Coherent Combining of Optical Pulses in Spatial, Spectral and Time Domains

Petawatt-level laser pulses have many potential applications in science and industry, but will require three orders of magnitude increase in pulse repetition rate from existing solid-state laser technology. Fiber lasers can operate at such repetition rates, but are limited in pulse energy. To overcome the gap between current achievable fiber-laser pulse energies (∼mJ) and required pulse energies for high-energy applications (up to 10J), this dissertation work explores four novel techniques: (1) Coherent beam combining in the spatial domain; (2) Coherent spectral combining in spatial and spectral domains; (3) Coherent pulse stacking amplification in the time domain; (4) N-squared coherent combining in spatial and time domains.;(1) We demonstrate coherent femtosecond pulse beam combining of up to four chirped-pulse fiber amplifier channels. Theoretical and experimental analysis of combining efficiency dependence on amplitude/phase noise shows the scalability to a large number of channels.;(2) We demonstrate coherent femtosecond pulse spectral synthesis by combining three parallel fiber chirped-pulse amplifiers, each amplifying different pulse spectra. This technique simultaneously overcomes individual-amplifier energy/power limitations, and spectral gain narrowing in a single fiber amplifier.;(3) We propose and demonstrate a new technique of coherent pulse stacking (CPS) amplification, which uses reflecting resonators to transform a sequence of phase/amplitude modulated optical pulses into a single output pulse. Experimental validation with a single resonator is demonstrated. We show theoretically that the extension to stacking a large number of equal-amplitude pulses can be achieved using multiple reflecting resonators, which enables the extraction of all stored energy in large-core fiber amplifiers.;(4) We propose and demonstrate N-squared coherent combining using resonant optical cavities, a novel pulse combining technique based on both spatial combining and temporal stacking. Its unique feature is in an N-channel system the combined pulse energy is enhanced by N-squared times.;This dissertation work provides the initial experimental and theoretical validations of several novel approaches that use coherent pulse synthesis/combining to achieve power and energy scaling using multiple small-aperture lasers, and serves as an initial step on the path towards future high average-power and petawatt peak-power laser technologies.