Two-Frequency Microwave Quenching of Highly Excited Hydrogen Atoms

We present the first experimental results of quenching (ionization) of $\mathrm{H}(n_0=43\mathrm{}-49)$ atoms by a linearly polarized microwave electric field consisting of two frequencies (7.58 and 11.89 GHz). Adding a second frequency increases the quenching probability over that for only one frequency, especially where there is local stability at scaled frequencies near certain rational fractions, e.g., $n_0^3\omega =\frac{1}{6} \mathrm{and} \frac{1}{5}$. Some, but not all, two-frequency quench curves display a rich structure that appears to be related to that observed in some single-frequency quench curves.