Seeded stimulated X-ray emission at 5.9 keV

Area of Science:

• Atomic and Molecular Physics
• Laser Physics
• Materials Science

Background:

• X-ray free-electron lasers (XFELs) enable the study of stimulated X-ray emission.
• Two primary schemes, amplified spontaneous emission (ASE) and seeded stimulated emission (SSE), are explored for coherent X-ray generation.
• SSE utilizes a secondary XFEL pulse to initiate stimulated emission.

Purpose of the Study:

• To investigate and compare amplified spontaneous emission (ASE) and seeded stimulated emission (SSE) of the Mn Kα1 fluorescence line.
• To determine the pump pulse intensity thresholds for both ASE and SSE.
• To assess the feasibility of SSE for generating coherent X-ray sources and for spectroscopic applications.

Main Methods:

• Utilized 7-femtosecond FWHM XFEL pulses at 6.6 keV to pump a 3.9 molar NaMnO4 solution.
• Measured the 5.9 keV Mn Kα1 fluorescence line.
• Varied pump pulse intensity to observe and quantify ASE and SSE phenomena.

Main Results:

• Amplified spontaneous emission (ASE) was observed at a pump pulse intensity of 1.7 × 10^19 W/cm^2.
• Seeded stimulated emission (SSE) was observed at significantly lower pump pulse intensities, down to 1.1 × 10^17 W/cm^2.
• The observed SSE intensities are compatible with existing XFEL facilities.

Conclusions:

• Seeded stimulated emission (SSE) is experimentally feasible at intensities accessible by current XFEL instruments.
• SSE offers a promising pathway for generating coherent X-ray pulses.
• SSE can be applied to spectroscopic studies of transition metal complexes and other advanced applications.