Open Access
Add to BibSonomy
Abstract
Laser damage thresholds (Ith) at 1.03 µm, as well as third-order nonlinear refractive indices (n2) and two photon absorption coefficients (β) at 1.55 µm of a number of Ge-As-S glasses were measured and systematically studied. The glass with the composition Ge0.12As0.24S0.64 showed a high Ith and the maximum figure of merit (fm= n2/(β·λ)), and therefore was selected as the core material for the fabrication of a step-index fiber. A compatible glass with the composition Ge0.18As0.1S0.72 was chosen as the cladding material. Based on the dispersion calculations, the fiber with a core diameter of ∼7–10 µm was designed. The designed fiber was fabricated by a multiple step rod-in-tube method. When the fiber with a core diameter of ∼9 µm and a length of ∼13.5 cm was pumped by ∼170 fs pulses (1 MHz) at 4.5 µm, the mid-infrared supercontinuum (SC) covering 1.3–8.1 µm was generated. These results demonstrate the good potential of Ge-As-S chalcogenide fibers for producing high-brightness broadband mid-infrared SC light sources.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
High-brightness broadband supercontinuum (SC) light sources operating in the mid-infrared spectral range have received growing interest in recent years [1–10] because of their great potential in numerous applications such as optical coherence tomography, optical frequency metrology, and molecular sensing. Experiments showed that it was an efficient method to generate broadband SC by pumping a nonlinear waveguide with ultrashort pulses [1,7,11,12]. In the last decade, a variety of optical fibers and planar waveguides made of mid-infrared optical materials such as tellurite [3,13], fluoride [2,14] and chalcogenide glasses [1,4–6,8–12] have been researched to generate wide mid-infrared SC. Due to the intrinsic multiphonon absorptions of the base materials, the generated SC in tellurite and fluoride waveguides were restricted to <5 µm and <6 µm, respectively. In comparison, chalcogenide glasses possess much longer infrared cut-off edges, as well as significantly higher nonlinear refractive indices (n2) [15], which make them ideal nonlinear materials for broadband mid-infrared SC generation. Since the early report of the SC extending from 2.1 to 3.2 µm produced in an As-Se fiber at 2005 [16], the SC generated in chalcogenide waveguides has been broadened rapidly. To date, the spectral coverage of the SC generated in S, Se and Te-based chalcogenide waveguides has reached 1.5–8 µm [17], 2–14 µm [12] and 2–16 µm [4], respectively.
In most practical applications, the mid-infrared SC light sources ought to have high brightness in addition to the wide spectral coverage. For example, hyperspectral imaging and air pollution monitoring typically require the spectral density of the light source to reach the level of mW/nm, thus the average power of the light source needs to be several watts provided that the bandwidth is several microns. In 2012, Gattass et al. [18] achieved ∼565 mW SC spanning from 1.9 to 4.8 µm in an As-S fiber. That is the highest average power SC generated in chalcogenide waveguides to date. Nevertheless, it is difficult to further increase the output power of the SC due to the limitation of the laser-induced damage on the As-S material. In order to acquire the materials with superior laser damage resistance, researchers [19–22] have recently investigated the laser damage characteristics of several chalcogenide glasses, and proposed related damage mechanisms as well as possible factors that affect the laser damage threshold (Ith). It was shown that the glass with higher average bond energy tended to show higher Ith [20], which is consistent with the fact that S-based chalcogenide glasses generally have higher Ith than Se and Te-based ones. Among sulfide glasses, those containing Ge element are expected to have superior laser damage resistance because of the relatively strong bond strength of Ge-S. In this work, we measured the Ith, as well as n2 and two-photon absorption (TPA) coefficients (β) of a number of Ge-As-S glasses. Based on the optimized composition, a step-index fiber was designed and fabricated. The potential of the fiber for SC generation was also assessed experimentally and numerically.
2. Experiment
The Ge-As-S glasses were synthesized by the conventional melt-quenching method [23]. High-purity S (6N), As (6N) and Ge (5N) elemental materials were weighed and loaded into a low-OH (<5 ppm) quartz tube in a glove box, where the oxygen and water concentrations were lower than 0.1 ppm. The tube containing the raw materials was then taken out from the glove box and connected to a vacuum system. Once the pressure in the tube was lower than 10−3 Pa, it was sealed using a H2-O2 torch. After that, the tube was inserted into a rocking furnace, which was subsequently heated to 850∼900 °C and held at the temperature for 12 h. In the final stage, the tube was taken out from the rocking furnace, quenched in water and annealed near the glass transition temperature (Tg) of the formed glass inside the tube. Because commercial arsenic and sulfur usually contain trace surface oxides and carbon, respectively, the former was pre-treated at 320 °C under vacuum for 2 h to eliminate the volatile surface oxides, and the latter was pre-sublimated under vacuum to minimize the carbon content.
