We report on a 2.3 m long air-clad ytterbium-doped large-mode-area photonic crystal fiber laser generating up to 80 W output power with a slope efficiency of 78%. Single transverse mode operation is ...achieved with a mode-field area of 350 /spl mu/m/sup 2/. No thermo-optical limitations are observed at the extracted /spl sim/35 W/m, therefore such fibers allow scaling to even higher powers.
High-power ultrafast fiber laser systems Limpert, J.; Roser, F.; Schreiber, T. ...
IEEE journal of selected topics in quantum electronics,
03/2006, Letnik:
12, Številka:
2
Journal Article
Recenzirano
The recent demonstration of rare-earth-doped fiber lasers with a continuous wave output power well above the kilowatt level with diffraction-limited beam quality has proven that fiber lasers ...constitute a power-scalable solid-state laser concept. To generate intense pulses from a fiber, several fundamental limitations have to be overcome. Nevertheless, novel experimental strategies and fiber designs offer an enormous potential toward laser systems with high average powers and high pulse energies. This paper reviews the challenges, achievements, and perspectives of ultrashort pulse generation and amplification in fibers.
We review the main challenges and give design guidelines for high-peak-power high-average-power fiber-based chirped-pulse amplification (CPA) systems. It is clearly pointed out that the lowest order ...fiber nonlinearity (NL), namely the self-phase modulation, limits the scalability of high-energy ultrashort pulse fiber amplifiers. Therefore, a distinguished difference arises between the consequences of accumulated nonlinear phase originating from the pulse envelope and initial weak modulations, resulting in a strong recommendation to operate an amplification system as linearly as possible in order to generate high-contrast pulses. Low-NL rare-earth-doped fibers, such as the recently available designs of photonic crystal fibers, are the key element for successful peak power scaling in fiber laser systems. In this paper, we present a detailed analysis and optimization of the extraction characteristics in connection with the accumulated nonlinear phase in such extreme fiber dimensions. Consequently, millijoule pulse energy femtosecond pulses at repetition rates in the 100 kHz range have already been demonstrated experimentally in a Yb-fiber-based CPA system that has even further scaling potential.
The coherent combination of ultra short laser pulses is a promising approach for scaling the average and peak power of ultrafast lasers. Fiber lasers and amplifiers are especially suited for this ...technique due to their simple singe-pass setups that can be easily parallelized. Here we propose the combination of the well-known approach of spatially separated amplification with the technique of divided-pulse amplification, i.e. an additionally performed temporally separated amplification. With the help of this multidimensional pulse stacking, laser systems come into reach capable of emitting 10’s of joules of energy at multi-kW average powers that simultaneously employ a manageable number of fibers.
We report on time-resolved measurements of the plasma evolution during metal ablation with ultrashort laser pulses in the range from 200 fs to 3.3 ps. The plasma transmission exhibits two distinctive ...minima. Almost total attenuation is observed a few nanoseconds after the ablation pulse, while a second decrease of the transmission to approximately 50% is observed after about 150 ns. Images taken with a gated ICCD-camera confirm these data and allow determining the expansion velocity of the plasma plume. The attenuation in the first nanoseconds can be attributed to electrons and sublimated mass emitted from the target surface, while attenuation after several 10 ns is due to particles and droplets after a thermal boiling process. The possibility of a normal or an explosive boiling process, also called phase explosion, is discussed. Despite of the physical insight into the ablation process, these data provide valuable information for scaling the speed of ultrashort pulse laser materials processing in a fluence regime of several J/cm2 since they allow estimating the maximum usable pulse repetition rate.
A high-average-power Yb-doped fiber chirped-pulse amplification system is presented. Compressed average power of 325 W at 40 MHz repetition rate corresponding to 8.2 muJ pulse energy is extracted. ...Compression in a highly efficient dielectric-grating-based compressor yields pulses as short as 375 fs, resulting in 22 MW of peak power.
We experimentally demonstrate a three-dimensional chiral optical metamaterial that exhibits an asymmetric transmission for forwardly and backwardly propagating linearly polarized light. The ...observation of this novel effect requires a metamaterial composed of three-dimensional chiral meta-atoms without any rotational symmetry. Our analysis is supported by a systematic investigation of the transmission matrices for arbitrarily complex, generally lossy media that allows deriving a simple criterion for asymmetric transmission in an arbitrary polarization base. Contrary to physical intuition, in general the polarization eigenstates in such three-dimensional and low-symmetry metamaterials do not obey fixed relations and the associated transmission matrices cannot be symmetrized.
PDF
