An erbium-doped borophosphate laser glass with low nonlinear refractive index

Abstract

The present application provides a kind of low nonlinear refractive index of refractive index coefficient in 1.24x10 ‑ 13 The erbium-doped borophosphate laser glass with low nonlinear refractive index of less than 0.0000001 esu contains, in terms of weight percentage, P2O5: 55.4-82.4%; Yb2O3: 2.4-25.4%; Al2O3: 3.5-9.9%; R2O: 1.5-9.0%; La2O3: 0.4-3.3%; Nb2O5: 0.5-2.7%; MgO: 0.6-2.3%; Er2O3: 0.3-1.4%. The laser glass has the characteristics of low nonlinear refractive index, which can avoid the self-focusing effect of laser beam during laser service and improve the laser power density that the laser glass can withstand. The present application can be widely used in the fields of laser radar, optical communication, laser ranging, medical equipment, etc.

Description

Technical Field

[0001] This invention relates to a gain medium for a 1.5µm band solid-state laser, which can be used as a third communication window and an eye-safe laser, specifically to an erbium-doped boron phosphate laser glass with a low nonlinear refractive index. Background Technology

[0002] Laser technology is an indispensable tool for human survival and development in an intelligent society. Among various types of lasers, solid-state lasers are characterized by stable performance, small size, and compact design. 3+ Ion solid-state lasers can generate laser beams of ~1.5µm or ~3µm. Among them, the 1.5µm band laser can be used as a third communication window and an eye-safe laser, and has been widely used in optical communication, laser ranging and other fields.

[0003] Lasers based on erbium phosphate laser glass gain media have attracted widespread attention due to their advantages over other 1.5μm lasers (such as semiconductor lasers and lamp-pumped Er:YAG lasers), including smaller size, higher efficiency, better stability, and lower cost. Because Er... 3+ Ions have weak absorption in the visible light band, while Yb 3+ The ions exhibit strong absorption in the 800–1100 nm wavelength range, and Yb 3+ Ions to Er 3+ Yb has a high ion energy transfer efficiency, so it is often used. 3+ Co-doping is used as a sensitizer. In the early stages of laser technology development, flash lamps were used as laser pump sources, with emission spectra distributed in a wide range from the visible to the near-infrared region. To better absorb the pump light, Nd:2-doped lasers were often used as sensitizers. 3+ Cr 3+ Ion co-doping as Yb 3+ The second sensitized ion. In the 1990s, the advent of semiconductor lasers further advanced the research on erbium lasers.

[0004] Solid-state lasers are increasingly being developed towards miniaturization and integration, and high-efficiency, high-output-power LD-pumped erbium phosphate glass microchip lasers align perfectly with this trend. When the length of the solid-state gain working medium is reduced to below 1 mm, the longitudinal mode spacing can potentially exceed the gain bandwidth, thus enabling single-mode operation. Single-mode microchip lasers are not only simple to manufacture but also easy to implement, requiring only close-range, unfocused semiconductor laser pumping. Single-mode microchip lasers will have significant application value in high-capacity, long-distance fiber optic communication, coherent optical transmission, lidar, laser ranging, laser sensing, laser medicine, and optical storage.

[0005] Existing literature and patents on erbium-doped laser glasses lack attention to their low nonlinear refractive index performance. A low nonlinear refractive index in laser glasses can prevent laser beam self-focusing during laser operation, increasing the laser power density that the glass can withstand. To address the trend towards high-power solid-state lasers, reducing the nonlinear refractive index coefficient of the gain medium is crucial. Currently, patents CN107021619A from SCHOOT and JP6107430A from HOYA report nonlinear refractive index coefficients greater than 1.28 × 10⁻⁶. -13 esu. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a refractive index coefficient of 1.24 × 10⁻⁶. -13 Erbium-doped boron phosphate laser glass with a low nonlinear refractive index below ESU.

