高功率激光驱动器受激拉曼散射控制的关键问题研究
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摘要
有效控制高功率激光脉冲传输放大过程中各类非线性效应一直是高功率激光驱动器研究的重点内容之一。其中,空气中受激转动拉曼散射(Stimulated Rotational Raman Scattering, SRRS)效应限制了激光脉冲长程传输的强度(峰值功率)或传输距离；大口径KDP晶体中横向受激拉曼散射(Transverse Stimulated Raman Scattering, TSRS)和大口径熔石英元件中横向受激布里渊散射(Transverse Stimulated Brillouin Scattering, TSBS)效应共同限制了三倍频激光脉冲的强度,与自聚焦效应(包括小尺度自聚焦和全光束自聚焦)共同构成驱动器总体输出能力的主要受限因素,通常称为“功率受限条件’
研制以聚变点火为主要目标、输出能力高达兆焦耳激光能量的巨型高功率激光驱动器,有效控制各类非线性效应既是确保光束质量和谐波转换效率的基本要求,也是驱动器安全、稳定运行的必要条件。同时,积极探索并研究突破“功率受限”的新技术途径,不但有可能在相同条件下有效提升驱动器输出能力,更将丰富高功率激光科学与技术基础理论,为高功率激光驱动器的持续发展提供必要的技术支撑。
为有效提升兆焦耳级高功率激光驱动器总体输出能力、降低研制成本,将驱动器运行通量进行了较大幅度的提升。其中,基频光(1ω)部分由浅度饱和放大区(FL-Fs)提高到深度饱和放大区(FL≧3Fs),运行通量达到(12-15)J/cm2；三倍频(3ω)运行通量也将提高数倍,达到(6-8)J/cm2；同时驱动器总体规模显著提升,因此高功率激光脉冲传输过程中受激拉曼散射效应(Stimulated Raman Scattering, SRS,包括TSRS与SRRS)的控制难度显著增加。一方面上百束光束的编组,使得1ω脉冲长程传输不可避免,已无法简单地通过在设计上缩短编组站光束管道长度控制空气中SRRS效应。另一方面,在包含谐波转换、谐波分离、光束聚焦、靶面光强控制、测量取样等系列3ω功能元件的终端光学系统中,“3ω短程传输”虽然为有效控制高功率3ω激光脉冲传输的SRRS效应创造了条件,但引入了高通量运行中杂散光、有机挥发物等对3ω元件的循环“污染”难以控制的难题,增加了元件损伤几率,进而限制驱动器总体输出能力。因此,在高功率3ω激光脉冲安全传输的距离内,适度拉开终端光学系统各光学元件的距离,有助于改善3ω元件运行环境,降低循环“污染”的影响,无疑对提升驱动器总体负载能力有利。
总之,在兆焦耳级高功率激光驱动器研制中,不能简单沿用“传统”的设计方法,以高功率脉冲传输的强度·距离积(Intensity-Length product, IL)判据定性地判断SRS对驱动器总体性能的影响程度,必须进一步研究其产生与增长规律,为总体设计及运行中SRS效应的主动控制奠定必要的理论基础。
本论文立足前人研究基础,重点研究高功率激光脉冲长程传输中SRRS和大口径KDP晶体中TSRS效应产生、增长的机理与规律,为兆焦耳级高功率激光驱动器总体设计中定量控制SRS效应提供必要的理论与实验基础；同时,提出利用“横向运动光永”抑制SRRS增长的研究思路,为突破高功率激光驱动器“功率受限条件”提供了新的研究途径。论文主要研究内容与取得的主要进步点总结如下：
1、研究并完善了SRRS物理模型,建立模拟程序,定量研究了高功率激光脉冲SRRS产生与增长规律的时域与空域特性,完成了物理模型和数值程序的实验验证,为兆焦耳级高功率激光驱动器总体设计中定量控制长程传输SRRS效应提供了必需的分析手段和实验依据。
建立了SRRS四维数值模型,可跟踪具有任意空域及时域分布的基频或三倍频激光脉冲在线性衍射与SRRS非线性过程共同作用下,自身及产生的斯托克斯(Stokes)光场的时-空演变特性。与国内外实验报道以及近期开展于神光-Ⅲ原型装置的实验结果校核,该数值模型的准确性得到了充分验证。研究结果表明,激光脉冲的近场分布及口径、时域调制及脉宽等都将影响SRRS增长过程。另外,SRRS的增长呈明显的阈值特性,一旦入射激光脉冲能量的1%转换为Stokes,传输距离的微小增加将导致入射脉冲能量迅速损耗、Stokes急剧增长；时域上入射脉冲下降沿提前,脉宽变窄；空域上,Stokes光近场呈现深调制的散斑分布,峰值功率密度迅速增长为入射脉冲强度的数倍。
2、根据SRRS产生、增长的机理与规律,提出基于“横向运动光束”抑制SRRS增长的研究思路,基于“光谱角扫描”原理,完成了抑制机理和规律的初步研究,得到了部分有意义的研究成果,初步验证了“横向运动光束”抑制SRRS增长的科学可行性,为高功率激光驱动器有效控制SRRS突破功率受限条件提供了一条有希望的技术途径。
