Table-top Laser Research Articles

Differentiating Three-Dimensional Molecular Structures Using Laser-Induced Coulomb Explosion Imaging.

Coulomb explosion imaging (CEI) with x-ray free electron lasers has recently been shown to be a powerful method for obtaining detailed structural information of gas-phase planar ring molecules [R. Boll et al., X-ray multiphoton-induced Coulomb explosion images complex single molecules, Nat. Phys. 18, 423 (2022).NPAHAX1745-247310.1038/s41567-022-01507-0]. In this Letter, we investigate the potential of CEI driven by a tabletop laser and extend this approach to differentiating three-dimensional structures. We study the static CEI patterns of planar and nonplanar organic molecules that resemble the structures of typical products formed in ring-opening reactions. Our results reveal that each molecule exhibits a well-localized and distinctive pattern in three-dimensional fragment-ion momentum space. We find that these patterns yield direct information about the molecular structures and can be qualitatively reproduced using a classical Coulomb explosion simulation. Our findings suggest that laser-induced CEI can serve as a robust method for differentiating molecular structures of organic ring and chain molecules. As such, it holds great promise as a method for following ultrafast structural changes, e.g., during ring-opening reactions, by tracking the motion of individual atoms in pump-probe experiments.

Compact terahertz harmonic generation in the Reststrahlenband using a graphene-embedded metallic split ring resonator array

Harmonic generation is a result of a strong non-linear interaction between light and matter. It is a key technology for optics, as it allows the conversion of optical signals to higher frequencies. Owing to its intrinsically large and electrically tunable non-linear optical response, graphene has been used for high harmonic generation but, until now, only at frequencies < 2 THz, and with high-power ultrafast table-top lasers or accelerator-based structures. Here, we demonstrate third harmonic generation at 9.63 THz by optically pumping single-layer graphene, coupled to a circular split ring resonator (CSRR) array, with a 3.21 THz frequency quantum cascade laser (QCL). Combined with the high graphene nonlinearity, the mode confinement provided by the optically-pumped CSRR enhances the pump power density as well as that at the third harmonic, permitting harmonic generation. This approach enables potential access to a frequency range (6-12 THz) where compact sources remain difficult to obtain, owing to the Reststrahlenband of typical III-V semiconductors.

Stable high repetition-rate laser-driven proton beam production for multidisciplinary applications on the advanced laser light source ion beamline.

Laser-driven proton accelerators are relevant candidates for many applications such as material science or medicine. Today, there are multi-hundred-TW table-top laser systems that can generate relativistic peak intensities >1018 W/cm2 and routinely reach proton energies in the MeV range. However, for most desired applications, there is still a need to optimize the quality and stability of the laser-generated proton beam. In this work, we developed a 0.625Hz high repetition-rate setup in which a laser with 2.5% RMS energy stability is irradiating a solid target with an intensity of 1019 to 1020 W/cm2 to explore proton energy and yield variations, both with high shot statistics (up to about 400 laser shots) and using different interaction targets. Investigating the above-mentioned parameters is important for applications that rely on specific parts of the proton spectrum or a high ion flux produced over quick multi-shot irradiation. We demonstrate that the use of a stable "multi-shot mode" allows improving applications, e.g., in the detection of trace elements using laser-driven particle-induced x-ray emission.

Dynamics of femtosecond heated warm dense copper with time-resolved L3-edge XANES.

Combining experimental set up and ab initio molecular dynamics simulations, we were able to follow the time evolution of the X-ray absorption near edge spectrum (XANES) of a dense copper plasma. This provides a deep insight into femtosecond laser interaction with a metallic copper target. This paper presents a review of the experimental developments we made to reduce the X-ray probe duration, from approximately 10 ps to fs duration with table-top laser systems. Moreover, we present microscopic scale simulations, performed with Density Functional Theory, as well as macroscopic simulations considering the Two-Temperature Model. These tools allow us to get a complete picture of the evolution of the target at a microscopic level, from the heating process to the melting and expansion stages, with a clear view of the physics involved during these processes. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.

