Periodic Reporting for period 4 - TerAqua (Compact and powerful strong-field terahertz light source for exploring water in new regimes)
Okres sprawozdawczy: 2023-10-01 do 2024-09-30
Water is undoubtedly the most important chemical solution for mankind - often referred to as the “solvent of life”. However many of its microscopic details and role in biological function remains mostly a mystery. In this project, the main target is to demonstrate a unique light tool that should contribute to make advances in this area and better understand one of the biggest mysteries of nature: the microscopic details of water.
More specifically, the light tool we aim to demonstrate is an ultrafast laser-driven, few-cycle Terahertz source with unprecedented efficiency, operating with high-average power and to apply this source for THz nonlinear spectroscopy of water-based solutions. Terahertz time-domain spectroscopy is a powerful technique for studying the dynamics of many fundamental constituents of matter. Recent progress in the generation of few-cycle THz pulses with electric field strengths exceeding several MV/cm has opened up exciting new directions in the area of nonlinear THz spectroscopy. However, many fields, including the wide field of physical chemistry studying aqueous solutions, suffer from a persistent lack of table-top THz sources combining high field strength and high repetition rate (i.e. sources operating with high average power). So far, these parameters can only be achieved by costly accelerator facilities with very restrictive access. In most cases, due to this persistent lack of convenient sources, scientists either abandon research lines where high pulse energy is required or operate at low repetition rate (typically well below 1 kHz). A low repetition rate imposes severe limits on the explored parameter space in many measurements, for which minuscule average powers result in very long integration time and low signal-to-noise ratio, or simply makes the study of relevant samples impossible.
The objective of this project is to fill this performance gap by achieving table-top strong-field pulsed THz sources with watt-level average power. The key feature is to leverage existing THz generation techniques to higher efficiency by driving THz generation inside the resonator of a high-power ultrafast thin-disk oscillator, operated in the little explored mid-infrared (2 μm) spectral region.
This groundbreaking THz source will have tremendous impact in various fields and subfields of physics, physical chemistry, engineering, biology and medicine. The vision of this project is to apply this source to bring answers to one specific long-standing scientific puzzle: understanding the microscopic details of water and its role as “the solvent of life”. Although THz spectroscopy is extremely well suited to study aqueous samples, so far, most THz studies in liquid phase have been performed in the linear domain, and in a very restricted parameter space due to the inadequacy of the THz sources. Our source will enable us to realize nonlinear THz-TDS of samples in aqueous phase at high repetition rate, enabling to study samples in biological conditions and disentangle the details of the dynamics involved.
More specifically, the light tool we aim to demonstrate is an ultrafast laser-driven, few-cycle Terahertz source with unprecedented efficiency, operating with high-average power and to apply this source for THz nonlinear spectroscopy of water-based solutions. Terahertz time-domain spectroscopy is a powerful technique for studying the dynamics of many fundamental constituents of matter. Recent progress in the generation of few-cycle THz pulses with electric field strengths exceeding several MV/cm has opened up exciting new directions in the area of nonlinear THz spectroscopy. However, many fields, including the wide field of physical chemistry studying aqueous solutions, suffer from a persistent lack of table-top THz sources combining high field strength and high repetition rate (i.e. sources operating with high average power). So far, these parameters can only be achieved by costly accelerator facilities with very restrictive access. In most cases, due to this persistent lack of convenient sources, scientists either abandon research lines where high pulse energy is required or operate at low repetition rate (typically well below 1 kHz). A low repetition rate imposes severe limits on the explored parameter space in many measurements, for which minuscule average powers result in very long integration time and low signal-to-noise ratio, or simply makes the study of relevant samples impossible.
The objective of this project is to fill this performance gap by achieving table-top strong-field pulsed THz sources with watt-level average power. The key feature is to leverage existing THz generation techniques to higher efficiency by driving THz generation inside the resonator of a high-power ultrafast thin-disk oscillator, operated in the little explored mid-infrared (2 μm) spectral region.
