本文選題：KDP(DKDP)晶體 + 晶格振動�。� 參考：《山東大學(xué)》2015年博士論文

【摘要】：磷酸二氫鉀(KH2PO4,簡稱KDP)晶體和磷酸二氘鉀(K(H1-xDx)2PO4,簡稱DKDP)晶體是一種性能優(yōu)良的的非線性光學(xué)晶體材料,其生長研究已有80多年的歷史。KDP和DKDP晶體具有較大的非線性系數(shù)、較高的激光損傷閾值等性能,被廣泛作為激光倍頻材料；另外,KDP和DKDP晶體還是良好的壓電、電光材料。近年來慣性約束核聚變(ICF)工程得到了越來越多國家的關(guān)注,ICF是一種可控制的熱核爆炸,為解決人類未來能源短缺問題提供了新的路徑。到目前為止,能滿足ICF研究所需要的高光學(xué)性能和大尺寸晶體僅有KDP、DKDP晶體,其在該系統(tǒng)中主要作為變頻材料和電光開關(guān)材料。在ICF系統(tǒng)中,高通量激光通過大尺寸KDP晶體組成的倍頻系統(tǒng)時,自發(fā)拉曼散射光與泵浦光場耦合使自發(fā)拉曼散射受激放大,受激拉曼散射在橫向獲得較大增益形成橫向受激拉曼散射(TSRS)。大尺寸KDP晶體中的TSRS不但會造成泵浦光能量損失,而且其強度可能超過激光的損傷閾值,造成晶體永久損傷。KDP晶體中的TSRS效應(yīng)嚴(yán)重制約了激光系統(tǒng)能量的提升,國內(nèi)外采取了一系列措施降低大尺寸晶體中的TSRS效應(yīng)。眾所周知利用DKDP晶體取代KDP晶體可有效降低其TSRS增益系數(shù),但DKDP晶體氘含量和其TSRS增益系數(shù)的定量關(guān)系尚未明確,難以得出降低TSRS效應(yīng)的最佳氘含量；另外,在更高激光功率條件下DKDP晶體中的TSRS效應(yīng)也將顯著,且DKDP晶體生長工藝?yán)щy,成本高。因此,繼續(xù)開展KDP、DKDP晶體TSRS效應(yīng)相關(guān)研究有重要意義。受激拉曼散射起源于晶體的自發(fā)拉曼散射,且其增益系數(shù)可根據(jù)其自發(fā)拉曼光譜評估,故受激拉曼散射與自發(fā)拉曼散射密切相關(guān)。本文系統(tǒng)地研究了KDP、DKDP晶體的拉曼散射特性,我們首先根據(jù)群論對KDP、DKDP晶體晶格振動模進行了詳細(xì)歸類并對拉曼峰進行了指認(rèn)；然后開展了KDP晶體的受激拉曼散射實驗,分析了三倍頻過程中的TSRS效應(yīng)；并研究了晶體生長方法、雜質(zhì)離子、氘含量和溫度等因素對KDP、DKDP晶體拉曼散射的影響。論文主要內(nèi)容如下：1.首先利用因子群分析法得到了KDP晶體的基本晶格振動模：T=4A1+5A2+6B1+7B2+13E,然后利用位置群分析法對振動模進行了詳細(xì)分類。驗證了背向拉曼散射時A1振動模的角度特性,A1振動模角度特性表明實際晶體的對稱性低于D2d。另外,退火和未退火晶體的拉曼光譜無明顯差別,故A1振動模的角度特性與晶體的內(nèi)應(yīng)力無關(guān),是由KDP晶體內(nèi)部結(jié)構(gòu)決定的。我們測量了KDP和DKDP晶體不同散射配置下的拉曼光譜,并對KDP和DKDP晶體的拉曼峰進行了指認(rèn)。結(jié)果表明,雖然所測光譜中存在和D2d拉曼選擇定則不符的情況,但是光譜整體上符合D2d拉曼選擇定則。2.根據(jù)受激拉曼散射理論推導(dǎo)了KDP晶體受激拉曼散射增益系數(shù)和激發(fā)波長和散射配置的關(guān)系。采用532 nm的皮秒激光脈沖泵浦在腔外單次通過方式下實現(xiàn)了KDP晶體的受激拉曼散射(SRS),實驗上只觀察到了增益系數(shù)最大的v1振動模的三階stokes光(559.43 nm、589.74 nm、623.5 nm)。另外,隨著SRS階次增高Stokes光的強度減弱,泵浦光的閾值功率呈非線性增長規(guī)律。因此,高功率激光系統(tǒng)中大尺寸KDP晶體中的TSRS效應(yīng)主要考慮v1振動模的一階受激拉曼散射。受激拉曼散射增益系數(shù)和激發(fā)波長和散射配置有關(guān),在三倍頻過程中KDP晶體中將會出現(xiàn)幾種不同類型的TSRS效應(yīng)。本文定量比較了Ⅰ類和Ⅱ類KDP晶體組成的三倍頻系統(tǒng)中的幾種不同類型的TSRS效應(yīng),結(jié)果表明在高的倍頻效率和激光通量下,三倍頻晶體中的TSRS效應(yīng)較為顯著,尤其是三倍頻光激發(fā)的TSRS效應(yīng)。根據(jù)本文結(jié)果在倍頻過程中若得到各階段的倍頻效率即可預(yù)測各種TSRS效應(yīng)的相對強度,并采取措施有效降低晶體坯片在使用過程中的激光損傷幾率。3.研究了生長方法(傳統(tǒng)法和快速法)、熱退火和雜質(zhì)離子(Cr3+和Ni2+)對KDP晶體拉曼光譜的影響,并分析了這些因素對KDP晶體v1振動模的受激拉曼散射的影響。結(jié)果表明這些因素對晶體的光學(xué)性能(透過率和散射顆粒)均有不同程度的影響,但對晶體拉曼光譜及v1振動模的受激拉曼散射增益系數(shù)的影響不明顯。另外,受激拉曼散射強度與還其作用范圍內(nèi)晶體的光學(xué)性能(透過率、散射顆粒等)有關(guān),并且相互作用長度越大受激拉曼散射傳輸過程中受晶體光學(xué)質(zhì)量的影響越顯著,故大尺寸KDP晶體中的TSRS效應(yīng)受生長方法、熱退火和雜質(zhì)離子等因素影響,這需要進一步的在線實驗驗證。4.測量了不同氘含量DKDP晶體X(ZZ)-X和X(YY)-X散射配置下v1振動模的自發(fā)拉曼光譜。隨著氘含量的增加v1振動模發(fā)生紅移,且X(ZZ)-X散射配置下的頻移大于X(YY)-X散射配置下的頻移,v1振動模半峰寬先增加后減小,而峰值強度隨氘含量的變化和半峰寬的變化趨勢相反。根據(jù)振動模耦合理論擬合了DKDP晶體的拉曼光譜,分析得出DKDP晶體v1振動模的紅移主要是由于v1振動模和δ(OD)振動模耦合引起的,而v1振動模和v3振動模耦合對v1振動模頻移也有較小貢獻。另外,基于DKDP晶體摻氘后晶體結(jié)構(gòu)的變化建立了DKDP晶體拉曼散射的強度疊加模型,根據(jù)這一模型計算了不同氘含量DKDP晶體的拉曼光譜,結(jié)果與實驗測得的光譜符合很好,根據(jù)這一模型解釋了氘含量對DKDP晶體半峰寬和峰值強度的影響,并且發(fā)現(xiàn)峰值強度隨氘含量的變化是由半峰寬的變化引起。采用和水的自發(fā)拉曼光譜對比法得出了KDP晶體和不同氘含量DKDP晶體的TSRS增益系數(shù),測量誤差為15%。結(jié)果發(fā)現(xiàn)KDP晶體的TSRS增益系數(shù)為0.3cm·GW-1,且隨著氘含量的增加DKDP晶體的TSRS增益系數(shù)先減小至KDP晶體的40.1%,后增大至KDP晶體的68.9%。