Synopsis: A double whammy of x rays

Scientists have for the first time observed two-photon absorption with x rays.
Synopsis figure
Credit: G. Doumy et al., Phys. Rev. Lett. (2011)

Photons can pair up to ionize an atom when individually they’re not energetic enough to do the job. However, this requires an intense light source so that the atom can absorb two photons in rapid succession. Using the world’s most powerful x-ray laser, scientists have for the first time observed two-photon absorption in the x ray part of the spectrum. In the experiment, which is presented in Physical Review Letters, x rays from the Linac Coherent Light Source (LCLS) stripped the innermost electrons of a neon atom at a rate over 100 times higher than predicted by theoretical models.

For fifty years now, physicists have been exploring two-photon absorption at energies corresponding to infrared, visible, and ultraviolet wavelengths. The technique has been used to study electronic properties of atoms and molecules, to image human tissues, and to improve the resolution for photolithography. Despite scientific interest in expanding this nonlinear optical effect to higher energies, x-ray sources with adequate intensity have been lacking until now.

Completed in 2009, the LCLS at the SLAC National Accelerator Laboratory produces ultrashort pulses of 10 trillion x-ray photons. In their experiments, Gilles Doumy, of The Ohio State University, and his colleagues placed a neon target in the beam path and tuned the energy of the x rays to just above and just below the energy threshold (1196eV) for ionizing electrons in the 1s shell of neon. By analyzing the ions that emerged from the target, the team found evidence of two-photon absorption. The authors expect their results will be an important step towards probing the interiors of solid samples with x rays. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Optics

Previous Synopsis

Astrophysics

Hyperon stars

Read More »

Next Synopsis

Superconductivity

Magnetism shortly before pairing

Read More »

Related Articles

Synopsis: Light Tuner Slows Down to Shift
Optics

Synopsis: Light Tuner Slows Down to Shift

A new design for an optical frequency shifter combines a tunable filter and slow-light techniques. Read More »

Focus: Polariton Laser Upgrade
Optics

Focus: Polariton Laser Upgrade

The emission from a polariton laser shows the coherence that is common to conventional lasers, a step toward using them as high-efficiency alternative light sources. Read More »

Synopsis: Bad Cavities for Precise Lasers
Optics

Synopsis: Bad Cavities for Precise Lasers

The frequency of a laser based on trapped ultracold atoms can be made insensitive to fluctuations in the laser cavity’s length. Read More »

More Articles