高功率全固態(tài)單頻激光器的實(shí)驗(yàn)研究
發(fā)布時(shí)間：2018-08-14 16:38
【摘要】：高功率全固態(tài)單頻綠光激光器具有結(jié)構(gòu)緊湊、光束質(zhì)量好、強(qiáng)度噪聲低等優(yōu)點(diǎn),已經(jīng)廣泛應(yīng)用于量子通信、全息成像、干涉測(cè)量等領(lǐng)域,還可通過倍頻產(chǎn)生深紫外光以及作為高功率鈦寶石激光器和OPO的泵浦源。但在進(jìn)一步提升高功率單頻綠光激光器的輸出功率的過程中,我們遇到了如下問題：1)當(dāng)進(jìn)一步增大泵浦功率以提升激光器的輸出功率時(shí),激光器的輸出功率不但沒有上升,反而會(huì)下降,同時(shí)激光光束會(huì)由單橫模退化為多橫模；2)激光器在升降泵浦功率的過程中存在類雙穩(wěn)現(xiàn)象,同時(shí)伴隨著輸出功率的突升突降,導(dǎo)致腔內(nèi)器件產(chǎn)生嚴(yán)重的熱致應(yīng)力突變進(jìn)而影響激光器的使用壽命。經(jīng)過研究,我們發(fā)現(xiàn)在高功率內(nèi)腔倍頻單頻激光器中,不但增益晶體的熱透鏡效應(yīng)對(duì)激光器性能有重要影響,而且光學(xué)單向器中的TGG晶體通過吸收腔內(nèi)基頻光產(chǎn)生的熱透鏡效應(yīng)同樣會(huì)嚴(yán)重影響激光器的工作狀態(tài)。本文的研究主要是圍繞TGG晶體的熱透鏡效應(yīng)對(duì)激光器工作狀態(tài)的影響以及如何緩解和補(bǔ)償TGG晶體的熱透鏡效應(yīng)展開的,另外我們還在考慮TGG晶體熱透鏡效應(yīng)的基礎(chǔ)上,研究了腔鏡曲率半徑對(duì)激光器工作狀態(tài)的影響。我們首先利用ABCD矩陣分析了TGG晶體的熱透鏡效應(yīng)對(duì)激光器工作狀態(tài)的影響,然后進(jìn)行實(shí)驗(yàn)驗(yàn)證。實(shí)驗(yàn)證明TGG晶體的熱透鏡效應(yīng)不但存在,而且對(duì)激光器的工作狀態(tài)有顯著影響：使穩(wěn)區(qū)變窄,降低最佳工作點(diǎn)對(duì)應(yīng)的泵浦功率,最終限制激光器的輸出功率。根據(jù)理論計(jì)算,我們可以通過縮短腔長去緩解TGG晶體熱透鏡效應(yīng)的影響,提升激光器最佳工作點(diǎn)對(duì)應(yīng)的泵浦功率進(jìn)而提升輸出功率,我們的實(shí)驗(yàn)結(jié)果和理論預(yù)期比較一致。但縮短腔長并不能消除TGG晶體熱透鏡效應(yīng)的影響,因此在改變泵浦功率的過程中觀察到激光器存在明顯的類雙穩(wěn)現(xiàn)象,同時(shí)伴隨著輸出功率的突升突降。我們對(duì)類雙穩(wěn)現(xiàn)象進(jìn)行了定性分析,進(jìn)一步證明TGG晶體的熱透鏡效應(yīng)源于TGG晶體對(duì)腔內(nèi)基頻光的吸收,而不是對(duì)泵浦光的吸收,這和增益晶體的熱透鏡效應(yīng)的產(chǎn)生機(jī)制是不同的。在分析了TGG晶體對(duì)激光器工作狀態(tài)的影響的基礎(chǔ)上,我們選擇具有負(fù)熱光系數(shù)的單軸晶體——DKDP晶體,對(duì)TGG晶體的熱透鏡效應(yīng)進(jìn)行自適應(yīng)性的動(dòng)態(tài)補(bǔ)償。首先我們確定了DKDP晶體薄片的切割方向,即光軸和通光方向的夾角為30°,以使DKDP晶體薄片的熱透鏡效應(yīng)盡可能的各向同性,以有效補(bǔ)償TGG晶體的熱透鏡效應(yīng)。然后在固定的腔長下,利用三片厚度不同的DKDP薄片分別對(duì)TGG晶體的熱透鏡效應(yīng)進(jìn)行補(bǔ)償,根據(jù)激光器最佳工作點(diǎn)對(duì)應(yīng)的泵浦功率的變化,我們擬合得到了DKDP晶體薄片的熱透鏡焦距公式。由此我們計(jì)算得到,在當(dāng)前的實(shí)驗(yàn)條件下,厚度為1.65 mm的DKDP薄片可以完全補(bǔ)償8 mm長的TGG晶體的熱透鏡效應(yīng),因此我們利用現(xiàn)有的1.6 mm的補(bǔ)償片進(jìn)行調(diào)試。通過補(bǔ)償,不但完全消除了激光器之前存在的類雙穩(wěn)現(xiàn)象,獲得極為平緩的輸出功率曲線,而且可將單頻532 nm激光的最大輸出功率從14.7 W提升至30.2 W。最后,針對(duì)早前文獻(xiàn)中關(guān)于高功率固體激光器應(yīng)該使用凸面腔鏡取代平面腔鏡以緩解增益晶體熱透鏡效應(yīng)從而提升激光器輸出功率的結(jié)論,我們首先進(jìn)行了理論分析,發(fā)現(xiàn)當(dāng)腔長固定時(shí),隨著腔鏡曲率半徑的增大,激光器的閾值泵浦功率和最佳工作點(diǎn)對(duì)應(yīng)的泵浦功率均降低；而如果在增大腔鏡曲率半徑的同時(shí)對(duì)腔長進(jìn)行適當(dāng)調(diào)節(jié),激光器也能獲得和采用曲率半徑較小的腔鏡時(shí)類似的工作狀態(tài)。然后我們選擇一組平面腔鏡和兩組曲率半徑分別為1500 mm和3000 mm的凸面腔鏡分別在腔長固定和腔長可變的條件下進(jìn)行實(shí)驗(yàn),實(shí)驗(yàn)結(jié)果和理論預(yù)期比較吻合。我們還計(jì)算了不同腔鏡曲率半徑下的激光器的最佳腔長,可為采用類似腔型的高功率單頻激光器的設(shè)計(jì)提供一定的理論指導(dǎo)。最后,我們采用平面腔鏡進(jìn)行調(diào)試,獲得最高輸出功率為12.97 W的單頻532 nm激光器。創(chuàng)新性工作：1.研究了TGG晶體的熱透鏡效應(yīng)對(duì)高功率單頻激光器工作狀態(tài)的影響,并通過縮短腔長去被動(dòng)適應(yīng)這種影響以提升激光器的輸出功率。對(duì)激光器的類雙穩(wěn)現(xiàn)象進(jìn)行了定性分析,進(jìn)一步證明TGG晶體的熱透鏡效應(yīng)源于TGG晶體對(duì)腔內(nèi)基頻光的吸收；2.在高功率單頻激光器中利用DKDP晶體薄片對(duì)TGG晶體的熱透鏡效應(yīng)進(jìn)行動(dòng)態(tài)補(bǔ)償,獲得30.2 W的全固態(tài)連續(xù)光內(nèi)腔倍頻單頻532 nm激光器,據(jù)我們所知,這是目前同類型單頻532 nm激光器所獲得的最高的輸出功率；3.研究了腔長和腔鏡曲率半徑的關(guān)系,指出先前文獻(xiàn)中關(guān)于高功率固體激光器應(yīng)當(dāng)采用凸面腔鏡以緩解增益晶體熱透鏡效應(yīng)這一結(jié)論的局限性,證明即使采用平面腔鏡,只要將腔長調(diào)整到適當(dāng)長度,激光器也能獲得和采用曲率半徑較小的凸面腔鏡時(shí)類似的工作狀態(tài)。
