04 Sep Turning gas into an XUV lens
Intense XUV laser pulses are difficult to shape using conventional optical elements. Conventional transmissive optics strongly absorb high-energy photons and are therefore of limited use for XUV light. A dense atomic gas can perform this task instead: Researchers led by the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg have demonstrated that such a gas can be used to modify both the spatial profile and the spectrum of intense XUV pulses.
Gas atoms as a refractive element
The effect is based on nonlinear interactions between intense XUV light and the atoms in the gas. When a strong XUV pulse passes through a dense atomic gas, it rapidly excites and de-excites the atomic energy levels. This process, known as Rabi oscillation, causes the electrons to oscillate between the quantum states involved.
Since a laser beam is more intense at its center than at its edges, the strength of the light-matter interaction also varies across the beam profile. As a result, the refractive index of the gas changes depending on the intensity. This effect is particularly pronounced near an atomic resonance. Combined with pulse propagation through the dense medium, this causes the gas atoms to act as a dynamic refractive element that affects XUV light in a similar way to a lens or prism.
Changes in the far-field pulse structure and spectral composition as a function of laser pulse intensity. Image: MPIK
Dynamic optics for short-wavelength light
In this way, the gas can be used as a time-dependent optical element capable of modifying the beam profile and spectral composition on very short timescales. The approach could open up new possibilities for the spatial and spectral shaping of coherent XUV pulses and, in the future, potentially X-ray pulses as well.
From spectroscopy to quantum technologies
The researchers see potential applications particularly in spectroscopy. Beyond this, the controlled shaping of short-wavelength pulses could in the future be used, for example, to control chemical reactions with structured light or for quantum technology applications on atomic length and time scales.
Original publication:
[Y. He et al.: Redirection and reshaping of intense extreme-ultraviolet radiation; Science Advances, 29. Mai 2026, Vol 12, Issue 22, DOI: 10.1126/sciadv.aef5300]
Source and image: www.mpi-hd.mpg.de