Comparison of various two-photon excitation schemes for laser-induced fluorescence spectroscopy in atomic hydrogen

Abstract

Various two-photon excitation schemes for laser-induced-fluorescence spectroscopy in atomic hydrogen have been experimentally investigated. The results are compared with one another and with theoretical predictions. A tunable narrow-bandwidth ArF excimer laser (oscillator–amplifier system) in combination with a Raman cell was used as the light source. Atomic hydrogen at room temperature and at densities of ~1014 cm−3 was provided by a flow-tube reactor. Excitation was from the ground state to the excited n = 3 and n = 4 states, and fluorescence light was observed at Balmer-α and -β wavelengths, respectively. Various wavelength combinations [(205 nm × 2) and (193 + 219 nm) for excitation to n = 3 and (193 + 195 nm) for excitation to n = 4], polarizations (linear, circular, and unpolarized), and bandwidths (110, 11, and 0.8 cm −1) were used for the excitation process.