杨晓东
论文题目：基于光学参量啁啾脉冲放大的台式化超强超短激光的研究与发展
作者简介：杨晓东，男，1969年12月出生，1997年09月师从于中科院上海光学精密机械研究所徐至展教授，于2002年03月获博士学位。
摘
要
基于啁啾脉冲放大（CPA）和光学参量放大（OPA）相结合的光学参量啁啾脉冲放大（OPCPA），是近年国际上正在积极探索开拓的持续创新发展超短超强激光的全新原理。OPCPA充分发挥了CPA与OPA各自的优点，又能克服CPA技术存在的缺点和局限性。正如CPA技术曾在上个世纪九十年代给激光科学技术特别是超短超强激光科学技术领域带来革命性突破一样，OPCPA新原理也有可能为激光科学技术的进一步发展开辟一个新时代，向超短超高超强更高层次的持续创新发展带来又一次革命性的推动,
具有重大的科学技术意义。
目前，国际上少数发达国家的著名实验室，如英国卢瑟福实验室、美国劳伦斯里弗莫尔国家实验室、日本大阪大学激光工程研究所、俄罗斯科学院应用物理研究所与俄罗斯联邦原子能研究中心等正在竞相开展OPCPA新原理探索研究，但都只是在较低能量与功率的水平上。迄今国际同类研究中已报道的最好水平是英国卢瑟福实验室获得的激光峰值输出功率1TW/300fs的结果。OPCPA目前虽还处于初期阶段，但显然蕴含强大的生命力。
本学位论文工作主要是瞄准OPCPA这一国际上提出不久并处于初级阶段的新概念,
重点开展了OPCPA新原理的理论模拟、实验验证,以及基于OPCPA新原理的小型化超强超短激光系统的研究与发展，创造性地解决关键科学技术问题,
建立并发展相关关键科学技术，如超短脉冲种子源的产生、小型化强激光泵浦源的研制及其脉冲的整形、信号光与泵浦光的精确同步、高效率光学参量放大及高保真脉冲展宽与压缩等关键技术，并在单元技术的总体集成方面取得了重大创新性进展与突破性研究成果，获得了国际上高量级泵浦条件下OPCPA激光研究中峰值输出功率最高且脉冲宽度最短的总体领先结果。概括起来，本学位论文工作的主要成果如下：
1.
进行了OPCPA新原理验证的基础理论研究,并在OPCPA小信号增益放大和饱和放大进行理论模拟的基础上提出独特创新方案，设计了一系列可直接移植到高功率激光装置上并实现10TW到1000TW级超强超短激光系统的技术方案。为充分利用国内已有高功率钕玻璃强激光装置的独特技术优势实现跳跃式发展提供了理论参考依据。
2.
创造性地解决关键科学技术问题,建立并发展了基于OPCPA新原理的台式化超强超短激光系统研究中涉及的若干关键单元创新技术，包括：
1)
完成了800nm/25fs尤其是1064nm/120fs飞秒脉冲种子源的产生、无像差飞秒脉冲的展宽和高保真脉冲压缩以及OPCPA原理验证所需的纳秒级强激光泵浦源的研究与性能优化改进等，为OPCPA原理验证提供了基础。
2)
成功解决了调Q激光脉冲泵浦OPCPA激光系统中的多路激光脉冲时间同步难题。将不同激光器输出的脉冲之间的时间抖动降低到1ns以下。这一结果优于以著名的日本大阪大学激光工程研究所报道为代表之一的国际上同类研究结果。
3)
OPCPA放大系统中精密时间同步创新方案的提出与实施。成功解决了在OPCPA超强超短激光系统研究发展中影响放大信号光能量稳定和光谱形状的泵浦激光脉冲与信号光脉冲之间精确同步的关键技术难题，
提出并发展了与国际同类研究不同的新方案，使OPCPA放大过程的信号光与泵浦光之间的时间抖动减小到5ps以下。而国际上如著名的英国卢瑟福国家实验室在同类研究采用的方案中，OPCPA放大过程的信号光与泵浦光之间的时间抖动却达100ps。
4)
首创利用前两级OPA放大器以1Hz运转来实现OPCPA放大系统中光路精确对准和时间同步调节的新技术，无需外加对准光源，精确的时间同步的调节与光路对准远比国际同类研究采用的方案简便、准确。
5)
完成了对第一类非共线宽带OPCPA原理验证实验研究。实现了OPCPA新原理的理论模拟与实验验证。为宽带非共线OPCPA超强超短激光系统的发展提供了有价值的参考数据。
3.
