•BBO and CLBO crystals are preferred for deep ultraviolet generation.•Overview given of LIDT measurements of BBO and CLBO.•LIDT is the crystallinity level and purity dependent.•Pulse duration is a ...factor substantially affecting LIDT.
Published data of laser induced damage thresholds (LIDT) of nonlinear BBO and CLBO crystals, which are used for the generation of deep-ultraviolet radiation, are collected and plotted against laser pulse duration. The LIDT measurement techniques are briefly described and their relevance relative to the intended application of the crystal is discussed. The intrinsic and extrinsic factors affecting the evolution of the LIDT are reported. Our own experience with the LIDT of BBO and CLBO crystals in the fifth harmonic generation (FiHG) process is presented. Lowering of the LIDT for crystals with antireflection coatings is treated.
The time-resolved measurements of thermally induced wavefront aberrations in a cryogenically cooled Yb:YAG crystal are presented in dependence on temperature in the range between 250 and 130 K under ...non-lasing condition. A wavefront sensor was utilized to determine the wavefront aberrations. The wavefront distortions were experimentally studied for a cryogenically cooled Yb:YAG crystal in detail for the first time. The wavefront aberrations were significantly reduced at cryogenic temperatures including defocus which was the dominant aberration and which was responsible for the so-called thermal lensing effect. We found that defocus aberration is caused not only by thermally induced effects (responsible for thermal lens), but also by electronically induced change in the refractive index due to excitation of ion activators which is responsible for the electronic lensing. Nevertheless, at pumping intensity of 6.3 kW/cm
2
and repetition rate of 100 Hz thermal effects were the dominant one. In addition, an improvement in the Strehl ratio along with an increase in absorbed pump energy was observed while the temperature of the gain medium was decreased. The measurements clearly show the advantages of cryogenic cooling of laser-active media for beam quality improvement.
This paper explores the possibility of damping actively the camera support mast of Gamma-ray telescopes with a configuration similar to the MAGIC telescope, where the camera is supported by a curved ...mast and an array of cables. This is achieved by replacing a set of passive cables by a set of active ones, controlled by active tendons. Each active tendon consists of a displacement actuator collocated to a force sensor with independent force feedback control loops. The paper outlines the theory of decentralized active damping of cable-structures, points out the main design parameters, and evaluates the amount of damping that the control system can provide. The effect of the control on the wind response and on the transient response of the telescope is estimated.
Abstract
A unique combination of the ultrashort high-energy pulsed laser system with exceptional beam quality and a novel Diffractive Optical Element (DOE) enables simultaneous production of 2601 ...spots organized in the square-shaped 1 × 1 mm matrix in less than 0.01 ms. By adjusting the laser and processing parameters each spot can contain Laser Induced Periodic Surface Structures (LIPSS, ripples), including high-spatial frequency LIPSS (HFSL) and low-spatial frequency LIPSS (LSFL). DOE placed before galvanometric scanner allows easy integration and stitching of the pattern over larger areas. In addition, the LIPSS formation was monitored for the first time using fast infrared radiometry for verification of real-time quality control possibilities. During the LIPSS fabrication, solidification plateaus were observed after each laser pulse, which enables process control by monitoring heat accumulation or plateau length using a new signal derivation approach. Analysis of solidification plateaus after each laser pulse enabled dynamic calibration of the measurement. Heat accumulation temperatures from 200 to 1000 °C were observed from measurement and compared to the theoretical model. The temperature measurements revealed interesting changes in the physics of the laser ablation process. Moreover, the highest throughput on the area of 40 × 40 mm reached 1910 cm
2
/min, which is the highest demonstrated throughput of LIPSS nanostructuring, to the best of our knowledge. Thus, showing great potential for the efficient production of LIPSS-based functional surfaces which can be used to improve surface mechanical, biological or optical properties.
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•Interference area is increased up to 1 mm in diameter to reach higher throughputs.•Parameters for fabrication of LIPSS-structured microcraters are investigated.•Throughputs up to ...30400 LSFL spots/s and 203200 HSFL spots/s are achieved.•Superhydrophobicity and structural colours are demonstrated on selected surfaces.
