We report on our results of the coherent combination of four Tm-doped rod-type fiber amplifiers. The chirped pulse amplification system emits an average output power of 188 W and a pulse energy of 1.86 mJ at 100.86 kHz repetition rate. The compressed pulses were measured via second order frequency optical gating. The retrieval reveals a compressed pulse duration of the laser system of 84 fs resulting in peak power of 17.7 GW. The amplifier interferometer was stabilized using locking of coherence by single-detector electronic frequency-tagging and piezo driven mirrors in front of the amplifier channels. The long term stability of the source was tracked with a thermal power sensor over a duration of 120 minutes and shows a stability of <0.1 % rms over this measurement period. To the best of our knowledge, this is the highest average power ultrafast mJ-class short-wavelength infrared laser to date. This proves the applicability of coherent combining techniques in Tm-doped fiber laser systems, opening the route towards performance scaling of ultrafast SWIR laser sources to kW-class average power levels with multi-mJ energies. Additionally this renders this technology the ideal candidate for frequency conversion into the soft X-ray, mid infrared and THz spectral region.
Yb:fiber-based pulses are split into 4-pulse bursts, sent into a gas-filled multipass cell for nonlinear pulse compression and recombined again to scale the supported output peak power and pulse energy. The pulse division and recombination are passively stable, being based on birefringent crystals, and enable a final output pulse energy of 3:4mJ at 32 fs pulse duration. Distributing the input energy over a 4-pulse burst allowed to work a factor two above the limitations of single-pulse operation regarding the occurrence of laser induced damage on the multipass cell mirrors. Overall, good efficiency, beam quality and temporal contrast are achieved.
We present a CEO-stable 1.1 kW CPA system that is designed to drive a few-cycle-generation stage (<6fs pulse duration) and a subsequent atto-second beamline at the ELI-ALPS facility in Szeged. It currently delivers >300W of average power at 100kHz repetition-rate providing <10fs pulses. The chirped-pulse-amplification system (CPA) demonstrates excellent noise properties with <220mrad of the integrated carrier-envelope-offset (CEO) noise (10Hz to 20MHz) at a pulse repetition rate of 80MHz while the relative-intensity-noise (RIN) stayed <0.3%. This is the first CEO-stable laser system at 1kW level average power.
We present a large-bandwidth high-power, high-energy fiber laser system based on coherent beam combination of 16 ytterbium-doped rod-type amplifiers. The CPA pulse stretching as well as extensive spectral shaping to counteract gain narrowing are implemented in a mostly fiber-integrated front end. A two-staged and partially helium-filled CPA grating compressor allows to compress the amplified pulses while maintaining a nearly diffraction-limited beam quality. Two laser operation regimes were investigated. The first one aimed for the shortest possible pulse duration, whereby 106 fs were reached at an average power of 910 W and a pulse energy of 910 μJ. In a second experiment, the primary aim of increasing the average power to 1 kW and the pulse energy to 10 mJ was successfully reached while the secondary objective, again being a minimum pulse duration, was optimized to 120 fs, posing a record value for fiber-CPA systems at this performance level.
We demonstrate the 6.5-fold compression of 1-mJ 200-fs pulses by spectral broadening in a gas-filled multi-pass cell and subsequent chirped-mirror compression. A coherently-combined fiber laser source is compressed with an overall power efficiency of ~95% resulting in a record compressed power of >950 W. In a second experiment, the same overall spectral broadening is obtained with the nonlinear phase per medium pass enhanced to well beyond 3 rad while still retaining all the favorable properties of the multi-pass cell configuration. This may enable an even higher power efficiency beyond 95%.
Here we present the latest experimental results of a high-power CEP-stable FCPA system. The 16-channel FCPA runs at 0.3% RMS power stability (>9hours) delivering more than 1kW and 10mJ after the compressor at a pulse duration of 280fs. To generate 6fs pulses, stretched hollow-core fibers are being employed. We present a significant up-scaling of this technique towards an output of 5mJ, 100kHz and 6fs.