通过对上述关键单元技术研究成果的总体集成，提出独特创新方案，成功解决了高量级泵浦条件下获得高能量转换效率OPCPA放大等关键科学技术难题，完成了OPCPA的宽带高增益放大原理验证。在此基础上，于2001年12月在国际上首次成功建立了一台基于OPCPA新原理的台式化太瓦级超强超短激光系统，实现了224mJ/153fs的脉冲输出，其峰值功率达到1.46TW。这是当时国际上OPCPA研究报道的结果中，输出脉冲宽度最短（153fs）、输出峰值功率最高（1.46TW）的领先总体结果。
本学位论文工作难度高。在新理论验证、开拓和关键技术集成创新的基础上，不但在关键单元技术与基础实验中取得了具有国际领先水平的创新成果，还提出与国际同类研究不同的更为先进的总体创新方案，成功实现基础性原理探索与工程性技术实施的结合，获得了当时国际上峰值输出功率最高(1.46TW)且对应输出脉冲宽度最短(153fs)的OPCPA研究领先总体结果。
本学位论文的研究工作是中国科学院知识创新工程重大项目、国家973计划项目和国家自然科学基金优秀国家重点实验室研究项目等的重要组成研究内容。
*获得博士学位后一年内在博士论文相同的研究领域内进一步取得的成果
在获得博士学位后一年内，继续工作并持续创新，在OPCPA系统总体研究中获得1.46TW/153fs的当时世界最好结果的基础上，进一步优化并提高小型化纳秒级Nd:YAG-Nd:glass混合型强激光泵浦源等关键技术的性能，2002年3月和2002年10月又相继获得3.67TW/155fs和16.7TW/120fs的结果（其中末级宽带OPCPA放大器的转换效率达到25.5％，为高量级泵浦条件下OPCPA研究的国际最高水平），使得高量级泵浦条件下OPCPA激光系统研究的总体结果突破到新的国际最高水平。
本学位论文的研究工作是研究成果：“小型化OPCPA（光学参量啁啾脉冲放大）超短超强激光装置研究”（本论文作者为第二完成人，第一完成人为项目首席科学家，是本论文作者的导师，项目的主要完成人共14人）的重要组成内容。该项研究成果已通过中国科学院组织的专家鉴定和验收，得到高度评价。在中国科学院2003年度工作会议上，列为全院高技术研究与发展领域的重大创新成果与贡献之一。今年又申报2003年度上海市科技进步奖（已被初评为一等奖）。
在攻读博士学位期间，及获得博士学位后一年以内，本人与他人合作已在国内外重要学术刊物上公开发表论文17篇（其中第一作者8篇），在国际学术会议上发表论文16篇（其中第一作者7篇,包括2篇在日本举行的重要国际学术会议上的大会特邀报告），已授权与受理专利共8项（其中发明专利5项，已授权专利5项）。
关键词：超强超短激光，光学参量啁啾脉冲放大，时间同步
Abstract
Optical
parametric chirped pulse amplification (OPCPA), combining the techniques of
chirped pulse amplification (CPA) and optical parametric amplification (OPA), is
a novel concept to develop the ultra-intense and ultra-short pulse laser. OPCPA
possesses the advantages of both CPA and OPA and it can overcome the shortages
of CPA. OPCPA is expected to open up a new epoch in the laser science and bring
a revolutionary development to ultra-intense and ultra-short laser technology.
Several
famous laboratories in the developed countries worldwide, such as Lawrence
Livermore National Laboratory (USA), Rutherford Laboratory (UK), Institute of
Laser Engineering of Osaka University (Japan) and Institute of Applied Physics
of Russia Academy of Sciences are engaged in the research on OPCPA. However, all
the reported results were demonstrated at low laser energy. In Rutherford
Laboratory, ~1-TW/300-fs laser pulse has been obtained from an OPCPA laser,
which is the best result on OPCPA research in foreign countries so far.
The
research work presented in this dissertation focused on developing the scheme
and techniques of OPCPA. This dissertation gives the results of the theoretical
and experimental investigation on OPCPA scheme. The validation of OPCPA at high
energy level was demonstrated successfully. And some important results were
achieved. Several key techniques related to developing table-top ultra-intense
and ultra-short OPCPA laser system were put forward, for example, the generation
of femtosecond seeding pulses, the precisely temporal synchronization of the
pump and signal pulses, the pulse stretching and recompression, the OPCPA
process with high energy conversion efficiency and etc. Based on the integration
of these key techniques, a 1.46-TW/153-fs OPCPA table-top ultra-intense and
ultra-high laser system has been developed, which, to the best of our knowledge,
has generated laser pulses with the shortest pulse duration and the highest peak
power among the joule level OPCPA systems in the world. The main results are
summarized as following:
1.
Theoretical design of ultra-intense and ultra-short pulse OPCPA laser
system based on a novel approach developed in this work.
