New energy levels of atomic lanthanum with small total angular momentum quantum number discovered by laser spectroscopic methods in the near IR

Optogalvanic spectroscopy as well as laser-induced fluorescence spectroscopy were applied in order to find new energy levels of atomic lanthanum. A hollow-cathode lamp and a tuneable continuous wave titanium-sapphire laser in the wavelength range from 750 nm to 850 nm were used for the measurements. Three energy levels of even parity with small values of total angular momentum quantum number J were discovered: 38 519.18 cm⁻¹ with J=1/2, 40 392.80 cm⁻¹ with J=3/2, and 42 191.24 cm⁻¹ with J=3/2. The existence of these three levels was confirmed by laser excitations of several spectral lines as well as by spectral lines from a Fourier transform spectrum. Magnetic dipole hyperfine structure constants of the three new levels were determined from fits of the experimental spectra of the laser lines.