建立了DKDP晶體TSRS增益系數(shù)和其v1振動模拉曼頻移的關(guān)系,利用此關(guān)系可以實現(xiàn)DKDP晶體TSRS增益系數(shù)及其均勻性在線無損測量。通過分析與T SRS增益系數(shù)有關(guān)的參數(shù),我們認(rèn)為氘含量引起的半峰寬的變化是引起其TSRS增益系數(shù)變化的主要原因,故尋求其它增大拉曼散射半峰寬的方法可達到抑制TSRS效應(yīng)的目的。此外,結(jié)合第三章中KDP晶體TSRS效應(yīng)的分析,我們給出了DKDP晶體作為三倍頻材料時3ω光激發(fā)TSRS效應(yīng)閡值強度和氘含量的關(guān)系。5.采用背向拉曼散射裝置測量了KDP晶體和不同氘含量DKDP晶體v1振動模在285.4 K～345.2 K范圍內(nèi)的拉曼光譜,并分析了溫度對其v1振動模拉曼頻移、半峰寬、散射強度和SRS增益系數(shù)的影響。隨著溫度的升高,KDP晶體中的v1振動模頻率逐漸減小,半峰寬逐漸增大。而溫度對DKDP晶體拉曼頻移和半峰寬的影響和其氘含量有關(guān),對于低氘和高氘的DKDP晶體,溫度對其拉曼散射的影響和KDP情況類似；對于其他氘含量的DKDP晶體,拉曼頻移和半峰寬隨溫度的變化規(guī)律表現(xiàn)出較大波動,我們認(rèn)為這主要是因為溫度同樣引起了O-D鍵的變化。另外,隨著溫度的升高KDP、DKDP晶體拉曼散射強度沒有明顯的變化趨勢,但其穩(wěn)態(tài)受激拉曼散射增益系數(shù)有所降低,對于KDP晶體與285.4 K相比,345.2 K時的增益系數(shù)降低了約12%。因此,在高功率激光系統(tǒng)中大尺寸KDP、DKDP晶體在較高溫度下應(yīng)用有助于降低TSRS效應(yīng)。
[Abstract]:KH2PO4 (KH2PO4, KDP) crystals and phosphoric acid two (H1-xDx) 2PO4 (H1-xDx) 2PO4 (abbreviated as DKDP) crystals are a kind of nonlinear optical crystal materials with excellent properties. Their growth studies have been studied for more than 80 years in the history of.KDP and DKDP crystals with larger nonlinear coefficients and higher laser damage thresholds, and are widely used as laser doubling materials. In addition, KDP and DKDP crystals are also good piezoelectric, electro-optic materials. In recent years, the inertial confinement fusion (ICF) engineering has attracted more and more attention. ICF is a controllable thermonuclear explosion, which provides a new way to solve the problem of human energy shortage in the future. So far, the high optical properties of ICF research are met. The energy and large size crystals are only KDP, DKDP crystals, which are mainly used as frequency conversion materials and electro-optical switching materials in this system. In ICF systems, when high throughput lasers are composed of large size KDP crystals, spontaneous Raman scattering light is coupled with the pump light field to induce spontaneous Raman scattering to be stimulated and stimulated, and stimulated Raman scattering is obtained in the transverse direction. The large gain form transverse stimulated Raman scattering (TSRS). The TSRS in large size KDP crystal not only causes the energy loss of the pump light, but also the intensity may exceed the laser damage threshold, resulting in the TSRS effect in the crystal permanent damage to the crystal, which seriously restricts the energy improvement of the laser system. A series of measures have been taken to reduce the large scale at home and abroad. TSRS effect in an inch crystal. It is known that using the DKDP crystal to replace the KDP crystal can effectively reduce the gain coefficient of the TSRS, but the quantitative relation between the deuterium content and the TSRS gain coefficient of the DKDP crystal is not clear, and it is difficult to obtain the best deuterium content to reduce the TSRS effect. In addition, the TSRS effect in the DKDP crystal will also be displayed under the higher laser power