Dielectric sesquioxide films (Sc2O3, Y2O3, and Lu2O3) were fabricated by pulsed-laser deposition and tested in terms of their laser damage properties for pulses of 500 fs duration, at a wavelength of 1030 nm and at a 10 Hz repetition rate. Comparable tests were performed with magnetron-sputtered thin films of established optical-coating materials (SiO2, HfO2, and Nb2O5), whose results served as a benchmark. The laser-induced damage thresholds of the sesquioxides are comparable to each other, and in the multi-pulse test regime show values close to ones of HfO2 coatings. A lower damage threshold was observed for the polycrystalline Lu2O3 film grown on sapphire compared to single-crystal Lu2O3 grown on yttrium aluminium garnet (Y3Al5O12), attributed to the highly textured morphology and potential for a greater density of defect states in these films. We conclude that pulsed-laser deposition is a potential fabrication method of sesquioxides for use in high-power resistant optical components for ultrashort-pulse lasers. |
1.IntroductionThe laser-induced damage threshold (LIDT) of optical components represents the limiting factor of the useful performance of ultrafast solid-state lasers.1,2 To improve the LIDT of optical materials, especially optical coatings, considerable efforts have been made to test diverse materials,3–5 develop new optimized coating designs,6–8 and advanced fabrication methods.9–11 Among the plethora of thin-film growth techniques, pulsed-laser deposition (PLD) is considered to be one of the most versatile and powerful.12 In comparison to other deposition techniques such as sputtering or chemical vapor deposition, PLD enables crystalline thin-film growth at relatively low substrate temperatures.13,14 PLD also provides the ability to deposit several multicomponent materials in situ with preserved stoichiometry.15 Since the pioneering PLD work from Smith and Turner in 1965,16 the technique has been used for deposition of a wide range of materials17 and recently proved to be a reliable method for optical-coating fabrication.18–22 In the past decade, mirrors based on the combination of , a high-refractive-index material, and , a low-refractive-index material, received considerable attention.6,23,24 However, the published sub-picosecond (ps) LIDT results for or films, indicate that sesquioxides might be good alternatives for .11,25–27 Especially , which is a promising high-refractive-index material that exhibits slightly larger optical bandgap (5.7 eV)28 than (5.55 eV).29,30 In fact, electron-beam-deposited and thin films, tested at 500 fs and 1030 nm by a single shot and 100 shots at 10 Hz repetition rate, showed LIDTs comparable to that of .11 The laser damage resistance at 500 fs and 1030 nm was also measured for ion-beam sputtered for which its 1-on-1 internal damage threshold reached a value of 3.1 J/cm2.25 It has to be pointed out that most of the laser damage studies of have been motivated by the development of optical interference coatings in the UV range.28,31–33 To the best of our knowledge, all the LIDT studies conducted on sesquioxide films focused either on amorphous or polycrystalline films. Consequently, the results might differ from films produced via PLD, which has the potential to grow single-crystal films.21,34,35 In this work, we prepared pulsed-laser deposited , , and sesquioxides and tested them in terms of sub-ps-pulse laser damage. Comparable tests were also performed with magnetron-sputtered (MS) thin films of established optical-coating materials (, , and ), whose results served as a benchmark. The LIDT values for these more standard materials have been reported in studies comparing them with numerous optical-coating materials.3,30 The thin films studied in this report are intended to be used in dielectric multilayer mirrors or diffractive gratings, particularly grating waveguide structures (GWSs).36 The latter elements offer the possibility to control the temporal,37 spectral,38 or spatial profile of light within or from high-power laser systems.39 This study intends to explore the sesquioxides as potentially interesting materials for use in high-power ultrashort-pulse laser systems. Moreover, the uniqueness of this study lies in the testing of non-traditional sesquioxide materials in their crystalline form. In the case of thin films, we are not aware of any laser damage-related publication in the sub-ps regime. The following sections describe the deposition techniques used: pulsed-laser deposition and magnetron sputtering. Then the tested samples and their parameters are introduced. This is followed by an explanation of the characterization methods used to qualify the thin-film materials. Afterward, the LIDT station and the procedure employed are described. Finally, the laser damage results are given and their dependence on the number of shots, material bandgap, refractive index, and deposition method is discussed. 