Abstract
We built a 1009 nm external cavity tapered amplifier Laser with 7 cm long cavity length. The laser have the advantages of high power (1.2 W), wavelength tunable (37 nm), single mode and narrow linewidth so this laser is very suitable for spectroscopy measurement. After we finish the laser construction we use a 2.5 cm long periodically poled lithium niobate crystal (PPLN) for the second harmonic generation to get the green light at 504.5 nm. Finally, we successfully observe the hyperfine spectrum of iodine by using the saturation absorption spectroscopy method. In the future, We will lock our laser on one of the iodine hyperfine transitions, and use it as the frequency reference for absolute frequency measurements of the 21S0-31D2 transitions of 3He and 4He atom.