Coherent combining of optical pulses in spatial, spectral and time domains
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Energetic ultrashort pulse lasers have become very powerful tools in scientific research as well as industrial applications, such as eye surgery, X-ray generation, material processing, and particle acceleration. Recently high power fiber laser emerges as a next-generation laser technology due to its advantages of power scalability, compactness, robustness, high efficiency, and excellent beam quality. While high power fiber lasers have recently been demonstrated at >10 kW of average power, the achievable short pulse (< ns) energies are limited at mJ level due to nonlinear effects. To overcome the large gap between the current achievable fiber laser pulse energies (~ mJ) and the required pulse energies for high energy applications (up to 10 J), multiple amplified ultrashort optical pulses from fiber amplifiers have to be coherently synthesized. This dissertation work consists of: (1) Coherent beam combining in spatial domain: We demonstrate femtosecond pulse beam combining of up to four chirped-pulse fiber amplifier channels and analyze the scalability to large numbers of channels. (2) Coherent spectral combining in spatial and spectral domains: We demonstrate femtosecond pulse spectral synthesis with three parallel fiber chirped-pulse amplifiers, each amplifying different ultrashort-pulse spectra. (3) Coherent pulse stacking amplification in time domain: We propose and demonstrate a new technique which uses reflecting resonators to transform a sequence of phase/amplitude modulated optical pulses into a single output pulse. (4) N-squared coherent combining in spatial and time domains: We propose and demonstrate a new multi-dimensional pulse multiplexing and beam combining technique based on resonant cavities, by which in a N-channel system the combined pulse energy is enhanced by N-squared times.