Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability,high peak and average power levels,pulse duration,and spectral bandwidth.For instance,spectros...Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability,high peak and average power levels,pulse duration,and spectral bandwidth.For instance,spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser,and therefore high average power,pulse duration of a few tens of fs,and maximal available spectral bandwidth.Contrarily,the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations.Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification(CPA)to the requirements of different nonlinear frequency converters while preserving the low-phase-noise(PN)properties of the system.To achieve spectral tunability,we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system.The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz.While gaining control over the spectral properties,we preserve the relative-intensity-noise and PN properties of the system.The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation(full width at half maximum of∼11 nm,compressed pulse duration of 230 fs)or a spectrum ideal for highly nonlinear processes such as high-harmonic generation(−10 dB level of>50 nm,transform-limited pulse duration of∼65 fs).展开更多
Intense laser fields focused into ambient air can be used to generate high-bandwidth current densities in the form of plasma channels and filaments.Excitation with bichromatic fields enables us to adjust the amplitude...Intense laser fields focused into ambient air can be used to generate high-bandwidth current densities in the form of plasma channels and filaments.Excitation with bichromatic fields enables us to adjust the amplitude and sign of these currents using the relative phase between the two light pulses.Two-color filamentation in gas targets provides a route to scaling the energy of terahertz pulses to microjoule levels by driving the plasma channel with a high-energy laser source.However,the structure of plasma channels is highly susceptible to drifts in both the relative phase and other laser parameters,making control over the waveform of the radiated terahertz fields delicate.We establish a clear link between the phase dependence of plasma currents and terahertz radiation by comparing in situ detection of current densities and far-field detection of terahertz electric fields.We show that the current measurement can be used as a feedback parameter for stabilizing the terahertz waveform.This approach provides a route to energetic terahertz pulses with exceptional waveform stability.展开更多
文摘Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability,high peak and average power levels,pulse duration,and spectral bandwidth.For instance,spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR driving laser,and therefore high average power,pulse duration of a few tens of fs,and maximal available spectral bandwidth.Contrarily,the parametric conversion efficiency is higher for pulses with a duration in the 100-fs range due to temporal walk-off and coating limitations.Here we suggest an approach to adjust the spectral characteristics of high-power chirped-pulse amplification(CPA)to the requirements of different nonlinear frequency converters while preserving the low-phase-noise(PN)properties of the system.To achieve spectral tunability,we installed a mechanical spectral shaper in a free-space section of the stretcher of an in-house-developed ytterbium-fiber-based CPA system.The CPA system delivers 100 W of average power at a repetition rate of 132.4 MHz.While gaining control over the spectral properties,we preserve the relative-intensity-noise and PN properties of the system.The high-power CPA can easily be adjusted to deliver either a spectrum ideal for mid-IR light generation(full width at half maximum of∼11 nm,compressed pulse duration of 230 fs)or a spectrum ideal for highly nonlinear processes such as high-harmonic generation(−10 dB level of>50 nm,transform-limited pulse duration of∼65 fs).
基金Canada Research ChairsNatural Sciences and Engineering Research Council of Canada+2 种基金Army Research Office(W911NF-19-1-0211)Defense Advanced Research Projects Agency(D18AC00011)Deutsche Forschungsgemeinschaft(MI 2434/1-1)。
文摘Intense laser fields focused into ambient air can be used to generate high-bandwidth current densities in the form of plasma channels and filaments.Excitation with bichromatic fields enables us to adjust the amplitude and sign of these currents using the relative phase between the two light pulses.Two-color filamentation in gas targets provides a route to scaling the energy of terahertz pulses to microjoule levels by driving the plasma channel with a high-energy laser source.However,the structure of plasma channels is highly susceptible to drifts in both the relative phase and other laser parameters,making control over the waveform of the radiated terahertz fields delicate.We establish a clear link between the phase dependence of plasma currents and terahertz radiation by comparing in situ detection of current densities and far-field detection of terahertz electric fields.We show that the current measurement can be used as a feedback parameter for stabilizing the terahertz waveform.This approach provides a route to energetic terahertz pulses with exceptional waveform stability.
