利用光纖雷射激發連續式光參數震盪器產生中紅外與全彩雷射

Fiber-laser-pumped CW OPO for Mid-IR and RGB Laser Generation

林碩泰(Shou-Tai Lin)

指導教授 ： 黃衍介

國立清華大學/電機資訊學院/光電工程研究所/博士(2009年)

摘要

Singly resonant optical parametric oscillators (SROs) based on periodic poled lithium niobate (PPLN) crystals can be efficient sources providing highly efficient, narrow-line and tunable laser radiations covering a spectrum from the visible to the mid-infrared. A fiber laser has also been widely adopted as a pump laser for a SRO due to its superior diffraction-limited beam profile and high accessible output power. This thesis, for the first time to my knowledge, demonstrated a single-frequency, fiber-laser pumped SRO oscillating at a mid-infrared wavelength and a fiber-laser pumped SRO with intra-cavity and extra-cavity wavelength converters for red, green, and blue laser generations.
To show the versatility of a PPLN crystal, we first demonstrated in this thesis a monolithic PPLN crystal as a wavelength converter and a laser Q-switch. We then demonstrated a single-longitudinal-mode (SLM), continuous-wave SRO at 3.2 um by using a MgO:PPLN crystal as the gain medium and a multi-longitudinal-mode (MLM) Yb fiber laser at 1064 nm as the pump laser. At 25-W pump power, the SRO generated 5.3 and 1.2 W at 1.58 and 3.23 um, respectively. The linewidth of the resonated 3.2-um wave is about 5 MHz. We observed optical bistability and thermally induced optical guiding in the SRO due to the weak absorption of the resonating wave inside the MgO:PPLN crystal. As soon as the intracavity power reaches the thermal guiding threshold at 30 W, the SRO shows a step increase in the parametric efficiency by a factor of 2.5. Measured hole burning in the pump spectrum indicates that the broad pump bandwidth is the cause of the clamped pump depletion.
By incorporating two sum-frequency generators (SFG) inside an infrared SRO, we up-converted the frequency of a pump laser at near infrared to the visible range. Specifically, we demonstrated in this thesis a continuous-wave (cw), watt-level, red, green, and blue (RGB) lasers pumped by an economical multi-mode Yb-fiber laser at 1.064 um. A singly resonant optical parametric oscillator (SRO) at 1.56 um is installed with two intracavity SFGs for red and blue laser generations and an extracavity second harmonic generator (SHG) for green laser generation. At 25 W pump power, the SRO generated 4, 0.48 and 0.057 W lasers at 633 (red), 532 (green), 450 nm (blue), respectively.

關鍵字

非線性光學 ； 光參數共振腔

並列摘要

利用週期性鋰酸鈮晶體建構一連續式、單波長光參數共振腔，進而產生一從可見光到中紅外光之可調雷射光源，為一個相當有效率的方法，其中的優點包含了高的轉換效率與極窄的輸出頻譜寬度。近來，由於連續式光纖雷射的迅速發展，其高輸出功率與近乎理想高斯分佈的空間特性，已經廣泛的被利用在光參數共振腔之幫浦光源上，這本論文發表了世界第一個，利用寬頻光纖雷射作為中紅外光參數共振腔的幫浦光源，並產生單頻之中紅外光源；同時，並利用光纖雷射幫浦一光參數共振腔，搭配腔內與腔外的波長轉換器，產生紅、藍、綠全彩雷射。
在此論文一開始，為了展現週期性鋰酸鈮晶體的多用途特性，我們先驗證了單一週期性鋰酸鈮晶體，可以同時當作波長轉換器與雷射Ｑ值調變器，接著，我們利用一寬頻(1 nm)的1064 nm光纖幫浦雷射與一摻鎂週期性鋰酸鈮晶體為增益介質，得到了一連續式、單頻的中紅外雷射，在幫浦功率為25瓦與輸出波長為1.58與3.2 um時，我們得到輸出功率分別為5.3 與1.2瓦； 此外，藉由量測，超過瓦級之3.2 um光源為單頻輸出，同時其頻譜線寬為5 MHz。由於週期性鋰酸鈮晶體對於共振之中紅外波長有輕微的吸收行為，我們觀察到熱吸收引起的雙穩態與熱波導效應，當共振腔內功率達到熱波導閾質３０瓦時，熱波導可以使光參數增益增加兩倍，由於幫浦雷射頻寬過寬，我們同時在幫浦雷射頻譜中觀察到燒洞現象。
波長可調的可見光雷射，可以藉由在紅外單波長光參數共振腔內串接兩級合頻產生器，將近紅外之幫浦雷射做頻率上轉換的方式來產生，我們將一寬頻的1064 nm光纖幫浦雷射光源轉換到可見光區域，並得到瓦級、連續式、紅、綠、藍全彩雷射，此近紅外單波長光參數共振腔之共振波長為1.56 um，並在共振腔內串接兩級合頻產生器得到紅、藍光，同時再利用一外部的倍頻器，將剩餘之幫浦雷射轉換到綠光，在25瓦幫浦功率時，我們得到4瓦的紅光(633 nm)、0.48瓦的綠光(532 nm) 、0.057瓦的藍光(450 nm)。

並列關鍵字

Nonlinear Optics ； Optical parametric oscillator

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