第一型相位匹配腔內倍頻二極體激發式固態雷射之綠光雜訊與PTR Grating 特性之研究

陳證文

指導教授 ： 楊士禮

國立清華大學/電機資訊學院/光電工程研究所/碩士(2006年)

摘要

腔內倍頻二極體激發的固態雷射，由於腔內不同縱向模態間互相耦合，使得倍頻輸出訊號有著極劇烈的擾動現象，限制了雷射的發展與應用，此即所謂的綠光雜訊 (green problem)，因此解決綠光雜訊為提高雷射應用的首要目標。
根據文獻上所提供的rate-equation，我們模擬第一型相位匹配的綠光雜訊行為；在實驗部份我們設計了兩種雷射共振腔，分別為Nd︰YCOB 自倍頻晶體與Nd︰GdVO4 雷射晶體和 BIBO 倍頻晶體所組成的雷射共振腔，期望操作在g=0 的情況下，消除不同偏振方向模態間的耦合來達成消除雜訊的目的，結果發現，當模態數大於1個時，雖然 g=0 可以消除不同方向模態間的混頻，但是同方向上模態互相耦合的情形依然會造雜訊的產生，對第一型相位匹配的晶體而言，若要真正消除綠光雜訊，必須將共振腔內模態數減少至1個模態。
最後，我們將一個 Volumetric Bragg Grating 置入共振腔中，利用它窄頻的特性，希望將共振腔內的模態數控制為單模操作，以期能達到消除綠光雜訊的效果。而實驗結果也發現，在單模操作之下，綠光倍頻輸出頗為穩定，一但腔內模態數大於1個，便有綠光雜訊產生，與模擬或是先前實驗結果符合。因此，Volumetric Bragg Grating的確能有效的減少腔內模態數目，甚至達到單模操作。

關鍵字

綠光雜訊

並列摘要

Due to the coupling between longitudinal modes in the intracavity doubled diode-pumped solid-state (DPSS) laser, large amplitude fluctuations have been observed in the green output. It restricts the development and applications of intracavity doubled DPSS laser, and this phenomenon knows as the “Green Problem”. In order to improve the applications of intracavity doubled DPSS laser, solving the green problem is the first target.
According to the rate-equations which were done in the previous work, we simulate the behavior of the Type I phase matching green output. In the experiment, we design two kinds of laser cavities, individually including self-frequency doubling crystal (Nd︰YCOB) laser system and Nd︰GdVO4 & BIBO double crystals laser system. We try to reduce the green noise which caused by coupling between different polarization modes by operating at g=0, but it cannot restrain the coupling modes in the same polarization when the number of modes in the laser cavity is larger than one. So, if we want to lower the Type I phase matching green noise, the most efficient method is single mode operation.
Finally, we hope to reduce the green noise by putting a Volumetric Bragg Grating into the cavity. In the experimental results, we really observe the stable green output when single mode operation in the laser cavity; also we can observe green noise when two modes survive in the cavity. Consequently, the method of putting a Volumetric Bragg Grating into the cavity is really reducing the number of modes in the cavity, and possible to obtain single mode operation.

並列關鍵字

green noise

參考文獻

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