S. N. Bagaev discovered new features in the absorption of laser radiation by gases at low pressures, which made it possible to observe narrow spectral lines at transitions between Doppler-broadened levels. This led to an increase in the resolution of spectroscopic methods in certain ranges.
S. N. Bagaev developed the physical principles of the femtosecond optical clocks, which made it possible to increase the accuracy of measuring time intervals in laser experiments. The accuracy of measurement with such a watch can reach 10–18 s. A super stable frequency standard has also been created based on {\ displaystyle Ne-He / CH_ {4}} {\ displaystyle Ne-He / CH_ {4}}. The frequency stability of the element is 10–15, which made it possible to measure the Rydberg constant with record accuracy.