Abstract
This dissertation studies the low-lying levels of ^{6,7}Li in a well-collimated atomic beam. We have built two laser systems, one of which frequency is stabilized on a confocal Fabry-Perot cavity and scans the lithium spectrum by tuning the cavity length as a spectroscopy laser. Another laser is locked to molecular iodine transition near lithium resonance line as a reference laser. The laser-induced fluorescence signal is detected by a photomultiplier, and the beat frequency between the spectroscopy laser and the reference laser is recorded. We have clari ed that the 2P_{1/2} hyperfi ne structure splitting and D1 isotope shift for stable ^{6,7}Li disagree with previous experiments. The 2P_{1/2} hyper fine interval are 26.108(9) MHz and 91.873(5) MHz for ^{6}Li and ^{7}Li, respectively. The D1 isotope shift is 10533.800(15) MHz. Combining the measured D1 isotope shift with the calculated energy shift determines the relative squared nuclear charge radius to be -0.720(6) fm^{2}. In order to test atomic calculations in other low-lying levels, we have also measured the hyperfi ne splitting of 3P_{1/2} state. Our result improves the precision by a factor of 6.7 compared to previous measurements. Furthermore, the absolute frequency is measured and the precision is three thousand times better than previous results.