以起源于自发辐射噪声的SRS过程中初始Stokes场呈“噪声”特性为突破点,考虑到“噪声”尖峰是SRS增长的主要贡献者,引入光束“横向运动”的概念,使得“噪声”尖峰处SRS效应(光与原子系统相互作用)由“宏观”稳态过程变为“微观”瞬态过程,拉曼增益显著下降。以“光谱角扫描”光束作为“横向运动光束”的一个例子,理论上证明了上述思路抑制SRS效应的可行性。
3、开展了高通量运行条件下,大口径KDP晶体内部TSRS效应的理论研究,建立了物理模型和数值模拟程序,完成了关键因素的定量研究,为有效控制TSRS效应奠定必要的理论基础。
建立了大口径元件中TSRS效应数值模型,计算了TSRS过程中产生的Stokes光在晶体内分布,与实验观察到的晶体损伤形貌基本吻合,初步证明TSRS效应与晶体高通量运行损伤间的关系；推导了Stokes光强增长的解析解,可直接计算任意光束口径及脉宽,任意晶体口径及边缘反射率条件下Stokes光场峰值强度,明确各参量对Stokes增长的定量影响关系,为TSRS的有效控制提供了必要的分析手段。
本论文建立的SRRS与TSRS数值模型与模拟软件,虽已与国内外相关实验结果校核,证明了具有一定的置信度,但仍需开展系列验证实验对其进一步完善。由于实验条件限制,论文仅开展了高功率激光脉冲长程传输SRRS效应的定量实验研究,而对于大口径晶体中TSRS效应,只有定性的实验现象。另外,论文研究的基于“横向运动光束”控制高功率激光脉冲非线性传输效应的技术途径还不成熟,论文虽然基于现阶段发展相对成熟的“光谱角扫描”技术,进行了抑制机理和规律的初步研究,但仍需要从理论与验两方面对该一技术途径进行完善。除此之外,“光谱角扫描”之外其它“横向运动光束”的实现途径,“横向运动光束”线性传输与非线性传输的物理图像及传输过程中光束时-空分布的控制等问题都值得开展更深入的理论研究与实验验证。
The effective control for various nonlinear optical effects during the propagation and amplification of high power laser pulses has been one of the focuses of the high power laser driver investigation. The stimulated rotational Raman scattering (SRRS) effect during the propagation of high intensity laser pulse through long air paths sets a limitation to the deliverable irradiation and propagation length, while the transverse stimulated Raman scattering (TSRS) effect in large-aperture KDP crystal, in combination with transverse stimulated Brillouin scattering (TSBS) effect in large silica optics limits the maximum third-harmonic output. These effects in addition to the self-focusing effect (including whole-beam self-focusing and small-scale beam breakup), contritube to main limitations of high power laser output ability and are called "power limits".
In the construction of immense high power laser driver for fusion ignition with output laser energy up to mega joule, the guarantee of high beam quality, frequency conversion efficiency and safe operation entails effective control for nonlinear propagation effects. Meanwhile, the exploration of new approach for breaking up the "power limits" and improving the output ability would enrich the theory of high power laser and lend indispensable support to the substantial development of high power laser driver.