condition. In addition, the growth of DKDP crystal is difficult and the cost is high. Therefore, it is important to continue to develop the KDP, the related research on the TSRS effect in the DKDP crystal is of great significance. The stimulated Raman scattering originated from the spontaneous Raman scattering of the crystal, and its gain coefficient can be evaluated according to its spontaneous Raman spectrum. The Raman scattering characteristics of KDP, DKDP crystal are studied. We first classify the lattice vibration modes of KDP and DKDP crystals in detail according to the group theory and identify the Raman peaks. Then the stimulated Raman scattering experiments of KDP crystals are carried out, the TSRS effect in the three frequency doubling process is analyzed, and the crystal growth method, impurity ions, deuterium are also studied. The influence of the content and temperature on the Raman scattering of KDP and DKDP crystals. The main contents of the paper are as follows: 1. first, the basic lattice vibration mode of the KDP crystal is obtained by the factor group analysis method, T=4A1+5A2+6B1+7B2+13E, and then the vibration modes are classified in detail by the position group analysis method. The A1 vibration mode of the backscattering Raman scattering is verified. The angle characteristic of the A1 vibration mode shows that the symmetry of the actual crystal is lower than that of D2d., and the Raman spectra of the annealed and unannealed crystals have no obvious difference. Therefore, the angle characteristic of the A1 vibration mode is independent of the internal stress of the crystal. It is determined by the internal structure of the KDP crystal. We measured the Raman spectra under the different scattering configuration of the KDP and DKDP crystals. The Raman peaks of KDP and DKDP crystals are identified. The results show that, although the spectra are not consistent with the D2d Raman selection rule, the spectrum is consistent with the D2d Raman selection rule, and.2. derives the relationship between the stimulated Raman scattering gain coefficient and the excitation wavelength and the scattering configuration of the KDP crystal based on the stimulated Raman scattering theory. The stimulated Raman scattering (SRS) of the KDP crystal is realized by a 532 nm picosecond laser pulse pump in a single pass through cavity. The three order Stokes light (559.43 nm, 589.74 nm, 623.5 nm) of the V1 vibration mode with the maximum gain coefficient is observed experimentally. In addition, the threshold power of the pump light decreases with the increase of the SRS order of Stokes light. Therefore, the TSRS effect in the large size KDP crystal in high power laser system mainly considers the first order stimulated Raman scattering of the V1 vibration mode. The stimulated Raman scattering gain coefficient is related to the excitation wavelength and the scattering configuration. In the three frequency doubling process, there will be