[0007] The solution adopted by the present invention to solve the above-mentioned technical problems is: (1) A low nonlinear refractive index erbium-doped boron phosphate laser glass, the composition of which is expressed as a weight percentage, contains: P2O5: 55.4-82.4%; Yb2O3: 2.4-25.4%; Al2O3: 3.5-9.9%; R2O: 1.5-9.0%; La2O3: 0.4-3.3%; Nb2O5: 0.5-2.7%; MgO: 0.6-2.3%; Er2O3: 0.3-1.4%, wherein the R2O is one or more of Li2O, Na2O, and K2O.

[0008] (2) The erbium-doped boron phosphate laser glass with low nonlinear refractive index according to (1) also contains, by weight percentage: B2O3: 0-10.5%.

[0009] (3) A low nonlinear refractive index erbium-doped boron phosphate laser glass, the composition of which is expressed as a weight percentage as follows: P2O5: 55.4-82.4%; Yb2O3: 2.4-25.4%; Al2O3: 3.5-9.9%; R2O: 1.5-9.0%; La2O3: 0.4-3.3%; Nb2O5: 0.5-2.7%; MgO: 0.6-2.3%; Er2O3: 0.3-1.4%; B2O3: 0-10.5%, wherein the R2O is one or more of Li2O, Na2O, and K2O.

[0010] (4) An erbium-doped boron phosphate laser glass with low nonlinear refractive index according to any one of (1) to (3), wherein the composition is expressed as a weight percentage, wherein: B2O3 / P2O5 is 0 to 19.0%, preferably B2O3 / P2O5 is 6.5% to 19.0%, and more preferably B2O3 / P2O5 is 12.0% to 18.0%.

[0011] (5) An erbium boron phosphate laser glass with low nonlinear refractive index according to any one of (1) to (3), wherein the composition is expressed as a weight percentage, wherein: Er2O3 / Yb2O3 is 2.4% to 10.7%, preferably Er2O3 / Yb2O3 is 2.4% to 4.8%, and more preferably Er2O3 / Yb2O3 is 2.5% to 4.5%.

[0012] (6) An erbium-doped boron phosphate laser glass with low nonlinear refractive index according to any one of (1) to (3), wherein the composition is expressed as a weight percentage, wherein: P2O5: 55.4-70.9%, preferably P2O5: 56.0-66.1%; and / or Yb2O3: 10.0-25.0%, preferably Yb2O3: 19.0-25.0%; and / or Al2O3: 4.1-6.8%, preferably Al2O3: 4.7-5.7%; and / or R2O: 1 0.5-3.5%, preferably R2O: 1.5-3.0%; and / or La2O3: 0.4-0.8%; and / or Nb2O5: 0.5-0.9%; and / or MgO: 1.2-1.8%, preferably MgO: 1.4-1.7%; and / or Er2O3: 0.5-1.3%; and / or B2O3: 3.0-10.5%, preferably B2O3: 7.3-10.4%, wherein the R2O is one or more of Li2O, Na2O, and K2O.

[0013] (7) An erbium-doped boron phosphate laser glass with low nonlinear refractive index according to any one of (1) to (3), wherein: Li2O: 0 to 3.1%, preferably Li2O: 0 to 2.5%, more preferably Li2O: 0.4 to 2.0%; and / or Na2O: 0.9 to 4.2%, preferably Na2O: 0.9 to 1.2%; and / or K2O: 0 to 7.7%.

[0014] (8) An erbium-doped boron phosphate laser glass with a low nonlinear refractive index according to any one of (1) to (3), wherein the nonlinear refractive index coefficient n2 of the laser glass is ≤1.24×10 -13 esu, preferably n2≤1.21×10 -13 esu.

