Rare earth-doped fibres are a diode-pumped,solid-state laser architecture that is highly scalable in average power.The performance of pulsed fibre laser systems is restricted due to nonlinear effects.Hence,fibre desig...Rare earth-doped fibres are a diode-pumped,solid-state laser architecture that is highly scalable in average power.The performance of pulsed fibre laser systems is restricted due to nonlinear effects.Hence,fibre designs that allow for very large mode areas at high average powers with diffraction-limited beam quality are of enormous interest.Ytterbium-doped,rod-type,large-pitch fibres(LPF)enable extreme fibre dimensions,i.e.,effective single-mode fibres with mode sizes exceeding 100 times the wavelength of the guided radiation,by exploiting the novel concept of delocalisation of higher-order transverse modes.The non-resonant nature of the operating principle makes LPF suitable for high power extraction.This design allows for an unparalleled level of performance in pulsed fibre lasers.展开更多
The development of high-power,broadband sources of coherent mid-infrared radiation is currently the subject of intense research that is driven by a substantial number of existing and continuously emerging applications...The development of high-power,broadband sources of coherent mid-infrared radiation is currently the subject of intense research that is driven by a substantial number of existing and continuously emerging applications in medical diagnostics,spectroscopy,microscopy,and fundamental science.One of the major,long-standing challenges in improving the performance of these applications has been the construction of compact,broadband mid-infrared radiation sources,which unify the properties of high brightness and spatial and temporal coherence.Due to the lack of such radiation sources,several emerging applications can be addressed only with infrared(IR)-beamlines in largescale synchrotron facilities,which are limited regarding user access and only partially fulfill these properties.Here,we present a table-top,broadband,coherent mid-infrared light source that provides brightness at an unprecedented level that supersedes that of synchrotrons in the wavelength range between 3.7 and 18μm by several orders of magnitude.This result is enabled by a high-power,few-cycle Tm-doped fiber laser system,which is employed as a pump at 1.9μm wavelength for intrapulse difference frequency generation(IPDFG).IPDFG intrinsically ensures the formation of carrierenvelope-phase stable pulses,which provide ideal prerequisites for state-of-the-art spectroscopy and microscopy.展开更多
Thermally induced refractive index gratings in Yb-doped fibers lead to transverse mode instability(TMI)above an average power threshold,which represents a severe problem for many applications.To obtain a deeper unders...Thermally induced refractive index gratings in Yb-doped fibers lead to transverse mode instability(TMI)above an average power threshold,which represents a severe problem for many applications.To obtain a deeper understanding of TMI,the evolution of the strength of the thermally induced refractive index grating with the average output power in a fiber amplifier is experimentally investigated for the first time.This investigation is performed by introducing a phase shift between the refractive index grating and modal interference pattern,which is obtained by applying a pump power variation to the fiber amplifier.It is demonstrated that the refractive index grating is sufficiently strong to enable modal energy coupling at powers that are significantly below the TMI threshold if the induced phase shift is sufficiently large.The experiments indicate that at higher powers,the refractive index grating becomes more sensitive to such phase shifts,which will ultimately trigger TMI.Furthermore,the experimental results demonstrate beam cleaning above the TMI threshold via the introduction of a positive phase shift.This finding paves the way for the development of a new class of mitigation strategies for TMI that are based on controlling the phase shift between the thermally induced refractive index grating and modal interference pattern.展开更多
The effect of transverse mode instability (TMI) is currently the main limitation for thefurther average-power scaling of fiber laser systems with diffraction-limited beamquality. In this work a main driving force for ...The effect of transverse mode instability (TMI) is currently the main limitation for thefurther average-power scaling of fiber laser systems with diffraction-limited beamquality. In this work a main driving force for TMI in fiber amplifiers is identified. Ourexperiments and simulations illustrate that the performance of fiber laser systems interms of their diffraction-limited output power can be significantly reduced whenthe pump or seed radiation exhibit intensity noise. This finding emphasizes the factthat the TMI threshold is not only determined by the active fiber but, rather, by thewhole system. In the experiment an artificially applied pump intensity-noise of 2.9%led to a reduction of the TMI threshold of 63%, whereas a similar seed intensitynoisedecreased it by just 13%. Thus, even though both noise sources have animpact on the TMI threshold, the pump intensity-noise can be considered as themain driver for TMI in saturated fiber amplifiers. Additionally, the work unveils thatthe physical origin of this behavior is linked to the noise transfer function insaturated fiber amplifiers. With the gained knowledge and the experimental andtheoretical results, it can be concluded that a suppression of pump-noise frequenciesbelow 20 kHz could strongly increase the TMI threshold in high-power fiber lasersystems.展开更多
基金The research leading to these results received funding from the European Research Council under the European Union’s Seventh Framework Programme(FP7/2007-2013)/ERC Grant Agreement No.[240460]the Thuringian Ministry of Education,Science and Culture under contract PE203-2-1(MOFA)and contract B514-10061(Green Photonics).FJ acknowledges financial support from the Abbe School of Photonics.