2.Sample Fabrication2.1.Pulsed-Laser DepositionThe deposition of the films investigated in this study was performed with the PLD setup depicted schematically in Fig. 1 and described in more details in Refs. 21, 35, and 40. The targets were fabricated by sintering powders of the materials of interest, which ensures a stoichiometric proportion of the elements, and had a final mass of of the expected mass for the pure crystalline material of the same volume. Target ablation was achieved using a KrF excimer laser operating at 248 nm, with a pulse duration of ns and a repetition rate of 100 Hz, yielding growth rates ranging from 10 () to (). The motion of the target was configured to obtain an effective bi-directional ablation, which was proven to significantly reduce the number of scattering points in the as-grown films.40 A Metricon (Model 2010) prism coupler equipped with a #200-P-2 prism, and a HeNe laser source operating at 633 nm was used to determine the refractive index and thickness of the films investigated. To achieve crystalline-film growth, during deposition the rear surface of the substrate was heated by a laser operating at . The original Gaussian intensity distribution of the beam was transformed by a ZnSe tetraprism41 into a nearly-uniform profile, which fits the substrate’s dimensions. The substrate temperature used for the deposition of the samples ranged from 950°C to 1100°C, depending on the material. The background pressure of the vacuum chamber could be tuned by manually adjusting an oxygen gas in-flow. All sesquioxide films analyzed in this report were deposited at a background pressure of . The deposition parameters of the investigated samples are listed in Table 1. Optimization of the parameters had been conducted previously and the samples for LIDT measurements were selected based on their crystalline properties and surface homogeneity (in terms of the number of scattering points visible under a dark field microscope). Table 1Deposition parameters and lattice properties of the sesquioxide films grown on sapphire (Al2O3) or yttrium-aluminum-garnet (YAG) substrates. The measurement of the XRD peaks and lattice constants are detailed in Sec. 3.2. The precision on the position of the (222) XRD peak is limited by the angular resolution of the incident beam, ±0.01 deg. The film lattice constant is calculated for a Cu Kα wavelength of 1.5418 Å and the resolution error is ±0.004 Å.
2.2.Magnetron SputteringMS samples were produced with a Helios coater developed by Bühler Leybold optics.42 The layers were deposited by the plasma-assisted reactive magnetron sputtering (PARMS) process. Inside the Helios coater, samples are placed on a rotating plate. At first, the sample passes under a mid-frequency dual magnetron, where a thin substoichiometric layer is deposited from a metallic target. Then the sample passes under a radio frequency plasma source where the thin layer is oxidized. The PARMS process, therefore, produces high-density oxide coatings.43 The speed of rotation and power of magnetron is adjusted to deposit nm of thin-film in each rotation. Each individual thin-film-layer thickness is controlled by in situ optical monitoring. Optical measurement is performed at each passing of the substrate under the measurement window. This allows the single-layer thickness to be controlled to better than 1 nm accuracy. Both monochromatic and broadband monitoring can be used in this setup. Typical pressure inside the vacuum chamber during deposition is 50 nbar. An argon and oxygen mix is used as a process gas for magnetron sputtering, while oxygen is used as the source gas in the plasma for thin-film oxidation. Both high- and low-index materials can be coated within one production cycle. Previous studies have been conducted on films produced by this machine and their LIDT values compared to a large set of samples produced by different methods and manufacturers, exhibiting LIDT in accordance with the state-of-the-art.3,30,44 3.Characterization of the Thin Films3.1.Samples to Be TestedThe tested samples were monolayers of , , , , , and (See Table 2). The crystalline sesquioxide materials (, , and ) were deposited on a -oriented sapphire substrate. In the case of material, one sample was deposited on a -oriented yttrium aluminum garnet (YAG) substrate. The amorphous metal oxides (, , and ) were deposited on fused silica (FS) using the magnetron sputtering process. Table 2Tested thin-film materials and their parameters, n means refractive index at 1030 nm wavelength. The Sc2O3, Y2O2, and Lu2O3 sesquioxides were PLD-grown in the Optoelectronics Research Centre (Southampton, United Kingdom). The HfO2, Nb2O5, and SiO2 were MS in the Institut Fresnel (Marseille, France).