[0015] (9) An erbium-doped boron phosphate laser glass with a low nonlinear refractive index according to any one of (1) to (3), wherein the radiation lifetime τ of the laser glass is... rad ≥4.3 ms, preferably τ rad ≥6.7 ms, further optimization of τ rad ≥7.4 ms; and / or effective fluorescence linewidth Δλ eff ≤4.50×10 -6 cm, preferably Δλ eff ≤4.11×10 -6 cm, further optimization of Δλ eff ≤3.96×10 -6 cm; and / or stimulated emission cross section ≥0.95×10 -20 cm 2 Preferably, the stimulated emission cross section is ≥0.99×10 -20 cm 2 .

[0016] (10) A laser containing an erbium-doped boron phosphate laser glass with a low nonlinear refractive index as described in any one of (1) to (9).

[0017] The beneficial effects of this invention are as follows: The laser glass of this invention features a low nonlinear refractive index, which avoids the self-focusing effect of the laser beam during laser service and increases the laser power density that the laser glass can withstand. This invention rationally selects the component content of the laser glass, optimizing the weight ratio between the network-forming components B2O3 and P2O5 in the glass matrix to control the network structure. By controlling the weight ratio between the sensitizer Yb2O3 and the radiative transition center Er2O3, the energy transfer between the sensitizer and the radiative transition center is optimized, effectively optimizing the nonlinear refractive index of the laser glass and effectively controlling the radiation lifetime and effective fluorescence linewidth. This results in a laser glass with a low nonlinear refractive index, excellent radiation lifetime, narrow effective fluorescence linewidth, and high stimulated emission cross-section, exhibiting excellent laser performance and suitable for use in 1.5 µm band solid-state lasers. This invention does not contain oxides such as lead, cadmium, or arsenic, and the production process generates no waste, making it environmentally friendly and widely applicable in fields such as lidar, optical communication, laser ranging, and medical equipment. Detailed Implementation

[0018] The composition and function of the glass of the present invention will be described in detail below. It should be noted that, unless otherwise specified, the content of each component is expressed as a weight percentage (wt%) relative to the total amount of laser glass material converted into oxide composition. Here, "converted into oxide composition" means that when the oxides, composite salts, and hydroxides used as raw materials for the laser glass of the present invention decompose and transform into oxides upon melting, the total weight of such oxides is taken as 100%.

[0019] Unless otherwise specified in the specific context, the numerical ranges listed herein include upper and lower limits. "Above" and "below" include endpoint values ​​and all integers and fractions within the range, not limited to the specific values ​​listed when the range is defined. The term "about" as used herein means that recipes, parameters, and other quantities and characteristics are not, and need not be, exact, and may be approximate and / or larger or lower if necessary, reflecting tolerances, conversion factors, and measurement errors, etc. The term "and / or" as used herein is inclusive; for example, "A; and / or B" means only A, or only B, or both A and B.

[0020] Alkali metal oxides (R₂O) are the outer layer of the glass network, which can reduce the viscosity of glass during high-temperature melting and lower the melting temperature. However, excessive introduction of alkali metal oxides will increase the tendency of glass crystallization and phase separation, and reduce the chemical stability of the glass. Too little will result in excessively high glass viscosity, making it difficult to melt. In this invention, the R₂O content ranges from 1.5% to 9.0%, preferably from 1.5% to 3.5%, and more preferably from 1.5% to 3.0%. The alkali metal oxides (R₂O) present in this invention include one or more of Li₂O, Na₂O, and K₂O, wherein the content of Li₂O is 0% to 3.1%, preferably 0% to 2.5%, and more preferably 0.4% to 2.0%; the content of Na₂O is 0.9% to 4.2%, preferably 0.9% to 1.2%; and the content of K₂O is 0% to 7.7%.

[0021] Alkaline earth metal oxide MgO can improve the physicochemical properties of glass, but excessive amounts can make glass melting difficult. In this invention, the MgO content ranges from 0.6% to 2.3%, preferably from 1.2% to 1.8%, and more preferably from 1.4% to 1.7%.

