Bright, coherent, ultrafast soft X-ray harmonics spanning the water window from a tabletop light source

Area of Science:

• Attosecond physics
• Soft X-ray science
• Quantum optics

Background:

• High harmonic generation (HHG) is a key process for producing ultrashort light pulses.
• The water window spectral region (≈100–1000 eV) is crucial for high-resolution imaging of biological and material samples.
• Extending HHG into the water window with high photon flux and coherence has been a significant challenge.

Purpose of the Study:

• To demonstrate fully phase-matched high harmonic emission spanning the water window spectral region.
• To generate the broadest bright coherent bandwidth from a single subfemtosecond burst.
• To extend bright, spatially coherent, attosecond pulses into the soft X-ray region.

Main Methods:

• Utilizing advanced laser systems to drive high harmonic generation.
• Implementing phase-matching techniques to optimize emission in the water window.
• Characterizing the spectral bandwidth and photon flux of the generated attosecond pulses.

Main Results:

• Fully phase-matched high harmonic emission was achieved across the water window.
• The broadest coherent bandwidth (≈300 eV) to date from a single subfemtosecond burst was generated.
• A 10³-fold increase in harmonic photon flux at 0.5 keV was observed compared to previous studies.
• Bright, spatially coherent, attosecond pulses were successfully extended into the soft X-ray region for the first time.

Conclusions:

• This work represents a significant advancement in attosecond science and soft X-ray generation.
• The demonstrated capabilities open new avenues for nano- and bioimaging, as well as materials and molecular dynamics studies.
• The enhanced photon flux and bandwidth pave the way for novel applications requiring high-intensity coherent soft X-ray sources.