[Abstract]:High-power all-solid-state single-frequency green laser has the advantages of compact structure, good beam quality and low intensity noise. It has been widely used in quantum communication, holographic imaging, interferometry and other fields. It can also generate deep ultraviolet light by frequency doubling and be used as the pump source of high-power Ti:sapphire laser and OPO. In the process of green laser output power, we encounter the following problems: 1) when the pump power is further increased to enhance the output power of the laser, the output power of the laser will not increase, but will decline, and the laser beam will degenerate from a single transverse mode to a multi-transverse mode; 2) in the process of raising and lowering the pump power of the laser. In high power intracavity frequency doubled single frequency lasers, not only the thermal lens effect of the gain crystal has an important effect on the performance of the lasers, but also the thermal lens effect of the gain crystal is found. The thermal lensing effect produced by TGG crystal in the optical unidirectional device through the fundamental frequency light in the absorption cavity will also seriously affect the working state of the laser. This paper mainly focuses on the influence of the thermal lensing effect of TGG crystal on the working state of the laser and how to mitigate and compensate the thermal lensing effect of TGG crystal. Considering the thermal lens effect of TGG crystal, the effect of the radius of curvature of the cavity mirror on the laser operating state is studied. First, the influence of the thermal lens effect of TGG crystal on the laser operating state is analyzed by ABCD matrix, and then verified by experiment. The experimental results show that the thermal lens effect of TGG crystal not only exists, but also affects the laser. According to the theoretical calculation, we can reduce the cavity length to alleviate the influence of the thermal lens effect of TGG crystal, increase the pump power corresponding to the optimal operating point of the laser, and then increase the output power. Our experimental results are in good agreement with the theoretical expectations. However, shortening the cavity length can not eliminate the thermal lens effect of TGG crystal. Therefore, the obvious bistability phenomenon is observed in the process of changing the pump power, accompanied by the sudden rise and fall of the output power. It is proved that the thermal lens effect of TGG crystal originates from the absorption of the fundamental frequency light in the cavity rather than the pump light, which is different from the thermal lens effect of gain crystal. Firstly, we determine the cutting direction of the DKDP crystal sheet, that is, the angle between the optical axis and the optical direction is 30 degrees, so that the thermal lens effect of the DKDP crystal sheet is as isotropic as possible to compensate the thermal lens effect of the TGG crystal effectively. Three DKDP sheets with different