Atomic ratio
The atomic ratio is a measure of the ratio of atoms of one kind (i) to another kind (j). A closely related concept is the atomic percent (or at.%), which gives the percentage of one kind of atom relative to the total number of atoms. The molecular equivalents of these concepts are the molar fraction, or molar percent. Atoms. Mathematically, the "atomic percent" is where "N" are the number of atoms of interest and "N" are the total number of atoms, while the "atomic ratio" is For example, the "atomic percent" of hydrogen in water (HO) is , while  the "atomic ratio" of hydrogen to oxygen is . Isotopes. Another application is in radiochemistry, where this may refer to isotopic ratios or isotopic abundances. Mathematically, the "isotopic abundance" is where "N" are the number of atoms of the isotope of interest and "N" is the total number of atoms, while the "atomic ratio" is For example, the "isotopic ratio" of deuterium (D) to hydrogen (H) in heavy water is roughly (corresponding to an "isotopic abundance" of 0.00014%). Doping in laser physics. In laser physics however, the "atomic ratio" may refer to the doping ratio or the doping fraction. Atomic ratio