文摘Rare earth-doped fibres are a diode-pumped,solid-state laser architecture that is highly scalable in average power.The performance of pulsed fibre laser systems is restricted due to nonlinear effects.Hence,fibre designs that allow for very large mode areas at high average powers with diffraction-limited beam quality are of enormous interest.Ytterbium-doped,rod-type,large-pitch fibres(LPF)enable extreme fibre dimensions,i.e.,effective single-mode fibres with mode sizes exceeding 100 times the wavelength of the guided radiation,by exploiting the novel concept of delocalisation of higher-order transverse modes.The non-resonant nature of the operating principle makes LPF suitable for high power extraction.This design allows for an unparalleled level of performance in pulsed fibre lasers.
基金supported by the German Federal Ministry of Education and Research(BMBF)under contract“NUKLEUS”(13N13973)the United States AFOSR(FA9550-15-10041)+2 种基金the United States ARO(W911NF-12-1-0450 and W911NF-17-1-0501)support by the Helmholtz-Institute Jenasupport by the Carl Zeiss Stiftung.
文摘The development of high-power,broadband sources of coherent mid-infrared radiation is currently the subject of intense research that is driven by a substantial number of existing and continuously emerging applications in medical diagnostics,spectroscopy,microscopy,and fundamental science.One of the major,long-standing challenges in improving the performance of these applications has been the construction of compact,broadband mid-infrared radiation sources,which unify the properties of high brightness and spatial and temporal coherence.Due to the lack of such radiation sources,several emerging applications can be addressed only with infrared(IR)-beamlines in largescale synchrotron facilities,which are limited regarding user access and only partially fulfill these properties.Here,we present a table-top,broadband,coherent mid-infrared light source that provides brightness at an unprecedented level that supersedes that of synchrotrons in the wavelength range between 3.7 and 18μm by several orders of magnitude.This result is enabled by a high-power,few-cycle Tm-doped fiber laser system,which is employed as a pump at 1.9μm wavelength for intrapulse difference frequency generation(IPDFG).IPDFG intrinsically ensures the formation of carrierenvelope-phase stable pulses,which provide ideal prerequisites for state-of-the-art spectroscopy and microscopy.
基金supported by the German Research Foundation(DFG)within the International Research Training Group(IRTG)2101by the European Research Council under the ERC grant“ACOPS”,agreement no.617173+1 种基金by the Fraunhofer and Max Planck cooperation program within the project“PowerQuant”by the German Federal Ministry of Education and Research(BMBF),project no.PT-VDI,TEHFA Ⅱ.
文摘Thermally induced refractive index gratings in Yb-doped fibers lead to transverse mode instability(TMI)above an average power threshold,which represents a severe problem for many applications.To obtain a deeper understanding of TMI,the evolution of the strength of the thermally induced refractive index grating with the average output power in a fiber amplifier is experimentally investigated for the first time.This investigation is performed by introducing a phase shift between the refractive index grating and modal interference pattern,which is obtained by applying a pump power variation to the fiber amplifier.It is demonstrated that the refractive index grating is sufficiently strong to enable modal energy coupling at powers that are significantly below the TMI threshold if the induced phase shift is sufficiently large.The experiments indicate that at higher powers,the refractive index grating becomes more sensitive to such phase shifts,which will ultimately trigger TMI.Furthermore,the experimental results demonstrate beam cleaning above the TMI threshold via the introduction of a positive phase shift.This finding paves the way for the development of a new class of mitigation strategies for TMI that are based on controlling the phase shift between the thermally induced refractive index grating and modal interference pattern.
基金Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-416342637,416342891,GRK 2101(259607349)Fraunhofer Gesellschaft–Fraunhofer Cluster of Excellence“Advanced Photon Sources”.
文摘The effect of transverse mode instability (TMI) is currently the main limitation for thefurther average-power scaling of fiber laser systems with diffraction-limited beamquality. In this work a main driving force for TMI in fiber amplifiers is identified. Ourexperiments and simulations illustrate that the performance of fiber laser systems interms of their diffraction-limited output power can be significantly reduced whenthe pump or seed radiation exhibit intensity noise. This finding emphasizes the factthat the TMI threshold is not only determined by the active fiber but, rather, by thewhole system. In the experiment an artificially applied pump intensity-noise of 2.9%led to a reduction of the TMI threshold of 63%, whereas a similar seed intensitynoisedecreased it by just 13%. Thus, even though both noise sources have animpact on the TMI threshold, the pump intensity-noise can be considered as themain driver for TMI in saturated fiber amplifiers. Additionally, the work unveils thatthe physical origin of this behavior is linked to the noise transfer function insaturated fiber amplifiers. With the gained knowledge and the experimental andtheoretical results, it can be concluded that a suppression of pump-noise frequenciesbelow 20 kHz could strongly increase the TMI threshold in high-power fiber lasersystems.