[0022] Al₂O₃, as a network intermediate, exhibits both glass-forming and glass-modifying properties. Al can form aluminum-oxygen tetrahedra with double-bonded oxygen atoms in glass, improving the glass's thermal and chemical stability. However, excessive Al₂O₃ reduces the stimulated emission cross-section and coefficient of thermal expansion of the laser glass. In this invention, the Al₂O₃ content ranges from 3.5% to 9.9%, preferably 4.1% to 6.8%, and more preferably 4.7% to 5.7%.

[0023] P2O5, as the main glass network former, has a content ranging from 55.4% to 82.4% in this invention, preferably from 55.4% to 70.9%, and more preferably from 56.0% to 66.1%.

[0024] B2O3 also acts as a glass network forger, but excessive B2O3 can make the glass difficult to melt. In this invention, the content is 0–10.5%, preferably 3.0–10.5%, and more preferably 7.3–10.4%.

[0025] The laser emission center of the glass in this invention is Er. 3+ The Er2O3 content has a significant impact on the laser performance of laser glass. Increasing the content can increase the number of luminescent centers, but excessive Er2O3 will cause concentration quenching, leading to a decrease in stimulated emission cross-section and radiation lifetime. In this invention, the Er2O3 content is 0.3% to 1.4%, preferably 0.5% to 1.3%.

[0026] Yb 3+ As a sensitizer in laser glass, it is responsible for transferring the energy of the pump light to Er. 3+ Increased Yb₂O₃ content is beneficial for energy transfer to Er. 3+ While the transfer of Yb₂O₃ is facilitated, excessive introduction of Yb₂O₃ increases the nonlinear refractive index coefficient of the glass and causes concentration quenching. Simultaneously, it increases the glass melting viscosity, making glass melting difficult. In this invention, the content of the sensitizer Yb₂O₃ ranges from 2.4% to 25.4%, preferably 10.0% to 25.0%, and more preferably 19.0% to 25.0%.

[0027] The present invention introduces a small amount of La2O3 to improve the chemical stability of glass and reduce its coefficient of thermal expansion. However, La 3+ The strong field, large radius, and tendency to accumulate reduce the glass formation range, and when introduced in large quantities, the glass is prone to crystallization. In this invention, the La2O3 content ranges from 0.4% to 3.3%, preferably from 0.4% to 0.8%.

[0028] Nb2O5 has the effect of improving the dispersion coefficient and improving the crystallization performance of glass. In this invention, the Nb2O5 content ranges from 0.5% to 2.7%, preferably from 0.5% to 0.9%.

[0029] The inventors of this invention discovered through repeated experiments and research that: Adjusting the weight ratio of B2O3 to P2O5 components in the glass network forging system can influence the glass network structure. The nonlinear refractive index of glass describes its refractive index change under strong electric or optical fields, and is affected by the internal ionic polarizability. Introducing a certain amount of B2O3 into phosphate can form BPO4 groups within the glass, transforming the original layered (or chain-like) structure of the phosphate into a framework structure. This makes the glass network structure more stable, and the ions within the glass less susceptible to polarization under applied electric or optical fields. Consequently, the refractive index of the glass is less prone to change under these fields, achieving better nonlinear refractive index performance. Furthermore, the ratio of B2O3 to P2O5 components in the glass composition can influence the performance of a laser with an Er emission center. 3+ The field strength of the surrounding environment has an impact, directly affecting its effective fluorescence linewidth Δλ. eff By increasing the B2O3 / P2O5 ratio, the effective fluorescence linewidth Δλ of the laser glass can be increased. eff The effect of gradually narrowing the fluorescence linewidth is achieved, but an excessively high B2O3 / P2O5 ratio can lead to a decrease in the effective fluorescence linewidth Δλ. eff The range is gradually broadened. In this invention, the B2O3 / P2O5 value is limited to 0–19.0%, preferably 6.5%–19.0%, and more preferably 12.0%–18.0%. Within the B2O3 / P2O5 range defined in this invention, the nonlinear refractive index coefficient n2 of the obtained laser glass is ≤1.24×10⁻⁶. -13 esu, preferably n2≤1.21×10 -13 esu. Within the B2O3 / P2O5 range defined in this invention, the obtained laser glass has Δλ eff ≤4.50×10 -6 cm, preferably Δλ eff ≤4.11×10 -6 cm, further optimization of Δλ eff ≤3.96×10 -6 cm.

