雷射二極體憑藉著質量與體積的輕巧、成本較低廉、高發光效率且可方便地透過驅動電流來調整功率等優點，而使其廣泛地應用於日常生活中，且在研究上逐漸佔有一席之地。然而，其雷射頻率容易受環境的溫度與注入電流影響而造成不穩定，以及雷射增益曲線常常有著較大的線寬，這種種特性使得在研究與應用上的諸多不便。
在過去通常採取腔內倍頻的技術，來尋求一個單頻的綠光雷射，但此種雷射往往體積較大且較為耗能。而在近年，利用氮化銦鎵為材料，來直接產生綠光雷射，有望可取代傳統的二極管泵浦固態雷射，因此，本論文以氮化銦鎵雷射二極體結合Littrow結構來建構出外腔式二極體綠光雷射，透過經由光柵所產生的一階繞射光作為回饋訊號，耦合回去雷射二極體上，並且以零階繞射光為輸出訊號，憑藉著此種簡單的設計，來尋求一線寬窄且可調式的雷射，並比較兩種不同腔長外腔雷射(ECDL)結構的不同操作電流之光譜變化，波長可調範圍以及偏振改變下的發光效率，並尋求相較於短腔長外腔雷射更短的雷射線寬。
我們仿照先前實驗室成員所製作3 cm外腔雷射的架構成功的建構出一6 cm的溫控式的外腔式綠光雷射，並成功地透過增加外部腔長來成功降低線寬，從 10.3 MHz降至5.32 Mhz，此6 cm外腔綠光雷射二極體波長為517 nm，且在兩倍的閾值電流下，可輸出約31 mW的輸出功率。
最後，本論文嘗試將頻率鎖在一條碘的躍遷譜線上，透過PID控制器來將實驗過程中產生的誤差訊號回饋至壓電致動器(PZT)，以電壓來調控雷射輸出頻率，使誤差訊號為零，進而來使頻率穩定，我們以Allen variance來量化雷射的穩定性。
而在先前，我們實驗室的成員們透過碘飽和吸收光譜直接將自由運轉下的氮化銦鎵二極體雷射拿來做穩頻，將頻率直接所在碘的超精細結構躍遷的飽和吸收譜線上，調製信號經由PID控制迴路回饋至二極體雷射，並透過操作電流來調製雷射輸出頻率，我們將其拿來與綠光外腔二極體雷射的穩頻來做比較。

Laser diodes are widely used in our daily life due to their light weight, low cost, high luminous efficiency, and easy adjustment of power through driving current, moreover, they occupy an important place, however, their laser frequencies are easily affected by the environment temperature and injection current, hence it cause them to be unstable, in addition, the laser gain curve often has a large linewidth, these characteristics make the research and application so inconvenient. In the past, a single longitudinal mode green laser can be obtained by using the intra cavity frequency-doubled design. But such lasers are often larger and more energy-consuming. In recently, the diode lasers based on indium gallium nitride compound semiconductors can directly emit green laser beam and are expected to replace the traditional diode-pumped solid state lasers.
Therefore, in this thesis, an diode laser based on indium gallium nitride compound semiconductors combined with a Littrow structure is used to construct an external cavity green diode laser. The first-order diffracted light generated by the grating is used as a feedback signal, and coupled to the laser diode, besides, the zero-order diffracted light is used as an output signal. With this simple design, we can chase down a narrow linewidth and adjustable laser, and compare the spectral changes of different operating currents between the two kinds of cavity length external cavity laser structures, explore the wavelength tunable range and the luminous efficiency under the change of polarization, moreover, we try to seek the shorter line width compare with the short cavity external cavity laser. We model the structure of the 3 cm external cavity laser produced by our previous lab members, and then successfully construct a 6 cm temperature-controlled external cavity green diode laser, and successfully reduce the linewidth by increasing the external cavity length from 10.3 MHz to 5.32 Mhz. The wavelength of this 6 cm external cavity diode laser is 517 nm, and the output power is 31 mW under the two times of the threshold current.
