可調單頻 Nd:GdVO4雷射及其光譜應用

Abstract

This thesis work developed a single frequency diode-pumped Nd:GdVO4 laser at 1070 nm using a volume Bragg grating as the output coupler of a short plano-concave cavity. After second harmonic generation with a periodically-poled lithium niobate (PPLN), this laser is an excellent source for parity non-conservation (PNC) experiments using thallium atom. The accuracy of atomic theory which is needed to determine the thallium PNC motivated us to include the precise frequency measurement of the thallium 6P3/2 → 7S1/2 transition as part of this thesis. The light source was also utilized realize the absolute frequency measurements of the hyperfine components of molecular iodine at 535 nm. The developed 1070 nm single frequency Nd:GdVO4 laser can achieve an output power of 300 mW. The beam propagation parameter at 200 mW was ~1.2, and the divergence angle was ~0.37. The single frequency range with cavity length tuning was 5.1 GHz at 100 mW output power. We also locked the laser frequency to a confocal reference cavity and a relative stability of 7.58 kHz was achieved. After amplification of the fiber amplifier, the frequency stabilized 1070 nm laser passed through a PPLN to obtain a 535 nm light source by second harmonic generation. The absolute frequency of the a1, a10, and a15 hyperfine components of molecular iodine P(28) 30-0 line at 535 nm were measured with the frequency doubled Nd:GdVO4 laser. The frequency doubled 1070-nm Nd:GdVO4 laser was frequency stabilized to a hyperfine component of I2 using the saturation absorption spectroscopy and the third harmonic demodulation technique. The frequency stability of 310-12 was achieved at 10 second averaging time when its frequency was stabilized to the a1 component. An optical frequency comb was used to measure its absolute frequency. The pressure shift was investigated to obtain the absolute frequency at zero pressure. The effect of pressure and power broadening of the a10 component were also investigated. The saturated absorption spectrum of the 6P3/2 → 7S1/2 transition of 203Tl and 205Tl in a hollow cathode lamp was observed with the frequency-doubled 1070 nm Nd:GdVO4 laser. Similar to the iodine spectrum measurement, the third-derivative spectrum of the hyperfine components were obtained using the wavelength modulation spectroscopy and used to stabilize the laser frequency. Analysis of the error signal showed that the frequency stability reaches 30 kHz at 1 s averaging time. Such a frequency-stabilized light source at 535 nm can be used for laser cooling of thallium and for investigating the PNC effect in thallium. The absolute frequencies of hyperfine components were measured with an accuracy of 30 MHz using a precision wavelength meter. Including the pressure shift correction, the center of gravity of the transition frequency was determined to an accuracy of 22 MHz for both isotopes. Meanwhile, the isotope shift (IS) derived was in good agreement with earlier measurement. The precision measurements of thallium atomic structure can serve as the experimental constraints and benchmarks for the improvements of thallium wavefunction calculations.