[0030] Adjusting the weight ratio of the sensitizer Yb₂O₃ component to the laser emission center Er₂O₃ component in the glass formulation can improve the sensitization effect of Yb₂O₃. 3+ To Er 3+ The energy transfer process is affected. By reducing the Er₂O₃ / Yb₂O₃ ratio, the radiation lifetime τ of the laser glass is reduced. rad Gradually increasing, but due to Yb 3+ If the value of Er2O3 / Yb2O3 is too high, resulting in an excessively low value of Yb, it will cause Yb 3+ Concentration quenching, radiation lifetime τ radThe Er₂O₃ / Yb₂O₃ ratio is reduced. In this invention, the Er₂O₃ / Yb₂O₃ value is limited to 2.4%–10.7%, preferably 2.4%–4.8%, and more preferably 2.5%–4.5%. Within the Er₂O₃ / Yb₂O₃ range defined in this invention, the obtained laser glass exhibits a lower τ. rad ≥4.3 ms, optimized τ rad ≥6.7 ms, further optimized τ rad ≥7.4 ms.

[0031] The testing methods for various indicators of the laser glass of this invention are as follows: [Nonlinear Refractive Index] Based on the relationship between the nonlinear refractive index and the dispersion characteristics of laser materials, the nonlinear refractive index is calculated as shown in formula (1): (1) Among them, υ d n is the dispersion coefficient of the material; d The refractive index at 587.6 nm. The nonlinear refractive index obtained from the above formula is in units of 10. -13 esu.

[0032] This paper uses a V-prism refractometer to measure the refractive index n of glass at 587.6 nm. d The refractive index n at 486.1 nm F The refractive index n at 656.3 nm C .

[0033] The dispersion coefficient is obtained through υ d It can be obtained through the following formula (2): υ d =(n d -1) / (n F -n C (2) The test method is based on the national standard: Test Methods for Colorless Optical Glass Part 1: Refractive Index and Dispersion Coefficient; Standard No.: GB / T 7962.1-2010.

[0034] Currently, the nonlinear refractive index parameter receives relatively little attention in laser glass research papers and patent literature. Under the influence of strong electric fields and strong light, the refractive index of glass changes; this refractive index, dependent on the electric field strength, is called the nonlinear refractive index. When a strong laser passes through, the laser glass, acting as a gain medium, exhibits a nonlinear effect, causing self-focusing of the laser beam, damaging its brightness, and even destroying the laser glass itself. The smaller the nonlinear refractive index coefficient, the weaker the self-focusing effect, and the higher the laser power density the laser glass can withstand. The nonlinear refractive index is a crucial and non-negligible property of laser gain media. In this patent, through the design of the glass's B, P, Yb, and Er components, an erbium laser glass with low nonlinear refractive index, high stimulated emission cross-section, narrow effective fluorescence linewidth, and excellent radiation lifetime is obtained.

[0035] [Laser performance—effective fluorescence linewidth, radiation lifetime, stimulated emission cross-section]

[0036] Laser performance can be measured using Judd-Oflet and Fuchtbauer-Ladenburg theories. Discussions of these theories can be found in E. Desurvire, Erbium Doped Fiber Amplifiers, John Wiley and Sons (1994). Both theories evaluate laser performance based on fluorescence emission curves. This paper uses a FluoroLog-3 fluorescence spectrometer to measure the fluorescence emission spectrum excited at 970 nm.