several different types of TSRS effects in the KDP crystal. This paper quantified Several different types of TSRS effects in the three frequency doubling system composed of class I and class II KDP crystals are compared. The results show that the TSRS effect in the three frequency doubling crystals is more significant at high frequency doubling efficiency and laser flux, especially the TSRS effect of three frequency doubling light excitation. The relative intensity of various TSRS effects can be predicted, and measures are taken to effectively reduce the laser damage probability in the use process of the crystal blank.3. to study the growth method (traditional method and fast method), the effect of thermal annealing and impurity ions (Cr3+ and Ni2+) on the Raman spectra of the KDP crystal, and the analysis of these factors on the V1 vibration modes of the KDP crystal. The effect of stimulated Raman scattering shows that these factors have different effects on the optical properties (transmittance and scattering particles) of the crystal, but the influence of the Raman scattering and V1 vibration modes on the stimulated Raman scattering gain coefficient is not obvious. The higher the interaction length is, the greater the interaction length is, the more significant the optical mass of the crystal is affected by the stimulated Raman scattering. So the TSRS effect in the large size KDP crystal is influenced by the growth method, the thermal annealing and the impurity ions. This requires an online experiment to verify that.4. has measured the DKDP crystal with different deuterium content. The spontaneous Raman spectra of the V1 vibration modes under the configuration of the bulk X (ZZ) -X and X (YY) -X scattering. With the increase of the deuterium content, the V1 vibration mode occurs red shift, and the frequency shift of the X (ZZ) -X scattering is larger than the frequency shift of the X. The half peak width of the vibration mode increases first and then decreases, while the peak intensity is opposite to the variation of deuterium content and the half peak width. According to the vibration mode coupling theory, the Raman spectra of the DKDP crystal are fitted. It is found that the red shift of the V1 vibration mode of the DKDP crystal is mainly caused by the coupling of the V1 vibration mode and the Delta (OD) vibration mode, while the V1 vibration mode and the V3 vibration mode coupling have little contribution to the V1 vibration mode frequency shift. In addition, the crystal structure changes based on the deuterium doping of the DKDP crystal have been established. The intensity superposition model of DKDP crystal Raman scattering is used to calculate the Raman spectra of DKDP crystals with different deuterium content. The results are in good agreement with the experimental spectra. According to this model, the effect of deuterium content on the half peak width and peak intensity of the DKDP crystal is explained, and the