Abstract
Helium is the simplest two-electron atomic system, and its theoretical calculations and experimental measurements are all very important. Many of atomic helium transitions have been measured, and we plan to measure the absolute frequency of 21S-31D two-photon transition line. This would allow us to obtain highly accurate 31D-33D difference using the precision measured frequencies of 21S-23S, and 23S-33D lines, and further test the correctness of theoretical calculations. The goal of this thesis is building a 1009 nm external cavity optical feedback tapered amplifier laser, using tapered amplifier which emission spectrum is from 1000 nm to 1025 nm as the gain medium, with Littman-Metcalf configuration. Preliminary results are as follows: maximum output power is 160 mW, single frequency, threshold current around 3300-3400 mA, slope efficiency is 0.125 mW/mA, wavelength tunability is 14 nm, and the beam profile is elliptical with high order transverse mode. We will improve the output power and use this laser as light source to measure 21S-31D transition frequency by two-photon resonance in the future.