As to improve the output ability and simultaneouslycut down the cost, the fluence of mega joule laser driver has advanced to (12～15) J/cm2 1ωand (6～8) J/cm2 3ω, with the adjustment from moderate saturation to deep saturation of amplification (FL≧3Fs). Besides, the scale-up of the driver adds to the difficulties of controlling stimulated Raman scattering (SRS, including SRRS and TSRS) effect during the propagation of high power laser pulse. One one hand, the direction of hundreds of laser beams to irradiate the target symmetrically makes long-path propagation of 1ωhigh power laser pulse inevitable. On the other, in the final optics system, which integrates a number of critical functions into a single compact package:frequency conversion, focusing, color separation, diagnostic beam sampling, vacuum isolation and debris shielding, although "shortening the propagation length of intense 3ωlaser pulse" helps to suppress SRRS effect, it brings in the difficulty to control various cycling "pollutions" (including stray light, organic volatiles and so on) contaminating the 3ωoptics during high fluence shots, adding to the risk of 3ωoptics damage, and limiting the maximum output. Therefore, within the safe propagation length of intense 3ωlaser pulse, distancing the 3ωoptics appropriately would improve the operation condition of 3ωoptics and load ability of the driver.
All the above analyses indicate that the traditional evaluation of SRS based on laser pulse intensity and path length product (Intensity-Length product, IL) is not applicable in the construction of mega joule high power laser driver. Further investigation of the mechanism and law of the generalization and growth of SRS is necessary, as a solid foundation for the effective control of SRS effect.
The mechanism and law of the generalization and growth of SRRS effect in long air paths and TSRS effect in large-aperture KDP crystal are extensively investigated in this paper, which lend sound theoretical and experimental support for the quantitative control of SRS effect in mega joule high power laser driver. A new effective control approach based on "transversely motive beam" is proposed, which has the potential to break up the "power limits" in high power laser driver.
The spotlights of this thesis are as follows:
1、The physical model of SRRS process is improved. Numerical simulation program is built which can quantitatively calculate the spatial-temporal characteristics during the generalization and growth of SRRS. Both the physical model and numerical code have been verified by corresponding experiments. Thus, this paper provides a reliable analyzing tool and experimental evidences for the quantitative control of SRRS effect in the design of mega joule high power laser driver.
A four-dimensional numerical model allowing the tracing of the propagation of 1ωor 3ωhigh power laser pulse with random distribution of spatial and temporal profile is built to investigate the spatial-and-temporal evolvement of the laser pulse and the Stokes produced under the interaction of linear diffraction and nonlinear SRRS effect. The numerical model passed a number of reality checks based on related experimental results in and aboard as well as the recent experiment carried on SG-III TIL facility. The results show that all the spatial, temporal intensity modulation, aperture and pulse width will affect the growth of SRRS. Besides, the growth of SRRS has an obvious characteristic of threshold. Once～1% of the laser pulse energy was scattered into Stokes, the minor increase of propagation length leads to sharp energy loss and Stokes increase. In terms of temporal evolvement, the tail of laser pulse shifts to an earlier date and the pulse width is shortened. In terms of spatial evolvement, the near-field of Stokes shows a deep modulated speckle pattern and the peak intensity grows sharply up to several times of input intensity.
2、Based on the mechanism and law of the generalization and growth of SRRS, a new control approach based on "transversely motive beam" is proposed and verified using the technology of "spectral angularly sweeping" as an example to generate "transversely motive beam". Some meaningful results convinced the scientific feasibility and showed the possibility to break up "power limits" in high power laser driver using "transversely motive beam".
In the SRRS process developing from spontaneous emission noise, the initial Stokes light has a "noise" characteristic and those peaks across near filed of the Stokes are main contributors to the growth of SRRS. The concept of "transversely motive beam" is proposed to drive those peaks move transversely across the near field, therefore the SRRS effect located at these peaks will shift from steady-state response to transient range, leading to a sharp decrease of Raman gain. With the "transversely motive beam" generated by "spectral angularly sweeping"as an example, the feasibility of above concept is theoretically verified.