We present a coherently-combined ultrafast fiber laser system consisting of twelve amplifier channels delivering 10.4 kW average power at 80 MHz repetition rate with a pulse duration of 240 fs FWHM and an almost diffraction-limited beam quality of M2 ≤ 1.2. The system incorporates an automated self-adjustment of the beam combination with 3 degrees of freedom per channel. The system today is, to the best of our knowledge, the world’s most average-powerful femtosecond laser. Thermographic analysis indicates that power scaling to 100 kW-class average power is feasible.
In this contribution, we present the newest results of the recently introduced pulse-energy-scaling technique electrooptically controlled divided-pulse amplification (EDPA) and its implementation in a high-power fiber laser system based on coherent combination. In this experiment, a burst of 8 stretched fs-pulses is amplified in two high-power fiber amplifier channels followed by coherent combination into a single pulse. Afterwards, the signal is compressed to a FWHM pulse duration of 255 fs with a pulse energy of 3 mJ and an average power of 105 W. The additional degrees of freedom provided by EDPA, such as direct access to the amplitudes and phases of all individual pulses in each burst, are exploited to compensate for gain saturation effects. Thus, a great temporal contrast of about 18.5 dB is reached and a very high combining efficiency of nearly 80%, including spatial as well as temporal combining, is reached. Furthermore, the system features three customized multi-pass cells as optical delay lines, minimizing the footprint of the combining stage to 0.5 m2. For the time being, two amplifiers are employed in order to initially optimize the parameters of EDPA and the performance of temporal combining. However, the laser system comprises a total of 16 parallel main amplifier channels, potentially enabling spatio-temporal combination of 128 separately amplified pulses with the currently applied bursts of 8 pulses. This extension is part of upcoming experiments and will allow for significant further scaling of the pulse energy in the near future.
We present the most recent results of ultrafast fiber-laser driven generation of broadband THz radiation based on two-color gas-plasma. The experiment shows how energetic fiber-lasers can improve on an application today mainly dominated by Ti:sapphire lasers and power-scalability of this kind of THz sources is discussed. With a high-power driving laser THz radiation with more than 4 mW of average power is generated. This is the highest average power using this scheme so far.
We present a novel approach for temporal contrast enhancement of energetic laser pulses by filtered SPM broadened spectra. A measured temporal contrast enhancement by at least 7 orders of magnitude in a simple setup has been achieved. This technique is applicable to a wide range of laser parameters and poses a highly efficient alternative to existing contrast-enhancement methods.
An ultrafast ytterbium-doped fiber laser system based on coherent beam combination of 16 amplifier channels is presented. The system delivers 1.83 kW average power at 2.3 mJ pulse energy and 240 fs pulse duration. The combining efficiency of 82% and the beam M2-value of 1.8 currently is limited by thermal lensing in some optical components, which were identified and are to be replaced.
We present a detailed investigation of different compositions of Yb3+-doped alumino-silicate glasses as promising materials for diode-pumped high-power laser applications at 1030 nm due to their beneficial thermo-mechanical properties. To generate comprehensive datasets for emission and absorption cross sections, the spectral properties of the materials were recorded at temperatures ranging from liquid nitrogen to room temperature. It was found that the newly developed materials offer higher emission cross sections at the center laser wavelength of 1030 nm than the so far used alternatives Yb:CaF2 and Yb:FP-glass. This results in a lower saturation fluence that offers the potential for higher laser extraction efficiency. Fluorescence lifetime quenching of first test samples was analyzed and attributed to the hydroxide (OH) concentration in the host material. Applying a sophisticated glass manufacturing process, OH concentrations could be lowered by up to two orders of magnitude, rising the lifetime and the quantum efficiency for samples doped with more than 6.1020 Yb3+ -ions per cm³. First laser experiments showed a broad tuning range of about 60 nm, which is superior to Yb:CaF2 and Yb:FP-glass in the same setup. Furthermore, measurements of the laser induced damage threshold (LIDT) for different coating techniques on doped substrates revealed the appropriateness of the materials for short pulse high-energy laser amplification.
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