Generation of collimated extreme ultraviolet radiation by single-photon process

Generating laser with short wavelength is a bottleneck problem in laser technology. The current applicable table-top extreme ultraviolet (EUV) lasers are all generated by multi-photon process with low efficiency. By utilizing metastable helium atoms excited by microwave and irradiated by a resonant laser, here we report the development of 58.4 nm collimated radiation by single-photon-excitation related anti-Stokes Raman scattering (ASRS). The conversion efficiency is much higher than that of high harmonic generation (HHG). The same divergence of 1.4 mrad as that of excitation laser indicates its stimulating character. Our results show an applicable path towards up-conversion by single-photon process to generate table-top EUV lasers.

Carbon Dioxide and Water Activation by Niobium Trioxide Anions in the Gas Phase.

Transition metals are important in various industrial applications including catalysis. Due to the current concentration of CO2 in the atmosphere, various ways for its capture and utilization are investigated. Here, we study the activation of CO2 and H2O at [NbO3]- in the gas phase using a combination of infrared multiple photon dissociation spectroscopy and density functional theory calculations. In the experiments, Fourier-transform ion cyclotron resonance mass spectrometry is combined with tunable IR laser light provided by the intracavity free-electron laser FELICE or optical parametric oscillator-based table-top laser systems. We present spectra of [NbO3]-, [NbO2(OH)2]-, [NbO2(OH)2]-(H2O) and [NbO(OH)2(CO3)]- in the 240-4000 cm-1 range. The measured spectra and observed dissociation channels together with quantum chemical calculations confirm that upon interaction with a water molecule, [NbO3]- is transformed to [NbO2(OH)2]- via a barrierless reaction. Reaction of this product with CO2 leads to [NbO(OH)2(CO3)]- with the formation of a [CO3] moiety.

Experimental study of medical isotopes 62,64Cu and 68Ga production using intense picosecond laser pulse

Radioisotopes are indispensable agents in medical diagnosis and treatment, among which copper-62, 64 (62,64Cu) and gallium-68 (68Ga) are medical isotopes widely used in positron emission tomography (PET) imaging. Experiments that generate these radioisotopes via laser-induced photonuclear reactions were performed on the XingGuangIII laser facility of the Laser Fusion Research Center in Mianyang. High-charge ( ∼ 40 nC) MeV electron (e− ) beams were generated with 100 terawatts, picosecond laser pulses. The e− beams were then impinged on a metal stack composed of Ta foil and activation plates (natural Cu and Ga2O3), producing high-energy bremsstrahlung x-rays and medical isotopes 62,64Cu and 68Ga, respectively. The characteristic emissions of the produced 62,64Cu and 68Ga were detected off-line , and the production yields of 62,64Cu and 68Ga were obtained to be of the order of 106 per laser shot. For electrons with energy higher than 8 MeV, the dependence of isotope production efficiency (per e− ) on electron temperature () is investigated through Geant4 simulations. It is found that the production efficiency increases with the . At ∼ 10 MeV, the values are 10−4 for 62Cu and 2 × 10 − 5 for 68Ga, respectively. The prospect of producing the medical isotopes 62,64Cu and 68Ga are further evaluated using a table-top femtosecond laser system of high repetition. With a repetition rate of 100 Hz, their activity is expected to reach 0.2 GBq for 62Cu, 0.1 GBq for 64Cu and 0.05 GBq for 68Ga, respectively. Such activity would meet the required dose for clinical PET imaging, indicating the great potential to produce medical isotopes with an all-optical, high-repetition laser system.

