High-power Laser Technology Research Articles

Analysis of continuous laser-irradiation resistance of liquid-crystal optical switch based on sapphire-substrate GaN

Developing high-power laser technology and its applications necessitates improvements in the laser-irradiation resistance of liquid-crystal modulation devices. In this study, the thermal characteristics of substrate and electrode materials, including sapphire-substrate indium tin oxide (ITO) electrodes, K9 glass-substrate ITO electrodes, sapphire-substrate gallium nitride (GaN) electrodes, and liquid-crystal optical switches, are investigated using simulation and experimental methods. Results show that the sapphire-substrate GaN electrode demonstrates the best heat dissipation and that the maximum temperature at the center of the spot under 75 W laser irradiation is 319 K, 52 K lower than that of an equally thick sapphire-substrate ITO electrode and 225 K lower than that of an equally thick K9 glass-substrate ITO electrode (steady state and test time >2min). Additionally, the experimental results show that the liquid-crystal optical switch, comprising a sapphire substrate and GaN electrode, can endure continuous laser irradiation up to 18 W with a switching ratio of approximately 20:1. The optical switch with GaN electrodes on a sapphire substrate can endure a power density of 156W/cm2, much higher than that (21W/cm2, steady state and test time >2min) tolerable by the liquid-crystal optical switch with ITO transparent electrodes and K9 glass substrates.

Study on thermal effects of high-power laser-coupled water jets and the influence on the stability of water jets

In water-guided laser technology, the stability of water jets is crucial to ensure the efficient transmission of laser energy. However, the thermal effects generated when high-power lasers are coupled with water jets are bound to impact the stability of the water jets, thus becoming a critical issue that restricts the development of high-power water-guided laser technology. In addressing this issue, this paper establishes a temperature model for coupling high-power lasers with water jets. Subsequently, with validation of the model's effectiveness through experimental data, simulations are conducted to analyze the temperature distribution within the water jet. During the simulation process, lasers with different parameters were coupled with water jets to analyze the temperature variation law of the water jets. Additionally, the maximum laser power coupled with water jets of different lengths was solved. Based on the calculated temperature values of the water jet, simulate the evolution of its profile over time when it has an initial temperature gradient. Simultaneously, perform a three-dimensional reconstruction of the obtained perturbed profile and conduct ray tracing to analyze the laser's transmission losses within the perturbed profile. Finally, high-speed cameras are utilized to capture the profile of the water jet, validating the laser-induced fragmentation behavior in the water jet. The research findings will provide a significant reference value for selecting laser parameters and controlling thermal effects in water-guided high-power technology.

Wavelength-Independent Performance of Femtosecond Laser Dielectric Ablation Spanning Over Three Octaves

Ultrafast laser breakdown of wide bandgap dielectrics is today a key for major technologies ranging from 3D material processing in optical materials to nanosurgery. However, a contradiction persists between the strongly nonlinear character of energy absorption and the robustness of processes to the changes of the bandgap/wavelength ratio depending on applications. While various materials and bandgaps have been studied, we concentrate here the investigations on the spectral domain with experiments performed with wavelength drivers varied from deep-ultraviolet (258 nm) to mid-infrared (3.5 $\mu$m). The measured fluence thresholds for single shot ablation in dielectrics using 200-fs pulses exhibit a plateau extending from the visible domain up to 3.5-$\mu$m wavelength. This is accompanied, after ablation crater analysis, by a remarkable invariance of the observed ablation precision and efficiency. Only at the shortest tested wavelength of 258 nm, a twofold decrease of the ablation threshold and significant changes of the machining depths are detected. This defines a lower spectral limit of the wavelength-independence of the ablation process. By comparison with simulations, avalanche ionization coefficients are extracted and compared with those predicted with the Drude model. This must be beneficial to improve predictive models and process engineering developments exploiting the new high-power ultrafast laser technologies emitting in various spectral domains.