3、Theoretical investigation of TSRS effect in large-aperture, high-fluence frequency conversion KDP crystal is carried out using improved physical and numerical model. The quantitative relationships between several key parameters and the growth of TSRS process are clarified, which provides an essential pre-condition to the investigation of effective control measurements of TSRS.
A numerical model for the simulation of TSRS effect in large-aperture optics is built and verified. The Stokes distribution in the crystal calculated with this model has several similarities with the experimentally observed damage pattern of the crystal, which shows a link between TSRS effect and the damage to large-aperture crystals in high-fluence operation. The analytic relationship between the intensity of the Stocks light and, the pulse width, and aperture of pump laser as well as the edge reflectivity of the large-aperture crystal has been deduced, which facilitates the evaluation of TSRS effect and effective control of TSRS in the high power laser driver.
The numerical model for both SRRS and TSRS effect built in this paper has passed a number of "reality checks", however, more code verifications is still needed for further improvement. As for the experimental investigation, the SRRS effect of high intensity pulse-shaped laser beam in long air path has received quantitative study, while the TSRS effect has only been observed in experiments with qualitative phenomenon. Besides, although the concept of controlling nonlinear propagation effect based on "transversely motive beam" is proposed and preliminarily verified using the example of "spectral angularly sweep" beam, it still demands further and extensive study both theoretically and experimentally. Other possible technology for the generation of "transversely motive beam", the physical mechanism and characteristics during the linear and nonlinear propagation of "transversely motive beam" and the interaction between linear diffraction and nonlinear effects as well as the approach for controlling the evolvement of the spatial-temporal profile during propagation all deserve further theoretical and experimental investigation.
研制以聚变点火为主要目标、输出能力高达兆焦耳激光能量的巨型高功率激光驱动器,有效控制各类非线性效应既是确保光束质量和谐波转换效率的基本要求,也是驱动器安全、稳定运行的必要条件。同时,积极探索并研究突破“功率受限”的新技术途径,不但有可能在相同条件下有效提升驱动器输出能力,更将丰富高功率激光科学与技术基础理论,为高功率激光驱动器的持续发展提供必要的技术支撑。
为有效提升兆焦耳级高功率激光驱动器总体输出能力、降低研制成本,将驱动器运行通量进行了较大幅度的提升。其中,基频光(1ω)部分由浅度饱和放大区(FL-Fs)提高到深度饱和放大区(FL≧3Fs),运行通量达到(12-15)J/cm2；三倍频(3ω)运行通量也将提高数倍,达到(6-8)J/cm2；同时驱动器总体规模显著提升,因此高功率激光脉冲传输过程中受激拉曼散射效应(Stimulated Raman Scattering, SRS,包括TSRS与SRRS)的控制难度显著增加。一方面上百束光束的编组,使得1ω脉冲长程传输不可避免,已无法简单地通过在设计上缩短编组站光束管道长度控制空气中SRRS效应。另一方面,在包含谐波转换、谐波分离、光束聚焦、靶面光强控制、测量取样等系列3ω功能元件的终端光学系统中,“3ω短程传输”虽然为有效控制高功率3ω激光脉冲传输的SRRS效应创造了条件,但引入了高通量运行中杂散光、有机挥发物等对3ω元件的循环“污染”难以控制的难题,增加了元件损伤几率,进而限制驱动器总体输出能力。因此,在高功率3ω激光脉冲安全传输的距离内,适度拉开终端光学系统各光学元件的距离,有助于改善3ω元件运行环境,降低循环“污染”的影响,无疑对提升驱动器总体负载能力有利。