The laser damage and Z-Scan measurements were conducted on glass discs with both sides polished to 20/10 level (US standard MIL-PRF-13830B). The samples were examined by a homemade perspective imaging detection system and a spectrophotometer (Lambda 950, Perkin Elmer) to ensure that no visible macroscopic and microscopic scattering defects inside the glasses, respectively. In the laser damage measurement, about 2 mm thick samples were used. The edge of the sample was clamped by a sample holder to avoid thermal contact of the sample surface with the holder. The irradiation source was a femtosecond (fs) laser with a central wavelength of 1030 nm, a pulse duration of 216 fs and a repetition rate of 1 MHz. The beam had a quality factor M2 < 1.2. The diameter of the irradiation spot on the sample surface was about 43 µm. The irradiation time was 60 s. The measurement scheme is similar to that described in [22]. In the Z-Scan measurement, about 1.2 mm thick samples were used. The experimental setup was shown in Fig. 1. The light with a central wavelength of 1.55 µm, a pulse duration of ∼170 fs and a repetition rate of 10 kHz was generated by an optical parametric amplifier (OPA, Orpheus, Light Conversion). A beam splitter was used to divide the beam into a test beam and a reference beam. A pair of InGaAs detectors were used for the power detection. The linear refractive indices (n0) of the samples were measured with an ellipsometer (IR-VASE, J. A. Woollam) [23]. The optical bandgaps (Eg) were derived based on the diffuse reflectance spectra of fine glass powders recorded by the Lambda 950 spectrometer [23]. The glass transition temperatures (Tg) were determined from the calorimetric curves measured at a heating rate of 10°C/min using a differential scanning calorimeter (DSC, Q2000, TA Instruments). The attenuation curves of the fiber with a large core diameter were recorded by a Fourier transform infrared spectrophotometer (FTIR, Tensor 27, Bruker) with the assistance of an external fiber coupling stage and a HgCdTe (MCT) detector.
3. Results and discussion
Table 1 lists the Ith of investigated Ge-As-S glasses. The dS represents the departure of the chemical composition from the stoichiometry, and is calculated by dS = (1−x−y)−2x−1.5y = 1−3x−2.5y for the composition GexAsyS1−x−y. Apparently, the Ith rises rapidly with increasing dS when sulfur is deficient (dS < 0), and reaches a maximum at the stoichiometric composition (dS = 0). As the sulfur content further increases (dS > 0), the Ith drops relatively gently (see Fig. 2). Such composition dependence of the Ith is in good agreement with the evolution of the average bond energy of the glass [22]. It is worth noting that the compositions with 0 ≤ dS ≤ 5 show the Ith exceeding 30 GW/cm2, which is remarkably higher than that of As2S3 glass (∼13 GW/cm2). The high Ith of the glasses make them more suitable for the applications involving high power lasers, such as the generation of high brightness SC.
Table 1. Measured parameters for the Ge-As-S glass samples
Figures 3(a) and 3(b) show representative Z-scan data collected in closed-aperture and open-aperture conditions, respectively. To calculate the nonlinear optical parameters n2 and β, these data were fitted according to the nonlinear transmission model detailed in [24]. The obtained results are listed in Table 1. For the convenience of correlating associated parameters, the measured n0 at 1.55 µm and Eg are also summarized in the table. It shows that the glass with a higher n0 generally possesses a higher n2. This feature is in consistence with the Miller’s rule, which is typically expressed by [15,24,25]:
Fig. 3. Z-scan curves measured at 1.55 µm for Ge0.175As0.15S0.675 glass: (a) in closed aperture condition; (b) in open aperture condition.
Fig. 4. Correlations between optical parameters in Ge-As-S glasses: (a) χ(3) vs ((n02−1)/(4π))4; (b) n2 vs n0.