Comparative effectiveness of high-power holmium laser lithotripsy for pediatric patients with kidney and ureteral stones

The comparative effectiveness of high-power laser technology for kidney stone surgery in pediatric patients is poorly understood. We compared outcomes for the 120W Holmium:yttrium-aluminum-garnet (Ho:YAG) laser with MOSES technology to 30W Ho:YAG laser for pediatric patients undergoing ureteroscopy with laser lithotripsy for kidney and ureteral stones. We evaluated the outcomes of the new MOSES laser technology as compared to low-power Ho:YAG lasers commonly used for kidney stone treatment in the pediatric population. We performed a retrospective cohort study of 131 consecutive patients aged 1-18 years who underwent ureteroscopy and laser lithotripsy for renal and ureteric calculi at a large freestanding children's hospital between 2013 and 2020. The primary outcome was the efficiency quotient, which incorporates stone clearance, auxiliary procedures, and retreatment rates. Outcomes were compared between groups using Chi-square or Fisher's exact tests and multivariable regression. A sensitivity analysis was performed extending the age limit to ≤21 years. Outcomes are summarized in the table below. Median age of the cohort was 14 years with 53% of patients being female. MOSES laser had a higher efficiency quotient and was associated with a lower odds of post-operative emergency department visits (OR 0.2, 95% CI 0.0-1.0; p=0.047). Operative time was similar. In the sensitivity analysis of patients ≤21 years, the statistical significance with fewer emergency department visits was lost and the efficiency quotient was lower. Our results show that stone clearance is similar between the 120W MOSES and 30W Ho:YAG lasers. However, there are indications that high-power laser lithotripsy is more efficient due to fewer auxiliary procedures and a reduction in retreatment. In addition, higher power lasers were associated with fewer emergency department visits. The benefits appear to be greater among children ≤18 years. These exploratory findings are important for pediatric patients due to the requirement for general anesthesia for each procedure and their associated impact on children and their caregivers. High-power laser lithotripsy may be more efficient than lower power laser lithotripsy, which is driven by the fewer auxiliary procedures and reduction in retreatment particularly among youth ≤18 years old.

Solvent-conjugation-induced ultrafast dynamics of enhanced reverse saturable absorption in lead phthalocyanine derivatives solutions

With the continued development of high-power laser technology, research on laser protection has become extremely important. In this study, an analysis of Z-scan and femtosecond transient absorption spectra data for lead (II) tetrakis (4-cumylphenoxy) phthalocyanine (4-PbPc) solutions prepared using different concentrations and solvents established that charge transfer plays an important role in the optical limiting dynamics of this molecule. Based on the correlation of decay-associated difference spectra (DADS) for different decay channels, it was confirmed that greater charge transfer efficiency was associated with more highly conjugated solvent molecules. In a dilute solution, the polarity of the solvent molecules will influence the optical limiting performance of the solution to an extent, whereas in a highly concentrated solution, the degree of conjugation of the solvent molecules is the main influence. Therefore, the more highly conjugated the solvent and the higher the solution concentration, the higher the excited state absorption cross-section and effective two-photon absorption coefficient, and the longer the triplet lifetime. These results should provide theoretical guidance and experimental clues for the design of materials with better optical limiting performance and promote the further development of laser protection.

Compact LWFA-Based Extreme Ultraviolet Free Electron Laser: Design Constraints

The combination of advanced high-power laser technology, new acceleration methods and achievements in undulator development offers the opportunity to build compact, high-brilliance free electron lasers driven by a laser wakefield accelerator. Here, we present a simulation study outlining the main requirements for the laser–plasma-based extreme ultraviolet free electron laser setup with the aim to reach saturation of the photon pulse energy in a single unit of a commercially available undulator with the deflection parameter K0 in the range of 1–1.5. A dedicated electron beam transport strategy that allows control of the electron beam slice parameters, including collective effects, required by the self-amplified spontaneous emission regime is proposed. Finally, a set of coherent photon radiation parameters achievable in the undulator section utilizing the best experimentally demonstrated electron beam parameters are analyzed. As a result, we demonstrate that the ultra-short, few-fs-level pulse of the photon radiation with the wavelength in the extreme ultraviolet range can be obtained with the peak brilliance of ∼7×1028 photons/pulse/mm2/mrad2/0.1%bw.