3.1.1.Refractive index measurementThe refractive indices of the MS samples were determined by spectrophotometry using numerical fitting methods to the transmittance and reflectance measurements in the low-absorptance spectral region. The values of refractive indices at 1030 nm are listed in Table 2. In the case of pulsed-laser deposited materials, the dispersion curves were determined using ellipsometry. The refractive indices of (1.90 @1030 nm) and (1.97 @1030 nm) correspond well with published values.46,47 Extinction coefficients were measured by ellipsometry, however, given the uncertainty of the method, we can only assess that the extinction coefficient values are below at 1030 nm. 3.1.2.Bandgap measurementThe optical bandgap values of the tested samples were derived from each film’s intrinsic absorption coefficient, , by plotting as a function of the photon energy and extrapolating the linear curve to the abscissa axis. The bandgap error margins were estimated using the photon energies corresponding to absorption coefficients of and .48,49 The value of bandgap was taken from Ref. 44 because the absorption edge could not be reached with our instruments. 3.2.X-Ray DiffractionEpitaxial growth of the , , and films on the -cut sapphire was expected to be predominantly in the -direction, since the lattice mismatch in this orientation is the smallest with substrate orientation, i.e., 4.9%, 2.9%, and 2.5%, respectively. Similarly, has a quasi-perfect lattice match with -cut YAG, that facilitates the growth of that orientation. The out-of-plane x-ray diffraction (XRD) patterns from the samples were recorded by a Rigaku Smartlab, equipped with a Ge(220) 2-bounce monochromator. Two different sets of parameters were selected for the scans. A wide scan with a 2 value from 20 deg to 80 deg and a step size of 0.02 deg was used to compare the proportion of the different orientations in the film. Since the films were expected to grow preferentially in the -direction, the (222) diffraction peak was our main peak of interest. Secondly, an additional high-resolution scan with a step size 0.002 deg was made around this primary peak. Figure 2 displays the XRD patterns of the films with each peak labeled with the corresponding orientation. The and films grew primarily in the -orientation, as demonstrated by the dominance of the (222) peak. The height ratio between the (222)-peak and the peaks corresponding to other orientations is greater than 3000. However, the film grown on sapphire exhibits strong polycrystalline characteristics, with several orientations that have a height ratio of with the (222) peak. On the contrary, the growth of -oriented is clearly favored on the YAG substrate: the XRD figure shows also that the (222) peak is 1500 times stronger than the next visible orientation (332) and is nearly perfectly superimposed with the YAG (400) peak at a angle of 29.8 deg. This aspect is highlighted in the high-resolution XRD pattern of that sample in Fig. 3b, with a clear double-peak lying at 29.8 deg. Figure 3 compares the position of the (222) peak of the different films, which was used to calculate their lattice constants. The results, summarized in Table 1, show that the lattice constant of the as-grown films is close to the value reported for the corresponding bulk materials.50,51 4.Description of LIDT Station and Test Procedure4.1.Test StationThe test station used for LIDT tests is described in Ref. 52 detailing the description of test procedures and metrology methods. For the results reported here in this study, the pulses of nearly Gaussian spatial profile and fs pulse duration at nm wavelength were incident at a repetition rate of 10 Hz. The maximum achievable pulse energy on a sample was 0.85 mJ. Characterization of the spatial and temporal profiles as well as an energy calibration were carried out before and after the LIDT test campaign. The LIDT tests were performed with samples placed at the focal plane of the lens with 30 cm focal length. The effective beam diameter, as defined by international standards,53 was in a plane perpendicular to the beam propagation. The LIDT tests were performed in an air environment at a room temperature of 25°C and humidity around 27%. A typical spatial beam profile at the focal plane, autocorrelation trace, and spectral distribution are shown in Fig. 4. 4.2.LIDT Procedure and Damage DetectionEach sample was irradiated at different spots with unique pulse energies that were changed with a energy increment in order to get statistical data. The procedure was repeated for different numbers of pulses—from single-shot up to 1000 shots at 10 Hz. The LIDT tests were done at a 45-deg incidence angle with P-polarization. The irradiated sites were analyzed ex situ using a Zeiss Axiotech differential interference contrast microscope with 20× objective magnification. Any observable material modification was evaluated as damage. The damage threshold was determined as the highest fluence that is lower than the lowest fluence causing damage in the experiment. The error bars correspond to the sum of variations of effective beam area near focal plane (), pulse energy (), and a half of pulse energy increment (). 