Considering the high Ith and the optimum fm, the glass with the composition Ge0.12As0.24S0.64 (Tg=215 °C) was chosen as the core glass to design a nonlinear optical fiber for SC generation. Initial tests indicated that the composition Ge0.18As0.1S0.72 (Tg=214 °C) with a lower n0 had a matching fiber drawing temperature (∼330 °C), and therefore was selected as the cladding material. The measured dispersion of n0 for the core and cladding glasses can be described by the Sellmeier Eqs. (3) and (4), respectively.
Fig. 5. Calculated GVD of Ge0.12As0.24S0.64/Ge0.18As0.1S0.72 fibers as a function of the core diameter.
The designed fiber was fabricated by the multiple step rod-in-tube approach that was detailed in [28]. The obtained fiber has a core diameter of ∼9 µm and a cladding diameter of ∼200 µm (see the inset of Fig. 6). A fiber with a larger core diameter of ∼74 µm was also fabricated for the loss measurement using the FTIR system. The losses of the fiber determined by the cut-back method are presented in Fig. 6. The fiber shows a background loss of about 1 dB/m. The relatively high losses around 2.9 µm, 4.1 µm and 4.9 µm are caused by the absorptions of impurities marked in the figure. These impurities could be eliminated or greatly reduced by adding scavenging chemicals and applying elaborated distillation processes [28–30] during the preparation.
Fig. 6. Attenuation of fabricated Ge0.12As0.24S0.64/Ge0.18As0.1S0.72 fiber with a core diameter of ∼74 µm and a cladding diameter of ∼400 µm. The inset is the cross section of the final fiber that has a core dimeter of ∼9 µm.
The SC generation in the fiber was investigated with the setup shown in Fig. 7. The pump light (∼3.8–4.5 µm, 170 fs, 1 MHz) from the OPA was coupled into the fiber with a diameter of 9 µm and a length of 13.5 cm using an NA = 0.57 molded chalcogenide aspheric lens with a focal length of ∼4 mm. The output light was collected by an NA = 0.30 reflective microscope objective (RMO). Once the alignment was optimized, the beam from the RMO was imaged onto the input slit of a monochromator (MS3504i, SOL instruments) and detected using an InAs and a liquid-nitrogen-cooled MCT detectors. The monochromator was equipped with four gratings (400 l/mm, 300 l/mm, 150 l/mm and 75 l/mm) to cover the full wavelength range from ∼1 µm to 20 µm. Long pass filters were used to prevent high-order grating reflections from entering the detectors. In order to obtain high dynamic range of the SC spectrum, the output beam from the fiber was chopped at about 50 Hz and the signal was processed by a lock-in amplifier. In the measurement, the fiber was coated with high-refractive-index gallium on both sides for removing the cladding modes. Figure 8 shows the evolution of measured SC with the average power of 4.5 µm pump light, where the fiber has a relatively low loss. The spectrum is broadened rapidly with the increase of the pump power. When the average pump power was 60 mW, that was the highest power the OPA could reach, the SC spanning from ∼1.3 to ∼8.1 µm with a dynamic range of 30 dB was generated. This bandwidth is comparable to that of the broadest SC generated in As-S fibers [17,31]. The input coupling loss was estimated to be ∼3 dB, hence the light injected into the fiber was ∼30 mW, corresponding to a peak power of 176 kW. The average output power of the SC exiting the output end of the fiber was ∼9 mW. When the fiber was pumped at 3.8 µm and 4.0 µm with an average power of 60 mW, SC spectra with coverages of ∼1.6–7.3 µm and ∼1.6–7.9 µm were obtained, respectively (Fig. 9). The relatively narrow bandwidths could be associated with the higher transmission loss of the fiber at these wavelengths.
Fig. 8. Experimental (exp) and theoretical (thr) SC when the Ge0.12As0.24S0.64/Ge0.18As0.1S0.72 fiber with a diameter of 9 µm and a length of 13.5 cm was pumped by 4.5 µm (170 fs, 1 MHz) light with different average powers.
Fig. 9. Measured SC generated in the Ge0.12As0.24S0.64/Ge0.18As0.1S0.72 fiber with a diameter of 9 µm when pumped at 3.8 µm and 4.0 µm (60 mW, 170 fs, 1 MHz).