总之,在兆焦耳级高功率激光驱动器研制中,不能简单沿用“传统”的设计方法,以高功率脉冲传输的强度·距离积(Intensity-Length product, IL)判据定性地判断SRS对驱动器总体性能的影响程度,必须进一步研究其产生与增长规律,为总体设计及运行中SRS效应的主动控制奠定必要的理论基础。
本论文立足前人研究基础,重点研究高功率激光脉冲长程传输中SRRS和大口径KDP晶体中TSRS效应产生、增长的机理与规律,为兆焦耳级高功率激光驱动器总体设计中定量控制SRS效应提供必要的理论与实验基础；同时,提出利用“横向运动光永”抑制SRRS增长的研究思路,为突破高功率激光驱动器“功率受限条件”提供了新的研究途径。论文主要研究内容与取得的主要进步点总结如下：
1、研究并完善了SRRS物理模型,建立模拟程序,定量研究了高功率激光脉冲SRRS产生与增长规律的时域与空域特性,完成了物理模型和数值程序的实验验证,为兆焦耳级高功率激光驱动器总体设计中定量控制长程传输SRRS效应提供了必需的分析手段和实验依据。
建立了SRRS四维数值模型,可跟踪具有任意空域及时域分布的基频或三倍频激光脉冲在线性衍射与SRRS非线性过程共同作用下,自身及产生的斯托克斯(Stokes)光场的时-空演变特性。与国内外实验报道以及近期开展于神光-Ⅲ原型装置的实验结果校核,该数值模型的准确性得到了充分验证。研究结果表明,激光脉冲的近场分布及口径、时域调制及脉宽等都将影响SRRS增长过程。另外,SRRS的增长呈明显的阈值特性,一旦入射激光脉冲能量的1%转换为Stokes,传输距离的微小增加将导致入射脉冲能量迅速损耗、Stokes急剧增长；时域上入射脉冲下降沿提前,脉宽变窄；空域上,Stokes光近场呈现深调制的散斑分布,峰值功率密度迅速增长为入射脉冲强度的数倍。
2、根据SRRS产生、增长的机理与规律,提出基于“横向运动光束”抑制SRRS增长的研究思路,基于“光谱角扫描”原理,完成了抑制机理和规律的初步研究,得到了部分有意义的研究成果,初步验证了“横向运动光束”抑制SRRS增长的科学可行性,为高功率激光驱动器有效控制SRRS突破功率受限条件提供了一条有希望的技术途径。
以起源于自发辐射噪声的SRS过程中初始Stokes场呈“噪声”特性为突破点,考虑到“噪声”尖峰是SRS增长的主要贡献者,引入光束“横向运动”的概念,使得“噪声”尖峰处SRS效应(光与原子系统相互作用)由“宏观”稳态过程变为“微观”瞬态过程,拉曼增益显著下降。以“光谱角扫描”光束作为“横向运动光束”的一个例子,理论上证明了上述思路抑制SRS效应的可行性。
3、开展了高通量运行条件下,大口径KDP晶体内部TSRS效应的理论研究,建立了物理模型和数值模拟程序,完成了关键因素的定量研究,为有效控制TSRS效应奠定必要的理论基础。
建立了大口径元件中TSRS效应数值模型,计算了TSRS过程中产生的Stokes光在晶体内分布,与实验观察到的晶体损伤形貌基本吻合,初步证明TSRS效应与晶体高通量运行损伤间的关系；推导了Stokes光强增长的解析解,可直接计算任意光束口径及脉宽,任意晶体口径及边缘反射率条件下Stokes光场峰值强度,明确各参量对Stokes增长的定量影响关系,为TSRS的有效控制提供了必要的分析手段。
本论文建立的SRRS与TSRS数值模型与模拟软件,虽已与国内外相关实验结果校核,证明了具有一定的置信度,但仍需开展系列验证实验对其进一步完善。由于实验条件限制,论文仅开展了高功率激光脉冲长程传输SRRS效应的定量实验研究,而对于大口径晶体中TSRS效应,只有定性的实验现象。另外,论文研究的基于“横向运动光束”控制高功率激光脉冲非线性传输效应的技术途径还不成熟,论文虽然基于现阶段发展相对成熟的“光谱角扫描”技术,进行了抑制机理和规律的初步研究,但仍需要从理论与验两方面对该一技术途径进行完善。除此之外,“光谱角扫描”之外其它“横向运动光束”的实现途径,“横向运动光束”线性传输与非线性传输的物理图像及传输过程中光束时-空分布的控制等问题都值得开展更深入的理论研究与实验验证。
The effective control for various nonlinear optical effects during the propagation and amplification of high power laser pulses has been one of the focuses of the high power laser driver investigation. The stimulated rotational Raman scattering (SRRS) effect during the propagation of high intensity laser pulse through long air paths sets a limitation to the deliverable irradiation and propagation length, while the transverse stimulated Raman scattering (TSRS) effect in large-aperture KDP crystal, in combination with transverse stimulated Brillouin scattering (TSBS) effect in large silica optics limits the maximum third-harmonic output. These effects in addition to the self-focusing effect (including whole-beam self-focusing and small-scale beam breakup), contritube to main limitations of high power laser output ability and are called "power limits".