4.3.Intrinsic LIDT FluenceSince the optical layers are the scene of interference effects, the distribution of the electric field inside the layer irradiated by the laser is not homogeneous. The electric field distribution is critical for understanding sub-ps LIDT results since the excitation of dielectrics is governed by electronic processes.2 To compare LIDT results, accounting for the conditions influencing the electric field distribution, e.g., angle of incidence, polarization, layer thickness, or refractive index, it is necessary to rescale the LIDT results with the electric field intensity (EFI) maximum () within the given layer. Therefore, the fluence values reported in this study correspond to intrinsic fluence determined using external fluence and the and the relation is given by where the represents the maximum value of the electric field in the layer and the means incident electric field amplitude.54 The correction factor of incidence angle during the damage tests (45 deg) is taken into account within the calculation. The distribution of the relative EFI for the layer used in our experiment is shown in Fig. 5.5.Laser Damage Results and Discussion5.1.Deterministic 0 to 1 TransitionTo evaluate the uniformity of the tested materials in terms of laser damage, the transition range of the damage probability, as indicated in Fig. 6(a), was calculated for each material and number of shots used, see Fig. 6(b). The 1-on-1 laser damage tests with , , , , and show deterministic results, i.e., narrow transition ranges of damage probability from 0 to 1. The transition range of damage probability was only a few percent in fluence, which suggests that the LIDT is limited by intrinsic material properties rather than by defects or impurities caused by the deposition process.55 However, in the case of , we found wider transition ranges that could be a consequence of film imperfections, especially in the case of the film grown on sapphire that could be connected to the polycrystalline nature of this film, see Fig. 7. The larger ranges for the multiple-pulse tests may be due to the stochastic formation of deep and shallow traps in the bandgap, which facilitates electron excitation and material modification.2 5.2.LIDT—Single ShotThe intrinsic LIDT fluence as a function of shot number for different thin-film materials is shown in Fig. 6(c). Among the tested materials, the film shows the highest LIDT while shows the lowest. In between, we find the other high-index materials, namely , , , and , that are interesting for high-power applications. , a widely used high-index material in optical mirrors, showed a single-shot LIDT of , which is higher than the values around published in the previous works11,56,57 performed under the conditions close to ones used in this study (1030 nm, 500 fs). The higher LIDT of the tested can be explained by the inclusion of in the deposited film, which was estimated from the dispersion curve to be around 1% to 2%.45 The effect of the admixture on the damage threshold is in agreement with previous work.3 5.3.LIDT—Multiple ShotsFor all materials, the LIDT is decreasing with an increasing number of shots, see Fig. 6(c). The results show a drop of of the threshold within the first 100 shots. In contrast, at the transition from 100 to 1000 pulses, we observe only a small decrease. These tendencies were already observed in works performed at similar irradiation conditions with metal oxide coatings.11,44,58 The gradual decrease is associated with the formation of laser-induced defects, leading to accessible energy levels within the bandgap. The deep or shallow traps can capture electrons from the conduction band even after a sub-threshold irradiation.59 In the case of , the drop in LIDT is more noticeable than for the other sesquioxides and reaches that of . The larger 1-on-1 LIDT of compared to was also observed in work with ion-beam sputtered (IBS) films25 which could be related to imperfect damage detection. Going to a higher number of pulses, the deposited on FS, on , on , and on YAG, samples show very similar LIDT, indicating that any of these materials could be recommended for high-power applications, as far as LIDT is concerned. The 1-on-1 and 100-on-1 LIDT values of , , and materials were determined to be close to each other in the study,11 devoted to electron-beam deposited (EBD) single-layers on FS substrates. The LIDT tests were performed at identical conditions to this work (500 fs, 1030 nm, and 10 Hz). In the case of deposition on an substrate, we observe significantly lower LIDT values, which could be explained by the polycrystalline and highly textured nature of the film (Fig. 7). The presence of multiple crystal orientations implies the existence of discontinuities in the lattice that may potentially modify the local bandgap of the material. These boundaries between domains of different orientations may initiate the damage. 