AVLIS

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An atomic vapor laser isotope separation experiment at LLNL. Green light is from a copper vapor pump laser used to pump a highly tuned dye laser which is producing the orange light.

AVLIS Is an acronym which stands for atomic vapor laser isotope separation and is a method by which specially tuned lasers are used to separate isotopes of uranium using selective ionization of hyperfine transitions.

In the largest technology transfer in U.S. government history, in 1994 AVLIS (atomic vapor laser isotope separation) process was transferred to the United States Enrichment Corporation for commercialization. However, on June 9, 1999 after a $100 million investment, USEC cancelled its AVLIS program.

The AVLIS process provides high energy efficiency comparable with gas centrifuges, high separation factor, and low volume of radioactive waste.

AVLIS continues to be developed by some countries and it presents some specific challenges to international monitoring ([1]). Iran is now known to have had a secret AVLIS program. However, since it was uncovered in 2003, Iran has claimed to have dismantled it ([2],[3]).

Similar technology, using molecules instead of atoms, is the molecular laser isotope separation, MLIS.

[edit] Principle

The absorption lines of ²³⁵U and ²³⁸U differ slightly due to hyperfine structure; for example, the ²³⁸U absorption peak shifts from 5027.4 angstroms to 5027.3 Å (502.74 nanometers to 502.73 nm) in ²³⁵U. AVLIS uses tunable dye lasers, which can be precisely tuned, so only ²³⁵U absorbs the photons and selectively undergoes excitation and then photoionization. The ions are then electrostatically deflected to a collector, while the neutral unwanted uranium-238 passes through.

The AVLIS system consists from a vaporizer and a collector, forming the separation system, and the laser system. The vaporizer produces a stream of pure gaseous uranium.

The laser commonly used is a two-stage tunable pulsed dye laser usually pumped by a copper vapor laser; the master oscillator is low-power but highly precise, and its power is increased by a dye laser amplifier acting as optical amplifier. Three frequencies ("colors") of lasers are used for full ionization of uranium-235. [4]