Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin–orbit effects that enable efficient spin–charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen–vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen–vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

Real-space imaging of non-collinear antiferromagnetic order with a single spin magnetometer

Using high-sensitivity confocal time-resolved photoluminescence (PL) techniques, we report an ultrafast PL (40 ps–5 ns) from impurity-free surface flaws on fused silica, including polished, indented, or fractured surfaces of fused silica, and from laser-heated evaporation pits This PL is excited by the single-photon absorption of sub-band gap light, and is especially bright in fractures Regions which exhibit this PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 35 eV nanosecond-scale laser pulses

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Metallic-like photoluminescence and absorption in fused silica surface flaws

Generation, optimization, and application of ultrashort femtosecond pulse in mode-locked fiber lasers

With wide applicability and low-cost processing advantages, laser processing, as a mature and versatile tool, is forming an alternative to conventional processing technologies. In recent years, the global laser market ushered in a broad new demand since the gradual increase in the penetration rate of laser processing in consumer electronics, automotive processing, aerospace, medical and other fields. Ultrafast laser and continuous wave (CW) laser are the representatives of high-quality and high-efficiency in laser processing, respectively, but it is a huge challenge to achieve high-quality and high-efficiency laser processing at the same time in the true sense, which has been the goal of the joint efforts of scientific researchers in recent decades. In this context, combined pulse laser (CPL), one of the hybrid laser processing technologies, has proven to be a reliable tool for the high-quality and high-efficiency processing through the processing advantages of different types of lasers and controlling the laser-matter interaction. In this review, the basic principles and characteristics of the CPL processing method are systematically introduced. Also, how the CPL method is for precisely and efficiently ablating, drilling, welding and structuring and their recent advancements are analyzed. Finally, a summary and outlook of the CPL technology is highlighted. 

Combined pulse laser: Reliable tool for high-quality, high-efficiency material processing

Although femtosecond lasers enable microfabrication of transparent materials, precise processing is difficult owing to the inevitable damage caused to the surroundings of the processed region. In the present work, we combine pump-probe imaging with a high-speed camera to capture the dynamics of pressure waves varying from pulse to pulse, before a desired shape is created by hundreds of pulses. The results demonstrate that the pressure waves change their forms and locations as the number of pulses increases. The numerical analyses explain that a tensile stress, much greater than the tensile strength, is distributed around the processed region during the travel of the pressure wave, and that repetitive pressure waves result in cracks. The identified mechanism of the damage generation will contribute to developing strategies to prevent damage and expand the range of applications of femtosecond laser processing.

Dynamics of pressure waves during femtosecond laser processing of glass.

In the original publication of the article, Fig. 5 was incorrect. The correct Fig. 5 appears as below.

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Correction to: Abrupt initiation of material removal by focusing continuous-wave fiber laser on glass

The extremely intense light emitted from femtosecond laser pulses enables micro-drilling of glass. However, there are problems in femtosecond laser drilling, including low drilling speed and the damage during drilling. Because the volume removed by one femtosecond laser pulse is too small, hundreds of pulses must be focused on a single spot to create a hole with a diameter of 10 μm and a depth of over 100 μm. Furthermore, strong stress waves generated during the processing cause damage around the hole. In our research, we achieved ultrafast and precision drilling by coaxially focusing a single femtosecond laser pulse and a fiber laser pulse, with a wavelength that is transparent to the glass. A hole with a diameter of 10 μm and a depth of 133 μm was created in 40 μs, which indicates that the drilling speed was over 5000 times faster than that of conventional femtosecond laser drilling. By investigating the phenomena occurring after laser irradiation, we demonstrated that ultrafast drilling occurred because the fiber laser pulse was selectively absorbed by a high-aspect-ratio filament induced by the femtosecond laser pulse. Moreover, damage generation was inhibited because the material was thermally removed. The results help expand the range of applications for femtosecond laser processing in industry.

Ultrafast and precision drilling of glass by selective absorption of fiber-laser pulse into femtosecond-laser-induced filament

The internal modification of glass using ultrashort pulse lasers has been attracting attention in a wide range of applications. However, the remarkably low processing speed has impeded its use in the industry. In this study, we achieved ultrafast internal modification of glass by coaxially focusing a single-pulse femtosecond laser and continuous-wave (CW) laser with the wavelength that is transparent to the glass. Compared with the conventional method, the processing speed increased by a factor of 500. The observation of high-speed phenomena revealed that the CW laser was absorbed by the seed electrons that were generated by the femtosecond laser pulse. This technique may help expand the applications of femtosecond lasers in the industry.

Ultrafast internal modification of glass by selective absorption of a continuous-wave laser into excited electrons.

The negatively-charged NV$^-$-center in diamond has shown great success in nanoscale, high-sensitivity magnetometry. Efficient fluorescence detection is crucial for improving the sensitivity. Furthermore, integrated devices enable practicable sensors. Here, we present a novel architecture which allows us to create NV$^-$-centers a few nanometers below the diamond surface, and at the same time in the mode field maximum of femtosecond-laser-written type-II waveguides. We experimentally verify the coupling efficiency, showcase the detection of magnetic resonance signals through the waveguides and perform first proof-of-principle experiments in magnetic field and temperature sensing. The sensing task can be operated via the waveguide without direct light illumination through the sample, which marks an important step for magnetometry in biological systems which are fragile to light. In the future, our approach will enable the development of two-dimensional sensing arrays facilitating spatially and temporally correlated magnetometry.

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An integrated magnetometry platform with stackable waveguide-assisted detection channels for sensing arrays.

The negatively charged nitrogen vacancy (N-V−) center in diamond has shown great success in nanoscale, high-sensitivity magnetometry. Efficient fluorescence detection is crucial for improving the sensitivity. Furthermore, integrated devices enable practicable sensors. Here, we present an integrated architecture which allows us to create N-V− centers a few nanometers below the diamond surface, and at the same time covering the entire mode field of femtosecond-laser-written type-II waveguides. We experimentally verify the coupling efficiency, showcase the detection of magnetic resonance signals through the waveguides and perform proof-of-principle experiments in magnetic field and temperature sensing. The sensing task can be operated via the waveguide without direct light illumination through the sample, which is important for magnetometry in biological systems that are sensitive to light. In the future, our approach will enable the development of two-dimensional sensing arrays facilitating spatially and temporally correlated magnetometry.

/pdf/integrated-magnetometry-platform-with-stackable-waveguide-1x9lartqh3.pdf

Reina Yoshizaki

Papers

Correction to: Abrupt initiation of material removal by focusing continuous-wave fiber laser on glass

Ultrafast and precision drilling of glass by selective absorption of fiber-laser pulse into femtosecond-laser-induced filament

Ultrafast internal modification of glass by selective absorption of a continuous-wave laser into excited electrons.

An integrated magnetometry platform with stackable waveguide-assisted detection channels for sensing arrays.

Integrated magnetometry platform with stackable waveguide-assisted detection channels for sensing arrays