5.4.BandgapSince the laser-damage initiation in the sub-ps regime is driven by nonlinear ionization, the bandgap represents a critical parameter that correlates with the laser-damage resistance.55 The behavior can be explained by taking into account the electron excitation processes playing a dominant role at the beginning of damage formation, i.e., multiphoton and impact ionization.2 The intrinsic threshold fluences of tested materials are plotted as a function of their bandgap values in Fig. 8(a). We observe a linear tendency of increasing single-shot LIDT with a larger bandgap value that is in agreement with the studies performed at similar irradiation conditions in Refs. 30 and 60. The deviations from the linear tendency in Fig. 8(a) can be explained by the challenges faced to observe the material modifications induced by single-shot irradiation, see Fig. 7. Moreover, some of the sesquioxide crystal films exhibit imperfections that include defect sites. For example, the lower LIDT of on sapphire could have been caused by its polycrystalline structure, enabling lower local bandgap values at domain boundaries for different lattice orientations. It should be highlighted that the Tauc method provides a measure of the bandgap at a macroscopic scale, while on the microscopy level there are likely to be numerous defects in the polycrystalline film. Even in the case of the near single-crystal on YAG, the error bars on the bandgap would be larger than that determined from the Tauc measurement method used. In this work, the LIDT (in ) tendency on bandgap (in eV) can be well fitted by the following equation The equation shows a higher slope, i.e., more dynamic dependence on the bandgap than the empirical description in Ref. 30 derived from results for numerous materials deposited by various methods. The differences from the published data could be explained by the limited number of tested samples or the selected method of bandgap determination. The bandgap values of sesquioxides are very close to each other with a slightly larger bandgap in the case of , see Fig. 8, whose single-shot LIDT was determined as the highest within the high-index materials. The determined bandgap value for the film tested (5.7 eV) is close to the bandgap of ion-beam sputtered (5.6 eV).25 However, larger bandgaps have been reported for electron-beam deposition (EBD) of (6.5 eV) or (6.1 eV)11 compared with the samples tested here grown by PLD, i.e., (5.7 eV) or (5.4 eV). It should be noted that care should be taken when comparing bandgaps across publications since the bandgap is not exactly defined and can be determined using different methods. 5.5.Refractive IndexFor the design of multilayer components and GWS in our case, the critical parameter is the refractive index. Thus, in Fig. 8(b), we plot the intrinsic 1-on-1 LIDT of the tested materials as a function of refractive index. The results confirm the trend of increasing refractive index with decreasing intrinsic 1-on-1 LIDT, which was also observed in works3,30 performed at similar irradiation conditions (500 fs, 1030 nm). Amorphous and single-crystal materials appear to follow the trend, while polycrystalline sesquioxides, such as and , seem to be susceptible to a lower LIDT. This could be due to local defects associated with domain boundary interfaces and the highly textured surface. Based on the comparison, seems to be the most promising of the sesquioxides, showing both high damage resistance and a high refractive index value. Furthermore, the pulsed-laser deposited (1.97) shows a higher refractive index @1030nm than the ion-beam sputtered one (1.93)25 or the EBD (1.82).11 The refractive index of the PLD samples studied here is the same as that of EBD (1.90).11 5.6.Deposition MethodsThanks to the LIDT studies11,25 performed under identical conditions using the same experimental setup like this work (500 fs, 1030 nm), we can compare the LIDT values of sesquioxides deposited by different fabrication methods as shown in Fig. 9. For both and , the laser damage resistance of the PLD samples is comparable to that of EBD layers. The thresholds of both PLD and EBD samples indicate a similar fatigue effect—decrease between the 1-on-1 and 100-on-1 thresholds. In the case of 1-on-1 thresholds, the differences between PLD, EBD, and IBS deposition methods can be explained by the difficulty of the detection of material changes. Furthermore, the higher 1-on-1 LIDT of layer fabricated by IBS compared with that of the PLD grown layer could be explained by a 1.6% Si fraction of Sc+Si content in the IBS layer.25 5.7.Sesquioxides in Multilayer CoatingsLattice-matching constraints strongly