High Power Laser Applications Research Articles

Combined method for the fabrication of high-power cladding light stripper using a buffered oxide etchant.

Cladding light strippers (CLSs) are vital and one of the critical components for high-power fiber laser applications. In this study, we show the first studies of the formation mechanisms and optimum conditions of a CLS device using a buffered oxide etchant by a combined method of stain (wet) etching and vapor-phase etching. This high-power CLS was shown to result in a stripping performance of ∼17.2 dB at the launched power of 333W (pump limited). The thermal imaging demonstrates that the maximum temperature reached when operating the device at maximum launched power was ∼75°C. The atomic force microscopy (AFM) results show that the combined method yields crystal-like structures with the height in microscales, whereas other conventional methods give only nanoscale roughness. The method also preserves the diameter of the CLS device close to the bare fiber with about 10μm tapering leads to a high surface area to strip unwanted light, which is good for heat dissipation. The combined method possesses the outcome of two methods, including both the crystal-like structures and nanosized hillocks, resulting in high-power stripping performance and robustness.

Understanding the role of fluorine-containing plasma on optical properties of fused silica optics during the combined process of RIE and DCE.

Reactive ion etching (RIE) is crucial for fabricating high-quality fused silica optics since this technique can be used as a first step before dynamic chemical etching (DCE) for tracelessly removing the fractured defects in subsurface layer. The final quality of the optics is dramatically influenced by the plasma etching condition but still lacks sufficient information for practical application. In this work, combination of RIE and DCE was investigated deeply on polished fused silica surface by changing the gas type and flow rate. We show that the proper choice of fluorine-containing plasma condition during the RIE process allows the simultaneous occurrence of high surface quality and a low concentration of etching-introduced defects on fused silica. This leads to an ultrahigh laser-induced damage threshold at 355 nm while substantially keeping the surface roughness unchanged. This study paves the way for designing and developing a next-generation surface modification ability of high-quality fused silica with the great potential for high-power laser application.

Absolute Absorption Measurements in Optical Coatings by Laser Induced Deflection

Absolute measurement of residual absorption in optical coatings is steadily becoming more important in thin film characterization, in particular with respect to high power laser applications. A summary is given on the current ability of the laser induced deflection (LID) technique to serve sensitive photo-thermal absorption measurements combined with reliable absolute calibration based on an electrical heater approach. To account for different measurement requirements, several concepts have been derived to accordingly adapt the original LID concept. Experimental results are presented for prominent UV and deep UV laser wavelengths, covering a variety of factors that critically can influence the absorption properties in optical coatings e.g., deposition process, defects and impurities, intense laser irradiation and surface/interface engineering. The experimental findings demonstrate that by combining high sensitivity with absolute calibration, photo-thermal absorption measurements are able to be a valuable supplement for the characterization of optical thin films and coatings.

Three-dimensional target monitoring technique based on a morphology correlation for high-power laser applications.

Existing monitoring and target positioning systems used in high-power laser fusion experiments have a complex structure and size, making their operation slow and calibration difficult. A simple and accurate positioning technique is proposed here that is based on cross-correlation between the morphology of the target measured at various positions. The morphology of the target is obtained using a spectral interferometer at a video frequency, and its three-dimensional (3D) position is determined by the position of the maximum spatial correlation coefficient. This technique can determine the 3D position and orientation of the target at the sub-micrometer range using only a single compact optical head. The proposed technique is quite simple in its structure and very convenient in operation. The feasibility and performance of the proposed technique is demonstrated in experiments.

Development of aluminosilicate glass fiber doped with high Pr3+ concentration for all-optical fiber isolator application

A new SiO2–Al2O3–B2O3–Pr6O11 glass fiber with high Pr3+ concentration was developed by the melt quenching technique and the fiber drawing process for all-optical fiber isolator application. The thermal analysis was carried for the Pr3+-doped bulk aluminosilicate glass by simultaneous thermal analyzer and its glass stability was found to be 206 °C. Magneto-optical characteristics of the fabricated aluminosilicate glass fiber with high Pr3+ concentration were studied and found that the measured Faraday rotation at 650 nm linearly increased from 0° to 85° with the increase of the magnetic field varied from 0 to 0.142 T. The Verdet constant of the fabricated fiber was determined to be 17.28 rad/(T m) at 650 nm, demonstrating its feasibility as an attractive candidate of all-optical fiber isolator for high power laser applications.

