Presidential Young Investigators Award: Ultrashort Laser- Matter Interactions

总统青年研究员奖：超短激光-物质相互作用

• 批准号: 8858062
• 负责人: Howard Milchberg
• 金额: $ 28.94万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-08-15 至 1994-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8858062&HistoricalAwards=false
• 关键词: Presidential; Young; Investigators; Award; Ultrashort

The advent of focusable subpicosecond laser pulses of energy greater than about 1 mJ has made possible a wide range of studies of laser- matter interactions at extremely high intensity and under very fine time resolution. The high repetition rate of these lasers allows the use of low noise correlation techniques such as pump-probe methods. The combination of high pulse energy and short duration makes possible the measurement of the electrical properties of solid materials over their transition from quantum solids to high temperature solid density plasmas. Recently, the resistivity of solid aluminum up to 106 oK has been inferred from reflectivity measurements. Onset toward and passage through a resistivity maximum at 200 -cm was observed as the material disorder and electron temperature increased, the first direct observation of this phenomenon. This research is being extended to materials exhibiting band absorption, such as copper, to study the effects on plasma behavior of the condensed state. Preliminary results indicate that considerable band absorption is still present even at elevated electron temperatures ( 50 eV). Short pulse continuum soft X-ray emission from these plasmas will be used to perform time resolved studies of semiconductor and metal conduction band plasmas, scattering from crystals with large atomic plane spacing (such as KAP), time resolved EXAFS, and preliminary experiments on pumping of soft X-ray laser transitions. The effect of ultrahigh fields on gases will be investigated by studying time-of-flight electron spectra and ion mass spectra from gases irradiated by energetic ultrashort pulses. Of particular interest is the transition of gas "breakdown" from the multiphoton ionization limit at low density to avalanche breakdown at high density.

可聚焦的亚皮秒激光脉冲的出现， 超过1 mJ的能量使得对激光的广泛研究成为可能， 在极高强度和极细的条件下， 时间分辨率 这些激光器的高重复频率允许 使用低噪声相关技术，例如泵浦-探测方法。 高脉冲能量和短持续时间的组合使得 固体材料电性能的测量 从量子固体到高温固体密度的转变 等离子 最近，固体铝的电阻率高达106 oK， 从反射率测量中推断出来。 开始走向和 观察到在200 -cm处通过电阻率最大值， 材料无序和电子温度增加，第一直接 观察这一现象。 这项研究正在扩大到 材料表现出带吸收，如铜，研究 对凝聚态等离子体行为的影响。 初步 结果表明，仍然存在相当大的带吸收 即使在升高的电子温度（50 eV）下也是如此。 短脉冲 这些等离子体的连续软X射线发射将用于 进行半导体和金属传导的时间分辨研究 带状等离子体，从具有大原子面间距的晶体散射 (such作为KAP），时间分辨EXAFS，和初步实验， 泵浦软X射线激光跃迁。 的影响 将通过研究飞行时间来研究气体的场 电子光谱和离子质谱的气体辐照 高能超短脉冲 特别值得注意的是， 气体“击穿”从多光子电离极限在低 在高密度下的雪崩击穿。