强激光与核反应-近代物理研究所

Plasma channeling
Laser
A plasma channel, denser toward the edges, guides the laser and allows it to form high-quality electron beams. As the laser pulse travels from left to right it excites a wake in the plasma, trapping and accelerating bunches of electrons to high energies (September 29, 2004 news of BNL)
Effect of the plasma channeling
Without a preformed channel (left) the drive laser pulse blows out after a few hundred micrometers, producing diffuse bunches of electrons with wide energy spread. A preformed channel through the plasma (right) confines the drive beam and produces bunches of electrons with nearly uniform high energy.
脉冲激光
• Short Pulse Lasers (Chirped Pulse Amplification) Extremely short duration pulse of the order of 1 ps. These lasers are based on recent advances in pulse compression techniques and can produce irradiances exceeding 1020 W cm-2. 32sets • Long Pulse Lasers Lasers whose pulse duration is of the order of 1 ns used for inertial confinement fusion research. These are some of the older generation of high power lasers such as the NOVA at Lawrence Livermore National Laboratories. 18sets
连续激光
Military Lasers Extremely high average power lasers which can be used to destroy missiles in the vulnerable launch phase.. •Gasdynamic Laser High power laser based on rapid adiabatic expansion of a high temperature gas, somewhat like the exhaust of a rocket nozzle. The first gasdynamic laser was successfully operated in 1966. •Ammonia Microware Laser Low power laser based on low energy molecular transitions. This was the first operational laser, it was constructed by Townes and Shawlow in 1954.
中科院近代物理研究所
强激光与核反应
•激光与物质的相互作用 •激光加速粒子的原理 •激光引起的核反应 •激光核反应的前景
激光分类
• Pulsed Lasers Pulse lasers operate for very short periods usually for much less than one second. They can produce extremely high peak powers but only for a very short period of time. Many pulsed lasers have very low average powers • Continuous Lasers (CW) Continuous lasers operate continuously for periods exceeding one second. These lasers usually have a relatively high average power and are often classified as military lasers.
Power levels available (W) Pulsed > 2 ´ 1013 > 109 > 107 > 1012 ∼ 1014 (10 beams) > 106 106 1010 5 · 104 106 105 - 106 > 106 > 109 CW > 105 > 100 30 1 - 103 1 1-5 1 1 - 50 · 10-3 1 - 20 1-5 140 500
Type
Wavelength
(μm)
Efficiency 0.01 - 0.02 （pulsed) 0.4 0.03 (lamp) 0.1 (diode) 0.003 0.001 - 0.06 (lamp) > 0.1 (diode) 10-3 > 0.1 ´ ηp < 10-3 10-4 10-3 > 0.1 ´ ηp 0.001 - 0.05 10-3 0.08
Xenon 0.175 0.02 > 108 * = Tunable sources, ηp=pump laser efficiency from page 50 of NRL Plasma Formulary
激光与物质的相互作用
激光特性 • 发散度极小（0.2－1mrad）－测距 • 单一波长，波长分散极小.（0.01 0.2nm, 或 1:100000 － 1:5000）－ 波长灵敏探测器 • 光脉冲可以很窄－高功率密度
激光与物质的相互作用
• 光的吸收 P ＝ε (ω) ε0 E ε (ω) ＝ε1 + iε2 nc(ω) = n + ik
电子振动产生的极化P与入射光场E的关系 物质复介电函数 折射指数
反射率
k=0时, 光在物质中的衰减规律
光吸收与等离子体的形成
• 在很高载流子密度 (N>1017cm–3)时,载流子 之间的碰撞相对载流子与晶格的碰撞占主 要部分，这时载流子表现出集体性，即形 成等离子体； • 激光功率密度> 106 W/cm2时, 材料的蒸发 和等离子体效应变得很重要。 • 激光功率密度更高(>109W/cm2)时, 等离子 体变得透明. 熔化压驱使击波进入材料， 从而在很宽范围内改变材料的结构和光学 性质；
高强度激光的获得
激光强度的提高方法 Q－switching Mode-locking Chirped pulse amplification
Q－switching
• 在泵浦激光将尽可能多的原子激发到高激 发态的过程中，共振腔的Q值一直保持在很 小，一旦泵浦完成，共振腔的Q值就恢复到 最佳值，同时有一激光脉冲输出。
激光器部件
Component Oscillator Optical Isolator Stretcher</A. < TH> Power Amplifier Spatial Filter Compressor Target Chamber Experiments Purpose Produce a low power high precision pulse which is to be further amplified in a separate power amplifier. Prevent damage from parasitic feedback from higher power stages back into lower power amplification stages. Decrease the intensity of a laser pulse by stretching it in time. Amplify a weak pulse and produce very high power pulse while maintaining the initial characteristics of the initial pulse. To remove wavefront distortions by focusing the beam through a pinhole. Increase the power of a laser pulse by compressing it in time. Provide a gas-free environment in which the laser pulse can be focused onto a target. To perform an experiment requires some form of diagnostic instrumentation to analyze results.
CPA －光路原理
强激光自聚焦现象（self-focusing）
电离电子数目与光强成 正比，受横向电场的作 用集中于光束的外测。
电 子
Three processes: diffraction, relativistic self-focusing ionization induced refraction
百度文库
锁模放大
多纵模光波的相干产生 窄脉冲激光输出。
Resulting train of pulses from the addition in phase of 10 modes
Chirped Pulse Amplification(CPA)
The oscillator output (O) is stretched in the grating stretcher (S) such that the red frequency components (r) travel ahead of the blue (b). The peak intensity is reduced in the process. The stretched pulse is then amplified in a regenerative or multipass amplifier (A) before recompression in a grating-pair compressor (C).
Self focusing
Spatial distribution of the electron density for a time moment of 35 ps. Thomson scattering image of laser-He jet interaction at a wavelength of 1.053 mm and a laser power of 4.3 TW. The direction of the main beam propagation is from the left to the right.
激 光 效 率 和 功 率 水 平
CO2 CO Holmium Iodine Nd-glass, YAG * Color center * Vibronic (Ti Sapphire) Ruby He-Ne * Argon ion * OPO N2 * Dye Kr - F
10.6 5 2.06 1.315 1.06 1-4 0.7 - 0.9 0.6943 0.6328 0.45 - 0.60 0.4 - 9.0 0.3371 0.3 - 1.1 0.26