Fundamental Investigations and Micromachining with Few-Cycle Pulses in the Volume of Wide-Bandgap Dielectrics

最初的研究计划题为“宽频带间隙介电体体积中短周期脉冲的基础研究和微加工”，在超短脉冲照射下等离子体形成以及短周期脉冲微加工的潜力方面取得了相当大的成就。等离子体形成的基本原理是通过记录和利用所谓布鲁内尔谐波的发射来研究的。为了将这项工作置于固体高谐波产生的充满活力的领域，我们已经证明，在我们的实验条件下，强场电离（SFI）的特征可以与所有其他伴随机制隔离开来。通过将时间分辨布鲁内尔光谱与基于时域型图的数值相位恢复算法相结合，重构了强场电离作用下等离子体密度的逐步演化特征。这一重要结果为进一步开展这些实验提供了理想的基础。根据这项更新建议，将从两个方向进行调查。首先，探讨激发波长变化时SFI与碰撞电离之间的竞争关系。其次，等离子体的形成将在微处理的背景下进行研究。这里将着重介绍两种情况，即Ti:Sapphire情况和YAG情况。研究微处理的少周期脉冲电位同样提供了很好的结果。特别是，少周期脉冲使得在原始熔融二氧化硅样品上直接激光书写体波导和表面波导成为可能。表面波导具有很好的折射率对比（接近0.01）。在这些波导上应用高折射率液体导致强模式泄漏，从而证明了这些微结构对环境的敏感性。这些成果为在综合生物传感方向上进行研究工作奠定了良好的基础。该更新方案旨在开发用于表面等离子体共振（SPR）传感的三维光子平台的直接激光打印，其中等离子体共振是由激光诱导的表面波导中传播的电磁波激发的。这种方法能够将SPR传感器的出色性能与集成光学器件提供的显着小型化程度相结合。

With the initial research proposal entitled 'Fundamental Investigations and Micromachining with Few-Cycle Pulses in the Volume of Wide-Bandgap Dielectrics', considerable achievements have been earned on the topics of plasma formation upon irradiation with ultrashort pulses as well as on the potential of few-cycle pulses for microprocessing.The fundamentals of plasma formation were studied by recording and exploiting the emission of the so-called Brunel harmonics. With the intent to place this work in the vibrant field of high harmonic generation in solids, we have demonstrated that in our experimental conditions, the signature of strong field ionization (SFI) could be isolated from all other concomittant mechanisms. By combining the time-resolved Brunel spectra with a numerical phase-retrieval algorithm based on time domain ptychography, the characteristic stepwise plasma density evolution due to strong field ionization was reconstructed. This important result provides an ideal basis to pursue these experiments. With this renewal proposal, investigations in two directions will be carried out. First, the competition between SFI and collisional ionization will be explored when the excitation wavelength changes. Second, plasma formation will be studied in the context of microprocessing. Two cases will be emphasized, the Ti:Sapphire scenario and the YAG scenario.Studying the potential of few-cycle pulses for microprocessing equally provided excellent results. In particular, few-cycle pulses enabled direct laser writing of bulk and surface waveguides on a pristine fused silica sample. The surface waveguides exhibited a very good refractive index contrast (close to 0.01). Applying a high refractive index liquid on these waveguides resulted in a strong mode leakage, thereby proving the sensitivity of these microstructures to their environment. These achievements set a perfect ground for pursuing research efforts in the direction of integrated biosensing. This renewal proposal aims at developing direct laser printing of three dimensional photonic platforms for surface plasmon resonance (SPR) sensing, where the plasmon resonance is excited by the electromagnetic waves propagating in the laser-induced surface waveguides. This approach enables combining the outstanding performance of SPR sensors with the remarkable degree of miniaturization offered by integrated optics devices.