John Ruppe

Coherent pulse stacking amplification using low-finesse Gires-Tournois interferometers

We demonstrate a new technique of coherent pulse stacking (CPS) amplification to overcome limits on achievable pulse energies from optical amplifiers. CPS uses reflecting resonators without active cavity-dumpers to transform a sequence of phase- and amplitude-modulated optical pulses into a single output pulse. Experimental validation with a single reflecting resonator demonstrates a near-theoretical stacked peak-power enhancement factor of ~2.5 with 92% and 97.4% efficiency for amplified nanosecond and femtosecond pulses. We also show theoretically that large numbers of equal-amplitude pulses can be stacked using sequences of multiple reflecting resonators, thus providing a new path for generating very high-energy pulses from ultrashort pulse fiber amplifier systems.

Coherent Pulse Stacking Amplification of Nanosecond and Femtosecond Pulses

Coherent stacking of several pulses into a single output pulse using Gires-Tourmois Interferometer reflecting resonators is demonstrated, enabling a new technique for achieving high energy pulses from short-pulse and ultrashort-pulse fiber amplifier systems.

Coherent pulse stacking extension of CPA to 9ns effectively-long stretched pulse duration

Coherent pulse stacking with a 9ns effectively-long burst of equal amplitude chirped pulses into a single pulse using a compact cascade of four Gires-Tournois interferometers is experimentally demonstrated with a fiber chirped pulse amplification system.

FPGA-Based Optical Cavity Phase Stabilization for Coherent Pulse Stacking

Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable, and distributed digital control system with firmware and software integration for algorithms, to support the CPS application. We model CPS as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection algorithm on an field-programmable gate array (FPGA). A two-stage (2+1 cavities) 15-pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5kHz, and stabilized at an individually-prescribed round-trip phase with 0.7deg and 2.1deg rms phase errors for Stages 1 and 2, respectively. Optical cavity phase control with nanometer accuracy ensures 1.2% intensity stability of the stacked pulse over 12 h. The FPGA-based feedback control system can be scaled to large numbers of optical cavities.

Coherent pulse stacking amplification — Extending chirped pulse amplification by orders of magnitude

A new technique of time-domain pulse combining — coherent pulse stacking amplification — is enabling nonlinearity-free energy extraction at the stored energy limit from rare-earth doped fiber based ultrashort pulse amplification systems.

High-energy pulse stacking via regenerative pulse-burst amplification

Here we present a coherent pulse stacking approach for upscaling the energy of a solid-state femtosecond chirped pulse amplifier. We demonstrate pulse splitting into four replicas, amplification in a burst-mode regenerative Yb:CaF2 amplifier, designed to overcome intracavity optical damage by colliding pulse replicas, and coherent combining into a single millijoule level pulse. The thresholds of pulse-burst-induced damage of optical elements are experimentally investigated. The scheme allows achieving an enhancement factor of 2.62 using a single-stage stacker cavity and, potentially, much higher enhancement factors using cascaded stacking.

Interferometer design and controls for pulse stacking in high power fiber lasers

In order to develop a design for a laser-plasma accelerator (LPA) driver, we demonstrate key technologies that enable fiber lasers to produce high energy, ultrafast pulses. These technologies must be scalable, and operate in the presence of thermal drift, acoustic noise, and other perturbations typical of an operating system. We show that coherent pulse stacking (CPS), which requires optical interferometers, can be made robust by image-relaying, multipass optical cavities, and by optical phase control schemes that sense pulse train amplitudes from each cavity. A four-stage pulse stacking system using image-relaying cavities is controlled for 14 hours using a pulse-pattern sensing algorithm. For coherent addition of simultaneous ultrafast pulses, we introduce a new scheme using diffractive optics, and show experimentally that four pulses can be added while a preserving pulse width of 128 fs.

Multi-mJ ultrashort pulse coherent pulse stacking amplification in a Yb-doped 85μm CCC fiber based system

Multi-mJ 81ns effectively-long burst of chirped pulses is amplified through fiber amplification system based on 85μm Yb-doped Chirally-Coupled-Core fiber and coherently stacked into a single pulse. 5.4mJ energy extraction at 1kHz repetition rate is demonstrated.

Multi-mJ energy extraction using Yb-fiber based coherent pulse stacking amplification of fs pulses (Conference Presentation)

We report multi-mJ energy (>5mJ) extraction from femtosecond-pulse Yb-doped fiber CPA using coherent pulse stacking amplification (CPSA) technique. This high energy extraction has been enabled by amplifying 10’s of nanosecond long pulse sequence, and by using 85-µm core Yb-doped CCC fiber based power amplification stage. The CPSA system consists of 1-GHz repetition rate mode-locked fiber oscillator, followed by a pair of fast phase and amplitude electro-optic modulators, a diffraction-grating based pulse stretcher, a fiber amplifier chain, a GTI-cavity based pulse stacker, and a diffraction grating pulse compressor. Electro-optic modulators are used to carve out from the 1-GHz mode-locked pulse train an amplitude and phase modulated pulse burst, which after stretching and amplification, becomes equal-amplitude pulse burst consisting of 27 stretched pulses, each approximately 1-ns long. Initial pulse-burst shaping accounts for the strong amplifier saturation effects, so that it is compensated at the power amplifier output. This 27-pulse burst is then coherently stacked into a single pulse using a multiplexed sequence of 5 GTI cavities. The compact-footprint 4+1 multiplexed pulse stacker consists of 4 cavities having rountrip of 1 ns, and one Herriott-cell folded cavity - with 9ns roundtrip. After stacking, stretched pulses are compressed down to the bandwidth-limited ~300 fs duration using a standard diffraction-grating pulse compressor.

10mJ Energy Extraction from Yb-doped 85µm core CCC Fiber using Coherent Pulse Stacking Amplification of fs Pulses

81ns effectively-long burst of chirped pulses is amplified to 10mJ with low nonlinearity in a Yb-doped 85µm core CCC-fiber based system, and coherently stacked with a multi-GTI arrangement, and compressed into a single <540fs pulse.