Foundry manufacturing of tight-confinement, dispersion-engineered, ultralow-loss silicon nitride photonic integrated circuits

The foundry development of integrated photonics has revolutionized today’s optical interconnect and datacenters. Over the last decade, we have witnessed the rising of silicon nitride (Si3N4) integrated photonics, which is currently transferring from laboratory research to foundry manufacturing. The development and transition are triggered by the ultimate need for low optical loss offered by Si3N4, which is beyond the reach of silicon and III-V semiconductors. Combined with modest Kerr nonlinearity, tight optical confinement, and dispersion engineering, Si3N4 has today become the leading platform for linear and Kerr nonlinear photonics, and it has enabled chip-scale lasers featuring ultralow noise on par with table-top fiber lasers. However, so far all the reported fabrication processes of tight-confinement, dispersion-engineered Si3N4 photonic integrated circuits (PICs) with optical loss down to few dB/m have only been developed on 4-inch (100 mm diameter) or smaller wafers. Yet, to transfer these processes to established CMOS foundries that typically operate 6-inch or even larger wafers, challenges remain. In this work, we demonstrate the first foundry-standard fabrication process of Si3N4 PICs with only 2.6 dB/m loss, thickness above 800 nm, and near 100% fabrication yield on 6-inch (150 mm diameter) wafers. Such thick and ultralow-loss Si3N4 PIC enables low-threshold generation of soliton frequency combs. Merging with advanced heterogeneous integration, active ultralow-loss Si3N4 integrated photonics could pave an avenue to addressing future demands in our increasingly information-driven society.

A multi-MeV alpha particle source via proton-boron fusion driven by a 10-GW tabletop laser

Nuclear fusion between protons and boron-11 nuclei has undergone a revival of interest thanks to the rapid progress in pulsed laser technology. Potential applications of such reaction range from controlled nuclear fusion to radiobiology and cancer therapy. A laser-driven fusion approach consists in the interaction of high-power, high-intensity pulses with H- and B-rich targets. We report on an experiment exploiting proton-boron fusion in CN-BN targets to obtain high-energy alpha particle beams (up to 5 MeV) using a very compact approach and a tabletop laser system with a peak power of ~10 GW, which can operate at high-repetition rate (up to 1 kHz). The secondary resonance in the cross section of proton-boron fusion (~150 keV in the center-of-mass frame) is exploited using a laser-based approach. The generated alpha particles are characterized in terms of energy, flux, and angular distribution using solid-state nuclear-track detectors, demonstrating a flux of ~105 particles per second at 10 Hz, and ~106 per second at 1 kHz. Hydrodynamic and particle-in-cell numerical simulations support our experimental findings. Potential impact of our approach on future spread of ultra-compact, multi-MeV alpha particle sources driven by moderate intensity (1016-1017 W/cm2) laser pulses is anticipated.

Considerations for a TeV collider based on dielectric laser accelerators

Particle acceleration in dielectric microstructures powered by infrared lasers, or “dielectric laser acceleration” (DLA), is a promising area of advanced accelerator research with the potential to enable more affordable and higher-gradient accelerators for energy frontier science and a variety of other applications. DLA leverages well-established industrial fabrication capabilities and the commercial availability of tabletop lasers to reduce cost, with axial accelerating fields in the GV/m range. Desirable luminosities would be obtained by operating with very low charge per bunch but at extremely high repetition rates. And as a consequence of its unique operating parameter regime, coupling of the laser to the accelerator can potentially be in the 50% range and with low beamstrahlung energy loss due at the interaction point, making DLA a promising approach for a future multi-TeV linear collider.

Subcycle terahertz field waveforms clocked by attosecond high-harmonic pulses from relativistic laser plasmas

A high-intensity ultrashort laser pulse interacting with a thin plasma target is shown to couple to plasma electrons, driving electron oscillations within the plasma and making these electrons bounce back and forth between plasma boundaries. Each time these recirculating electrons traverse the plasma boundary, they emit bright subcycle terahertz (THz) field waveforms via laser-driven coherent transition radiation. As a concurrent process, laser-driven electrons near the front surface of the plasma target are accelerated to relativistic velocities to emit high-order harmonics (HHs), giving rise to attosecond pulses of vacuum-ultraviolet radiation. These attosecond pulses are shown to provide a high-precision clock for subcycle THz field waveforms. We demonstrate that the delay time between HH pulses and THz waveforms can be tuned with an attosecond precision by varying the thickness of the plasma target, thus opening an avenue toward HH-pump–THz-probe studies of ultrafast processes on the attosecond time scale with table-top laser sources.

