Proposed gamma-ray laser could emit 'nuclear light'

“Photons in a normallaserare emitted by atoms, by ions, and so on,” Tkalya toldPhysOrg.com.“In the nuclear gamma-ray laser, the photons are emitted by atomicnuclei.”

In the study, which is published in a recent issue ofPhysical Review Letters, Tkalya explains that a nuclear gamma-ray laser has to overcome at least two basic problems: accumulating a large amount of isomeric nuclei (nuclei in a long-lived excited state) and narrowing down the gamma-ray emission line. The new proposal fulfills these requirements by taking advantage of thorium’s unique nuclear structure, which enables some of the photons from an external laser to interact directly with thorium’s nuclei rather than its electrons.

Tkalya’s proposal uses a lithium-calcium-aluminum-fluoride (LiCaAlF₆) compound, in which some of the calcium is replaced with thorium. After a sufficient amount of isomeric thorium nuclei have been excited by an external laser, the nuclei can interact with a surrounding electric or magnetic field to create a population inversion, so that the system contains more excited nuclei than unexcited nuclei. (In a regular laser, a population inversion usually involves getting more electrons in a higher energy level than a lower energy level.) Then, Tkalya showed that the nuclei can emit or absorb photons without recoil, allowing them to produce light without losing energy.

“The nuclear gamma-ray laser considered in my article can emit‘visible’ (vacuum ultraviolet {VUV}) light (orgamma-raysof the optical range) only,” Tkalya said.

As Tkalya explained, a nuclear gamma-ray laser could open up several interesting applications, although he has not thoroughly investigated them yet. One possibility is that the gamma-ray emission of the excitedthoriumnuclei is in the optical range called“nuclear light.”

“In my opinion, it is interesting to see a‘nuclear light,’” he said.“An application of nuclear light is the nuclear metrological standard of frequency, or the‘nuclear clock.’”

In addition, the device could be used to test many fundamental properties of nature, such as the exponentiality of the decay law and the effect of the variation of the fine structure constant.

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