Resonant cavity based time-domain multiplexing techniques for coherently combined fiber laser systems (original) (raw)

A concept for multiterawatt fibre lasers based on coherent pulse stacking in passive cavities

Light: Science & Applications, 2014

Since the advent of femtosecond lasers, performance improvements have constantly impacted on existing applications and enabled novel applications. However, one performance feature bearing the potential of a quantum leap for high-field applications is still not available: the simultaneous emission of extremely high peak and average powers. Emerging applications such as laser particle acceleration require exactly this performance regime and, therefore, challenge laser technology at large. On the one hand, canonical bulk systems can provide pulse peak powers in the multi-terawatt to petawatt range, while on the other hand, advanced solid-state-laser concepts such as the thin disk, slab or fibre are well known for their high efficiency and their ability to emit high average powers in the kilowatt range with excellent beam quality. In this contribution, a compact laser system capable of simultaneously providing high peak and average powers with high wall-plug efficiency is proposed and analysed. The concept is based on the temporal coherent combination (pulse stacking) of a pulse train emitted from a high-repetition-rate femtosecond laser system in a passive enhancement cavity. Thus, the pulse energy is increased at the cost of the repetition rate while almost preserving the average power. The concept relies on a fast switching element for dumping the enhanced pulse out of the cavity. The switch constitutes the key challenge of our proposal. Addressing this challenge could, for the first time, allow the highly efficient dumping of joule-class pulses at megawatt average power levels and lead to unprecedented laser parameters.

All-fiber passive Coherent Arrays Combining Four High Power Fiber Lasers

In this paper, we experimentally demonstrate all-fiber and all-passive coherent beam combining of two, three, and four high power lasers without using any active control and describe the power scaling characteristics of these arrays. A schematic of a coherent array combining four lasers is shown in Fig. 1. The coherent array consists of four fiber laser cavities with polarization-maintaining (PM) fibers and three couplers. Each laser cavity has a high-reflector (HR) grating, PM Yb-doped double-clad fiber (DCF), and a length of PM passive fiber. In our configuration, PM Yb DCF fiber is single-mode (SM) and it has NA of 0.11, V number of 2.2 at 1060 nm, mode-field diameter (MFD) of 7.6 µm at 1060 nm, Yb cladding absorption of 2.0 dB/m at the 975 nm wavelength, and PM beat length of 2.3 mm at 1060 nm. The HR grating has a center wavelength of 1083.0 nm with a 3 dB bandwidth of 1.2 nm and a reflectivity of > 99%. The length of the Yb fiber in each cavity is 10.2 m. The laser cavity i...

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

Optics express, 2015

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.

Simultaneous passive coherent beam combining and mode locking of fiber laser arrays

Optics Express, 2012

We present a dynamic model of simultaneous passive coherent beam combining and passive mode locking for coupled fiber lasers. The presence of a saturable absorber in the composite cavity results in the generation of packets of mode locked pulse trains. Within each packet the repetition rate of the pulses is determined by the length difference between the fibers.

Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers

Photonics

Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high-power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges is discussed, along with reporting some practical architectures for both conti...

Extracting cavity and pulse phases from limited data for coherent pulse stacking

Chinese Optics Letters, 2018

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 and high average power. A Z-domain model targeting the pulsed laser is assembled to describe the optical interference process. An algorithm, extracting the cavity phase and pulse phases from limited data, where only the pulse intensity is available, is developed to diagnose optical cavity resonators. We also implement the algorithm on the cascaded system of multiple optical cavities, achieving phase errors less than 1.0°(root mean square), which could ensure the stability of CPS.

Model for passive coherent beam combining in fiber laser arrays

Optics Express, 2009

We present a new model for studying the beam combining mechanism, spectral and temporal dynamics, the role of nonlinearity, and the power scaling issue of discretely coupled fiber laser arrays. The model accounts for the multiple longitudinal modes of individual fiber lasers and shows directly the formation of the composite-cavity modes. Detailed output power spectra and their evolution with increasing array size and pump power are also explored for the first time. In addition, it is, to our knowledge, the only model that closely resembles the real experimental conditions in which no deliberate control of the fiber lengths (mismatch) is required while highly efficient coherent beam combining is still attained.