Development of an Ultrabroadband Terahertz Emission Spectrometer for Materials Research

[802743 . mittleman]该奖项为莱斯大学用于材料研究的超波段太赫兹发射光谱仪的开发提供了部分支持。最近，在开发基于远红外线或太赫兹电磁波谱范围的新光谱方法方面有大量的活动。这是由于在这个光谱范围内活跃的许多物理现象的重要性，以及使用传统方法产生和探测太赫兹辐射的相对困难。其中一个更有趣的系统被称为太赫兹时域光谱复制（THz-TDS）。这项技术依靠飞秒激光技术，结合传统的电子技术，产生亚皮秒的太赫兹辐射脉冲，在极宽的带宽上具有非常高的信噪比。近年来，这种独特的系统作为一种新的光谱工具被用于许多不同材料的研究。相干探测方案的最新发展使可访问带宽显著提高，提高幅度高达一个数量级。该奖项将利用这些新技术，以便更好地理解各种电子材料中的超快电荷载流子动力学。特别是，这一进展在太赫兹发射光谱领域具有特别重要的意义。在这里，样品被超快激光脉冲激发后发出的太赫兹辐射可以用来监测载流子的加速。通过精确测量发射电场ETHz(t)，可以推断出载流子的弹道运动、载流子筛选和空间电荷效应以及位移极化动力学等有价值的信息。近年来，这种发射光谱在许多不同材料体系的研究中越来越有价值。结合泵浦探测技术，它可以用来观察10飞秒时间尺度上的载流子动力学。然而，如果发射的辐射带宽大大超出了研究中使用的探测器的可接受带宽，则在此类实验中收集的信息是不完整的。最近的进展涉及扩展这一接受带宽将大大提高这一实验技术的价值。这种令人兴奋的新能力将用于研究许多材料系统中涉及载流子输运的超快动力学过程，包括体半导体、异质结构和超导系统。这一发展努力将指向一个多功能超宽带太赫兹发射光谱仪的建设，用于材料研究。它将被配置为执行线性和非线性太赫兹发射实验，具有尽可能宽的检测带宽。提出了三个初步实验；这将为几种重要材料中极化动力学的基本输运提供有价值的新信息。此外，该光谱仪的独特功能将为赖斯大学纳米科学与技术中心的几位研究人员提供互动的机会，该中心是一项新材料研究工作。因此，这一发展项目预计将产生广泛的影响，不仅对PI的研究计划，而且通过与物理，化学，电气和计算机工程系成员的互动。%%%***

9802743MittlemanThis award provides partial support for the development of an ultrabroad band terahertz emission spectrometer for materials research at Rice University. Recently, there has been a great deal of activity in the development of new spectroscopic methods based in the far infrared, or terahertz, range of the electromagnetic spectrum. These have been driven by the importance of the numerous physical phenomena which are active in this spectral range, and by the relative difficulty in generating and detecting terahertz radiation using conventional means. One of the more interesting of these systems is known as terahertz time-domain spectrocopy (THz-TDS). This technique relies on femtosecond laser technology, in combination with conventional electronics, to generate sub-picosecond pulses of terahertz radiation, with very high signal-to-noise ratios over extremely broad bandwidths. This unique system has been used in recent years as a novel spectroscopic tool in studies of many different materials. Very recent developments in the coherent detection scheme have led to dramatic enhancements in the accessible bandwidths, by as much as an order of magnitude.This award will exploit these new techiques, in order to gain a better understanding of the ultrafast charge carrier dynamics in a broad range of electronic materials. In particular, this advance is of particular importance in the area of terahertz emission spectroscopy. Here, the THz radiation emitted by a sample which has been excited by an ultrafast laser pulse can be used to monitor the acceleration of charge carriers. By accurately measuring the emitted electric field ETHz(t), valuable information can be inferred about the ballistic motion of charge carriers, carrier screening and space charge effects, and displacement polarization dynamics. This emission spectroscopy has been increasingly valuable in recnet years in studies of many different material systems. In combination with pump-probe techniques, it can be used to observe charge carrier dynamics on a 10 femtosecond time scale. However, the information gleaned in such experiments is incomplete if the emitted radiation bandwidth extends substantially beyond the acceptance bandwidth of the detectors used in the study. The recent advances involving the extension of this acceptance bandwidth will greatly enhance the value of this experimental technique. This exciting new capability will be used to study the ultrafast dynamical processes involved in carrier transport in a number of material systems, including bulk semiconductors, heterostructures, and superconducting systems.This development effort will be directed towards the construction of a versatile ultrabroadband THz emission spectrometer, for use in materials research. It will be configured to perform both linear and non-linear THz emission experiments, with the broadest possible detection bandwidth. Three initial experiments are proposed; these should provide valuable new information about the fundamental transport of polarization dynamics in several important classes of materials. Additionally, the unique capabilities of this spectrometer will provide the opportunity for interaction with several researchers affiliated with the Center for Nanoscale Science and Technology, a new materials research effort at Rice University. Consequently, this development project is expected to have a broad impact, not only on the PI's research program, but also through interactions with members of the Physics, Chemistry, and Electrical and Computer Engineering Departments.%%%***