In the construction of immense high power laser driver for fusion ignition with output laser energy up to mega joule, the guarantee of high beam quality, frequency conversion efficiency and safe operation entails effective control for nonlinear propagation effects. Meanwhile, the exploration of new approach for breaking up the "power limits" and improving the output ability would enrich the theory of high power laser and lend indispensable support to the substantial development of high power laser driver.
As to improve the output ability and simultaneouslycut down the cost, the fluence of mega joule laser driver has advanced to (12～15) J/cm2 1ωand (6～8) J/cm2 3ω, with the adjustment from moderate saturation to deep saturation of amplification (FL≧3Fs). Besides, the scale-up of the driver adds to the difficulties of controlling stimulated Raman scattering (SRS, including SRRS and TSRS) effect during the propagation of high power laser pulse. One one hand, the direction of hundreds of laser beams to irradiate the target symmetrically makes long-path propagation of 1ωhigh power laser pulse inevitable. On the other, in the final optics system, which integrates a number of critical functions into a single compact package:frequency conversion, focusing, color separation, diagnostic beam sampling, vacuum isolation and debris shielding, although "shortening the propagation length of intense 3ωlaser pulse" helps to suppress SRRS effect, it brings in the difficulty to control various cycling "pollutions" (including stray light, organic volatiles and so on) contaminating the 3ωoptics during high fluence shots, adding to the risk of 3ωoptics damage, and limiting the maximum output. Therefore, within the safe propagation length of intense 3ωlaser pulse, distancing the 3ωoptics appropriately would improve the operation condition of 3ωoptics and load ability of the driver.
All the above analyses indicate that the traditional evaluation of SRS based on laser pulse intensity and path length product (Intensity-Length product, IL) is not applicable in the construction of mega joule high power laser driver. Further investigation of the mechanism and law of the generalization and growth of SRS is necessary, as a solid foundation for the effective control of SRS effect.
The mechanism and law of the generalization and growth of SRRS effect in long air paths and TSRS effect in large-aperture KDP crystal are extensively investigated in this paper, which lend sound theoretical and experimental support for the quantitative control of SRS effect in mega joule high power laser driver. A new effective control approach based on "transversely motive beam" is proposed, which has the potential to break up the "power limits" in high power laser driver.
The spotlights of this thesis are as follows:
1、The physical model of SRRS process is improved. Numerical simulation program is built which can quantitatively calculate the spatial-temporal characteristics during the generalization and growth of SRRS. Both the physical model and numerical code have been verified by corresponding experiments. Thus, this paper provides a reliable analyzing tool and experimental evidences for the quantitative control of SRRS effect in the design of mega joule high power laser driver.
A four-dimensional numerical model allowing the tracing of the propagation of 1ωor 3ωhigh power laser pulse with random distribution of spatial and temporal profile is built to investigate the spatial-and-temporal evolvement of the laser pulse and the Stokes produced under the interaction of linear diffraction and nonlinear SRRS effect. The numerical model passed a number of reality checks based on related experimental results in and aboard as well as the recent experiment carried on SG-III TIL facility. The results show that all the spatial, temporal intensity modulation, aperture and pulse width will affect the growth of SRRS. Besides, the growth of SRRS has an obvious characteristic of threshold. Once～1% of the laser pulse energy was scattered into Stokes, the minor increase of propagation length leads to sharp energy loss and Stokes increase. In terms of temporal evolvement, the tail of laser pulse shifts to an earlier date and the pulse width is shortened. In terms of spatial evolvement, the near-field of Stokes shows a deep modulated speckle pattern and the peak intensity grows sharply up to several times of input intensity.