limit the potential combinations of materials involving crystalline sesquioxides. Among the materials studied, and have the largest refractive index contrast, i.e., 0.2 at the wavelength of 1030 nm. Despite a lattice mismatch of only 2.5%, the fundamentally different lattice structure of and (space group Ia and Rc, respectively) can potentially make the fabrication of / multilayer coatings more complex than pairs of cubic sesquioxides. However, for example, the lattice mismatch of a combination is too large, at 7.6%, for robust thick-multilayer epitaxial growth. Another challenge derives from the lower index contrast between these PLD-grown sesquioxide materials. For instance, a quarter-wave stack of needs a minimum of 25 layers to reach 99.9% reflectivity at normal incidence for the wavelength of 1030 nm, while an equivalent mirror would require 73 layers. The resulting multilayer stack would have a full-thickness on the order of , which is within the scope of PLD crystalline growth.22 Furthermore, owing to the high deposition rates achievable (15 to ), around 10 times faster than magnetron sputtering, dimensions are entirely feasible within reasonable growth-run times. 6.Conclusion, , and sesquioxide crystalline films, deposited by pulsed-laser deposition, were tested for sub-ps laser damage. Similar intrinsic LIDT fluences of 1.3 to were found for the well-grown sesquioxides, i.e., on sapphire, on sapphire, and on YAG, when tested with multiple pulses (100 or 1k). The LIDT tests on grown on sapphire revealed significantly lower damage thresholds than on YAG. This result is explained by the polycrystalline structure of grown on sapphire, deduced from XRD characterization. The highly textured polycrystalline structure contains discontinuities in the lattice that most probably initiate the damage. The high-index PLD sesquioxides show high bandgap values indicating good damage resistance in optical coatings. In terms of observed damage thresholds, sesquioxides can compete with , a frequently used high-index material in dielectric multilayers. The study shows that pulsed-laser deposition is a candidate for optical-coating fabrication and that the sesquioxides are promising high-index materials that could be used in applications relating to high-power ultrashort-pulse lasers. AcknowledgmentsThis project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 813159. The authors acknowledge the EPSRC for financial support of the Rigaku SmartLab via Grant Nos. EP/K009877/1, EP/K00509X/1, and EP/V035975/1, an EPSRC Doctoral Prize EP/T517859/1, and Grant Nos. EP/N018281/1 and EP/P027644/1. The authors declare no conflicts of interest. Data, Materials, and Code AvailabilityData underlying the results presented in this paper are not publicly available now but may be obtained from the authors upon reasonable request. ReferencesW. Koechner,
“Damage of optical elements,”
Solid-State Laser Engineering, 1 680
–701 Springer, New York
(2006). Google Scholar
L. Emmert, W. Rudolph,
“Femtosecond laser-induced damage in dielectric materials,”
Laser-Induced Damage in Optical Materials, 127
–152 CRC Press, Boca Raton, Florida
(2014). Google Scholar
B. Mangote et al.,
“Femtosecond laser damage resistance of oxide and mixture oxide optical coatings,”
Opt. Lett., 37 1478
(2012). https://doi.org/10.1364/OL.37.001478 OPLEDP 0146-9592 Google Scholar
V. Csajbók et al.,
“Femtosecond damage resistance of femtosecond multilayer and hybrid mirrors,”
Opt. Lett., 41 3527
(2016). https://doi.org/10.1364/OL.41.003527 OPLEDP 0146-9592 Google Scholar
J. Vanda et al.,
“Comparative LIDT measurements of optical components for high-energy HiLASE lasers,”
High Power Laser Sci. Eng., 4 e11
(2016). https://doi.org/10.1017/hpl.2016.11 2095-4719 Google Scholar
S. Chen et al.,
“Femtosecond laser-induced damage of HfO2/SiO2 mirror with different stack structure,”
Appl. Opt., 51 6188
(2012). https://doi.org/10.1364/AO.51.006188 APOPAI 0003-6935 Google Scholar
T. Willemsen et al.,
“Enhancement of the damage resistance of ultra-fast optics by novel design approaches,”
Opt. Express, 25 31948
(2017). https://doi.org/10.1364/OE.25.031948 OPEXFF 1094-4087 Google Scholar
M. Chorel et al.,
“Robust optimization of the laser induced damage threshold of dielectric mirrors for high power lasers,”
Opt. Express, 26 11764
(2018). https://doi.org/10.1364/OE.26.011764 OPEXFF 1094-4087 Google Scholar
J. B. Oliver et al.,
“Plasma-ion-assisted coatings for 15 femtosecond laser systems,”
Appl. Opt., 53 A221
(2014). https://doi.org/10.1364/AO.53.00A221 APOPAI 0003-6935 Google Scholar
T. Willemsen et al.,
“Tunable optical properties of amorphous Tantala layers in a quantizing structure,”
Opt. Lett., 42 4502
(2017). https://doi.org/10.1364/OL.42.004502 OPLEDP 0146-9592 Google Scholar
A. Hervy et al.,
“Femtosecond laser-induced damage threshold of electron beam deposited dielectrics for 1-m class optics,”
Opt. Eng., 56 011001
