HyperTerahertz - High precision terahertz spectroscopy and microscopy

在过去的20年里，太赫兹频率科学和工程领域取得了显著的发展，已经成熟为一个充满活力的国际研究领域。可以说，现代的太赫兹场始于脉冲(单周期)太赫兹发射器--半导体光导开关--的发展，以及随后太赫兹时域光谱学(TDS)的发展。从那时起，这种和其他太赫兹光源的进一步发展取得了相当大的成功，包括单行载流子光电二极管(UTC)和量子级联激光器(QCL)。然而，尽管如此，只有太赫兹-TDS技术已经发展得足够成熟，可以作为一个完整的系统进行商业化，其他太赫兹设备、部件和技术仍然局限于学术实验室。这是不幸的，因为尽管THz-TDS技术取得了成功，但该技术存在一些缺点，包括以飞秒激光为主的高成本、低功率和有限的频率和空间分辨率，如果QCL和UTC技术被设计成适当的仪器，这些缺点可以通过QCL和UTC技术来解决。事实上，与邻近的微波和光学频谱区域的粗略比较表明，THz频率科学和技术仍处于初级阶段，而不仅仅是在商业吸收的背景下。例如，太赫兹地区在解决气体固有的尖锐光谱特征所需的精密光谱仪器的可用性方面明显滞后，例如在大气分析中，或在具有长激发态寿命的材料中。太赫兹技术在非线性光谱学和相干控制领域也明显落后，在这两个领域中，强大而可控的电磁辐射脉冲与物质相互作用，并操纵其性质。在光学和微波领域，包括电子自旋共振和核磁共振在内的迷人现象是重大突破，揭示了丰富的新的科学和工程应用。这些技术现在是许多学科的标准，支持许多当代的研究和技术活动。太赫兹技术与其他光谱范围相比的另一个例子是在太赫兹显微镜和低于衍射极限的分析的背景下，这本质上限制了这种测量仅限于对例如纳米颗粒、纳米晶体或纳米结构域的尺寸、结构、取向和密度的平均物理性质的总体采样。虽然近场成像方法已从可见光/红外区改编为能够在微纳尺度上进行太赫兹测量，但目前没有太赫兹仪器提供所需的空间分辨率和灵敏度，也不能处理巨大的长度尺度范围(从电子约束长度(&lt；10 nm)到太赫兹波长(~300微米)，跨越五个数量级)，也不能在低温下工作。事实上，在这一点上，太赫兹场甚至在提供基本技术方面也是不足的，例如将低损耗的太赫兹信号传输到低温恒温器或工业设备所需的波导和耦合光学。在这个计划中，我们将创建第一个用于精确太赫兹频谱、显微镜和相干控制的综合仪器。这将基于我们独特和专有的能力来产生和操纵前所未有的窄(赫兹)线宽和亚波长空间分辨率的太赫兹信号。然后将利用该仪器在电子和大气传感的无损测试和光谱分析方面创造新的挑战引领的应用，以及在物理学、量子技术、材料科学、大气化学和天文学等领域由发现引领的机会。

The last 20 years have witnessed a remarkable growth in the field of THz frequency science and engineering, which has matured into a vibrant international research area. The modern THz field arguably began with the development of a pulsed (single-cycle) THz emitter - the semiconductor photoconductive switch - and the subsequent development of THz time-domain spectroscopy (TDS). Since then, considerable success has been achieved in the further development of this and other THz sources, including the uni-travelling carrier (UTC) photodiode and the quantum cascade laser (QCL). However, notwithstanding this, it is only the THz-TDS technology that has been developed sufficiently for commercialization as a complete system, leaving other THz devices, components and techniques still restricted to the academic laboratory. This is unfortunate, since despite the success of THz-TDS, the technique has a number of shortcomings including its high fs-laser dominated cost, low power, and limited frequency and spatial resolution, which could be addressed by QCL and UTC technologies if they were to be engineered into appropriate instruments.In fact, a cursory comparison with the neighbouring microwave and optical regions of the spectrum reveals that THz frequency science and technology is still in its infancy, and not just in the context of commercial uptake. For example, the THz region significantly lags in the availability of precision spectroscopy instrumentation required to address sharp spectral features inherent to gases, for example, in atmospheric analysis, or in materials with long excited state lifetimes. THz technology also significantly lags in the fields of non-linear spectroscopy and coherent control, where powerful and controlled pulses of electromagnetic radiation interact with matter and manipulate its properties. In the optical and microwave regions, fascinating phenomena including electron-spin resonance and nuclear magnetic resonance were major breakthroughs, revealing a wealth of new science and engineering applications. These techniques, now standard across many disciplines, support much contemporary research and technology activity.A further example of how THz technology compares unfavourably with other spectral ranges is in the context of THz microscopy and analysis below the diffraction limit, which intrinsically restricts such measurements to ensemble sampling of physical properties averaged over the size, structure, orientation and density of, for example, nanoparticles, nanocrystals or nanodomains. Although near-field imaging approaches have been adapted from the visible/infrared regions enabling THz measurements on the micro/nano-scale, no THz instrument currently provides the required spatial resolution and sensitivity, nor can address the enormous range of length-scales (spanning five orders of magnitude from electron confinement lengths (<10 nm) to the THz wavelength (~300 um)), nor can operate at cryogenic temperatures. In fact, on this point, the THz field is deficient even in the provision of basic technologies such as waveguides and coupling optics required to deliver THz signals with low loss into cryostats or industrial apparatus.In this programme we will create the first comprehensive instrumentation for precise THz frequency spectroscopy, microscopy, and coherent control. This will be based upon our unique and proprietary capabilities to generate, and manipulate photonically, THz signals of unprecedentedly narrow (Hz) linewidth and with sub-wavelength spatial resolution. The instrumentation will then be exploited to create new challenge-led applications in non-destructive testing and spectroscopic analysis for electronics and atmospheric sensing, inter alia, as well as discovery-led opportunities within physics, quantum technologies, materials science, atmospheric chemistry and astronomy.