High-power Ytterbium femtosecond laser amplifier system

本课题组的研究重点之一是腔量子电动力学（c-QED）结构和新型材料的非线性太赫兹光谱。我们最近改进的腔体设计已经实现了极端的光-物质耦合强度，和光-物质杂交状态同时扩展多达6个光学倍频，从< 0.1太赫兹到bbb6太赫兹。下一步，我们将研究这些结构的非线性极化动力学，包括超越正模近似的极化模混合、非经典光的产生、极化模的动态压缩和纠缠以及真空辐射的产生。强耦合的大光谱范围和多模式特性要求一种新的二维强场光谱方法，提供同时具有几个难以统一的特征的太赫兹脉冲：几个100 kV/cm的强电场振幅，接近单周期极限的短持续时间和无间隙的超宽带光谱。有了所需的设备，我们将通过结合最近建立的几种太赫兹产生方法来实现新一代的2D太赫兹光谱。该方法基于Yb飞秒激光放大器系统，提供以1030nm波长为中心的超短脉冲，脉冲能量高达数mJ，重复频率可调，范围从100 kHz到MHz。该光源具有非常低的噪声水平，接近相对脉冲到脉冲能量波动的10^-3，出色的脉冲能量可扩展性和高的长期可靠性。激光功率将分成三个部分：一个用于电光探测的弱脉冲和两个强脉冲，两个强脉冲通过声光调制器以脉冲对脉冲的方式单独切换，频率高达重复率的一半。这种独特的设计可以实现1兆赫量级的快速调制，大大超过通过机械手段实现的常用kHz-rate调制，并且相应地提供非常低的噪声水平。进一步优化我们系统信噪比的措施包括基于我们小组开发的FPGA技术的定制检测电子设备，以及光束稳定系统。为了达到所需的太赫兹带宽，激光脉冲将通过基于Heriott-cell、多通、多板连续体生成和啁啾补偿被压缩到< 50 fs。宽带太赫兹强场产生将随后使用水冷、大面积自旋电子发射器结构进行，该结构提供单周期太赫兹强场脉冲，其无间隙光谱从0.1太赫兹延伸到bbb10太赫兹-二维强场光谱的前所未有的宽光谱范围，这将为太赫兹范围内的非线性开辟新的前景。

One of the research foci of my group is nonlinear THz spectroscopy of cavity quantum electrodynamical (c-QED) structures and novel materials. Our recently improved cavity designs have enabled extreme light-matter coupling strengths with light-matter hybridized states extending over as many as six optical octaves simultaneously, from < 0.1 THz to > 6 THz. As a next step, we seek to investigate the nonlinear polarization dynamics of these structures which is expected to include mixing of polariton modes beyond the normal-mode approximation, the generation of non-classical light, dynamical squeezing and entanglement of polariton modes as well as the generation of vacuum radiation. The large spectral range and multi-mode nature of extremely strong coupling requires a new approach to two-dimensional strong-field spectroscopy providing THz pulses which simultaneously feature several features that are difficult to unite: strong electric field amplitudes on the order of several 100 kV/cm, short durations close to the single-cycle limit and gap-free, ultrabroadband spectra. With the requested equipment, we will implement a new generation of 2D THz spectroscopy by combining several only recently established approaches for THz generation. The approach is based on an Yb femtosecond laser amplifier system delivering ultrashort pulses centred at a wavelength of 1030 nm, pulse energies of up to several mJ, and tuneable repetition rates ranging from 100 kHz to the MHz range. The light source features remarkably low noise levels approaching 10^-3 of relative pulse-to-pulse energy fluctuations, excellent pulse energy scalability, and high long-term reliability. The laser power will be split into three parts: a weak pulse which serves for electro-optic detection and two strong ones which are individually switched on a pulse-to-pulse basis by acousto-optic modulators at a rate of up to half the repetition rate. This unique design enables fast modulation on the order of 1 MHz, greatly exceeding the commonly employed kHz-rate modulation achieved by mechanical means, and correspondingly, provides exceptionally low noise levels. Further measures to optimize the signal-to-noise ratio of our system include custom-cut detection electronics based on FPGA technology developed in our group, as well as optical beam stabilization systems. In order to achieve the required THz bandwidth, the laser pulses will be compressed to < 50 fs by Heriott-cell based, multi-pass, multi-plate continuum generation and chirp compensation. Broadband THz strong-field generation will subsequently be performed using water-cooled, large-area spintronic emitter structures which provide single-cycle THz strong-field pulses with a gap-free spectrum extending from 0.1 THz up to > 10 THz – an unprecedentedly broad spectral range for two-dimensional strong-field spectroscopy which will open up new vistas for nonlinearities in the THz range.