Surface Damage Threshold Research Articles

Second- and third-order optical studies of 4-Bromoanilinium hydrogen phthalate single crystal for nonlinear optical device applications

A new organic NLO material 4-Bromoanilinium hydrogen phthalate was grown by slow evaporation technique. The solubility and metastable zone width were determined. The crystal belongs to monoclinic system with space group C2. Optical transmittance spectrum confirms the wide optical window. Absorption coefficient and band gap were calculated from transmittance. The thermal stability, laser-induced surface damage threshold and mechanical behaviour were analysed. The particle size-dependent second harmonic generation efficiency was evaluated by Kurtz–Perry powder method and existence of phase matching. The third-order optical study was measured by Z-scan studies. The dispersion of birefringence behaviour was studied.

ITER-relevant transient heat loads on tungsten exposed to plasma and beryllium

Tungsten (W) is presently the most attractive plasma facing material for future fusion reactors. Off-normal transient events such as edge localized modes and disruptions are simulated with a pulsed laser system in the PISCES-B facility, providing pulses with 1–10 ms duration with absorbed heat flux factors up to ∼90 MJ m−2 s−1/2. This paper characterizes surface morphology changes and damage thresholds under transient heating on W exposed to He plasma or D plasma with and without Be coatings. W is damaged in the form of grain growth, surface roughening, melting and cracking. With a Be coating on the order of μm thick, the laser pulse produces a variety of Be surface changes including Be–W alloying, vaporization of the Be layer, melting and delamination.

Efficient delivery of 60 J pulse energy of long pulse Nd:YAG laser through 200 μm core diameter optical fibre

Most of today’s industrial Nd:YAG lasers use fibre-optic beam delivery. In such lasers, fibre core diameter is an important consideration in deploying a beam delivery system. Using a smaller core diameter fibre allows higher irradiances at focus position, less degradation of beam quality, and a larger stand-off distance. In this work, we have put efforts to efficiently deliver the laser output of ‘ceramic reflector’-based long pulse Nd:YAG laser through a 200 μm core diameter optical fibre and successfully delivered up to 60 J of pulse energy with 90% transmission efficiency, using a GRADIUM (axial gradient) plano-convex lens to sharply focus down the beam on the end face of the optical fibre and fibre end faces have been cleaved to achieve higher surface damage thresholds.

Synthesis, crystal growth, structural, thermal, optical and mechanical properties of solution grown 4-methylpyridinium 4-hydroxybenzoate single crystal

Organic nonlinear optical material, 4-methylpyridinium 4-hydroxybenzoate (4MPHB) was synthesized and single crystal was grown by slow evaporation solution growth method. Single crystal and powder X-ray diffraction analyses confirm the structure and crystalline perfection of 4MPHB crystal. Infrared, Raman and NMR spectroscopy techniques were used to elucidate the functional groups present in the compound. TG-DTA analysis was carried out in nitrogen atmosphere to study the decomposition stages, endothermic and exothermic reactions. UV–visible and Photoluminescence spectra were recorded for the grown crystal to estimate the transmittance and band gap energy respectively. Linear refractive index, birefringence, and SHG efficiency of the grown crystal were studied. Laser induced surface damage threshold and mechanical properties of grown crystal were studied to assess the suitability of the grown crystals for device applications.

Growth and physical properties of an organic crystal for NLO applications: Guanidinium phenyl arsonate (GPA)

Single crystals of organic material guanidinium phenyl arsonate (GPA) of size 28×14×10mm3 were grown from propanol–water mixed solvent by slow solvent evaporation technique. The crystal belongs to monoclinic system with noncentrosymmetric space group Cc. The lattice parameter values of GPA crystals are a=18.453Å, b=7.609Å, c=12.592Å and β=121.856°. The grown crystal was subjected to X-ray diffraction (XRD) study to identify its morphology and structure. Chemical etching study using propanol–water as etchant reveals the mechanism of growth. The formation of synthesized compound was confirmed by Fourier transform infrared (FT-IR) spectroscopy analysis. Optical transmittance and second harmonic generation (SHG) of the grown crystals were studied by UV–vis–NIR spectrum and Kurtz powder technique respectively. The transmittance of GPA has been used to calculate the refractive index ‘n’ and the extinction coefficient ‘k’. The laser induced surface damage threshold for the grown crystal was determined using Nd:YAG laser. The mechanical behavior of GPA was analyzed using Vickers microhardness test.