Ultrafast Imaging of Molecular Dynamics Using Ultrafast Low-Frequency Lasers, X-ray Free Electron Lasers, and Electron Pulses.

The requirement of high space-time resolution and brightness is a great challenge for imaging atomic motion and making molecular movies. Important breakthroughs in ultrabright tabletop laser, X-ray, and electron sources have enabled the direct imaging of evolving molecular structures in chemical processes, and recent experimental advances in preparing ultrafast laser and electron pulses resulted in molecular imaging with femtosecond time resolution. This Perspective presents an overview of the versatile imaging methods of molecular dynamics. High-order harmonic generation imaging and photoelectron diffraction imaging are based on laser-induced ionization and rescattering processes. Coulomb explosion imaging retrieves molecular structural information by detecting the momentum vectors of fragmented ions. Diffraction imaging encodes molecular structural and electronic information in reciprocal space. We also present various applications of these ultrafast imaging methods in resolving laser-induced nuclear and electronic dynamics.

Progress, challenges, and opportunities of terahertz emission from liquids

Broadband terahertz (THz) wave emission from flowing liquid targets has been demonstrated under short optical pulse excitation. Observations have been reported by using liquid THz sources, including optimal angle of incidence, preference of subpicosecond pulse excitation, and strong sideway emission. Compared with solid targets, the fluidity of liquid allows each laser pulse to interact with a fresh area, which makes it possible to use a table-top laser with a high repetition rate for excitation. Liquids with a comparable material density to solids make them promising candidates for the study of high-density plasma and bright THz sources. In this paper, we review recent progress, challenges, and opportunities of THz emission from liquids. This topic may offer new possibilities in the exploration of THz liquid photonics and may play an indispensable role in the study of laser-liquid interaction.

Micro-size picosecond-duration fast neutron source driven by a laser–plasma wakefield electron accelerator

Abstract A pulsed fast neutron source is critical for applications of fast neutron resonance radiography and fast neutron absorption spectroscopy. However, due to the large transversal source size (of the order of mm) and long pulse duration (of the order of ns) of traditional pulsed fast neutron sources, it is difficult to realize high-contrast neutron imaging with high spatial resolution and a fine absorption spectrum. Here, we experimentally present a micro-size ultra-short pulsed neutron source by a table-top laser–plasma wakefield electron accelerator driving a photofission reaction in a thin metal converter. A fast neutron source with source size of approximately 500 μm and duration of approximately 36 ps has been driven by a tens of MeV, collimated, micro-size electron beam via a hundred TW laser facility. This micro-size ultra-short pulsed neutron source has the potential to improve the energy resolution of a fast neutron absorption spectrum dozens of times to, for example, approximately 100 eV at 1.65 MeV, which could be of benefit for high-quality fast neutron imaging and deep understanding of the theoretical model of neutron physics.

Table-top soft X-ray laser in the ‘water window’

Table-top soft X-ray laser in the ‘water window’

Revealing the Structure and Noncovalent Interactions of Isolated Molecules by Laser-Desorption/Ionization-Loss Stimulated Raman Spectroscopy and Quantum Calculations.

The structural and dynamical characteristics of isolated molecules are essential, yet obtaining this information is difficult. We demonstrate laser-desorption jet-cooling/ionization-loss stimulated Raman spectroscopy to obtain Raman spectral signatures of nonvolatile molecules in the gas phase. The vibrational features of a test substance, the most abundant conformer of tryptamine, are compared and found to match those resulting from the scaled harmonic Raman spectrum obtained by density functional theory calculations. The vibrational signatures serve to identify the most prominent gauche conformer and evaluate its predicted electronic structure. These findings, together with noncovalent interaction (NCI) analysis, provide new insights into electron densities and reduced density gradients, assessing the hydrogen bonds (N-H···π and C-H···H-C) and interplay between attractive and repulsive NCIs affecting the structure. This approach accesses vibrational signatures of isolated nonvolatile molecules by tabletop lasers at uniform resolution and in a broad frequency range, promising great benefit to future studies.