change of the peak intensity with deuterium content is from the half peak width. The TSRS gain coefficient of KDP crystal and DKDP crystal with different deuterium content was obtained by the comparison with the spontaneous Raman spectroscopy of water. The measurement error was 15%. and the TSRS gain coefficient of KDP crystal was 0.3cm. GW-1, and with the increase of deuterium content the TSRS gain of DKDP crystal decreased first to 40.1% of KDP crystal and then increased to KDP. The relationship between the gain coefficient of the DKDP crystal TSRS and the Raman shift of its V1 vibration mode is established by the 68.9%. crystal. Using this relationship, the gain coefficient and the uniformity of the DKDP crystal TSRS gain coefficient and its on-line nondestructive measurement can be realized. By analyzing the parameters related to the gain coefficient of T SRS, we believe that the variation of the half peak width caused by the deuterium content is the cause of the TSRS gain system. The main reason for the change is to find other methods to increase the half peak width of Raman scattering. In addition, in combination with the analysis of the TSRS effect of the KDP crystal in the third chapter, we give the relationship between the 3 Omega light excitation TSRS effect and the deuterium content when the DKDP crystal is a three frequency doubling material, and.5. uses the back Raman scattering. The Raman spectra of KDP crystal and V1 vibration modes of different deuterium content DKDP crystals in the range of 285.4 K to 345.2 K were measured, and the effects of temperature on the Raman shift, half peak width, scattering intensity and SRS gain coefficient of the V1 vibration modes were analyzed. With the increase of temperature, the frequency of V1 vibratory mode in KDP crystal gradually decreased and the half peak width gradually increased. The influence of degree on the Raman shift and the half peak width of DKDP crystal is related to its deuterium content. For low deuterium and high deuterium DKDP crystal, the effect of temperature on its Raman scattering is similar to that of KDP. For other deuterium content DKDP crystals, the Raman shift and the half peak width vary with the temperature. We think this is mainly due to the temperature. Degree also causes the change of O-D bond. In addition, with the increase of temperature KDP, the Raman scattering intensity of DKDP crystal has no obvious change trend, but the gain coefficient of the stable stimulated Raman scattering is reduced. The gain coefficient of the KDP crystal is reduced by about 12%. when compared with 285.4 K, so the large size KDP and DK in the high power laser system are in DK. The application of DP crystals at higher temperatures helps to reduce the TSRS effect.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：O734;O614.113

【參考文獻】

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1 仲維卓,于錫鈴,羅豪，

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