(2016). https://doi.org/10.1117/1.OE.56.1.011001 Google Scholar
F. Craciun, T. Lippert, M. Dinescu,
“Pulsed laser deposition: fundamentals, applications, and perspectives,”
Handbook of Laser Micro- and Nano-Engineering, 1
–33 Springer, Cham
(2020). Google Scholar
D. Rasic et al.,
“Room temperature growth of epitaxial titanium nitride films by pulsed laser deposition,”
Cryst. Growth Des., 17 6634
–6640
(2017). https://doi.org/10.1021/acs.cgd.7b01278 CGDEFU 1528-7483 Google Scholar
D. Rasic, J. Narayan,
“Epitaxial growth of thin films,”
Crystal Growth, IntechOpen, Rijeka
(2019). Google Scholar
T. Venkatesan et al.,
“Laser processing of high-Tc superconducting thin films,”
IEEE J. Quantum Electron., 25 2388
–2393
(1989). https://doi.org/10.1109/3.42070 IEJQA7 0018-9197 Google Scholar
H. M. Smith and A. F. Turner,
“Vacuum deposited thin films using a ruby laser,”
Appl. Opt., 4 147
(1965). https://doi.org/10.1364/AO.4.000147 APOPAI 0003-6935 Google Scholar
K. B. Masood et al.,
“A comprehensive tutorial on the pulsed laser deposition technique and developments in the fabrication of low dimensional systems and nanostructures,”
Emergent Mater., 4 737
–754
(2021). https://doi.org/10.1007/s42247-020-00155-5 Google Scholar
M. Filipescu et al.,
“Antireflective coatings with high damage threshold prepared by laser ablation,”
Appl. Phys. A, 125 815
(2019). https://doi.org/10.1007/s00339-019-3110-y Google Scholar
A. Bercea et al.,
“Optical coatings for ELI experiments prepared by laser ablation,”
Rom. J. Phys., 63 606
(2018). Google Scholar
E. N. Sirjita et al.,
“Properties of hafnium and aluminium silicates coatings obtained by PLD,”
Coatings, 11 753
(2021). https://doi.org/10.3390/coatings11070753 CPPPDE 0099-0701 Google Scholar
J. J. Prentice et al.,
“Yb-doped mixed-sesquioxide films grown by pulsed laser deposition,”
J. Cryst. Growth, 491 51
–56
(2018). https://doi.org/10.1016/j.jcrysgro.2018.03.039 JCRGAE 0022-0248 Google Scholar
K. A. Sloyan et al.,
“Crystalline garnet Bragg reflectors for high power, high temperature, and integrated applications fabricated by multi-beam pulsed laser deposition,”
Appl. Phys. Lett., 101 081117
(2012). https://doi.org/10.1063/1.4748107 APPLAB 0003-6951 Google Scholar
L. O. Jensen et al.,
“Investigations on SiO2/HfO2 mixtures for nanosecond and femtosecond pulses,”
Proc. SPIE, 7842 68
–77
(2010). https://doi.org/10.1117/12.867238 PSISDG 0277-786X Google Scholar
L. Lamaignère et al.,
“Round-robin measurements of the laser-induced damage threshold with sub-picosecond pulses on optical single layers,”
Opt. Eng., 60 031005
(2020). https://doi.org/10.1117/1.OE.60.3.031005 Google Scholar
M. Mende et al.,
“Laser damage resistance of ion-beam sputtered Sc2O3/SiO2 mixture optical coatings,”
Appl. Opt., 52 1368
(2013). https://doi.org/10.1364/AO.52.001368 APOPAI 0003-6935 Google Scholar
C. S. Menoni et al.,
“Advances in ion beam sputtered Sc2O3 for optical interference coatings,”
Proc. SPIE, 7842 784202
(2010). https://doi.org/10.1117/12.855604 PSISDG 0277-786X Google Scholar
E. M. Krous et al.,
“Scandium oxide thin films deposited by dual ion beam sputtering for high-power laser applications,”
in Opt. Interference Coatings,
(2010). Google Scholar
D. Grosso and P. Sermon,
“Scandia optical coatings for application at 351 nm,”
Thin Solid Films, 368 116
–124
(2000). https://doi.org/10.1016/S0040-6090(00)00924-X THSFAP 0040-6090 Google Scholar
J. Aarik et al.,
“Optical characterization of HfO2 thin films grown by atomic layer deposition,”
Thin Solid Films, 466 41
–47
(2004). https://doi.org/10.1016/j.tsf.2004.01.110 THSFAP 0040-6090 Google Scholar
L. Gallais and M. Commandré,
“Laser-induced damage thresholds of bulk and coating optical materials at 1030 nm, 500 fs,”
Appl. Opt., 53 A186
(2014). https://doi.org/10.1364/AO.53.00A186 APOPAI 0003-6935 Google Scholar
F. Rainer et al.,
“Scandium oxide coatings for high-power UV laser applications,”
Appl. Opt., 21 3685
(1982). https://doi.org/10.1364/AO.21.003685 APOPAI 0003-6935 Google Scholar
F. Rainer et al.,
“Materials for optical coatings in the ultraviolet,”
Appl. Opt., 24 496
(1985). https://doi.org/10.1364/AO.24.000496 APOPAI 0003-6935 Google Scholar
S. Tamura et al.,
“Laser-damage threshold of Sc2O3/SiO2 high reflector coatings for a laser wavelength of 355 nm,”
Thin Solid Films, 228 222
–224
(1993). https://doi.org/10.1016/0040-6090(93)90603-M THSFAP 0040-6090 Google Scholar
S. J. Beecher et al.,
“Ytterbium-doped-garnet crystal waveguide lasers grown by pulsed laser deposition,”
Opt. Mater. Express, 7 1628
(2017). https://doi.org/10.1364/OME.7.001628 Google Scholar
G. A. Govindassamy et al.,
“Effect of laser repetition rate on the growth of Sc2O3 via pulsed laser deposition,”
Appl. Phys. A,
(2022). Google Scholar
G. Quaranta et al.,
“Recent advances in resonant waveguide gratings,”
Laser Photonics Rev., 12 1800017
(2018). https://doi.org/10.1002/lpor.201800017 Google Scholar
M. Rumpel et al.,
