Power scaling of ultrashort pulses by spatial and temporal coherent combining

Ytterbium-doped solid-state lasers are versatile tools for the generation of intense ultrashort pulses, which are the key for many industrial and scientific applications. High pulse-peak powers and high average powers are desired at the same time, e.g. to initiate a physical process of interest while providing fast data-acquisition times. Although sophisticated state-of-the-art laser concepts have already demonstrated remarkable performance figures, their working principles hamper the simultaneous delivery of both high peak power and high average power. Coherent combination of pulses provided by an amplifier array constitutes a novel concept for scaling both the average power and the peak power. Although this technique is applicable to any laser concept, it is especially well suited for fibers due to their high single-pass gain and their reproducible, excellent beam quality. As the number of amplifier channels may become too large for the ambitious energy levels being targeted, divided-pulse amplification (DPA) the coherent combination of a pulse burst into a single pulse can be applied as another energy-scaling approach, which is the focus of this thesis. In this regard, the energy-scalability of DPA implementations as an extension to well established chirped-pulse amplification (CPA) is analyzed and actively-controlled DPA is demonstrated. Moreover, the potential of merging spatial and temporal coherent combining concepts in a power- and energy-scalable architecture has been demonstrated. Based on the findings, a state-of-the-art high-power fiber-CPA system is extended by eight parallel main-amplifier channels, in which bursts of up to four pulse replicas are amplified that are eventually stacked into a single pulse. With this technique < 300 fs pulses of 12 mJ pulse energy at 700 W average power have been achieved, which is an order of magnitude improvement in both energy and average power compared to the state-of-the-art at the beginning of this work

1 kW 1 mJ eight-channel ultrafast fiber laser

An ultrafast fiber chirped-pulse amplifier comprising eight coherently combined amplifier channels is presented. The laser delivers 1 kW average power at 1 mJ pulse energy and 260 fs pulse duration. Excellent beam quality and low-noise performance are confirmed. The laser has proven suitable for demanding scientific applications. Further power scaling is possible right away using even more amplifier channels

Energetic sub-2-cycle laser with 216 W average power

Few-cycle lasers are essential for many research areas such as attosecond physics that promise to address fundamental questions in science and technology. Therefore, further advancements are connected to significant progress in the underlying laser technology. Here, two-stage nonlinear compression of a 660 W femtosecond fiber laser system is utilized to achieve unprecedented average power levels of energetic ultrashort or even few-cycle laser pulses. In a first compression step, 408 W, 320 mu J, 30 fs pulses are achieved, which can be further compressed to 216 W, 170 mu J, 6.3 fs pulses in a second compression stage. To the best of our knowledge, this is the highest average power few-cycle laser system presented so far. It is expected to significantly advance the fields of high harmonic generation and attosecond science. (C) 2016 Optical Society of Americ

12 mJ kW-class ultrafast fiber laser system using multidimensional coherent pulse addition

An ultrafast fiber-chirped-pulse amplification system using a combination of spatial and temporal coherent pulse combination is presented. By distributing the amplification among eight amplifier channels and four pulse replicas, up to 12 mJ pulse energy with 700 W average power and 262 fs pulse duration have been obtained with a system efficiency of 78% and excellent beam quality. To the best of our knowledge, this is the highest energy achieved by an ultrafast fiber-based laser system to date

Lasersystem mit Überlagerung von zeitlich und räumlich separaten Laserpulsen

Die Erfindung betrifft ein Lasersystem mit - wenigstens einer Laserpulsquelle (1), die Eingangslaserpulse (7) bei einer Eingangsrepetitionsfrequenz erzeugt, - wenigstens einem Kombinationselement (8, 10), das zwei oder mehr der Eingangslaserpulse (7) in jeweils einem Ausgangslaserpuls (11) überlagert und so einen Ausgangslaserpulszug bei einer Ausgangsrepetitionsfrequenz erzeugt, wobei dem Kombinationselement (8, 10) wenigstens ein Phasenstellelement (14, 15) zugeordnet ist, das die relative Phasenlage der in dem Ausgangslaserpuls (11) überlagerten Eingangslaserpulse (7) beeinflusst, - einem Fehlersignaldetektor (16), der aus dem Ausgangslaserpulszug ein Fehlersignal (18) ableitet, und - einem Regler (19), der aus dem Fehlersignal (18) ein Regelsignal (20) zur Ansteuerung des Phasenstellelementes (14, 15) bildet. Aufgabe der Erfindung ist es, ein gegenüber dem Stand der Technik verbessertes Lasersystem mit aktiv stabilisierter Kombination von zeitlich und räumlich separaten Eingangslaserpulsen zu Ausgangslaserpulsen hoher Leistung bereit zu stellen. Diese Aufgabe löst die Erfindung dadurch, dass der Fehlersignaldetektor (16) den Ausgangslaserpulszug periodisch mit der Ausgangsrepetitionsfrequenz abtastet. Alternativ schlägt die Erfindung vor, dass der Fehlersignaldetektor (16) die momentane Leistung des Ausgangslaserpulszuges bewertet. Außerdem betrifft die Erfindung Verfahren zur Erzeugung von Laserpulsen

Analysis of divided-pulse amplification for high-energy extraction

Divided-pulse amplification employing passive coherent beam combining implementations causes a strong degradation in efficiency. In this contribution typical implementations are analyzed and a solution using an active stabilization system is presented. With this 380 fs pulses at 1.25 mJ corresponding to a peak power of 2.9 GW have been achieved demonstrating the potential of this approach

Electro-optically controlled divided-pulse amplification

A novel technique for divided-pulse amplification is presented in a proof-ofprinciple experiment. A pulse burst, cut out of the pulse train of a mode-locked oscillator, is amplified and temporally combined into a single pulse. High combination efficiency and excellent pulse contrast are demonstrated. The system is mostly fiber-coupled, enabling a high interferometric stability. This approach provides access to the amplitude and phase of the individual pulses in the burst to be amplified, potentially allowing the compensation of gain saturation and nonlinear phase mismatches within the burst. Therefore, this technique enables the scaling of the peak power and pulse energy of pulsed laser systems beyond currently prevailing limitations

Multidimensional coherent pulse addition of ultrashort laser pulses

Spatially and temporally separated amplification and subsequent coherent addition of femtosecond pulses is a promising performance-scaling approach for ultrafast laser systems. Herein we demonstrate for the first time the application of this multidimensional scheme in a scalable architecture. Applying actively controlled divided-pulse amplification producing up to four pulse replicas that are amplified in two ytterbium-doped step-index fibers (6 µmcore), pulse energies far beyond the damage threshold of the single fiber have been achieved. In this proof-of-principle experiment, high system efficiencies are demonstrated at both high pulse energies (i.e., in case of strong saturation) and high accumulated nonlinear phases