2、Based on the mechanism and law of the generalization and growth of SRRS, a new control approach based on "transversely motive beam" is proposed and verified using the technology of "spectral angularly sweeping" as an example to generate "transversely motive beam". Some meaningful results convinced the scientific feasibility and showed the possibility to break up "power limits" in high power laser driver using "transversely motive beam".
In the SRRS process developing from spontaneous emission noise, the initial Stokes light has a "noise" characteristic and those peaks across near filed of the Stokes are main contributors to the growth of SRRS. The concept of "transversely motive beam" is proposed to drive those peaks move transversely across the near field, therefore the SRRS effect located at these peaks will shift from steady-state response to transient range, leading to a sharp decrease of Raman gain. With the "transversely motive beam" generated by "spectral angularly sweeping"as an example, the feasibility of above concept is theoretically verified.
3、Theoretical investigation of TSRS effect in large-aperture, high-fluence frequency conversion KDP crystal is carried out using improved physical and numerical model. The quantitative relationships between several key parameters and the growth of TSRS process are clarified, which provides an essential pre-condition to the investigation of effective control measurements of TSRS.
A numerical model for the simulation of TSRS effect in large-aperture optics is built and verified. The Stokes distribution in the crystal calculated with this model has several similarities with the experimentally observed damage pattern of the crystal, which shows a link between TSRS effect and the damage to large-aperture crystals in high-fluence operation. The analytic relationship between the intensity of the Stocks light and, the pulse width, and aperture of pump laser as well as the edge reflectivity of the large-aperture crystal has been deduced, which facilitates the evaluation of TSRS effect and effective control of TSRS in the high power laser driver.
The numerical model for both SRRS and TSRS effect built in this paper has passed a number of "reality checks", however, more code verifications is still needed for further improvement. As for the experimental investigation, the SRRS effect of high intensity pulse-shaped laser beam in long air path has received quantitative study, while the TSRS effect has only been observed in experiments with qualitative phenomenon. Besides, although the concept of controlling nonlinear propagation effect based on "transversely motive beam" is proposed and preliminarily verified using the example of "spectral angularly sweep" beam, it still demands further and extensive study both theoretically and experimentally. Other possible technology for the generation of "transversely motive beam", the physical mechanism and characteristics during the linear and nonlinear propagation of "transversely motive beam" and the interaction between linear diffraction and nonlinear effects as well as the approach for controlling the evolvement of the spatial-temporal profile during propagation all deserve further theoretical and experimental investigation.
引文
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2 J.M.Dawson. Phys Fluids.1964,7:981
3 Wang GC. Suggestion of Neutron Generation with Powerful lasers[J].Chinese J of Lasers,1987, 14(11):61-645
4 J.H.Nuckolls, L.Wood, A.Thiessen and G.B.Zimmermam. Laser compression of matter to super-high densities:thermonuclear (CTR) application[J]. Nature,1972,39(9):139-142.
5 C.A.Haynanm, R.A.Sacks, P.J.Wegner,M.W.Bowers. The National Ignition Facility 2007 Laser Performance Statu[J]. Journal of Physics:Conference Series,2007,112(2008) 032004
6 G.Thiell, H.Graillot, P.Joly, A.Boscheron. Laser physcis studies with Phebus as part of the megajoule laser project. Fusion Engineering and Design,1999,44(1999)
