A rare earth ion doped disordered high-entropy fluoride ultrafast laser crystal, a preparation method and application thereof

Abstract

This invention relates to a rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, its preparation method, and its applications. The disordered high-entropy laser crystal is based on Pr:CaSrBaF6 and Pr:M1M2CaSrBaF6. 12 Represented by Pr, the doping range of praseodymium (Pr) ions is 0.003–0.05 (M1 and M2 are one of the trivalent non-luminescent ions such as Y, La, Lu, Gd, and Sc). The doped rare-earth luminescent ions are not limited to Pr ions, but can also include other luminescent ions such as Yb, Nd, Er, Ho, Tm, Dy, and Tb. Examples include Pr:CaSrBaF6 and Pr:M1M2CaSrBaF6. 12 Crystalline fluorides, compared to other fluorides, possess a more disordered localized structure, enabling them to achieve... 3 H6 and 3 F2 3 F3 and 3 At F4 levels, energy level merging and overlap occur, resulting in overlapping and non-uniform broadening of fluorescence spectra. Compared with existing technologies, the crystal material of this invention enables ultra-wideband emission in the visible band of praseodymium-doped laser crystals, solving the current problem of narrow fluorescence bands in praseodymium-doped laser crystals, and accelerating the development and application of all-solid-state femtosecond ultrafast lasers in the visible band in biomedicine and optical communication.

Description

Technical Field

[0001] This invention relates to the field of laser materials technology, specifically to a rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, its preparation method, and its application. Background Technology

[0002] In recent years, solid-state ultrafast laser technology based on artificial crystals has rapidly developed towards practical application, and the exploration of novel, compact, ultrashort, and ultraintense pulse light sources has become an important research area in contemporary science and technology. Visible light lasers have significant application demands in fields such as displays, communications, biomedicine, optical sensing, spectroscopy, and high-end manufacturing. With the rapid development of these application areas, there is an urgent need for visible light laser sources with higher efficiency, better stability, and more compact structures. However, the development of femtosecond ultrafast lasers in the visible light band is relatively lagging, and related materials and devices are currently at the forefront and hot topic of international laser research. Currently, there are three main methods for visible light laser output: 1) achieving visible light laser output by frequency doubling of near-infrared lasers using a nonlinear crystal; 2) using upconversion, which is relatively simpler than nonlinear frequency doubling; and 3) obtaining visible light laser output by directly pumping a gain medium doped with activating ions (rare earth ions or transition element ions) using a diode. In recent years, with the rapid development of blue LDs, researchers in related fields internationally have turned their attention to a third way of generating visible ultrafast lasers: using rare earth ions with strong emission lines in the visible light band as gain media, and directly pumping the LD to generate visible ultrafast lasers.

[0003] Currently, visible rare earth ions are mainly concentrated in Pr 3+ Dy 3+ 、Tb 3+ and Sm 3+ Due to limitations imposed by the pump source and the laser material itself, only praseodymium ions (Pr...) can be used. 3+ Pr is a rare-earth ion that directly emits visible laser light, and its application is relatively mature. 3+ The absorption cross-section reaches 10 at approximately 440-450 nm. -19 cm 2 The order of magnitude of this wavelength range perfectly matches the emission wavelength of InGaN blue semiconductor lasers. As blue semiconductor lasers become increasingly mature, Pr... 3+ It is evident that laser research is also showing a vigorous development trend. Compared with other rare earth ions, Pr 3+ Possessing the richest visible light radiative transitions, its emission range covers important bands such as red, orange, green, and blue. Currently, the output of Pr:LiYF4 all-solid-state continuous lasers has reached nearly 10W, with a maximum laser output slope efficiency of up to 60%. Pr:LiYF4 in the 639nm band has been the first to achieve practical application. Therefore, Pr...3+ Doped laser materials are currently the most promising laser materials in the visible light band.