Research progress of high-power single-frequency erbium-doped fiber laser technology (Invited)

Research progress of high-power single-frequency erbium-doped fiber laser technology (Invited)

Beamline design with weak-focusing magnetic field for applications of laser-driven proton beams

<sec>With the development of high-power laser technology, laser plasma acceleration has developed rapidly due to its excellent acceleration structure. Nearly one-hundred-MeV proton beams and several GeV electron outputs are obtained. The laser-driven proton beams have excellent quality of μm-scale sizes and ps-scale pulse lengths. Owing to the existence of the accelerating laser field, direct application is difficult, so the proton beams need to be transmitted to the application terminal through the beamline. However, the wide energy spectrum and large divergence angle bring difficulties in transmitting the beam. The weak focusing in the constant gradient magnetic field is neglected in the transmission of laser-driven particle beams because of the relatively weak focusing force. But weak focusing has special advantages: simultaneous focusing in the horizontal direction and the vertical direction, energy analysis in the horizontal direction, focusing force in the horizontal and vertical direction distributed by the field index <i>n</i>, and smaller influence of chromatic aberration effect.</sec><sec>In this paper, we propose the beam transmission with weak-focusing magnet. The requirements for the focusing of proton beams with the same energy and different divergence angles in the <i>X</i> direction and <i>Y</i> direction in the weak-focusing magnetic field are explored by studying the linear beam dynamics of the beams. Then the conditions of precise energy analysis for particle beams with large divergence angle can be determined. For beams with 2% energy spread, the lengths of the drift space before and after the weak-focusing magnet and deflection radius are scanned to find out the minimum beam size and the shortest pulse length after transmission. It is found that a certain combination of drift space and deflection radius can minimize the beam size or the pulse length. Focusing and energy selection can be achieved while compressing the pulse length and effectively reducing the size of the beamline, which has significant advantages. When the deflection radius is 0.65 m, the proton beam with 20 MeV energy, 2% energy spread, and an initial divergence angle of ±50 mrad has the root-mean-square size of 108 μm in both the <i>X</i> direction and the <i>Y</i> direction, and a pulse length of 154 ps at the application terminal.</sec><sec>Comparing with common beam transmission elements such as quadrupole lenses and deflection magnets, the laser-accelerated ion beam benefits from the integration of focusing and energy analysis of weak-focusing magnetic fields (focusing and energy analysis exist at the same time and continuously change with deflection angle), as well as the horizontal and vertical focusing forces can be distributed by the magnetic field index <i>n</i> (the larger the <i>n</i>, the stronger the focusing force in the vertical direction is and the weaker the focusing force in the horizontal direction). When the proton beam is transmitted in a weak-focusing magnetic field, the advantages of the focusing element and the energy selection element are combined, so the influence of the chromatic aberration effect can be reduced, the pulse length can be compressed, and the beamline size can be effectively reduced.</sec>

An evaluation of sustainability and societal impact of high-power laser and fusion technologies: a case for a new European research infrastructure

Abstract Fusion energy research is delivering impressive new results emerging from different infrastructures and industrial devices evolving rapidly from ideas to proof-of-principle demonstration and aiming at the conceptual design of reactors for the production of electricity. A major milestone has recently been announced in laser fusion by the Lawrence Livermore National Laboratory and is giving new thrust to laser-fusion energy research worldwide. Here we discuss how these circumstances strongly suggest the need for a European intermediate-energy facility dedicated to the physics and technology of laser-fusion ignition, the physics of fusion materials and advanced technologies for high-repetition-rate, high-average-power broadband lasers. We believe that the participation of the broader scientific community and the increased engagement of industry, in partnership with research and academic institutions, make most timely the construction of this infrastructure of extreme scientific attractiveness.

Photonic Laser Thruster: 100 Times Scaling-Up and Propulsion Demonstration

The Photonic Laser Thruster (PLT) efficiently uses photons as propellant and thus promises to enable innovative space endeavors beyond the reach of propellant-based conventional thrusters. Previously, the proof-of-principle demonstration of PLT used a neodymium-doped yttrium aluminum garnet (Nd:YAG) rod gain medium and resulted in the maximum thrust of . This Paper reports 100 times scaling up of PLT using a ytterbium-doped yttrium aluminum garnet (Yb:YAG) thin-disk gain medium and thought first demonstration of propelling and stopping a 0.75 kg mock cube satellite over 2 m in a Class-1000 cleanroom. A thrust stand for PLT was established with a radiation pressure sensor that reduced the thermal convection effect and the configuration complexity. The maximum achieved thrust and specific thrust were and , respectively. Further development of PLT using existing high-power laser technologies is projected to increase its specific thrust to , on a par with electric thrusters. The present results conclude that innovative PLT applications, such as propellant-free orbit maneuvering and stationkeeping, are within the reach of existing spacecraft and high-power laser technologies. In addition, the feasibility of PLT-based launchers and landers is discussed.

