Fourier-limited seeded soft x-ray laser pulse.

Area of Science:

• Atomic, Molecular, and Optical Physics
• Plasma Physics
• X-ray Science

Background:

• High-order harmonic generation (HHG) is a key process for producing coherent extreme ultraviolet (XUV) and soft X-ray radiation.
• Seeding HHG with a specific laser can control and enhance the properties of the generated X-ray beam.
• Understanding the spectral characteristics and pulse duration of seeded soft x-ray lasers is crucial for their application in various scientific fields.

Purpose of the Study:

• To experimentally measure the spectral properties of a soft x-ray laser seeded by a high-order harmonic beam.
• To determine the spectral profile and deduce the shortest possible pulse duration of the seeded laser.
• To compare the experimental results with theoretical predictions and assess if the laser has reached its Fourier transform limit.

Main Methods:

• Generation of a seeded Ni-like krypton soft x-ray laser (32.8 nm) using optical field ionization.
• Utilizing an interferometric method to experimentally determine the spectral profile of the seeded laser.
• Investigating gain dynamics to determine the upper limit of the soft x-ray pulse duration.

Main Results:

• The spectral profile of the seeded Ni-like krypton soft x-ray laser was experimentally determined.
• The source exhibited a Voigt spectral profile with a full width at half maximum (FWHM) of 3.1 ± 0.3 mÅ.
• A Fourier-transform pulse duration of 4.7 ps was deduced, comparable to the experimentally determined upper limit, indicating the laser reached the Fourier limit.

Conclusions:

• The spectral bandwidth of the seeded soft x-ray laser is in good agreement with radiative transfer code predictions.
• The seeded soft x-ray laser has achieved its Fourier transform limit for pulse duration.
• This work provides the first measurement of spectral properties for a soft x-ray laser seeded by HHG, advancing the field of X-ray laser science.