Effect of the finite speed of light in ionization of extended molecular systems

We study propagation effects due to the finite speed of light in ionization of extended molecular systems. We present a general quantitative theory of these effects and show under which conditions such effects should appear. The finite speed of light propagation effects are encoded in the non-dipole terms of the time-dependent Shrödinger equation and display themselves in the photoelectron momentum distribution projected on the molecular axis. Our numerical modeling for the hbox {H}_{2}^{+} molecular ion and the hbox {Ne}_2 dimer shows that the finite light propagation time from one atomic center to another can be accurately determined in a table top laser experiment which is much more readily accessible than the ground breaking synchrotron measurement by Grundmann et al. (Science 370:339, 2020).

Short-term stability of Cs microcell-stabilized lasers using dual-frequency sub-Doppler spectroscopy

The combination of atomic spectroscopy, integrated photonics, and microelectromechanical systems leads the way to the demonstration of microcell-based optical atomic clocks. Here, we report the short-term stability budget of table-top Cs microcell-stabilized lasers based on dual-frequency sub-Doppler spectroscopy (DFSDS). The dependence of the sub-Doppler resonance properties on key experimental parameters is studied. The detection noise budget and absolute phase noise measurements are in good agreement with the measured short-term frequency stability of the laser beatnote, at the level of 1.1 × 10 − 12 τ − 1 / 2 until 100 s, currently limited by the intermodulation effect from a distributed-feedback laser setup. The fractional frequency stability of the laser beatnote at 1 s is about 100 times greater than that of commercial microwave chip-scale atomic clocks and validates interest in the DFSDS approach for the development of high-performance microcell-based optical standards.

Exciting the Isomeric ^{229}Th Nuclear State via Laser-Driven Electron Recollision.

We propose a new approach to excite the isomeric ^{229}Th nuclear state, which has attracted much attention recently as a potential "nuclear clock." Our approach is based on a laser-driven electron recollision process, the core process of strong-field atomic physics. Bringing together knowledge of recollision physics and of the related nuclear physics, we calculate the isomeric excitation probability. This new approach does not require precise knowledge of the energy of the isomeric state. The excitation is well timed which may be exploited to control the coherence of the isomeric state. Experimental realization is within reach using tabletop laser systems.

Optically synchronized fibre links using spectrally pure chip-scale lasers

Precision frequency and phase synchronization between distinct fiber interconnected nodes is critical for a wide range of applications, including atomic timekeeping, quantum networking, database synchronization, ultra-high-capacity coherent optical communications and hyper-scale data centers. Today, many of these applications utilize precision, tabletop laser systems, and would benefit from integration in terms of reduced size, power, cost, and reliability. In this paper we report a record low 3x10^-4 rad^2 residual phase error variance for synchronization based on independent, spectrally pure, ultra-high mutual coherence, photonic integrated lasers. This performance is achieved with stimulated Brillouin scattering lasers that are stabilized to independent microcavity references, realizing sources with 30 Hz integral linewidth and a fractional frequency instability less than or equal to 2x10^-13 at 50 ms. This level of low phase noise and carrier stability enables a new type of optical-frequency-stabilized phase-locked loop (OFS-PLL) that operates with a less than 800 kHz loop bandwidth, eliminating traditional power consuming high bandwidth electronics and digital signal processors used to phase lock optical carriers. Additionally, we measure the residual phase error down to a received carrier power of -34 dBm, removing the need to transmit in-band or out-of-band synchronized carriers. These results highlight the promise for a path to spectrally pure, ultra-stable, integrated lasers for network synchronization, precision time distribution protocols, quantum-clock networks, and multiple-Terabit per second coherent DSP-free fiber-optic interconnects.