| Summary: | 碩士 === 國立清華大學 === 物理學系 === 106 === In this thesis, we used a home-made external cavity diode laser (ECDL) at 778 nm to seed a commercial tapered amplifier (Newport TA-7600), which can boost the laser power up to more than 500 mW. After the tapered amplifier, the laser beam was split into two beams. One was sent to a waveguide PPLN to double the frequency of 778 nm and the other one was referenced to an optical fiber comb system in our lab. We used the beam of 2 mW at 389 nm to perform saturated absorption spectroscopy and measured the helium 2^(3)S to 3^(3)P transition. The absolute frequency was measured by the Erbium-doped fiber frequency comb. We used the beat frequency between the ECDL and fiber comb system and an offset lock circuit to lock our laser on fiber comb system. The frequency stabilization of the ECDL can reach 1.3 × 10^(−11). Therefore, we can be precisely measured the absolute frequency of our laser and the targeted transition.
The results of the transition frequencies were as follow : 2^(3)S_(1) → 3^(3)P_(2) f = 770 724 067.399(161) MHz and 2^(3) S_(1) → 3^(3)P_(1) f = 770 724 726.246(180) MHz, The precision of the results reached 2.3 × 10^(−10), The fine structure splitting between 3^(3)P_(2) and 3^(3)P_(1) states was also measured, and ν_(12) = 658.847(45) MHz,which is in agreement with theoretical calculation.
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