Optimising of the material and laser parameters for high-power laser spatial beam smoothing based on stimulated Brillouin scattering

In this paper, we numerically study the influence of material and laser parameters on laser spatial beam uniformity improvement based on stimulated Brillouin scattering (SBS). Owing to the intensity dependent property of SBS, the higher intensity parts of the laser beam experience a deep reflection, while the other parts transmit through the medium with weak reflection. Then, the uniformity of the input laser beam is improved. A single frequency laser with a 20th order super-Gaussian shaped output pulse was used as the pump. Five typical liquid materials were adopted as the Brillouin medium for comparison. The laser wavelength was set to 527 nm and 1053 nm; and the pulse duration was set to 3 ns and 5 ns, respectively. The numerically calculated results indicate that low gain coefficient and short phonon lifetime mediums (such as FC-70) are more suitable for the above-mentioned laser beam smoothing scheme. Meanwhile, short wavelength and pulse duration would be helpful for laser beam uniformity improvement. The energy efficiency is above 90% when the laser beam uniformity is greatly improved with an optimized input laser intensity. The calculated results are quite useful for high-power laser applications.

A Tale of Two Tantalum Borides as Potential Saturable Absorbers for Q-Switched Fiber Lasers

In this paper, we analyze the performance of two tantalum-based boride (TaB and TaB 2 ) microparticles as potential saturable absorbers for high-power fiber lasers. Both materials are ultrahigh temperature ceramics with melting points above 3000 °C, but with different crystalline structures: TaB has an orthorhombic structure (nearly isotropic), whereas TaB 2 has a hexagonal structure (uniaxial, anisotropic). Despite their different crystalline structures, the microparticles have a similar low fluence attenuation (between 2.3 and 2.60 dB/μm) and modulation depths (around 2.0 dB/μm), but remarkable different saturation fluences: TaB has a saturation fluence of 160 μJ/cm 2 , whereas TaB 2 has a saturation fluence of 110 μJ/cm 2 . The measured damage thresholds are 112 and 10 6 mJ/cm 2 /pulse for TaB and TaB 2 , respectively. When incorporated to a fiber laser, the materials produce pulses with durations of 345 ns, lower than those reported by our group in previous papers. The results show that the materials can find potential applications in high-power Q-switched lasers.

Numerical investigation of the dependence of stimulated Brillouin scattering threshold on the pump intensity fluctuation

AbstractIn this paper, the dependence of stimulated Brillouin scattering (SBS) threshold on the sinusoidal modulated properties of pump pulse is studied. A 527-nm-wavelength, 5 ns square laser pulse with sinusoidal temporal modulation is used as the pump source, and a 600 mm liquid heavy fluorocarbon material FC-40 is used as the Brillouin medium. The numerically calculated results indicate that the SBS threshold increases with the increase of both temporal intensity modulation index and modulation frequency of the pump pulse. However, when the intensity distortion criterion is below 30% or the duration of modulation peaks below three times the phonon lifetime, the SBS threshold tends to remain stable. The numerical results provide assistance to judge the SBS threshold for unsmoothed pump pulses, especially for high power laser applications.

Large Second Harmonic Generation (SHG) Effect and High Laser‐Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide

AbstractA big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59–25 μm is also significantly wider than that of AGS (ca. 0.48–≈11.4 μm). The occurrence of the strong SHG responses and good phase‐matching indicate that the structure of the new Ga2Se3 phase can only be non‐centrosymmetric and have a lower symmetry than the cubic γ‐phase. The observed excellent SHG and phase‐matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

Large Second Harmonic Generation (SHG) Effect and High Laser-Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide.

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2 Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59-25 μm is also significantly wider than that of AGS (ca. 0.48-≈11.4 μm). The occurrence of the strong SHG responses and good phase-matching indicate that the structure of the new Ga2 Se3 phase can only be non-centrosymmetric and have a lower symmetry than the cubic γ-phase. The observed excellent SHG and phase-matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

Effect of AlPO4 join concentration on optical properties and radiation hardening performance of Yb-doped Al2O3-P2O5-SiO2 glass

A series of Yb-doped silica glasses containing equimolar amounts of P2O5 and Al2O3 were prepared using a sol–gel method combined with high-temperature sintering. Raman spectroscopy confirmed the formation of AlPO4 join with a P/Al ratio of 1. However, for a P/Al ratio slightly larger than 1, both the AlPO4 join and P=O bond are formed. Based on the absorption, emission spectra, and electron paramagnetic resonance measurements, it was determined that the increase of the AlPO4 join concentration in Yb-doped silica glass leads to (i) a decrease in the refractive index with a factor of 1.1005 × 10−4 (which allows for a low numerical aperture facilitating single-mode laser), (ii) the sustained spectroscopic properties of Yb3+, (iii) a decrease in Yb cluster concentration, and (iv) an improved radiation hardening performance (beneficial to high-power space lasers). These results suggest that Yb-doped Al2O3-P2O5-SiO2 glass with an appropriate concentration of AlPO4 join has potential applications in high-power space fiber lasers.

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.