To validate the measured SC, numerical simulations were performed by solving the generalized nonlinear Schrodinger equation according to the parameters of the fiber and the pumping light used in the experiment. The nonlinear parameter (γ) was set to be 0.02 W−1m−1 provided that n2 of the glass at 4.5 µm is about 30% of that at 1.55 µm [15,27]. The dispersion was 12.9 ps/(nm·km) at 4.5 µm. The simulations show reasonable agreement with the acquired experimental spectra as shown in Fig. 8. The initial broadening of the spectrum around the pump wavelength is induced by the self-phase modulation effect. Subsequently, the soliton fission effect expands the spectrum to the longer wavelength. Meanwhile, the generated dispersive waves make the spectrum broaden towards the shorter wavelength.
4. Conclusion
The Ge-As-S glasses have the Ith (@ 1.03 µm) of 14.7–32.6 GW/cm2, the n2 of 0.79–3.10×10−14 cm2/W (@ 1.55 µm), and the β of as low as <10−13 m/W. The compositions with 0 ≤ dS ≤ 5 have the Ith exceeding 30 GW/cm2, which are remarkably higher than that of As2S3 glass (∼13 GW/cm2). The composition Ge0.12As0.24S0.64 has the maximum fm, making it more suitable for nonlinear optical devices. Using Ge0.12As0.24S0.64 as the core glass and Ge0.18As0.1S0.72 as the cladding glass, a fiber with a NA of ∼0.72 can be drawn at ∼330 °C. The core and the cladding glasses have the ZDWs of 4.48 µm and 4.42 µm, respectively. The ZDW of the fiber can be shifted to ∼3.6 µm when the core diameter was ∼7–10 µm. When the Ge0.12As0.24S0.64/ Ge0.18As0.1S0.72 fiber with a core dimeter of 9 µm and a length of ∼13.5 cm was pumped by ∼170 fs pulses (1 MHz) at 4.5 µm, SC spanning from ∼1.3 to ∼8.1 µm can be generated. These results indicate that Ge-As-S chalcogenide fibers are promising nonlinear media for producing high-brightness broadband mid-infrared SC light sources.
Funding
National Natural Science Foundation of China (61575086, 61405079, 61805109, 51772223); Priority Academic Program Development of Jiangsu Higher Education Institutions; Jiangsu Collaborative Innovation Centre of Advanced Laser Technology and Emerging Industry.
References
1. C. R. Petersen, U. Møller, I. Kubat, B. B. Zhou, S. Dupont, J. Ramsay, T. Benson, S. Sujecki, N. Abdel-Moneim, Z. Q. Tang, D. Furniss, A. Seddon, and O. Banget, “Mid-infrared supercontinuum covering the 1.4–13.3 µm molecular fingerprint region using ultra-high NA chalcogenide step-index fibre,” Nat. Photonics 8(11), 830–834 (2014). [CrossRef]
2. X. Jiang, N. Y. Joly, M. A. Finger, F. Babic, G. K. L. Wong, J. C. Travers, and P. S. Russell, “Deep-ultraviolet to mid-infrared supercontinuum generated in solid-core ZBLAN photonic crystal fibre,” Nat. Photonics 9(2), 133–139 (2015). [CrossRef]
3. H. X. Shi, X. Feng, F. Z. Tan, P. Wang, and P. Wang, “Multi-watt mid-infrared supercontinuum generated from a dehydrated large-core tellurite glass fiber,” Opt. Mater. Express 6(12), 3967–3976 (2016). [CrossRef]
4. Z. M. Zhao, B. Wu, X. S. Wang, Z. H. Pan, Z. J. Liu, P. Q. Zhang, X. Shen, Q. H. Nie, S. X. Dai, and R. P. Wang, “Mid-infrared supercontinuum covering 2.0–16 µm in a low-loss telluride single-mode fiber,” Laser Photonics Rev. 11(2), 1700005 (2017). [CrossRef]