Laser energy absorption prediction of silicon substrate surface from a mid- and high-spatial frequency error.

Additional laser energy absorption of optical elements limits the further development of high-energy laser systems. In engineering, inexpensive and precise absorption test technology is essential. We attempt to predict energy absorption via surface spatial error value based on the roughness-induced absorption (RIA) theory. However, the absorption coefficients cannot match roughness values measured with an atomic force microscope or white light interferometer. We find three influencing factors and optimize the definition of RIA to spatial error-induced absorption (SEIA). SEIA is proportional to δ2 of a mid- and high-spatial frequency error in a certain frequency range. This range depends on laser diameter, wavelength, and coating. Excluding the absorption induced by fabrication defects, the total absorption can be classified into SEIA and background absorption (BGA). BGA is decided by material and process technology, which can be obtained by calculations. The sum of SEIA and BGA is predictable because both can be estimated. The substrate absorption of high-energy optics can be semi-quantificationally predicted. SEIA provides a new angle to research element-absorbed laser energy for high-power laser technologies.

Extreme Raman red shift: ultrafast multimode nonlinear space-time dynamics, pulse compression, and broadly tunable frequency conversion

Ultrashort high-energy pulses at wavelengths longer than 1 µm are now desirable for a vast variety of applications in ultrafast and strong-field physics. To date, the main answer to the wavelength tunability for energetic, broadband pulses still relies on optical parametric amplification (OPA), which often requires multiple and complex stages, may feature imperfect beam quality, and has limited conversion efficiency into one of the amplified waves. In this work, we present a completely different strategy to realize an energy-efficient and scalable laser frequency shifter. This relies on the continuous red shift provided by stimulated Raman scattering (SRS) over a long propagation distance in nitrogen-filled hollow-core fibers (HCF). We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with a conversion efficiency higher than 70% and high beam quality. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between higher-order modes of the HCF, can be readily employed to generate pulses ( ∼ 20 f s ) significantly shorter than the pump ones ( ∼ 200 f s ) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules. We envision that this technique, coupled with the emerging high-power Yb laser technology, has the potential to answer the increasing demand for energetic multi-TW few-cycle sources tunable in the near-IR.

A miniature thermal neutron source using high power lasers

The continuous improvement of high power laser technologies is recasting the prospects of small-scale neutron sources to enable scientific communities and industries performing experiments that are currently offered at extensive accelerator-driven facilities. This paper reports moderation of laser-driven fast neutrons to thermal energies using a compact, modular, moderator assembly. A significant thermal (∼25 meV) flux of ∼106 n/sr/pulse was measured from water and plastic moderators in a proof-of-principle experiment employing a relatively moderate power laser delivering 200 J on the target in 10 ps. Using Monte Carlo N-Particle eXtended simulations, the experimental results are reproduced and discussed.

Impact of Nonlinear Kerr Effect on the Focusing Performance of Optical Lens with High-Intensity Laser Incidence

The rapid development of high-energy and high-power laser technology provides an important experimental means for the research of extreme physical state in the laboratory and for the design of large laser facilities for realizing inertial confinement fusion. However, when the incident laser field is very strong, the Kerr effect of materials affects the nominal performance of optical elements. In this work, the impact of Kerr effect on the focusing performance of an optical lens is studied by calculating and comparing the filed patterns of focal spots for three different incident laser beams together with three different levels of light intensities. The traditional transfer function of an optical lens is firstly modified according to the theory of nonlinear Kerr effect. We use the two-dimensional fast Fourier transform algorithm and angular spectrum algorithm to numerically calculate the field distributions of focal spots in the nominal focal plane of lens and its adjacent planes based on the Fresnel diffraction integral formula. The obtained results show that the Kerr effect affects the focusing characteristics of lens, especially for the incidence of high-order Gaussian beams, such as Hermite-Gaussian beams and Laguerre-Gaussian beams. At the same time, the focal length and refractive index of lens also change the field patterns of focal spots. The presented methodology is of great value in engineering applications where the practical problem with beam size up to 100 mm can be calculated using a common laptop computer. The work provides an efficient numerical technique for high-intensity incident laser beams focused by lens that takes Kerr effect into consideration, which has potential applications in high energy density physics and large laser facilities for inertial confinement fusion.