Based
on the theoretical study on OPCPA operating in small signal gain and gain
saturation, a novel OPCPA approach was proposed. A series of practical designs
of Nd:glass laser-based OPCPA system were proposed. With a high power Nd:glass
laser system, the OPCPA systems are designed, which are expected to generate
10TW to PW laser pulses.
2. Several key techniques for the table-top ultra-intense and ultra-short OPCPA laser system:
1) Developed 800-nm/25-fs and 1064-nm/120-fs seed laser sources, an aberration-free pulse stretcher and re-compressor, and a high-power and high-performance nanosecond pumping source for OPCPA laser system, etc.
2)
Developed a novel technique for the temporal synchronization of multi-laser
pulses in the Q-switched laser pumped OPCPA. With this technique, the timing
jitter between different lasers was reduced to less than 1ns, which is better
than the result of 2ns reported by Osaka University of Japan.
3) Proposed and demonstrated a novel scheme to realize the precise timing synchronization of the pump and signal pulse in OPCPA. With our designed scheme, the timing jitter of less than 5ps between signal and pump laser pulses is achieved, which is much better than the result of 100ps reported by Rutherford Laboratory of UK.
4)
Proposed a new and effective technique to align accurately and synchronize
precisely in the OPCPA stages, by running the two OPCPA pre-amplifiers at 1Hz.
This method not only save an additional alignment light source, and more
important, but also it makes the optical alignment and adjustment of temporal
synchronization much more simple and precise than the schemes used by other
researchers.
5)
Successfully demonstrated a Type-I non-collinear broadband OPCPA laser based on
BBO crystal. The results are very useful for the development of non-collinear
broadband OPCPA laser system pumped by Q-switched laser.
3.
Based on the integration of the above key techniques, signal pulses were
amplified in OPCPA stages with high energy-extraction efficiency. By the end of
2001, a compact OPCPA laser system pumped with a Nd:YAG - Nd:glass
laser was developed. And an output of 224-mJ/153-fs pulses with a peak power of
1.46TW was achieved. This OPCPA laser system, has generated laser pulses with
the shortest pulse duration and the highest peak power among the joule level
OPCPA systems in the world at that time.
The
work related to the dissertation is extremely challenged. Based on the
validation and development of the new concept and the integration of the key
techniques, great achievements leading in the world were obtained in the
research on key unit techniques and fundamental experiments in OPCPA. We
proposed a unique and advanced system design of OPCPA laser. This work
integrated successfully the exploration of basis scheme with the implementation
of engineering technique. The results of laser pulses with pulse duration of
153fs and peak power of 1.46TW among the joule level OPCPA systems were the best
in the world at that time.
The
work of this dissertation is the important component of the Major Project of Knowledge Innovation Program of CAS,
the National 973 Project and the Excellent Native Key Laboratory Research
Project of National Natural Science Foundation.
*
Further achievement obtained in the same field within one year after Dr.
Yang Xiaodong got his Ph.D. degree
Within
one year after I got my PhD degree, I worked continually on this project. Based
on our obtained results (1.46TW/153fs) leading in the world on OPCPA, by
improving a series of key techniques such as a compact nanosecond Nd: YAG - Nd:
Glass laser as pumping source of OPCPA laser, we upgraded the output peak power
of OPCPA laser system to 3.67TW(155fs) and 16.7TW (120fs) in March and October
2002, respectively. In addition, an energy conversion efficiency of >25% in
the final OPCPA amplifier stage was achieved, which is also the best result in
this field in the world. To the best of our knowledge, these are the latest best
results in the research of high energy pumping OPCPA in the world.
The
work of this dissertation is the major component of the research project
“Tabletop Ultra-intense and ultra-short pulse OPCPA laser system”. (The
author is the second contributor to this project and his supervisor is the chief
scientist and the first contributor of this project. There are 14 major
contributors to this project). The
achievement of this project has been highly appraised, verified and accepted by
the specialists and scientists assigned by Chinese Academy of Sciences. And this
project was highly evaluated by the experts. At the annual meeting of Chinese
Academy of Sciences in 2003, this work was appraised as one of the Major
Innovation Achievements and Contributions in the field of High Technology
R&D of Chinese Academy of Sciences. In this year, we applied for the Award
of the Progress in Science and Technique in Shanghai Municipality with the
achievements of this project. (It has been awarded preliminary as the first
class award.)
During
the period of my study for Ph.D. degree and one year after I got my Ph.D.
degree, cooperated with colleagues, I have published 17 papers in the important
domestic and foreign scientific journals (8 papers among them as the first
author), and 16 papers at the international scientific conferences (7 papers as
the first author and two of the 7 papers are invited talks of important
international conferences held in Japan). In addition, I have applied for 8
patents (5 of them are invention patents) and 5 of these patents have been
authorized.
Key
words: Ultra-intense
and ultra-short pulse laser, Optical parametric chirped pulse
amplification, Temporal synchronization