thickness are used to compensate the thermal lens effect of TGG crystal. According to the change of the pump power corresponding to the optimum operating point of the laser, we fit the thermal lens focal length formula of DKDP crystal sheet. From this, we calculate that the DKDP sheet with a thickness of 1.65 mm can be used under the current experimental conditions. The thermal lens effect of 8 mm long TGG crystal is completely compensated, so we use the existing 1.6 mm compensator to debug. By compensating, not only the bistability phenomenon existing before the laser is eliminated completely, but also the output power curve is very gentle, and the maximum output power of 532 nm single frequency laser can be increased from 14.7 W to 30.2 W. Finally, in view of the conclusion that convex mirrors should be used to replace planar mirrors in high-power solid-state lasers to mitigate the thermal lens effect of gain crystals and enhance the output power of lasers in previous literatures, we first made theoretical analysis and found that when the cavity length is fixed, the threshold pumping power of lasers increases with the increase of the curvature radius of cavity mirrors. The pump power corresponding to the rate and the optimum operating point decreases, and if the radius of curvature of the cavity mirror is increased and the length of the cavity is adjusted properly, the laser can achieve the same working state as that of the cavity mirror with a smaller radius of curvature. The experimental results are in good agreement with the theoretical expectation. The optimum cavity lengths of lasers with different radius of curvature are calculated, which can provide some theoretical guidance for the design of high power single frequency lasers with similar cavities. The mirror is debugged to obtain a single frequency 532 nm laser with a maximum output power of 12.97 W. Innovative work: 1. The influence of the thermal lens effect of TGG crystal on the working state of the high power single frequency laser is studied, and the output power of the laser is enhanced by reducing the cavity length to passively adapt to this effect. Qualitative analysis further proves that the thermal lens effect of TGG crystal originates from the absorption of fundamental frequency light by TGG crystal. 2. The thermal lens effect of TGG crystal is dynamically compensated by DKDP crystal sheet in high power single frequency laser, and a 30.2 W all-solid-state CW intracavity frequency doubling 532 nm laser is obtained. 3. The relationship between cavity length and the radius of curvature of cavity mirror is studied. It is pointed out that convex cavity mirror should be used to alleviate the thermal lens effect of gain crystal in high power solid-state lasers. It is proved that the cavity length should be kept as long as the plane cavity mirror is used. By adjusting the laser length to a suitable length, the laser can operate in a similar manner to the convex cavity mirror with a smaller radius of curvature.