Beam diameter dependence of surface damage threshold of fused silica fibers and preforms for nanosecond laser treatment at 1064 nm wavelength

Optical fibers made of fused silica are a common method of transmitting high laser pulse energies. Failure of those fibers is a significant risk. The determination of laser-induced damage thresholds (LIDT) on fiber end facets according to ISO 21254 standard is needed. In the past, single pulse nanosecond laser experiments showed an improvement of LIDT with increasing fiber core diameter for 1064nm wavelength and a constant beam diameter of 50μm.This paper pays particular attention to the influence of the laser beam diameter on damage resistance. All-silica fiber types (LEONI) with different core diameters (100–600μm) were investigated using beam diameters in a range from 30μm to 100μm. For comparison experiments on fused silica preform material (Heraeus F300) were performed. On one hand, surface LIDT of fused silica preform material decreases significantly with increasing beam size. A model considering a random distribution of point defects explains the experimental data qualitatively. On the other hand, LIDT of fiber end facets stays constant. White light microscopy results suggest that the point defect density on fiber end facets is lower compared to the preform surface due to an excellent surface polish quality.

Studies on Structural, Spectral, and Optical Properties of Organic Nonlinear Optical Single Crystal: 2-Amino-4,6-dimethylpyrimidinium p-Hydroxybenzoate

2-Amino-4,6-dimethylpyrimidinium p-hydroxybenzoate (ADPHB), a novel organic material, was synthesized, and crystals were grown by slow evaporation solution growth method. The cell parameters and crystalline perfection of the grown crystal were studied by single crystal and powder X-ray diffraction analyses. The presence of various functional groups of the grown crystal was confirmed using Fourier Transform infrared spectral analysis. UV-Visible spectrum shows that ADPHB crystals have high transmittance in the range 305–900 nm. The refractive index and transient photoluminescence properties of the grown crystal were analyzed. The laser induced surface damage threshold, optical birefringence, and second harmonic generation efficiency of the grown crystal were studied.

Growth and anisotropic studies on potential nonlinear optical crystal imidazole–imidazolium picrate monohydrate (IIP) in different orientations for NLO device fabrications

A new organic NLO material Imidazole–imidazolium picrate monohydrate (IIP) was grown by the slow evaporation technique using acetonitrile as a solvent. The solubility and meta stable zone width was determined. The IIP crystal belongs to orthorhombic system with noncentrosymmetric space group P212121. The morphology of the IIP crystal was studied. Optical transmittance spectrum confirms a wide optical window exhibited by IIP crystal. The transmittance of IIP crystal was used to calculate the extinction coefficient (k) and absorption coefficient (α). The thermal stability of the crystal was determined using TG-DTA studies. The laser induced surface damage threshold and mechanical behavior of the IIP crystal were analyzed in different planes at different temperatures. The second harmonic generation (SHG) effective nonlinearity of IIP is 3.6 times that of standard reference material potassium dihydrogen phosphate (KDP) crystal.

Linear and nonlinear optical properties of a new organic NLO l-asparaginium l-tartarate (AST) single crystal

A new organic NLO material l-asparaginium l-tartarate (AST) was synthesized and good quality crystals were grown from aqueous solution. The solubility and metastable zone width for AST solution were determined. Single crystal X-ray diffraction and powder X-ray diffraction analyses were carried out to confirm structure and crystalline nature of AST crystal. Optical transmittance and second harmonic generation efficiency (SHG) of the grown crystal were studied by UV⿿vis⿿NIR spectrum and Kurtz powder technique respectively. The transmittance of AST crystal was used to calculate the refractive index (n), the extinction coefficient (k) and reflectance (R). The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser.

Formation of Porous Structure with Subspot Size under the Irradiation of Picosecond Laser Pulses

A study was presented in this paper on porous structure with microsize holes significantly smaller than laser spot on the stainless steel 304 target surface induced by a picosecond Nd:van regenerative amplified laser, operating at 1064 nm. The target surface variations were studied in air ambience. The estimated surface damage threshold was 0.15 J/cm2. The target specific surface changes and phenomena observed supported a complementary study on the formation and growth of the subspot size pit holes on metal surface with dependence of laser pulse number of 50–1000 and fluences of 0.8 and 1.6 J/cm2. Two kinds of porous structures were presented: periodic holes are formed from Coulomb Explosion during locally spatial modulated ablation, and random holes are formed from the burst of bubbles in overheated liquid during phase explosion. It can be concluded that it is effective to fabricate a large metal surface area of porous structure by laser scanning regime. Generally, it is also difficult for ultrashort laser to fabricate the microporous structures compared with traditional methods. These porous structures potentially have a number of important applications in nanotechnology, industry, nuclear complex, and so forth.

