Separation of even-even from even-odd isotopes using ultrafast lasers

TL;DR

This paper introduces a laser isotope separation method based on nuclear spin selectivity using ultrafast lasers, enabling efficient enrichment of specific isotopes without relying on isotope shifts.

Contribution

The proposed technique leverages hyperfine interactions and Ramsey pulse sequences to distinguish isotopes by nuclear spin, offering a new approach to isotope separation with high efficiency.

Findings

Density matrix simulations show near 100% selectivity for I > 0 isotopes.

Single-pass enrichment exceeding 90% is achievable under realistic conditions.

Method is applicable to isotopes like ${}^{235}$U, ${}^{87}$Sr, and ${}^{57}$Fe.

Abstract

We propose a laser isotope separation mechanism in which selectivity arises from nuclear spin rather than isotope shifts, enabling the use of broadband ultrafast lasers. A Ramsey pulse sequence is applied to paramagnetic molecular isotopologues possessing two electronic states coupled by a dipole transition. For even-even isotopologues (nuclear spin $I = 0$), each electronic state is a single level and the time-reversed sequence returns all population to the ground state exactly. For even-odd isotopologues ($I > 0$), the hyperfine interaction splits each state into multiple levels with coupling amplitudes set by Wigner $6j$ symbols; incommensurate phase evolution during the dark interval prevents the echo from closing, trapping a fraction $P_m$ of the population in the excited manifold. In the impulsive limit ($\Omega \gg A_{\rm HF}$), $P_m$ depends only on the angular momentum quantum numbers $(J_g, J_m, I)$ and is independent of laser intensity or bandwidth. Density matrix simulations confirm $P_m = 0$ for $I = 0$ and $P_m \approx 0.23$-$0.47$ for $I > 0$ across representative systems including ${}^{235}$U, ${}^{87}$Sr, and ${}^{57}$Fe. Under realistic collisional conditions, single-pass enrichment exceeding 90% from natural feed is achievable without cascading.