Atomic Laser Capable of Operating at The Shortest Wavelengths

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The creation of lasers that can generate a coherent stream of X-ray radiation at short wavelengths has long been a goal for scientists. The primary aim of such ‘X-ray lasers’ is to produce high quality, high resolution images of tiny targets, such as molecules. However, the wavelengths of lasers developed to date are still too large to result in clear, detailed images of such targets.

Now, Hitoki Yoneda and co-workers at the University of Electro-Communications in Tokyo, together with scientists across Japan, have built an atomic X-ray laser with the shortest wavelength yet, producing a stable beam with a wavelength of 1.5 ångström, or 0.15 nanometers. This tiny wavelength is nearly ten times shorter than that of previously-reported atomic lasers.

Lasers work by using an energy source to excite a laser medium, which then release a concentrated stream of photons. This stimulated emission process can increase the coherence of laser light with proper conditions. This work demonstrated that this is true, even in X-ray region.

The team built their atomic laser based on copper atoms. The researchers exposed the foil to two X-ray pulses of different energies, generated by an X-ray free-electron laser; one pulse was tuned as a pump source and the other as a seed for the main laser beam (see image). Yoneda and his team found that using the pumped copper medium in combination with the X-ray pulse acting as a seed for the main laser beam, greatly enhanced the coherence and energy extraction efficiency of the short-wavelength beam.

The researchers hope their ‘hard X-ray inner-shell atomic laser’ will eventually produce ultrastable, high quality X-ray images, and could feasibly transform the fields of medicine, quantum optics and particle physics.