Editing Isotope separation (section)

===Laser===
In this method a [[laser]] is tuned to a wavelength which excites only one isotope of the material and ionizes those atoms preferentially. For atoms, the resonant absorption of light for an isotope depends on<ref>{{Cite journal |last1=Stern |first1=R. C. |last2=Snavely |first2=B. B. |date=January 1976 |title=The Laser Isotope Separation Program at Lawrence Livermore Laboratory.: Laser Isotope Separation |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.1976.tb41598.x |journal=Annals of the New York Academy of Sciences |language=en |volume=267 |issue=1 Third Confere |pages=71–80 |doi=10.1111/j.1749-6632.1976.tb41598.x |s2cid=97058155 |issn=0077-8923}}</ref>

* the nuclear mass (noticeable mainly with light elements)
* the nuclear volume (causing a deviation from the [[Electric potential energy|Coulomb potential]], noticeable for heavier elements) 
* [[hyperfine structure|hyperfine]] splitting of electronic transitions, if the nucleus has a spin,

allowing finely tuned lasers to interact with only one isotope. After the atom is ionized it can be removed from the sample by applying an [[electric field]]. This method is often abbreviated as AVLIS ([[atomic vapor laser isotope separation]]). This method has only been developed as laser technology has improved in the 1970s to 1980s. Attempts to develop it to an industrial scale for uranium enrichment were successively given up in the 1990s "due to never ending technical difficulties" and because centrifuges have reached technical maturity in the meantime.<ref>Werner Fuß: ''Laser isotope separation and proliferation risks''. (PDF) Max-Planck-Institut für Quantenoptik, 2015, https://www.mpq.mpg.de/5178012/MPQ346.pdf</ref><ref>Schneider, K. R., LIS: the view from Urenco (1995). (https://inis.iaea.org/search/search.aspx?orig_q=rn:27014297)</ref> However, it is a major concern to those in the field of [[nuclear proliferation]], because it may be cheaper and more easily hidden than other methods of isotope separation. [[Tunable laser]]s used in AVLIS include the [[dye laser]]<ref>[[F. J. Duarte]] and L.W. Hillman (Eds.), Dye Laser Principles (Academic, New York, 1990) Chapter 9.</ref> and more recently [[diode laser]]s.<ref>F. J. Duarte (Ed.), Tunable Laser Applications, 2nd Ed. (CRC, 2008) Chapter 11</ref>

A second method of laser separation is known as [[molecular laser isotope separation]] (MLIS). In this method, an infrared laser is directed at [[uranium hexafluoride]] gas (if enrichment of uranium is desired), exciting molecules that contain a [[uranium-235|U-235]] atom. A second laser, either also in the IR ([[infrared multiphoton dissociation]]) or in the UV, frees a [[fluorine]] atom, leaving [[uranium pentafluoride]] which then precipitates out of the gas. Cascading the MLIS stages is more difficult than with other methods because the UF<sub>5</sub> must be fluorinated back to UF<sub>6</sub> before being introduced into the next MLIS stage. But with light elements, the isotope selectivity is usually good enough that cascading is not required.

Several alternative MLIS schemes have been developed. For example, one uses a first laser in the near-infrared or visible region, where a selectivity of over 20:1 can be obtained in a single stage. This method is called OP-IRMPD (Overtone Pre-excitation—[[infrared multiphoton dissociation|IR Multiple Photon Dissociation]]). But due to the small absorption probability in the overtones, too many photons remain unused, so that the method did not reach industrial feasibility. Also some other MLIS methods suffer from wasting of the expensive photons.

Finally, the '[[Separation of isotopes by laser excitation]]' (SILEX) process, developed by [[Silex Systems]] in Australia, has been licensed to General Electric for the development of a pilot enrichment plant. For uranium, it uses a cold molecular beam with UF<sub>6</sub> in a carrier gas, in which the <sup>235</sup>UF<sub>6</sub> is selectively excited by an infrared laser near 16&nbsp;μm. In contrast to the excited molecules, the nonexcited heavier isotopic molecules tends to form clusters with the carrier gas, and these clusters stay closer to the axis of the molecular beam, so that they can pass a skimmer and are thus separated from the excited lighter isotope.

Quite recently{{when|date=January 2018}} yet another scheme has been proposed for the [[deuterium]] separation using Trojan wavepackets in circularly polarized electromagnetic field. The process of [[Trojan wave packet]] formation by the adiabatic-rapid passage depends in ultra-sensitive way on the [[reduced mass|reduced]] electron and nucleus mass which with the same field frequency further leads to excitation of Trojan or anti-Trojan wavepacket depending on the kind of the isotope. Those and their giant, rotating [[electric dipole moment]]s are then <math>\pi</math>-shifted in phase and the beam of such atoms splits in the gradient of the electric field in the analogy to [[Stern–Gerlach experiment]].{{Citation needed|date=January 2014}}