Determination of the mid-IR femtosecond surface-damage threshold of germanium

To assess the potential uses of germanium as a nonlinear material in the mid IR we have measured the surface-damage threshold of germanium optical windows using femtosecond pulses at a wavelength of 3.9 μm. By working with a wavelength corresponding to a photon energy of less than half the band-gap energy, free-carrier generation due to one- and two-photon absorption was eliminated. The laser pulses had an energy of 5.5 μJ, a duration of 255 fs, and were focused to a waist size of approximately 100 μm. The multi-shot damage threshold of the germanium windows was estimated to be approximately 94 GW/cm2. The data should be of immediate benefit to industrial laser researchers and applications engineers working in the mid-IR region.

Lithium d-Isoascorbate Monohydrate, a New Nonlinear Optical Material

Single crystals of lithium D-isoascorbate monohydrate (LDAM), (C6H7O6Li center dot H2O), are grown by a solution growth method. The crystal structure of LDAM is solved using single crystal X-ray diffraction. The space group is orthorhombic P2(1)2(1)2(1) with four formula units per unit cell and lattice parameters a = 7.7836(3) angstrom, b = 8.7456(3) angstrom, and c = 11.0368(4) angstrom. Solubility of the material in water is determined thermogravimetrically and found to have a positive temperature coefficient of solubility. Large optical quality single crystals are subsequently grown from aqueous solution by a slow cooling method. The crystal has a bulky prismatic habit and among the prominent faces the c face appears as the only principal morphological face. The crystal exhibits a (010) cleavage. Dielectric spectroscopy reveals a nearly Debye type Cole-Cole behavior with anisotropy in relaxation. Optical transmission range is found to be from 300 to 1400 nm. The principal refractive indices of this biaxial crystal, measured using Brewster's angle method, at wavelengths 405, 543, and 632.8 nm, show high dispersion. The crystal is negative biaxial with 2V(z) = 107.8 degrees (405 nm) and belongs to the Hobden class 3. Theoretically generated type 1 and type 2 second order phase matching curves match very well with the experimental results. The second-order nonlinear coefficient d(14) was determined to be 7 x 10(-13) m/V. For the optimum phase matching direction (type 2), the second-order effective nonlinear coefficient and the walk off angle are determined to be 0.84 times d(14) and 3.5 degrees respectively. The crystal possesses high multiple surface damage thresholds of 18 GW/cm(2) and 8 GW/cm(2) at laser wavelengths 1064 and 532 nm, respectively.

Optical and Mechanical Studies on Methyl N- Phenylsuccinamate (MPS)

Single crystal of organic material Methyl N- phenylsuccinamate (MPS) has been grown by the slow evaporation technique using methanol as a solvent. The crystal belongs to orthorhombic system with non centrosymmetric space group Pna21. Optical transmittance and second harmonic generation efficiency of the grown crystals have been studied by UV-vis-NIR spectrum and Kurtz powder technique respectively. The transmittance of MPS crystal has been used to calculate the refractive index (n), the extinction coefficient (k) and reflectance (R). The laser induced surface damage threshold for the grown crystal has been measured using Nd:YAG laser. The mechanical behaviour of the MPS crystal has also been analyzed.

Optical properties of non-linear crystal grown from the melt GaSe–AgGaSe2

Modified GaSe single crystal was grown from the melt with charge composition GaSe+10 mass% of AgGaSe2. Lattice structure, visible to mid-IR and further THz range optical properties, as well as Raman spectra were studied in details. The grown crystal was identified as ε-GaSe:Ag (0.04 mass%). This silver content in GaSe has resulted in 6% decreased non-linearity that was over compensated in CO2 laser SHG efficiency by vanished of bulk damages and 10–20% improved surface damage threshold. About 30% increased microhardness is promising for cut and polishing at arbitrary direction and ε-GaSe:Ag applications in out-of-door systems.

Selective single pulse femtosecond laser removal of alumina (Al2O3) from a bilayered Al2O3/TiAlN/steel coating

We studied surface modification of a double layer protective coating on steel induced by single fs laser pulse irradiation in ambient air. The outer alumina (Al2O3) layer, which protects against aggressive environments, was 1.7μm thick and the titanium aluminum nitride (TiAlN) layer in contact with the steel surface had a thickness of 1.9μm. The pulses (λ=775nm, τ=200fs) were generated by a Ti:sapphire laser source. The pulse energy was varied from 0.32μJ to 50μJ, corresponding to an incident laser fluence of 0.11Jcm−2 to 16.47Jcm−2. The surface damage threshold was found to be 0.20Jcm−2 and the alumina layer removal was initiated at 0.56Jcm−2. This selective ablation of alumina was possible in a wide range of fluences, up to the maximum applied, without ablating the TiAlN layer beneath.

