雷射二極體體積小、成本低廉、發光效率高，已成為實驗主要的光源，但其多模、線寬大，頻率容易受到環境溫度與操作電流影響，對於實驗造成許多不利的地方。外腔雷射透過在雷射二極體前面放置光柵，使光柵繞射光回饋給予雷射二極體，兩者中間出現新的共振腔場並篩選頻率，外腔雷射輸出光能夠單模、線寬小等優點，並且能透過改變光柵角度與位置調整輸出光頻率，成為可調式雷射光源。於本論文，我們將研究藍光二極體與Littrow架構外腔雷射系統的特性。
我們測量445 nm 輸出功率80 mW 雷射二極體(Thorlabs , PL450B)，於不同操作電流與溫度下的輸出跟光譜變化，雷射二極體於不同操作電流下其輸出光模態會隨之改變，從低到高電流變化為單模，雙模，到多模。雷射二極體單模時的線寬大小，約為19.59 MHz，此時的溫度15 °C，輸出功率為3.5 mW。仿造之前實驗室制作的3公分外腔雷射系統，使用2400 lines/mm Holographic光柵架設了一台Littrow架構的3公分外腔雷射，具有約8.6 MHz左右的線寬大小，輸出功率約為40 mW，我們也透過光譜儀分析不同操作電流與溫度下的雷射光譜，位於高電流下能夠達到單模，並且能透過轉動光柵角度改變其波長範圍，約為4.3 nm。
最後，我們替換更換兩種不同條數與種類的光柵，1800 lines/mm Ruled與 3600 lines/mm Holographic光柵與原本的光柵比較，使用3600 lines/mm 的光柵能夠得到最高功率69.5 mW的單模輸出光，其線寬大小約為8.45 MHz。

Laser diode (LD) has small volume, low cost and high luminous efficiency, and now has been seen as important light sources in experiment. However, the optical characteristics of LDs, including multi spatial modes, wider linewidth, and frequency jitters due to the diode temperature and the operating current, was regarded as disadvantages in experiment. External cavity diode laser (ECDL) has a grating in front of LD, so that the diffracted light on the grating surface fed back to LD. In addition, ECDL output can be single longitudinal mode and narrow linewidth. The laser frequency can be adjusted by changing the grating angle and position. In this thesis, we studied characteristics of the blue LD and ECDL in the Littrow configuration.
We measured the output power, spectrum, and linewidth of a 445-nm LD with 80-mW output power at different operating currents and temperatures. The spectral mode of blue LD was changed with the operating currents. From low to high operating currents, the spectral mode of blue LD varied from single mode, dual mode and multimode. The linewidth of LD in single mode was estimated about 19.59 MHz when the diode temperature is 15 °C, and the output power is 3.5 mW. Using 30-mm cavity length ECDL system designed in our laboratory, we used a 2400 lines/mm holographic grating to set up a Littrow-type 30-mm cavity length ECDL with 8.6-MHz linewidth and 40-mW output power. We also analyzed spectrum at different operating currents and diode temperatures by spectrometer. It can single-mode operate at high current and its wavelength range is about 4.3 nm by rotating the grating angle.
Finally, we replaced two types of the grating, 1800 lines/mm (Ruled) and 3600 lines/mm (Holographic). Using 3600 lines/mm grating can get the highest output power 69.5 mW and single mode. The linewidth is about 8.45 MHz.

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