gratings (CVBGs) in a high average power CPA system. We found that absorbed incident power induces a volumetric thermal gradient in CVBGs that led to significant chromatic aberrations at approximately 1 kW average power; however, we also found that thermally induced warping of the CVBG can introduce significant beam distortions in the form of spatial chirp at an average power one order of magnitude lower, although this can be controlled by proper mechanical mounting conditions or by proper CVBG fabrication. CVBG-based fiber CPA lasers can enable practical high average power systems with a variety of material science and biomedical applications. We built a 50 W, 10 μJ CVBG-based CPA system with variable repetition rate to explore select potential applications of the system, namely the formation of high spatial frequency laser-induced periodic surface structures on Si as well as subsurface laser surgery in the sclera. The scattering properties of the tissue limit the precision with which the surgery could be performed, but we developed a model using naturally-occurring second harmonic generation in ex vivo porcine sclera that can be used as a non-invasive probe to measure scattering properties and predict the pulse energy needed for subsurface incisions in the sclera.