Using four beam direct laser interference patterning (DLIP) Laser Induced Periodic Surface Structures (LIPSS, ripples) are simultaneously generated on surface of AISI 316L steel in more than thousands of spots at once. Both low-spatial frequency LIPSS (LSFL) and high-spatial frequency LIPSS (HFSL) are possible to fabricate with optimized parameters of 1030 nm, 1.7 ps PERLA laser system, developed and operated at HiLASE center. A novel large-beam DLIP technique applied for the redistribution of initial laser energy per pulse results in fabrication of ~1520 spots with LSFL in 50 ms and ~1016 spots with HSFL in 5 ms, thus significantly improving the productivity in comparison with the single beam approach. Efficient production of LIPSS structures over large area, required for applications such as a production of security diffractive elements and surfaces with superhydrophobic properties is also demonstrated. Possible steps for further increase of processing speed are discussed.
Biocompatibility is one of the key issues for implants, especially in the case of stainless steel with medium to low biocompatibility, which may lead to a lack of osseointegration and consequently to ...implant failure or rejection. To precisely control preferential cell growth sites and, consequently, the biocompatibility of prosthetic devices, two types of surfaces were analyzed, containing periodic nanogrooves laser induced periodic surface structure (LIPSS) and square-shaped micropillars. For the fast and efficient production of these surfaces, the unique combination of high energy ultrashort pulsed laser system with multi-beam and beamshaping technology was applied, resulting in increased productivity by 526% for micropillars and 14 570% for LIPSS compared to single beam methods.
analysis revealed that micro and nanostructured surfaces provide a better environment for cell attachment and proliferation compared to untreated ones, showing an increase of up to 496% in the number of cells compared to the reference. Moreover, the combination of LIPSS and micropillars resulted in a precise cell orientation along the periodic microgroove pattern. The combination of these results demonstrates the possibility of mass production of functionalized implants with control over cell organization and growth. Thus, reducing the risk of implant failure due to low biocompatibility.
We introduce the Czech national R&D project HiLASE which focuses on strategic development of advanced high-repetition rate, diode pumped solid state laser (DPSSL) systems that may find use in ...research, high-tech industry and in the future European large-scale facilities such as HiPER and ELI. Within HiLASE we explore two major concepts: thin-disk and cryogenically cooled multislab amplifiers capable of delivering average output powers above 1 kW level in picosecond-to-nanosecond pulsed regime. In particular, we have started a programme of technology development to demonstrate the scalability of multislab concept up to the kJ level at repetition rate of 1-10 Hz.
For the first time, a dynamic beamshaping technology has been utilized for the efficient production of periodic nanostructures on top of AlTiN coating to enable dry machining without costly and ...environmentally hazardous cutting fluids. First, a variety of periodic nanostructures with periods in a range of 740-273 nm were produced utilizing different wavelengths. Additionally, beamshaping technology increased productivity by 4008% up to 105 cm
2
min
−1
by shaping the Gaussian beam into a rectangular beam of 500 × 30 µm. To simulate the application load and resulting heat production during manufacturing, friction analysis was performed at room and elevated temperature to 500°C. The analysis revealed a significant reduction in the friction coefficient - up to 27% and 19% at room temperature and 500°C, respectively. The combination of these results demonstrates that the proposed method can be scaled up for the mass production of functionalized machining tools for dry machining.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This work reports on a liquid-nitrogen-cooled, SESAM mode-locked Yb:YGAG (Yb:Y(3)Ga(2)Al(3)O(12)) ceramic laser. The Yb:YGAG has a similar structure to Yb:YAG, but its emission spectrum at low ...temperature remains much broader, which is suitable for ultrashort pulse generation and amplification. A stable pulse train with 119-MHz repetition rate was obtained at a wavelength of 1026 nm. The measured pulse duration is 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG. Furthermore, laser performance of the Yb:YGAG ceramics in continuous-wave operation and wavelength tunability at 80 K was investigated.
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