Growth, structural, thermal, linear and nonlinear optical and laser damage threshold studies of Picolinium tartrate monohydrate single crystals

Picolinium tartrate monohydrate (PTM), a novel organic nonlinear optical material was synthesized and bulk crystals were grown from aqueous solution by slow cooling technique. The cell parameters of the grown crystal were found by single and powder X-ray diffraction analyses. The crystalline perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. The presence of functional groups in the grown crystal was identified by FTIR and FT-Raman spectral analyses. UV–Vis spectral studies reveal PTM crystals are transparent in the wavelength region of 295–1100nm. The thermal characteristics of PTM were analyzed by TGA/DTA studies. The dielectric and mechanical behaviours of PTM crystals were investigated. Dislocation density was estimated to be 2.89×103cm−2 on the flat-surface of PTM crystals from the etching studies. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. Its second harmonic generation relative efficiency was measured by Kurtz and Perry powder technique and was observed to be comparable with KDP crystal.

Superficial changes on the Inconel 600 superalloy by picosecond Nd:YAG laser operating at 1064, 532, and 266 nm: Comparative study

AbstractA comparative study of superficial changes on the superalloy Inconel 600, induced by a picosecond Nd:YAG laser operating at 1064, 532, and 266 nm, is presented. All of the laser wavelengths, as well as the used fluences of 2.5 (1064 nm), 4.3 (532 nm), and 0.6 J/cm2 (266 nm) were found to be adequate for inducing surface variations. Quite different surface features were produced depending on the laser wavelength used. The measured surface damage thresholds were 0.25, 0.13 and 0.10 J/cm2 for 1064, 532, and 266 nm, respectively. Drastic differences, in function of the wavelength used, were recorded for the crater depths, as well the appearance of hydrodynamic effects and periodic surface structures. Differences in crater depths were explained via an easier propagation of the first harmonic laser radiation (1064 nm) through the ejected material and plasma compared to a radiation at 532 and 266 nm. Finally, changes in the surface oxygen content caused by ultrashort laser pulses were considered.

Incubation effect and its influence on laser patterning of ITO thin film

Results are presented on the surface damage thresholds of ITO thin films induced by single- and multi-pulse laser irradiation at a pulse duration of 10 ps and a wavelength of 1064 nm. For multi-pulse ablation the incubation effect results in a reduction of the damage threshold, especially apparent at low pulse numbers and very small film thicknesses. The incubation effect attributes to the accumulation of defect sites and/or the storage of thermal stress-strain energy induced by the incident laser pulses. An incubation coefficient of S=0.82 has been obtained which is independent on the film thickness in the range of 10–100 nm. In practical applications, the incubation effect determines the laser patterning structure of ITO films while increasing the pulse overlapping rate. The width of the patterned line can be predicted by the proposed model involving the laser fluence, the overlapping rate and the incubation coefficient.

Experimental investigation on laser-induced surface damage threshold of Nd-doped phosphate glass

Nd-doped phosphate glass is the dominant amplifier material used in solid state high average power laser systems. Surface imperfection and subsurface damage (SSD) of the glass, resulting from the optical fabrication process, limit the increment of laser system energy output. Thus, it is important to enhance the surface damage threshold of Nd-doped phosphate glass surface. The in°uence of abrasive size, polishing powder, grinding mode, and chemical treatment on the laser-induced damage threshold (LIDT) of Nd-doped phosphate glass surface is investigated. Results show that the LIDT is affected little by different polishing powders and grinding modes. The LIDT correlates with the abrasive size, which produced different depths of SSD. A suitable acid etching treatment can remove the imperfection and the SSD for improving the LIDT of Nd-doped phosphate glass surface. The combination of several effective techniques and methods, which are low-cost and practical, should be useful to enhance the LIDT of Nd-doped phosphate glass surface.

Studies on growth, spectral and mechanical properties of new organic NLO crystal: Guanidinium 4-nitrobenzoate (GuNB)

A new organic nonlinear optical single crystal guanidinium 4-nitrobenzoate (GuNB) was successfully grown by solution growth using the slow evaporation technique. Solubility and metastable zone width were determined for different solvents. The structure of the grown crystal has been determined by single crystal x-ray diffraction analysis. The presence of functional groups and coordination of para nitro benzoate ions in the GuNB crystal have been identified by FTIR and FT Raman spectroscopic studies. The optical transparency range has been studied through UV–vis–NIR spectroscopy. The second harmonic generation efficiency of the grown GuNB crystal has been obtained by the Kurtz–Perry powder technique. The laser induced surface damage threshold for the grown crystal has been measured using Nd: YAG laser. The mechanical behavior has also been studied by Vicker's microhardness test.