We show that resonant enhanced two-photon spectroscopy is a very powerful and promising diagnostic method for trapped atomic hydrogen and antihydrogen. This method, in which photons of different wavelengths are used to excite H atoms from thc IS to the 3D or 3S level, uses the resonant enhancement of the intermediate 2P level to obtain high sensitivity while at the same time offering potentially much higher spectral resolution than single photon (Lyman-a) excitation.

Hyperfine Interact.

Hijmans, T. W., Pinkse, P. W. H., Mosk, A., Weidemüller, M., Reynolds, M. W., Walraven, J. T. M., & Zimmermann, C. (2000). Resonance-enhanced two-photon spectroscopy of magnetically trapped atomic hydrogen. Hyperfine Interact., 127, 175–180.