5. C. R. Petersen, R. D. Engelsholm, C. Markos, L. Brilland, C. Caillaud, J. Trolès, and O. Bang, “Increased mid-infrared supercontinuum bandwidth and average power by tapering large-mode-area chalcogenide photonic crystal fibers,” Opt. Express 25(13), 15336–15348 (2017). [CrossRef]
6. R. A. Martinez, G. Plant, K. W. Guo, B. Janiszewski, M. J. Freeman, R. L. Maynard, M. N. Islam, F. L. Terry, O. Alvarez, F. Chenard, R. Bedford, R. Gibson, and A. I. Ifarraguerri, “Mid-infrared supercontinuum generation from 1.6 to >11 µm using concatenated step-index fluoride and chalcogenide fibers,” Opt. Lett. 43(2), 296–299 (2018). [CrossRef]
7. C. F. Yao, Z. X. Jia, Z. R. Li, S. J. Jia, Z. P. Zhao, L. Zhang, Y. Feng, G. S. Qin, Y. Ohishi, and W. P. Qin, “High-power mid-infrared supercontinuum laser source using fluorotellurite fiber,” Optica 5(10), 1264–1270 (2018). [CrossRef]
8. K. Jiao, J. M. Yao, Z. M. Zhao, X. G. Wang, N. Si, X. S. Wang, P. Chen, Z. G. Xue, Y. M. Tian, B. Zhang, P. Q. Zhang, S. X. Dai, Q. H. Nie, and R. P. Wang, “Mid-infrared flattened supercontinuum generation in all-normal dispersion tellurium chalcogenide fiber,” Opt. Express 27(3), 2036–2043 (2019). [CrossRef]
9. D. Jayasuriya, C. R. Petersen, D. Furniss, C. Markos, Z. Tang, M. S. Habib, O. Bang, T. M. Benson, and A. B. Seddon, “Mid-IR supercontinuum generation in birefringent, low loss, ultra-high numerical aperture Ge-As-Se-Te chalcogenide step-index fiber,” Opt. Mater. Express 9(6), 2617–2629 (2019). [CrossRef]
10. H. Ren, Y. Yu, C. C. Zhai, B. Zhang, A. P. Yang, K. Z. Tian, X. Feng, Z. Y. Yang, P. F. Wang, and B. Luther-Davies, “Chalcogenide glass fibers with a rectangular core for polarized mid-infrared supercontinuum generation,” J. Non-Cryst. Solids 517, 57–60 (2019). [CrossRef]
11. Y. Yu, X. Gai, P. Ma, K. Vu, Z. Y. Yang, R. P. Wang, D. Choi, S. Madden, and B. Luther-Davies, “Experimental demonstration of linearly polarized 2–10 µm supercontinuum generation in a chalcogenide rib waveguide,” Opt. Lett. 41(5), 958–961 (2016). [CrossRef]
12. T. L. Cheng, K. Nagasaka, T. H. Tuan, X. J. Xue, M. Matsumoto, H. Tezuka, T. Suzuki, and Y. Ohishi, “Mid-Infrared supercontinuum generation spanning 2.0 to 15.1 µm in a chalcogenide step-index fiber,” Opt. Lett. 41(9), 2117–2120 (2016). [CrossRef]
13. S. Kedenburg, C. Strutynski, B. Kibler, P. Froidevaux, F. Desevedavy, G. Gadret, J. C. Jules, T. Steinle, F. Morz, A. Steinmann, H. Giessen, and F. Smektala, “High repetition rate mid-infrared supercontinuum generation from 1.3 to 5.3 µm in robust step-index tellurite fibers,” J. Opt. Soc. Am. B 34(3), 601–607 (2017). [CrossRef]
14. L. Y. Yang, B. Zhang, D. H. Jin, T. Y. Wu, X. He, Y. J. Zhao, and J. Hou, “All-fiberized, multi-watt 2–5 µm supercontinuum laser source based on fluoroindate fiber with record conversion efficiency,” Opt. Lett. 43(21), 5206–5209 (2018). [CrossRef]
15. T. Wang, X. Gai, W. H. Wei, R. P. Wang, Z. Y. Yang, X. Shen, S. Madden, and B. Luther-Davies, “Systematic z-scan measurements of the third order nonlinearity of chalcogenide glasses,” Opt. Mater. Express 4(5), 1011–1022 (2014). [CrossRef]
16. L. B. Shaw, P. A. Thielen, F. H. Kung, V. Q. Nguyen, J. S. Sanghera, and I. D. Aggarwal, “IR supercontinuum generation in As-Se photonic crystal fiber,” in Advanced Solid-State Photonics (Optical Society of America, 2005), TuC5.