7 M.A.Henesian, C.D.Swift, and J.R.Murray. Stimulated rotational Raman scattering in nitrogen in long air path [J]. Opt. Lett.,1985,10(11):565-567
8 M.A.Henesian, C.D.Swift, and J.R.Murray. Summary of Stimulated Raman Scattering Experiments in the Nova Air-Path and projected Nova and Nova Ⅱ system performance limits[R]. UCRL-TR-234110, 2007, LRD 85-342:1-12
9 P.J.Wegner, M.A Henesian, D.R. Speck. Harmonic conversion of large-aperture 1.05-um laser beams for inertial-confinement fusion research [J].Appl. Opt,1992,31(30):6414-6426
10 Y.Lin,T.J.Kessler,J.J.Armstrong. Laser system power balance effects from stimulated rotational Raman scattering in air [J]. SPIE,1993,1870:14-25
11 Y.Lin,T.J.Kessler,G.N.Lawrence. Raman scattering in air:four-dimensional analysis [J]. Appl. Opt., 1994,33(21):4781-4791
12 E.Bordenave, T.Chies. Numerical stimulation of stimulated Raman scattering in LIL transport section with Miro propagation code and comparison with ENOLIT diagnostic result[J]. J.Phys.Ⅳ France., 2006,133:661-663
13 Bruno M.Van Wonterghem, Scott C.Burkhart and Christopher A.Haynam et.al.National Ignition Facility commissioning and performance[J].Proc.SPIE 5341,55(2004)
14 P.Wegner, J.Auerbach, T.Biesiada, S.Dixit. NIF final optics system:frequency conversion and beam conditioning [J].2004
15 Action Needed to Address Scientific and Technical Challenges and Management weakness at the National Ignition Facility. United States Government Accountability Office,2010, GAO-10-488, Nuclear weapons:1-37
16 R.A.Sacks, C.E.Barker, R.B.Erlich. Stimulated Raman scattering in large-aperture, high-fluence frequency-conversion crystals[C]. ICF quarterly report[R], LLNL,1992,2(4):179
17 C. E. Barker, R. A. Sacks, B.M.Van Wonterghem et.al. Transverse stimulated Raman scattering in KDP[C]. SPIE,1995,2633:501-505
18 S. A. Belkov, G.C.Kochemasov, S.M.Kulikov et. al. Stimulated Raman scattering in frequency conversion crystal[C].SPIE,1995,2633:506-512
19 V. N. Novikov, S. A. Belkov, S. A. Buiko, et al. Transverse SRS in KDP, and KD*P crystal[C]. SPIE, 1998,3493:1009-1018
20 N.A.Kurnit, T.Shimada, M.S. Sorem, A.J.Taylor, G.Rodriguez, Measurement and control of optical nonlinearities of importance to glass laser fusion system[C]. Second Annual Solid-State Lasers for Applications to ICF International Conference, Paris, France,1996
21 John T. Hunt, National Ignition Facility Performance Review 1999[R]. UCRL-ID-138120-99,2000:7-2
22张小民,魏晓峰,满永在,叶金祥,隋展,袁晓东等.大气受激转动拉曼散射[A].见：惯性约束聚变与强激光技术,中国工程物理研究院核物理与化学所,内部报告,1989：380-404
23 M.D.Skeldon and R.Bahr, Stimulated rotational Raman scattering in air with a high-power broadband laser [J]. Opt. Lett.,1991,16(6):366-368
24 S.N.Dixit, D.Munro and J.R.Murray et.al. Polarization Smoothing on the National Ignition Facility [J]. J.Phys.Ⅳ,133(2006):717-720
25 Chen-Show Wang, Theory of Stimulated Raman Scattering [J].Phys. Rev.,1969,82(2):482-494
26 M.G.Raymer, J.Mostowski. Stimulated Raman Scattering:Unified treatment of spontaneous initiation and spatial propagation [J]. Phys.Rev.A.,1981,24(4):1980-1993
27沈元壤.非线性光学原理[M].北京：科学出版社,1987：201
28钱士雄,王恭明.非线性光学—原理与进展[M].上海：复旦大学出版社,2001
29石顺祥,陈国夫,赵卫,刘继芳.非线性光学[M].西安：西安电子科技大学出版社,2003：277
30 R.L.Carman, F.Shimizu, C.S.Wang, N.Bloembergen. Theory of Stokes pulse shapes in transient stimulated Raman scattering [J]. Phy.Rev.A.,1970,2:60-72
31 M.Trippenbach, K.Rzazewski and M.G.Raymer. Stimulated Raman Scattering of colored chaotic light [J]. J.Opt.Soc.Am.B.,1984,1 (4):671-675
32 N.Zhavoronkov, F.Noack and V.Petrov. Chirped-pulse stimulated Raman scattering in barium nitrate with subsequent recompression [J]. Opt. Lett.,2001,26(1):47-49
33 John Eggleston and Robert L. Byer, Steady-State Stimulated Raman Scattering by a Multimode Laser [J]. IEEE Journal of Quantum Electronics,1980, QE-16(8):850-854
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