Erbium-ring-doped fiber laser for transverse vector modes output

We propose a few-mode erbium-ring-doped fiber laser with high slope efficiency towards an individual transverse vector mode output. Based on the rate equation, specific transverse vector mode output is achieved through numerical investigations of the position and the thickness of the transverse erbium-doped region. Our results show that a thinner erbium-doped region is favorable for increasing the number of available output transverse vector mode, and the position selects desired transverse vector mode to excite. Moreover, high-order vector modes up to the third-order can be excited with appropriate erbium-doped locations. The laser output using the proposed method has merit of high slope efficiency and high mode purity. The slope efficiency and the mode purity can reach 61.25% and 99.99%, respectively. Our work may find potential applications in high-power lasers and high-order transverse mode operation of fiber lasers.

Characterization of terbium containing cubic zirconia crystal for high power laser applications

A magneto-active terbium containing cubic zirconia crystal is an attractive material for creating Faraday isolators thanks to a high value of its Verdet constant and low absorption coefficient. The optical anisotropy parameter of this crystal which shows the distribution of orientations of the axes of thermally induced birefringence in a thermally loaded optical element has negative value. It means that there exists a dedicated orientation of crystallographic axes, at which the axes of thermally induced birefringence are arranged in the one direction and thermally induced depolarization may be reduced substantially. For assessing potential of this crystal for high-power applications we have investigated its temperature dependence of the Verdet constant that proved to correspond to the paramagnetic behavior. Thermo-optical characteristics are also of principal importance when operating with high-power laser radiation. We present results of measurements of thermo-optical characteristics Q and P which determines values of polarization and phase distortions of passing laser radiation. Measured values can be used to determine the characteristics of Faraday isolators based terbium containing cubic zirconia crystals in various implementations of their optical schemes for various parameters of laser radiation.

Strengthening of very large crystalline and polycrystalline Nd:YAG rods for high-power laser applications

A multistep thermochemical etching procedure was applied to very large Nd3+:YAG rods to increase their fracture strength. The strengthening procedure combined selection of high-quality material, fine centerless grinding, thermochemical etching, and (after completion of the lapping, polishing and AR coating) an additional hot thermochemical etching, with rod ends protected with poly-tetra-fluoro-ethylene (Teflon) caps. The final cleaning step, not previously reported, is essential in removing fracture causing contaminations on the rod surface. A unique thermal load-to-fracture technique was applied on test rods to measure their fracture strength. The rods were thermally loaded up to fracture by means of optical pumping in a specially designed laser pump chamber. The results thus obtained were analyzed by Weibull distribution statistics appropriate to these tests. The strengthened laser rods of this study sustained a maximum pump power density of $$ I_{{\ell_{\hbox{max} } }} $$ = 500 W cm−1. This value is higher by a factor of four over untreated rods and also higher than any previously published data for such large rods. High-power diode-pumped laser heads were operated with the strengthened crystalline and polycrystalline Nd:YAG rods, yielded output power of ~ 3 kW, when pumped with 7 kW. Such performance was routinely achieved without any instance of rod fracture. Reliability of the strengthening procedure was further demonstrated by the failure-free operation of an azimuthally polarized high-power master-oscillator power-amplifier system (composed of oscillator, preamplifier, and six power amplifiers), emitting an output power in excess of 10 kW.

Application of high powered Laser Technology to alter hard rock properties towards lower strength materials for more efficient drilling, mining, and Geothermal Energy production

Resources such as minerals, geothermal energy, and unconventional hydrocarbons need to be excavated from deeper and harder geologic formations than in the past 100 years. Although, oil & gas drilling technologies have been continuously enhanced to enable more efficient and economic drilling processes, yet their performance suffers significantly in deep and hard formations. Problems mainly include low rate of penetrations, very high drill-bit wear-rates, short drill bit service life, and ultimately result in a high overall drilling cost. Laser Jet Drilling could potentially be such next fundamental drilling process for delivering more and alternative energy to the bit and breaking the rock more efficiently and thus, substantially improve drilling of deep hard rock formations. The application of high-power laser for rock breaking and drilling processes has been demonstrated in this study via Laser (thermally) induced rock softening. A comprehensive experimental approach has been chosen to study the LaserJet drilling process and its rock interaction. Multiple rock types including sandstones, granites, and metamorphic quartzite rocks were characterized to offer a comprehensive overview of possible effects of rock parameters on laser–rock interaction. The initial research results proved that various rock types including very hard ones could be transformed into a drillable state using a high-power laser through thermally induced rock softening. The rock strength, drilling strength and fracture toughness of the studied samples were obtained by means of scratch testing. The overall analysis of the results suggests that thermal rock softening allows to efficiently facilitate a combined laser mechanical assisted drilling system with a possible increase in the rate of penetration of the cutting tool with reduced drilling torque and weight on bit requirements and therefore having a lower energy consumption. Additionally, the drilling costs could be noticeably lessened by improving the drill bit life and reducing the overall drilling time.