[0004] Ultrafast pulsed lasers, characterized by ultrashort response times and high peak power, are clearly a key area for future development in the visible light laser band. The earliest international report on ultrafast lasers in the visible light band was in 1995, when S. Ruan et al. at Imperial College London used a 476nm argon-ion laser to pump a Pr:LiYF4 laser crystal, achieving Kerr lens-mode-locked ultrafast laser output of red (639nm) and orange (607nm) light, with an output power of approximately 20mW and a pulse width of approximately 8-10ps. A year later, the same team again used the same laser material and mode-locking mechanism to achieve 400fs ultrafast laser output at 613nm, which is currently the only Pr-doped laser to achieve this. 3+ The reported femtosecond laser in visible light is also the ultrawide laser with the shortest pulse in the visible band. However, because the pump source is an argon-ion laser, this Pr... 3+ Femtosecond lasers have struggled to find practical applications. Until 2014, the University of Hamburg in Germany achieved a 16mW ultrafast red laser output (639nm) with a pulse width of 18ps in a Pr:LiYF4 laser crystal using a 480nm optically pumped semiconductor laser (2ω-OPSL) as the pump source and a semiconductor saturable absorber mirror (SESAM) as the mode-locking modulation device. In 2016, Keio University in Japan reported a visible-light ultrafast laser pumped from a Pr:LiYF4 crystal using an InGaN blue LD, with a SESAM as the mode-locking modulation device, a wavelength of 639nm, and a pulse width of 45ps. Related research institutions in my country have been conducting research on visible-light ultrafast lasers in parallel with their international counterparts. In 2016, Zhang Yuxia et al. used a blue-light LD-pumped Pr:GdLiF4 crystal to achieve self-mode-locked high-repetition-rate pulsed laser output at four different visible wavelengths, with a repetition rate of approximately 3 GHz and a pulse width of approximately 50-70 ps. This was the first time that LD-pumped all-solid-state visible ultrafast laser output had been achieved. In 2017, using the two-dimensional material MoS2 as a mode-locking modulation device, passively mode-locked lasers at three wavelengths of 522 nm, 607 nm, and 639 nm were obtained in a blue-light LD-pumped Pr:LiGdF4 crystal, with pulse widths between 25-46 ps. In 2019, Yu Haohai's team at Shandong University reported a Pr:LiLuF4 crystal Kerr lens mode-locked laser, achieving an ultrafast laser with a pulse width of 1.1 ps at a wavelength of 604 nm, which is the shortest pulsed laser output in the visible light band under semiconductor pumping. In 2022, Cai Zhiping's team at Xiamen University also used LD pumping and Pr:LiYF4 as the gain medium to achieve femtosecond laser output of Pr3+ ions in the near-infrared 915nm band for the first time. The pulse width was 451fs, the average power was 257mw, and the repetition frequency was 85.5MHz.

[0005] According to the uncertainty principle, to obtain femtosecond laser output with shorter pulse widths, a sufficiently broad fluorescence spectrum is necessary. In the last decade or so, Pr-doped lasers have been used... 3+ Research progress on visible-light ultrafast lasers has been slow, mainly due to the Pr-doped lasers used in mode-locking experiments. 3+ The fluorescence spectra of each visible light channel of laser crystals are generally narrow (FWHM is about 0.7-3nm), making it difficult to realize LD-pumped all-solid-state femtosecond ultrafast lasers. This bottleneck problem has also seriously restricted the research and development and commercialization of all-solid-state femtosecond ultrafast lasers in the visible band. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, its preparation method, and its applications, using Pr:CaSrBaF6 and Pr:M1M2CaSrBaF6 as examples. 12 As the representative.

[0007] The objective of this invention can be achieved through the following technical solution: a rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, comprising X:CaSrBaF6 or X:M1M2CaSrBaF6. 12 X is one of Pr, Yb, Nd, Er, Ho, Tm, Dy, Tb ions, with a doping range of 0.003-0.05, and M1 and M2 are one of Y, La, Lu, Gd, Sc ions.

[0008] Preferably, X is a Pr ion.

[0009] Preferably, M1 is a La ion and M2 is a Y ion.

[0010] Or, to put it another way, a rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, such as Pr:CaSrBaF6 or Pr:M1M2CaSrBaF6. 12 For example, praseodymium ions are doped in the range of 0.003-0.05 (M1 and M2 are one of the trivalent non-luminescent ions such as Y, La, Lu, Gd, and Sc). The doped rare earth luminescent ions are not limited to Pr ions, but may also include other luminescent ions such as Yb, Nd, Er, Ho, Tm, Dy, and Tb.