17. G. T. Li, X. F. Peng, S. X. Dai, Y. Y. Wang, M. Xie, L. Yang, C. F. Yang, W. Y. Wei, and P. Q. Zhang, “Highly coherent 1.5–8.3 µm broadband supercontinuum generation in a tapered As–S chalcogenide fibers,” J. Lightwave Technol. 37(9), 1847–1852 (2019). [CrossRef]
18. R. R. Gattass, L. B. Shaw, V. Q. Nguyen, P. C. Pureza, I. D. Aggarwal, and J. S. Sanghera, “All-fiber chalcogenide-based mid-infrared supercontinuum source,” Opt. Fiber Technol. 18(5), 345–348 (2012). [CrossRef]
19. S. H. Messaddeq, R. Vallée, P. Soucy, M. Bernier, M. El-Amraoui, and Y. Messaddeq, “Self-organized periodic structures on Ge-S based chalcogenide glass induced by femtosecond laser irradiation,” Opt. Express 20(28), 29882–29889 (2012). [CrossRef]
20. C. Y. You, S. X. Dai, P. Q. Zhang, Y. S. Xu, Y. Y. Wang, D. Xu, and R. P. Wang, “Mid-infrared femtosecond laser-induced damages in As2S3 and As2Se3 chalcogenide glasses,” Sci. Rep. 7(1), 6497 (2017). [CrossRef]
21. M. Xie, S. X. Dai, C. Y. You, P. P. Zhang, C. F. Yang, W. Y. Wei, G. T. Li, and R. P. Wang, “Correlation among structure, water peak absorption, and femtosecond laser ablation properties of Ge-Sb-Se chalcogenide glasses,” J. Phys. Chem. C 122(3), 1681–1687 (2018). [CrossRef]
22. M. J. Zhang, T. T. Li, Y. Y. Yang, H. Z. Tao, X. Zhang, X. Yuan, and Z. Y. Yang, “Femtosecond laser induced damage on Ge-As-S chalcogenide glasses,” Opt. Mater. Express 9(2), 555–561 (2019). [CrossRef]
23. Y. Yang, Z. Y. Yang, P. Lucas, Y. W. Wang, Z. J. Yang, A. P. Yang, B. Zhang, and H. Z. Tao, “Composition dependence of physical and optical properties in Ge-As-S chalcogenide glasses,” J. Non-Cryst. Solids 440, 38–42 (2016). [CrossRef]
24. M. J. Zhang, Z. Y. Yang, L. Li, Y. W. Wang, J. H. Qiu, A. P. Yang, H. Z. Tao, and D. Y. Tang, “The effects of germanium addition on properties of Ga-Sb-S chalcogenide glasses,” J. Non-Cryst. Solids 452, 114–118 (2016). [CrossRef]
25. R. C. Miller, “Optical second harmonic generation in piezoelectric crystals,” Appl. Phys. Lett. 5(1), 17–19 (1964). [CrossRef]
26. M. Dinu, “Dispersion of phonon-assisted nonresonant third-order nonlinearities,” IEEE J. Quantum Electron. 39(11), 1498–1503 (2003). [CrossRef]
27. B. Zhang, Y. Yu, C. C. Zhai, S. S. Qi, Y. W. Wang, A. P. Yang, X. Gai, R. P. Wang, Z. Y. Yang, and B. Luther-Davies, “High brightness 2.2–12 µm supercontinuum generation in a nontoxic chalcogenide step-index fiber,” J. Am. Ceram. Soc. 99(8), 2565–2568 (2016). [CrossRef]
28. B. Zhang, W. Guo, Y. Yu, C. C. Zhai, S. S. Qi, A. P. Yang, L. Li, Z. Y. Yang, R. P. Wang, D. Y. Tang, G. M. Tao, and B. Luther-Davies, “Low Loss, high NA chalcogenide glass fibers for broadband mid-infrared supercontinuum generation,” J. Am. Ceram. Soc. 98(5), 1389–1392 (2015). [CrossRef]
29. V. S. Shiryaev, A. P. Velmuzhov, Z. Q. Tang, M. F. Churbanov, and A. B. Seddon, “Preparation of high purity glasses in the Ga-Ge-As-Se system,” Opt. Mater. 37, 18–23 (2014). [CrossRef]
30. M. Meneghetti, C. Caillaud, R. Chahal, E. Galdo, L. Brilland, J. L. Adam, and J. Troles, “Purification of Ge-As-Se ternary glasses for the development of high quality microstructured optical fibers,” J. Non-Cryst. Solids 503–504, 84–88 (2019). [CrossRef]
31. F. Theberge, P. Mathieu, N. Thire, J. F. Daigle, B. E. Schmidt, J. Fortin, R. Vallee, Y. Messaddeq, and F. Legare, “Mid-infrared nonlinear absorption in As2S3 chalcogenide glass,” Opt. Express 24(21), 24600–24610 (2016). [CrossRef]