In this thesis, we attempt to lock the laser frequency on an iodine transition line. In the experiment, PID controller is used to feed back the error signal to the piezoelectric actuator. We adjust the laser output frequency with voltage make the error signal zero, and then we make the frequency stable. At last, we use Allen variance to quantify the stability of lasers. Our lab members directly took the free-running indium gallium nitride diode laser to do frequency stabilization. We direct locked of the laser frequency to the saturation–absorption line of the hyperfine structural transition of iodine. The modulated signal is fedback to the diode laser via the PID control loop, and the laser output frequency was modulated by adjusting operational current. We compare it with the frequency stabilization of the green external cavity diode laser.

1. R. Lang, and K. Kobayashi, "External Optical Feedback Effects on Semiconductor Injection-Laser Properties," IEEE J Quantum Elect 16, 347-355 (1980).
2. K. Martin, W. Clarkson, and D. Hanna, "3 W of single-frequency output at 532 nm by intracavity frequency doubling of a diode-bar-pumped Nd: YAG ring laser," Optics Letters 21, 875-877 (1996).
3. Y.-F. Chen, T.-M. Huang, C.-L. Wang, and L.-J. Lee, "Compact and efficient 3.2-W diode-pumped Nd: YVO 4/KTP green laser," Applied optics 37, 5727-5730 (1998).
4. A. Avramescu, T. Lermer, J. Muller, C. Eichler, G. Bruederl, M. Sabathil, S. Lutgen, and U. Strauss, "True Green Laser Diodes at 524 nm with 50 mW Continuous Wave Output Power on c-Plane GaN," Appl. Phys Express 3 (2010).
5. R. L. Barger and J. L. Hall, Phys. Rev. Lett. 22, 408 (1969)
6. G. R. Hanes and C. E. Dahlstrom, Appl. Phys. Lett. 14, 362 (1973)
7. A. Arie and Robert L. Byer, "Laser heterodyne spectroscopy of 127I2 hyperfine structure near 532 nm," J. Opt. Soc. Am. B, 10, 1990-1997 (1993)
8. A. Arie and Robert L. Byer, "The hyperfine spectroscopy of the I2 R(119)35-0 transition," Opti. Common. 111, 253-258 (1994)
9. A. S. Arnold, J. S. Wilson, and M. G. Boshier, "A simple extended-cavity diode laser," Review of Scientific Instruments 69, 1236-1239 (1998).
10. C. J. Hawthorn, K. P. Weber, and R. E. Scholten, "Littrow configuration tunable external cavity diode laser with fixed direction output beam," Review of Scientific Instruments 72, 4477-4479 (2001).
11. K. C. Harvey, and C. J. Myatt, "External-Cavity Diode-Laser Using a Grazing-Incidence Diffraction Grating," Optics Letters 16, 910-912 (1991).
12. S. Lecomte, E. Fretel, G. Mileti, and P. Thomann, "Self-aligned extended-cavity diode laser stabilized by the Zeeman effect on the cesium D-2 line," Appl. Optics 39, 1426-1429 (2000).
13. Arimondo, E. N. Inguscio and P. Violino, Rev. Mod. Phys. 49,31 (1997)
14. W. E. Lamb, Phys. Rev. A 134, 1429 (1964)
15. W. Demtroder, "Laser Spectroscopy ", 439-454 (1981).
16. K. Libbrecht and M. Libbrecht, "Interferometric measurement of the resonant absorption and refractive index in rubidium gas," American journal of physics 74, 1055-1060 (2006).
17. M. Fleischhauer, A. Imamoglu, and J. P. Marangos, "Electromagnetically induced transparency: Optics in coherent media," Rev Mod Phys 77, 633-673 (2005).
18. T. Hager, G. Brüderl, T. Lermer, S. Tautz, A. Gomez-Iglesias, J. Müller, A. Avramescu, C. Eichler, S. Gerhard, and U. Strauss, "Current dependence of electro-optical parameters in green and blue (AlIn) GaN laser diodes," Applied Physics Letters 101, 171109 (2012).