Compatibility of CO2 laser surgery and fluorescence detection in head and neck cancer cells.

Surgical treatment of cancer requires tumor excision with emphasis on function preservation which is achieved in (early stage) laryngeal cancer by transoral carbon dioxide (CO2 ) laser surgery. Whereas conventional laser surgery is restricted by the surgeon's visual recognition of tumor tissue, new approaches based on fluorescence-guided surgery (FGS) improve the detection of the tumor and its margin. However, it is unclear whether fluorophores are compatible with high-power laser application or whether precision is compromised by laser-induced bleaching of the dye. We applied topology-controlled 3D laser resection of fluorescent tumors cell in vitro and laser-induced autofluorescence analysis ex vivo. Laser-induced bleaching of fluorescent dyes in the visible and near-infrared light spectrum (650-900 nm) ranges below the resolution range of operation microscopes. Furthermore, specific fluorescent signals in an FGS mouse model is 104 higher than laser-induced autofluorescence in mouse tissue. Laser-induced lateral photobleaching is negligible indicating a path forward for fluorescence-guided laser surgery in head and neck cancer.

Structural, optical and piezoelectric investigation on brucinium bromide hydrate non linear optical single crystal for optical parametric oscillators, high-power laser, piezo-sensors and transducers applications

In the present work, a good transparent semi-organic brucinium bromide hydrate (BBH) single crystal was grown from the saturated solution by slow evaporation method. The single crystal XRD study reveals that, BBH crystallize in Triclinic crystal system with non-centrosymmetric space group P1. Presences of chemical elements such as Carbon, Hydrogen and Nitrogen are C = 38.79%, H = 44.10% and N = 3.48% respectively. The morphological study concludes that, the growth rate along ‘c’ direction is more expeditious than that of a & b. The UV–Visible spectrum confirms the good transparency of the crystal and diverse optical parameters such as cut-off wavelength, band gap, UV-resonance energy and refractive index values were calculated and relation between the different optical parameters were also discussed in detail. Chemical bonding nature of BBH crystal was identified with the aid of optical electro-negativity value. The Urbach energy value was found to be 0.1238 eV. LDT value of BBH crystal was found to be 6.43 GW/cm2 and it is compared with other standard materials such as KTP, KDP and Urea. To find the suitability of crystal in the field of nonlinear optical application, the second harmonic generation value was determined using Kurtz-Perry powder technique. The spectroscopic investigations were done by vibrational analysis in order to identify the different functional groups in BBH compound. The value of piezo-electric charge co-efficient (d33) was quantified by PM-300 piezometer. Fluorescence spectral study provides the knowledge about electron excitation and also life time of the molecules. Title crystal does not contain any internal structural grain boundaries which are confirmed by HRXRD analysis.

High-Power Passive Fiber Components for All-Fiber Lasers and Amplifiers Application—Design and Fabrication

The most important components for application in high-power all-fiber lasers and amplifiers are, most of all, power combiners, but also mode field adaptors. This paper summarizes recent achievements in the area of development and fabrication of high-power passive fiber components. The principles of operation and basic design and fabrication criteria, which have to be taken into account while designing the aforementioned components, are explained in detail. The most recent impressive achievements are summarized and described.

Impact of the Polishing Suspension Concentration on Laser Damage of Classically Manufactured and Plasma Post-Processed Zinc Crown Glass Surfaces

The laser-induced damage threshold of optics is an issue of essential importance in high-power laser applications. However, the complex and partially interacting mechanisms as well as the underlying reasons for laser damage of glass surfaces are not yet fully understood. The aim of the present work is to contribute to a better understanding of such damage mechanisms by providing original results on the impact of classical glass surface machining on the laser-induced damage threshold. For this purpose, glass samples were prepared with well-defined process conditions in terms of the used lapping and polishing agents and suspensions. Further, the samples were post-processed by atmospheric pressure plasma for precision cleaning. The laser-induced damage threshold and surface contamination by residues from the manufacturing process were determined before and after plasma post-processing. It is shown that the polishing suspension concentration has a certain impact on the laser-induced damage threshold and surface contamination by residues from used working materials. The highest damage threshold of 15.2 J/cm² is found for the lowest surface contamination by carbon which occurs in the case of the highest polishing suspension concentration. After plasma treatment for merely 60 s, this value was increased to 20.3 J/cm² due to the removal of surface-adherent carbon. The results thus imply that the laser-induced damage threshold can notably be increased by first choosing appropriate process parameters during classical manufacturing and second plasma post-processing for surface finishing.