This groundbreaking THz source will have tremendous impact in various fields and subfields of physics, physical chemistry, engineering, biology and medicine. The vision of this project is to apply this source to bring answers to one specific long-standing scientific puzzle: understanding the microscopic details of water and its role as “the solvent of life”. Although THz spectroscopy is extremely well suited to study aqueous samples, so far, most THz studies in liquid phase have been performed in the linear domain, and in a very restricted parameter space due to the inadequacy of the THz sources. Our source will enable us to realize nonlinear THz-TDS of samples in aqueous phase at high repetition rate, enabling to study samples in biological conditions and disentangle the details of the dynamics involved.
During the project, we have made significant steps forward both in ultrafast laser technology and corresponding table-top Terahertz sources, and first steps towards applications of these sources in spectroscopy.
With regards to laser technology: we demonstrated several record-holding laser sources in the targeted wavelength region of 2.1 µm: the first 100W fundamental mode thin-disk laser operating in this wavelength region, and the highest average power modelocked laser in this wavelength region achieving 50W of average power. We also extended these demonstrations to shorter pulse durations based on a new gain material, Ho:CALGO. This new material and the corresponding laser systems was the basis for a spinoff company.
Concerning Terahertz sources, the main result achieved during the project was the demonstration of an intra-laser THz source operated inside the resonator of a thin-disk laser, at hundreds of watts of intracavity driving power. This was the first time this could be achieved at these power levels using nonlinear crystals intracavity, which will open many possibilities in future studies and source developments. Last but not least, this result could only be achieved with a deep study and understanding of the limitations of the generation mechanisms at high average power. In this regard, several studies pertaining to understanding repetition rate scaling of nonlinear crystals and other THz generation methods were performed, that will enable us and other researchers in future works to continue scaling these sources. Furthermore, first results of water spectroscopy using these unique sources are currently underway.
With regards to laser technology: we demonstrated several record-holding laser sources in the targeted wavelength region of 2.1 µm: the first 100W fundamental mode thin-disk laser operating in this wavelength region, and the highest average power modelocked laser in this wavelength region achieving 50W of average power. We also extended these demonstrations to shorter pulse durations based on a new gain material, Ho:CALGO. This new material and the corresponding laser systems was the basis for a spinoff company.
Concerning Terahertz sources, the main result achieved during the project was the demonstration of an intra-laser THz source operated inside the resonator of a thin-disk laser, at hundreds of watts of intracavity driving power. This was the first time this could be achieved at these power levels using nonlinear crystals intracavity, which will open many possibilities in future studies and source developments. Last but not least, this result could only be achieved with a deep study and understanding of the limitations of the generation mechanisms at high average power. In this regard, several studies pertaining to understanding repetition rate scaling of nonlinear crystals and other THz generation methods were performed, that will enable us and other researchers in future works to continue scaling these sources. Furthermore, first results of water spectroscopy using these unique sources are currently underway.
The laser sources demonstrated in the 2 µm region represent the state-of-the-art of ultrafast lasers in this wavelength region in terms of average power and short pulse durations, placing us in a unique position. Future research will focus on energy scaling of the laser system beyond the targets of the proposal and pulse shortening to few-cycle pulses. Concerning THz generation, the sources we realized have also re-defined the state-of-the-art of sources based both on nonlinear crystals, but also other methods. Our group currently has in place the highest average power laser-driven THz source so far demonstrated.
Our detailed methodology to explore the limitations and compromises to be realized from the nonlinear materials is in most cases a first and will guide future scaling works beyond the watt-level. Furthermore, these sources promise to open new application fields, not only in spectroscopy, but also in imaging and other areas.
Our detailed methodology to explore the limitations and compromises to be realized from the nonlinear materials is in most cases a first and will guide future scaling works beyond the watt-level. Furthermore, these sources promise to open new application fields, not only in spectroscopy, but also in imaging and other areas.