【學(xué)位授予單位】：山西大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TN248
[Abstract]:High-power all-solid-state single-frequency green laser has the advantages of compact structure, good beam quality and low intensity noise. It has been widely used in quantum communication, holographic imaging, interferometry and other fields. It can also generate deep ultraviolet light by frequency doubling and be used as the pump source of high-power Ti:sapphire laser and OPO. In the process of green laser output power, we encounter the following problems: 1) when the pump power is further increased to enhance the output power of the laser, the output power of the laser will not increase, but will decline, and the laser beam will degenerate from a single transverse mode to a multi-transverse mode; 2) in the process of raising and lowering the pump power of the laser. In high power intracavity frequency doubled single frequency lasers, not only the thermal lens effect of the gain crystal has an important effect on the performance of the lasers, but also the thermal lens effect of the gain crystal is found. The thermal lensing effect produced by TGG crystal in the optical unidirectional device through the fundamental frequency light in the absorption cavity will also seriously affect the working state of the laser. This paper mainly focuses on the influence of the thermal lensing effect of TGG crystal on the working state of the laser and how to mitigate and compensate the thermal lensing effect of TGG crystal. Considering the thermal lens effect of TGG crystal, the effect of the radius of curvature of the cavity mirror on the laser operating state is studied. First, the influence of the thermal lens effect of TGG crystal on the laser operating state is analyzed by ABCD matrix, and then verified by experiment. The experimental results show that the thermal lens effect of TGG crystal not only exists, but also affects the laser. According to the theoretical calculation, we can reduce the cavity length to alleviate the influence of the thermal lens effect of TGG crystal, increase the pump power corresponding to the optimal operating point of the laser, and then increase the output power. Our experimental results are in good agreement with the theoretical expectations. However, shortening the cavity length can not eliminate the thermal lens effect of TGG crystal. Therefore, the obvious bistability phenomenon is observed in the process of changing the pump power, accompanied by the sudden rise and fall of the output power. It is proved that the thermal lens effect of TGG crystal originates from the absorption of the fundamental frequency light in the cavity rather than the pump light, which is different from the thermal lens effect of gain crystal. Firstly, we determine the cutting direction of the DKDP crystal sheet, that is, the angle between the optical axis and the optical direction is 30 degrees, so that the thermal lens effect of the DKDP crystal sheet is as isotropic as possible to compensate the thermal lens effect of the TGG crystal effectively. Three DKDP sheets with different thickness are used to compensate the thermal lens effect of TGG crystal. According to the change of the pump power corresponding to the optimum operating point of the laser, we fit the thermal lens focal length formula of DKDP crystal sheet. From this, we calculate that the DKDP sheet with a thickness of 1.65 mm can be used under the current experimental conditions. The thermal lens effect of 8 mm long TGG crystal is completely compensated, so we use the existing 1.6 mm compensator to debug. By compensating, not only the bistability phenomenon existing before the laser is eliminated completely, but also the output power curve is very gentle, and the maximum output power of 532 nm single frequency laser can be increased from 14.7 W to 30.2 W. Finally, in view of the conclusion that convex mirrors should be used to replace planar mirrors in high-power solid-state lasers to mitigate the thermal lens effect of gain crystals and enhance the output power of lasers in previous literatures, we first made theoretical analysis and found that when the cavity length is fixed, the threshold pumping power of lasers increases with the increase of the curvature radius of cavity mirrors. The pump power corresponding to the rate and the optimum operating point decreases, and if the radius of curvature of the cavity mirror is increased and the length of the cavity is adjusted properly, the laser can achieve the same working state as that of the cavity mirror with a smaller radius of curvature. The experimental results are in good agreement with the theoretical expectation. The optimum cavity lengths of lasers with different radius of curvature are calculated, which can provide some theoretical guidance for the design of high power single frequency lasers with similar cavities. The mirror is debugged to obtain a single frequency 532 nm laser with a maximum output power of 12.97 W. Innovative work: 1. The influence of the thermal lens effect of TGG crystal on the working state of the high power single frequency laser is studied, and the output power of the laser is enhanced by reducing the cavity length to passively adapt to this effect. Qualitative analysis further proves that the thermal lens effect of TGG crystal originates from the absorption of fundamental frequency light by TGG crystal. 2. The thermal lens effect of TGG crystal is dynamically compensated by DKDP crystal sheet in high power single frequency laser, and a 30.2 W all-solid-state CW intracavity frequency doubling 532 nm laser is obtained. 3. The relationship between cavity length and the radius of curvature of cavity mirror is studied. It is pointed out that convex cavity mirror should be used to alleviate the thermal lens effect of gain crystal in high power solid-state lasers. It is proved that the cavity length should be kept as long as the plane cavity mirror is used. By adjusting the laser length to a suitable length, the laser can operate in a similar manner to the convex cavity mirror with a smaller radius of curvature.
【學(xué)位授予單位】：山西大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TN248
【參考文獻(xiàn)】
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1 王W毻，
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