“Broadband pulse compression gratings with measured 99.7% diffraction efficiency,”
Opt. Lett., 39 323
(2014). https://doi.org/10.1364/OL.39.000323 OPLEDP 0146-9592 Google Scholar
M. M. Vogel et al.,
“Single-layer resonant-waveguide grating for polarization and wavelength selection in Yb:YAG thin-disk lasers,”
Opt. Express, 20 4024
(2012). https://doi.org/10.1364/OE.20.004024 OPEXFF 1094-4087 Google Scholar
M. A. Ahmed et al.,
“Applications of sub-wavelength grating mirrors in high-power lasers,”
Adv. Opt. Technol., 1 381
–388
(2012). https://doi.org/10.1515/aot-2012-0036 1687-6393 Google Scholar
J. J. Prentice et al.,
“Particulate reduction in PLD-grown crystalline films via bi-directional target irradiation,”
Appl. Phys. A, 125 152
(2019). https://doi.org/10.1007/s00339-019-2456-5 Google Scholar
T. C. May-Smith et al.,
“Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO2 laser for pulsed laser deposition experiments,”
Appl. Opt., 47 1767
–1780
(2008). https://doi.org/10.1364/AO.47.001767 APOPAI 0003-6935 Google Scholar
D. Depla, S. Mahieu, J. Greene,
“Sputter deposition processes,”
Handbook of Deposition Technologies for Films and Coatings, 253
–296 3rd edWilliam Andrew Publishing, Boston
(2010). Google Scholar
M. Scherer,
“Magnetron sputter-deposition on atom layer scale,”
Vak. Forsch. Prax., 21 24
–30
(2009). https://doi.org/10.1002/vipr.200900391 Google Scholar
D.-B. Douti, L. Gallais and M. Commandré,
“Laser-induced damage of optical thin films submitted to 343, 515, and 1030 nm multiple subpicosecond pulses,”
Opt. Eng., 53 122509
(2014). https://doi.org/10.1117/1.OE.53.12.122509 Google Scholar
H. Hagedorn et al.,
“Plasma assisted reactive magnetron sputtering of demanding interference filters,”
in SVC TechCon,
(2012). Google Scholar
Y. Nigara,
“Measurement of the optical constants of yttrium oxide,”
Jpn. J. Appl. Phys., 7 404
–408
(1968). https://doi.org/10.1143/JJAP.7.404 Google Scholar
A. Belosludtsev et al.,
“Correlation between stoichiometry and properties of scandium oxide films prepared by reactive magnetron sputtering,”
Appl. Surf. Sci., 427 312
–318
(2018). https://doi.org/10.1016/j.apsusc.2017.08.068 ASUSEE 0169-4332 Google Scholar
O. Stenzel et al.,
“Mixed oxide coatings for optics,”
Appl. Opt., 50 C69
–C74
(2011). https://doi.org/10.1364/AO.50.000C69 APOPAI 0003-6935 Google Scholar
E. C. Freeman and W. Paul,
“Optical constants of RF sputtered hydrogenated amorphous Si,”
Phys. Rev. B, 20 716
–728
(1979). https://doi.org/10.1103/PhysRevB.20.716 Google Scholar
C. Krankel,
“Rare-earth-doped sesquioxides for diode-pumped high-power lasers in the 1-, 2-, and 3-μm spectral range,”
IEEE J. Sel. Top. Quantum Electron, 21 250
–262
(2015). https://doi.org/10.1109/JSTQE.2014.2346618 IJSQEN 1077-260X Google Scholar
Y. Kuzminykh, A. Kahn and G. Huber,
“Nd3+ doped Sc2O3 waveguiding film produced by pulsed laser deposition,”
Opt. Mater., 28 883
–887
(2006). https://doi.org/10.1016/j.optmat.2005.09.051 OMATET 0925-3467 Google Scholar
M. Stehlík et al.,
“Beam-size effects on the measurement of sub-picosecond intrinsic laser induced damage threshold of dielectric oxide coatings,”
Appl. Opt., 60 8569
–8578
(2021). https://doi.org/10.1364/AO.433935 APOPAI 0003-6935 Google Scholar
“Lasers and laser-related equipment—test methods for laser-induced damage threshold—part 1: definitions and general principles,”
Geneva
(2011). Google Scholar
K. Ohta and H. Ishida,
“Matrix formalism for calculation of electric field intensity of light in stratified multilayered films,”
Appl. Opt., 29 1952
(1990). https://doi.org/10.1364/AO.29.001952 APOPAI 0003-6935 Google Scholar
M. Mero et al.,
“Scaling laws of femtosecond laser pulse induced breakdown in oxide films,”
Phys. Rev. B, 71 115109
(2005). https://doi.org/10.1103/PhysRevB.71.115109 Google Scholar
A. Hervy et al.,
“Electron-beam deposited materials for high-reflective coatings: femtosecond LIDT,”
in Opt. Interference Coat.,
(2013). Google Scholar
L. Gallais et al.,
“Laser-induced damage of hafnia coatings as a function of pulse duration in the femtosecond to nanosecond range,”
Appl. Opt., 50 C178
–C187
(2011). https://doi.org/10.1364/AO.50.00C178 APOPAI 0003-6935 Google Scholar
D. N. Nguyen et al.,
“The effect of annealing on the subpicosecond breakdown behavior of hafnia films,”
Proc. SPIE, 7132 71320N
(2008). https://doi.org/10.1117/12.804452 PSISDG 0277-786X Google Scholar
L. A. Emmert, M. Mero and W. Rudolph,
“Modeling the effect of native and laser-induced states on the dielectric breakdown of wide band gap optical materials by multiple subpicosecond laser pulses,”
J. Appl. Phys., 108 043523
(2010). https://doi.org/10.1063/1.3457791 JAPIAU 0021-8979 Google Scholar
B. Mangote et al.,
“A high accuracy femto-/picosecond laser damage test facility dedicated to the study of optical thin films,”
Rev. Sci. Instrum., 83 013109
(2012). https://doi.org/10.1063/1.3677324 Google Scholar
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