[0011] This invention relates to rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystals, specifically Pr:CaSrBaF6 and Pr:LaYCaSrBaF6. 12 Represented by CaSrBaF6 and LaYCaSrBaF. 12Besides possessing lower phonon energies and higher 5d level positions, which significantly reduces the probability of nonradiative transitions caused by multiphonon relaxation and the absorption of excited states in the laser upper level due to the low 5d level position, the crystal also exhibits ultra-high disordered distribution in its local structure due to the equiatomic distribution of various cations. Furthermore, we note that Pr... 3+ Two sets of lower energy levels in the ion emission bands of 600–640 nm (peak wavelengths at 607 nm and 639 nm, respectively) and 700–720 nm (peak wavelengths at 697 nm and 720 nm, respectively). 3 H6 and 3 F2 3 F3 and 3 The F4 energy levels are very close in position, as in the LiYF4 matrix. 3 H6 and 3 F2 and 3 F3 and 3 The energy level differences between the F4 levels are 255 cm⁻¹. -1 and 232cm -1 This highly disordered distribution of cations can effectively activate disordered ions, thereby achieving... 3 H6 and 3 F2 3 F3 and 3 At F4 levels, energy level merging and overlap occur, resulting in overlapping fluorescence lines and non-uniform broadening. This solves the problem of existing Pr-doped fluorescence. 3+ The key scientific challenge of narrow crystal fluorescence spectra (FWHM 0.7–3 nm) can be addressed by combining research on femtosecond laser technology in the visible light band, which holds promise for achieving all-solid-state femtosecond ultrafast laser output.

[0012] A method for preparing the above-mentioned rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal is adopted by temperature gradient growth.

[0013] Preferably, the method for preparing the rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal uses Pr:CaSrBaF6 or Pr:LaYCaSrBaF6 as the substrate. 12 As a representative, it includes the following steps:

[0014] (1) Using single crystal particles or powders of PrF3, YF3, LaF3, CaF2, SrF2 and BaF2 as raw materials, and with a doping concentration of praseodymium ions of 0.003 to 0.05, the chemical formulas are xPr:CaSrBaF6 and xPr:LaYCaSrBaF6. 12 (x ranges from 0.003 to 0.05), calculate the required mass of each raw material and weigh it accurately;

[0015] (2) Grind the weighed raw materials thoroughly to make them evenly mixed, then put them into a graphite crucible and cover the crucible with the lid;

[0016] (3) Place the graphite crucible filled with material in the hot field and evacuate it. Fill the furnace with inert gas and raise the temperature to ensure complete melting and impurity removal. Then, follow the set slow cooling program to grow the crystal. After the growth is completed, cool it to room temperature and then take out the crystal.

[0017] This invention employs a temperature gradient method to grow praseodymium-doped CaSrBaF6 and LaYCaSrBaF6. 12 The crystals are grown in an inert atmosphere. A graphite crucible with a lid is used for growth to prevent excessive evaporation of the melt at high temperatures and to prevent the entry of oxygen, which would otherwise degrade the crystal quality.

[0018] More preferably, the purity of the PrF3, YF3, LaF3, CaF2, SrF2 and BaF2 single crystal particles or powders mentioned in step (1) is 5N purity. Compared with chemically analytical grade and 4N purity raw materials, 5N purity has less impurity content, which can avoid problems such as difficulty in obtaining crystals and poor crystal quality caused by impurities reacting with crucible and raw materials during the growth process.

[0019] More preferably, the grinding in step (2) is carried out in an agate mortar for 40-60 minutes, and the mixing process can be carried out in a mixer.

[0020] More preferably, in step (2), the ground raw material is placed into a graphite crucible and the crucible is sealed with a lid to prevent the large amount of melt from evaporating at high temperature and to prevent the entry of oxygen environment, which would cause a decrease in crystal quality.

[0021] More preferably, the vacuuming in step (3) is performed by coarse vacuuming with a mechanical pump and fine vacuuming with a molecular pump, achieving a vacuum level of less than 8 Pa.