高功率金刚石激光技术研究进展（特邀）

高功率金刚石激光技术研究进展（特邀）

高功率金刚石激光技术研究进展（特邀）

With the highest thermal conductivity, low thermal expansion coefficient, high chemical inertness, and excellent optical properties among known materials, diamond can meet the application requirements of many extreme conditions in the fields of mechanics, optics, and materials, etc. In recent years, with the improvement of the chemical vapor deposition preparation technology, the optical quality of synthetic diamond has been rapidly improved, which leads to the optical grade diamond crystals excellent power improvement, coherence enhancement, and frequency conversion ability due to their excellent Raman and Brillouin characteristics. Meanwhile, diamond lasers overcome the thermal effect in the particle number inversion laser based on the traditional gain media, and the difficulty to consider both the wavelength and power. The research progress of high-power diamond laser technology was summarized, and the development trend and application of diamond lasers were prospected.

Transient temperature effects on the optical power wavelength shift of a high-power laser system

The effect of junction temperature change on the wavelength shift and optical power output of high-power laser systems utilizing a fiber laser design is investigated using a mathematical model. Several laser diode array configurations, along with two different cooling fluids, are used to analyze the laser performance by numerically calculating the optical power out of the fiber laser for each case. The modeling approach presented here captures the dependence of optical power output on laser diode junction temperature by way of the optical power interactions between the laser diodes and fiber gain media components. Through the presented research, the beginning of a Multiphysics modeling approach has been created for better understanding the thermal requirements for a robust and practical high-power laser system. Future research will build off this and focus on the temperature dependent aspects of individual components (laser diodes, fiber gain media, and combining optics) in high power laser systems. In conjunction, high fidelity modeling of the listed components will provide a clear picture of the aggregate system-level thermal requirements. Gains in system-level thermal knowledge are instrumental for progress in high power laser technology and application.

A Control System Based on Microprocessor and FPGA for 1470nm High-power Semiconductor Laser

An intelligent control system for a medical high-power semiconductor laser has been developed. The system combines 1470nm high-power semiconductor laser and intelligent control technology. The control technique applies an ARM Cortex-M3 microprocessor STM32F103 as the core, an FPGA to drive the digital constant current source module and the power feedback loop to realize constant power control. Furthermore, the display and storage of the output data, and the driver of the touch screen are realized by designing the main control module and human-computer interaction module with the microprocessor. Finally, the Micro-Controller Development Kit (MDK) platform is used for programming. The safety performance of the whole control system conforms to the national standard of medical electrical safety.

High Power Diamond Raman Lasers

Laser gain materials possessing high thermal conductivity and robust mechanical properties are key prerequisites for high power lasers. We show that diamond, when configured as a Raman laser, enables access to these and other extreme properties, providing an important new route to high power and high brightness beam generation. Recent achievements in pulsed and continuous wave oscillators, beam combining amplifiers, and single longitudinal mode oscillators are summarized, along with wavelength extension of these concepts through adaption to other pumps, use of Raman cascading, and intracavity harmonic generation. To date, diamond laser powers have attained 750 W with efficiency and beam quality so far unperturbed by nonlinear or thermally induced side-effects. Large factor brightness enhancement of low coherence inputs is demonstrated using multiple pump beams (via Raman beam combination) or highly multimode pumps for oscillator and amplifier configurations. Future directions for direct diode pumping, and for realizing extraordinary power and power density through reduced temperature operation and isotopically enriched diamond, are also discussed. Our results indicate that diamond is emerging as a generic high-power laser technology with advantages in terms of brightness (high average power and high beam quality) and wavelength range.

A viable laser driver for a user plasma accelerator

The construction of a novel user facility employing laser-driven plasma acceleration with superior beam quality will require an industrial grade, high repetition rate petawatt laser driver which is beyond existing technology. However, with the ongoing fast development of chirped pulse amplification and high average power laser technology, options can be identified depending on the envisioned laser–plasma acceleration scheme and on the time scale for construction. Here we discuss laser requirements for the EuPRAXIA infrastructure design and identify a suitable laser concepts that is likely to fulfill such requirements with a moderate development of existing technologies.