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High precision, high quality, and high throughput of ultrashort pulse laser ablation of bulk material are the most demanded properties that are required to let this process technology compete with other micro-machining techniques. Previous attempts to increase volumetric ablation rates of ultrashort pulse laser processes were based on the increase of fluence or pulse repetition rates. They run into limitations mainly set by the occurrence of bumpy surfaces due to overheating of bulk material. In this work, the potential of laser beam shaping for the enhancement of ablation rates is studied systematically for the first time. The question regarding the physically shortest possible process time for ablation of 2.5D-structures by means of an ultrashort pulse laser is answered using a heat conduction model, which is extended by the ability to consider spatially shaped beams. The strategy of laser beam stamping is implemented in a novel optical setup and proven both theoretically and experimentally to have a great potential for increasing ablation rates.

Emerging Laser Technologies for High-Power and Ultrafast Science includes chapters from leading experts devoted to the most recent achievements in the field. Including cutting-edge topics such as high energy/high average power laser systems, the most current developments for high repetition rate high average power infrared fiber laser systems, breakthroughs of the development of CPA based on chromium doped zinc selenide gain material, infrared/mid-infrared laser systems based on high average power Ytterbium pumped OPCPA, and generation of ultrashort laser pulses in the UV spectral range. This book will serve as an important reference for students, researchers, scientists, and engineers interested in the development of next generation of ultrafast laser technologies.

Increasing numbers of studies demonstrated that picosecond lasers (Picos) were effective and safe for melasma. However, A limited number of randomized controlled trials (RCTs) regarding Picos contribute to a modest level of evidence. Topical hydroquinone (HQ) remains to be the first-line therapy. To compare the efficacy and safety of non-fractional picosecond Nd:YAG laser (PSNYL), non-fractional picosecond alexandrite laser (PSAL), and 2% HQ cream in the treatment of melasma. Sixty melasma patients with Fitzpatrick skin types (FST) III-IV were randomly assigned to the PSNY, PSAL, and HQ groups at a 1:1:1 ratio. Patients in PSNYL and PSAL groups received 3 laser sessions at 4-week intervals. The 2% HQ cream was applied twice daily for 12 weeks in patients of the HQ group. The primary outcome, the melasma area and severity index (MASI) score, was evaluated at weeks 0, 4, 8, 12, 16, 20, and 24. The patient assessment score by quartile rating scale was rated at weeks 12, 16, 20, and 24. Fifty-nine (98.3%) subjects were included in the analysis. Each group showed significant change from baseline in MASI scores from week 4 to week 24. The MASI score in the PSNYL group showed the greatest reduction compared to the PSAL group (  = 0.016) and HQ group (  = 0.018). The PSAL group demonstrated comparable MASI improvement as the HQ group (  = 0.998). The PSNYL group had the highest patient assessment score, followed by the PSAL group and then the HQ group, although only the differences between PSNYL and HQ groups at weeks 12 and 16 were significant. Four patients (6.8%) experienced recurrence. Other unanticipated events were transient and subsided after 1 week to 6 months. The efficacy of non-fractional PSNYL was superior to that of non-fractional PSAL, which was not inferior to 2% HQ, thus non-fractional Picos providing an alternative for melasma patients with FSTs III-IV. The safety profiles of PSNYL, PSAL, and 2% HQ cream were similar. https://www.chictr.org.cn/showprojen.aspx?proj=130994, ChiCTR2100050089.

The Internet today transmits hundreds of terabits per second, consumes 9% of all electricity worldwide and grows by 20–30% per year1,2. To support capacity demand, massively parallel communication links are installed, not scaling favourably concerning energy consumption. A single frequency comb source may substitute many parallel lasers and improve system energy-efficiency3,4. We present a frequency comb realized by a non-resonant aluminium-gallium-arsenide-on-insulator (AlGaAsOI) nanowaveguide with 66% pump-to-comb conversion efficiency, which is significantly higher than state-of-the-art resonant comb sources. This enables unprecedented high data-rate transmission for chip-based sources, demonstrated using a single-mode 30-core fibre. We show that our frequency comb can carry 661 Tbit s–1 of data, equivalent to more than the total Internet traffic today. The comb is obtained by seeding the AlGaAsOI chip with 10-GHz picosecond pulses at a low pump power (85 mW), and this scheme is robust to temperature changes, is energy efficient and facilitates future integration with on-chip lasers or amplifiers5,6.

