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

• Applicant: Dr. Alexandre Mermillod-Blondin
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 269423143

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.

• DFG Programme: Research Grants