[0037] For erbium laser glasses, the radiation lifetime and cross-sectional laser performance of stimulated absorption and emission are typically calculated using Judd-Oflet theory combined with Fuchtbauer-Ladenburg theory. A detailed description is provided in Hu et al., *Laser Glass and Its Applications*, Shanghai Science and Technology Press (2019), which is incorporated herein by reference. MD Shinn et al., *Optical transitions of Erbium*... 3+ The ions of fluorozirconate glass are also described in Physical Review B (1983), which is cited and incorporated herein by reference.

[0038] The radiation lifetime is determined by the following formula (3): (3) Where A[(S,L)J;(S',L'}J'] is the spontaneous emission relaxation rate of the electric dipole from the initial state (S,L)J to the final state (S',L')J', which can be calculated by Judd-Oflet theory.

[0039] The stimulated emission cross section is determined by the following formula (4): (4) Where I(λ) is the fluorescence emission curve obtained by fluorescence spectrophotometer, and A is the spontaneous emission transition probability between the upper and lower energy levels.

[0040] The effective linewidth Δλ of fluorescence at the emission peak value eff It is represented by the following formula (5): (5) The erbium-doped boron phosphate laser glass with low nonlinear refractive index of the present invention has the following properties: 1) The nonlinear refractive index coefficient n2 of the borophosphate laser glass of the present invention is ≤1.24×10⁻⁶. -13 esu, preferably n2≤1.21×10 -13 esu.

[0041] 2) The radiation lifetime τ of the borophosphate glass of the present invention rad ≥4.3 ms, preferably τ rad ≥6.7 ms, further optimization of τ rad ≥7.4 ms.

[0042] 3) The effective fluorescence linewidth Δλ of the borophosphate glass of the present invention eff ≤4.50×10 -6 cm, preferably Δλ eff ≤4.11×10 -6 cm, further optimization of Δλ eff ≤3.96×10 -6 cm.

[0043] 4) The stimulated emission cross section of the borophosphate glass of the present invention is ≥0.95×10⁻⁶. -20 cm 2 Preferably, the stimulated emission cross section is ≥0.99×10 -20 cm 2 .

[0044] [Manufacturing method of erbium-doped boron phosphate laser glass]

[0045] The method for preparing laser glass according to the present invention includes the following steps: weighing the oxide raw materials according to the weight percentage of the components in the present invention, mixing them thoroughly, adding them to a quartz crucible, melting them at 1200-1300°C while paying attention to atmosphere control, clarification, homogenization, and cooling; pouring the molten glass into a metal mold preheated to about 400°C to form it, and circulating cooling air is introduced to ensure that the glass does not crystallize; placing the formed glass and the metal mold together in an annealing furnace for heat preservation and annealing, and then cooling it with the furnace after power is turned off to obtain laser glass with narrow effective fluorescence linewidth, excellent radiation lifetime, high stimulated emission cross section, and low nonlinear refractive index coefficient.

[0046] [Laser]

[0047] The laser glass obtained by this invention can be used to manufacture lasers.

[0048] Example

[0049] To further clarify and illustrate the technical solution of the present invention, the following non-limiting embodiments are provided. While the embodiments of the present invention have made considerable efforts to ensure numerical accuracy, some errors and deviations must be taken into account.

[0050] In these embodiments E1 to E39, the laser glasses shown in Tables 1 to 4 were obtained using the manufacturing method of the present invention. Furthermore, the characteristics of each laser glass were measured using the testing method described in the present invention, and the measurement results are shown in Tables 1 to 4.

[0051] Table 1

[0052] Table 2

[0053] Table 3

[0054] Table 4

Claims

1. An erbium-doped boron phosphate laser glass with low nonlinear refractive index, characterized in that, Its composition, expressed as a weight percentage, contains: P2O5: 55.4–82.4%; Yb2O3: 15.2–25.4%; Al2O3: 3.5–9.9%; R2O: 1.5–9.0%; La2O3: 0.4–3.3%; Nb2O5: 0.5–2.7%; MgO: 0.6–2.3%; Er2O3: 0.3–1.4%, with the sum of all components being 100%. The Er2O3 / Yb2O3 ratio is 2.4%–9.2%. The R2O is one or more of Li2O, Na2O, and K2O. The radiation lifetime τ of the laser glass is... rad ≥6.9 ms.

