| 摘要: | 本論文中，我們研究雷射穩頻的機制，其中包含氣態、固態和半導體雷射。 在氣態雷射穩頻方面，我們首先研究一波長為612 nm之短共振腔內鏡式氦氖雷射的偏振特性。我們發現在雷射功率輪廓中間附近會有一凸出部份，經研究得知雷射共振模在此一小區域中含有互相垂直的兩個偏振分量，此一區域亦即所謂的偏振轉變之處。然而，當雷射的兩個共振模位於對稱位置時，這兩個模都是線性偏振且其偏振方向互相垂直。因此我們即可用雙模穩頻法將雷射頻率穩定，且其穩定度可達5 ×10-10。此外，我們還研究了一支波長1523 nm 之內鏡式氦氖雷射的偏振特性，我們發現這雷射在正常工作下及外加橫向磁場時，皆無法使用簡單的雙模穩頻法來作雷射穩頻，唯有在外加軸向磁場時才可使用雙模穩頻法。當外加軸向磁場在12 mT 附近時，這雷射可以有單模輸出，且該模位於雷射增益輪廓中央附近並含有左旋或右旋之偏振分量。另外，由於模與模之間的互相競爭，當兩共振模位於對稱位置附近時，兩共振模僅是左旋或右旋之偏振模。因此我們即可用雙模穩頻法將雷射頻率穩定，且其穩定度可達1 MHz以內。這穩頻雷射的特徵是可以選擇為一含有左旋或右旋偏振分量之單模輸出，此兩分量之頻率差為400kHz；也可以選擇輸出為強度相同且僅為左旋或右旋偏振之雙模。 在固態雷射穩頻方面，我們使用一支半導體雷射幫浦的單石Nd:YAG雷射嘗試著去發展簡單新的穩頻系統。首先，我們將一矽玻璃材質的法布里－泊羅共振腔施以外力或加軸向磁場，使其產生雙折射作用，並利用雙折射效應所造成兩分離共振頻的強度差作為誤差信號來穩定雷射頻率。經測量這矽玻璃在1064 nm 的光波長中，它的光應力係數和Verdet 常數分別為 1.7×10-12 m2/N 和 2.95 rad．Tesla-1．M-1。對我們雷射頻率的穩定而言，欲得到適當的雙折射，外加應力應為 60 g/cm2 ，而外加磁場應為 20 mT。我們獲得的雷射頻率穩定度為 2 kHz。其次，我們利用一週期性區域反轉之鈮酸鋰晶體來作為光倍頻器，獲得532 nm 波長的倍頻光，並利用一震動鏡的方法來研究碘分子在532 nm 之調頻飽和吸收光譜，進而將雷射頻率穩定在碘分子的躍遷譜線上。 在半導體雷射穩頻方面，我們首度應用一倍頻的α-DFB 半導體雷射來觀察碘分子在531 nm 波長的躍遷譜線，並將雷射頻率鎖在碘分子之 R(94) 34-0 或 R(70) 33-0 第a10 的超精細躍遷譜線上。所得到的頻率穩定度為5 × 10-11。這樣的穩頻系統由於具備著體積小、價格低和可靠性高等優點，這穩頻雷射成為未來在531 nm 波段的頻率標準應是指日可待的。 In this thesis, we study the frequency stabilization of lasers, which includes the gas laser, solid state laser, and semiconductor laser. For frequency stabilization of the gas laser, we studied the first the polarization properties of a short internal-mirror 612 nm He-Ne laser. We found that polarization flip did not occur at the symmetric two-mode location but near the center of the power profile. Therefore, the laser could be frequency-stabilized using the two-mode method, and the stability achieved was better than 5 ×10-10 . This laser can be used as a light source in length measurements using multi-color interferometers. On the other hand, we studied the polarization properties of an internal-mirror 1523 nm He-Ne laser without and with a magnetic field. When the axial magnetic field was around 12 mT, the laser operated in single mode with two opposite circularly polarized components near the center of gain profile. In addition, due to the competition between these two opposite circularly polarized components, each mode had only one circularly polarized component survived when the laser operated in the two-mode region. We could stabilize the laser frequency at either the center of gain profile or the symmetric two-mode taking advantage of the power difference between the two circularly polarized components of the laser output, and the stability achieved was better than 1 MHz. For frequency stabilization of the solid state laser, we attempted to develop a new method of simple and low cost to stabilize a diode pumped monolithic Nd:YAG laser. First, we measured the birefringence of a Fabry-Perot etalon under applied stress and axial magnetic field. The stress optical coefficient and Verdet constant of fused silica obtain were 1.7×10-12 m2/N and 2.95 rad．Tesla-1．M-1 at wavelength of 1064 nm. For frequency stabilization of our laser, the suitable birefringence of the Fabry-Perot etalon was generated by applying stress of 60 g/cm2 or an axial magnetic field of 20 mT. The frequency stability obtained was 2 kHz. Next, we studied frequency modulation (FM) saturated absorption spectroscopy of 127I2 near 532 nm by using a periodically-poled LiNbO3 single-pass frequency doubler. The hyperfine transition of iodine near 532 nm was observed by a vibrating mirror. For frequency stabilization of semiconductor laser, we report, for the first time, the observation of the iodine hyperfine transitions at 531 nm using a frequency-doubled angled-grating DFB (α-DFB) semiconductor laser. The moderate high power of the α-DFB laser allows us to generate the second harmonic light by a periodically-poled LiNbO3 single-pass frequency doubler. We can stabilize this laser frequency to the hyperfine component a10 of R(94) 34-0 or R(70) 33-0 I2 line, and the preliminary frequency stability was about 5 × 10-11. This laser system is an attractive frequency standard at 531 nm due to its compact size, high reliability, and low cost. |