In this work, experimentally measured characteristics of a kilohertz laser‐driven Cu plasma X‐ray source that was recently commissioned at the ELI Beamlines facility are reported. The source can be driven either by an in‐house developed high‐contrast sub‐20 fs near‐infrared terawatt laser based on optical parametric chirped‐pulse amplification technology or by a more conventional Ti:sapphire laser delivering 12 mJ and 45 fs pulses. The X‐ray source parameters obtained with the two driving lasers are compared. A measured photon flux of the order up to 1012 Kα photons s−1 (4π)−1 is reported. Furthermore, experimental platforms for ultrafast X‐ray diffraction and X‐ray absorption and emission spectroscopy based on the reported source are described. A laser‐driven plasma X‐ray source with sub‐picosecond pulses at 1 kHz repetition rate for various time‐resolved experiments has been commissioned at ELI Beamlines. This article features a comprehensive overview of the driving‐laser parameters and X‐ray beam characteristics and outlines possible applications of the source.

Titanium:sapphire (Ti:sapphire) lasers have been essential for advancing fundamental research and technological applications, including the development of the optical frequency comb 1 , two-photon microscopy 2 and experimental quantum optics 3 , 4 . Ti:sapphire lasers are unmatched in bandwidth and tuning range, yet their use is restricted because of their large size, cost and need for high optical pump powers 5 . Here we demonstrate a monocrystalline titanium:sapphire-on-insulator (Ti:SaOI) photonics platform that enables dramatic miniaturization, cost reduction and scalability of Ti:sapphire technology. First, through the fabrication of low-loss whispering-gallery-mode resonators, we realize a Ti:sapphire laser operating with an ultralow, sub-milliwatt lasing threshold. Then, through orders-of-magnitude improvement in mode confinement in Ti:SaOI waveguides, we realize an integrated solid-state (that is, non-semiconductor) optical amplifier operating below 1 μm. We demonstrate unprecedented distortion-free amplification of picosecond pulses to peak powers reaching 1.0 kW. Finally, we demonstrate a tunable integrated Ti:sapphire laser, which can be pumped with low-cost, miniature, off-the-shelf green laser diodes. This opens the doors to new modalities of Ti:sapphire lasers, such as massively scalable Ti:sapphire laser-array systems for several applications. As a proof-of-concept demonstration, we use a Ti:SaOI laser array as the sole optical control for a cavity quantum electrodynamics experiment with artificial atoms in silicon carbide 6 . This work is a key step towards the democratization of Ti:sapphire technology through a three-orders-of-magnitude reduction in cost and footprint and introduces solid-state broadband amplification of sub-micron wavelength light. A photonic platform enables miniaturization and scalability of titanium:sapphire photonic technology, reducing footprint and cost by three orders of magnitude.

Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the geometric phase of the constituting electronic bands: the Berry connection. This photocurrent, termed shift current, is expected to emerge on the timescale of primary photoexcitation process. We observe ultrafast evolution of the shift current in a prototypical ferroelectric semiconductor antimony sulfur iodide (SbSI) by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the bandgap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection on interband optical transition. The shift excitation carries a net charge flow and is followed by a swing over of the electron cloud on a subpicosecond timescale. Understanding these substantive characters of the shift current with the help of first-principles calculation will pave the way for its application to ultrafast sensors and solar cells.

We report on a laser producing bursts of GHz picosecond pulses with pulse repetition rate between 1 and 7.5 GHz, tens to thousands pulses per burst, 1 kW average power and inJ energy per burst. © 2024 The Author(s).

The development of lasers capable of producing high-intensity pulses has opened a new area in the study of light-matter interactions. The corresponding laser fields are strong enough to compete with the Coulomb forces in controlling the dynamics of atomic systems and give rise to multiphoton processes. This book presents a unified account of this rapidly developing field of physics. The first part describes the fundamental phenomena occurring in intense laser-atom interactions and gives the basic theoretical framework to analyze them. The second part contains a detailed discussion of Floquet theory, the numerical integration of the wave equations and approximation methods for the low- and high-frequency regimes. In the third part, the main multiphoton processes are discussed: multiphoton ionization, high harmonic and attosecond pulse generation, and laser-assisted electron-atom collisions. Aimed at graduate students in atomic, molecular and optical physics, the book will also interest researchers working on laser interactions with matter.