2. The erbium-doped boron phosphate laser glass with low nonlinear refractive index according to claim 1, characterized in that, Its components are expressed as a weight percentage, and it also contains: B2O3: 0-10.5%.

3. An erbium-doped boron phosphate laser glass with low nonlinear refractive index, characterized in that, Its composition, expressed as a weight percentage, consists of P2O5: 55.4–82.4%; Yb2O3: 15.2–25.4%; Al2O3: 3.5–9.9%; R2O: 1.5–9.0%; La2O3: 0.4–3.3%; Nb2O5: 0.5–2.7%; MgO: 0.6–2.3%; Er2O3: 0.3–1.4%; and B2O3: 0–10.5%, with the sum of all components being 100%. The Er2O3 / Yb2O3 ratio is 2.4%–9.2%. The R2O is one or more of Li2O, Na2O, and K2O. The radiation lifetime τ of the laser glass is... rad ≥6.9ms.

4. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its components are expressed as a weight percentage, of which: B2O3 / P2O5 is 0 to 18.0%.

5. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its components are expressed as a weight percentage, of which: B2O3 / P2O5 is 6.5% to 18.0%.

6. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its components are expressed as a weight percentage, of which: B2O3 / P2O5 is 12.0% to 18.0%.

7. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its composition is expressed as a weight percentage, of which: Er2O3 / Yb2O3 is 2.4% to 4.8%.

8. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its components are expressed as a weight percentage, of which: Er2O3 / Yb2O3 is 2.5% to 4.5%.

9. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its components are expressed as weight percentages, wherein: P2O5: 55.4–70.9%; and / or Yb2O3: 15.2–25.0%; and / or Al2O3: 4.1–6.8%; and / or R2O: 1.5–3.5%; and / or La2O3: 0.4–0.8%; and / or Nb2O5: 0.5–0.9%; and / or MgO: 1.2–1.8%; and / or Er2O3: 0.5–1.3%; and / or B2O3: 3.0–10.5%, wherein the R2O is one or more of Li2O, Na2O, and K2O.

10. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, Its components are expressed as weight percentages, wherein: P2O5: 56.0–66.1%; and / or Yb2O3: 19.0–25.0%; and / or Al2O3: 4.7–5.7%; and / or R2O: 1.5–3.0%; and / or MgO: 1.4–1.7%; and / or B2O3: 7.3–10.4%, wherein the R2O is one or more of Li2O, Na2O, and K2O.

11. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, in: Li2O: 0–3.1%; and / or Na2O: 0.9–4.2%; and / or K2O: 0–7.7%.

12. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, in: Li2O: 0–2.5%; and / or Na2O: 0.9–1.2%.

13. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, in: Li2O: 0.4–2.0%.

14. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, The nonlinear refractive index coefficient n2 of the laser glass is ≤1.24×10⁻⁶. -13 esu.

15. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, The nonlinear refractive index coefficient n2 of the laser glass is ≤1.21×10⁻⁶. -13 esu.

16. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, The radiation lifetime τ of the laser glass rad ≥7.4 ms; and / or effective fluorescence linewidth Δλ eff ≤4.50×10 -6 cm; and / or stimulated emission cross section ≥0.95×10 -20 cm 2 .

17. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, The effective fluorescence linewidth Δλ of the laser glass eff ≤4.11×10 -6 cm; and / or stimulated emission cross section ≥0.99×10 -20 cm 2 .

18. A low nonlinear refractive index erbium-doped boron phosphate laser glass according to any one of claims 1 to 3, characterized in that, The effective fluorescence linewidth Δλ of the laser glass eff ≤3.96×10 -6 cm.

19. A laser, characterized in that, An erbium-doped boron phosphate laser glass with a low nonlinear refractive index as described in any one of claims 1 to 18.

Images