[0022] More preferably, the inert gas in step (3) is high-purity argon or a fluorine-containing atmosphere.

[0023] More preferably, the fluorine-containing atmosphere is a gas containing CF4 or HF. After the inert gas is introduced, the atmosphere is charged to zero positive bias, and the heating program is started.

[0024] More preferably, the heating rate in step (3) to ensure complete material processing and impurity removal is 100-200℃ / h, the temperature is raised to 1350-1400℃, and the holding time is 8-12h.

[0025] More preferably, the isothermal time in step (3) is 8-10 hours.

[0026] More preferably, the crucible described in step (3) is slowly cooled down using a slow cooling program of 1.5℃ / h.

[0027] More preferably, the slow cooling process described in step (3) involves slow cooling at a rate of 1.5℃ / h, with a total cooling range of 150℃.

[0028] More preferably, after the growth described in step (3) is completed, the temperature is lowered to room temperature at a rate of 5-20°C / h.

[0029] More preferably, after the growth described in step (3) is completed, the temperature is lowered to room temperature at a rate of 10-20°C / h.

[0030] An application of the above-mentioned rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, using Pr:CaSrBaF6, Pr:M1M2CaSrBaF6, etc. 12 As an example, the laser crystal described above can accelerate the research and development of visible-band all-solid-state femtosecond ultrafast lasers and their application in biomedicine and optical communication.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. This invention selects CaSrBaF6 and LaYCaSrBaF6 with equiatomic ratios and disordered distribution of various cations. 12 Besides possessing lower phonon energies and higher 5d level positions, which significantly reduce the probability of nonradiative transitions caused by multiphonon relaxation and absorption of excited states in laser upper levels due to lower 5d level positions, the highly disordered distribution of cations in crystals can effectively form disordered activating ions, thus achieving… 3 H6 and 3 F2 3 F3 and 3 At F4 levels, energy level merging and overlap occur, resulting in overlapping fluorescence lines and non-uniform broadening. This solves the problem of existing Pr-doped fluorescence. 3+ The key scientific challenge of narrow fluorescence spectra in crystals (FWHM 0.7–3 nm) can be addressed by combining research on femtosecond laser technology in the visible light band, which holds promise for achieving all-solid-state femtosecond ultrafast laser output.

[0033] 2. This invention uses Pr:CaSrBaF6 and Pr:M1M2CaSrBaF6. 12 Crystalline fluorides, compared to other fluorides, possess a more disordered localized structure, enabling them to achieve... 3 H6 and 3 F2 3 F3 and 3 The energy levels of F4 are similar and merge and overlap, resulting in the overlapping and non-uniform broadening of fluorescence spectral lines.

[0034] 3. The present invention relates to disordered high-entropy Pr:CaSrBaF6 and Pr:LaYCaSrBaF6. 12 Crystals can achieve a wider fluorescence band in the visible band than existing fluorides and are more promising laser materials for achieving all-solid-state femtosecond laser output;

[0035] 4. The crystal material of this invention can achieve ultra-wideband emission in the visible band of praseodymium ion-doped laser crystals, solving the current problem of narrow fluorescence band of praseodymium ion-doped laser crystals;

[0036] 5. The crystal material of this invention can accelerate the research and development and application of all-solid-state femtosecond ultrafast lasers, and can be applied to fields such as laser display, optical communication, deep-sea exploration and biomedicine. Attached Figure Description

[0037] Figure 1 The visible fluorescence spectrum of the praseodymium ion-doped high-entropy fluoride CaSrBaF6 crystal of this invention is shown.

[0038] Figure 2 This invention relates to praseodymium ion-doped high-entropy fluoride LaYCaSrBaF. 12 Visible fluorescence spectrum of the crystal. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0040] Example 1

[0041] 0.6% Pr:CaSrBaF6 crystals were grown using a temperature gradient method, specifically prepared by the following method:

[0042] 0.6% Pr:CaSrBaF6 crystals were grown using a temperature gradient method. 60g of the raw material was placed in a graphite crucible, which was then covered. The furnace was evacuated and filled with high-purity argon as a protective atmosphere. The temperature was increased to approximately 1350℃ at a rate of 100℃ / h and held at this temperature for 12 hours until the raw material was completely melted and impurities were thoroughly removed. Crystal growth was then carried out according to a pre-defined slow cooling program: a cooling rate of 1.5℃ / h and a cooling gradient of 150℃. After the slow cooling growth was completed, the temperature was lowered to room temperature at a rate of 15℃ / h, and the crystal was then removed. The obtained sample was cut and polished to obtain a 0.6% Pr:CaSrBaF6 crystal with good optical quality, which was then used for spectral analysis. Gaussian fitting of the 640nm red fluorescence band yielded a full width at half maximum (FWHM) of 8.67nm, demonstrating a significant spectral broadening effect compared to other matrices.

[0043] Example 2

[0044] 1% Pr:CaSrBaF6 crystals were grown using a temperature gradient method, specifically prepared by the following method:

[0045] 1% Pr:CaSrBaF6 crystals were grown using a temperature gradient method. 60g of the raw material was placed in a graphite crucible, which was then covered. The furnace was evacuated and filled with high-purity argon as a protective atmosphere. The temperature was increased to approximately 1350℃ at a rate of 100℃ / h and held at this temperature for 10 hours until the raw material was completely melted and impurities were thoroughly removed. Crystal growth was then carried out according to a pre-set slow cooling program of 1.5℃ / h with a cooling gradient of 150℃. After the slow cooling growth was completed, the temperature was lowered to room temperature at a rate of 15℃ / h, and the crystal was then removed. The obtained sample was cut and polished to obtain a 1% Pr:CaSrBaF6 crystal with good optical quality, which was then used for spectroscopic analysis.

[0046] Example 3

[0047] 0.6% Pr:LaYCaSrBaF was grown using a temperature gradient method. 12 Crystals are prepared specifically through the following methods:

[0048] 0.6% Pr:LaYCaSrBaF was grown using a temperature gradient method. 12 For crystal formation, 60g of raw material was placed in a graphite crucible, covered, and the furnace was evacuated and filled with high-purity argon as a protective atmosphere. The temperature was increased to ~1400℃ at a rate of 100℃ / h and held at this temperature for 12 hours until the raw material was completely melted and impurities were thoroughly removed. Then, crystal growth was carried out according to a pre-set slow cooling program of 1.5℃ / h with a cooling gradient of 150℃. After the slow cooling growth was completed, the temperature was lowered to room temperature at a rate of 15℃ / h, and the crystal was then removed. The obtained sample was cut and polished to obtain a 0.6% Pr:LaYCaSrBaF crystal with good optical quality. 12 The crystal was used for spectral testing. Gaussian fitting was performed on the 640nm red fluorescence band, and the full width at half maximum (FWHM) was 7.76nm, which showed a significant spectral broadening effect compared to other matrices.

[0049] Example 4

[0050] 0.6% Pr:LaLuCaSrBaF was grown using a temperature gradient method. 12 Crystals are prepared specifically through the following methods:

[0051] 0.6% Pr:LaLuCaSrBaF was grown using a temperature gradient method. 12For crystal formation, 60g of raw material was placed in a graphite crucible, covered, and the furnace was evacuated and filled with high-purity argon as a protective atmosphere. The temperature was increased to ~1400℃ at a rate of 100℃ / h and held at this temperature for 12 hours until the raw material was completely melted and impurities were thoroughly removed. Then, crystal growth was carried out according to a pre-set slow cooling program of 1.5℃ / h with a cooling gradient of 150℃. After the slow cooling growth was completed, the temperature was lowered to room temperature at a rate of 15℃ / h, and the crystal was then removed. The obtained sample was cut and polished to obtain a 0.6% Pr:LaLuCaSrBaF crystal with good optical quality. 12 Crystals are used for spectral testing.

[0052] Example 5

[0053] 0.6% Pr:LaScCaSrBaF was grown using a temperature gradient method. 12 Crystals are prepared specifically through the following methods:

[0054] 0.6% Pr:LaScCaSrBaF was grown using a temperature gradient method. 12 For crystal formation, 60g of raw material was placed in a graphite crucible, covered, and the furnace was evacuated and filled with high-purity argon as a protective atmosphere. The temperature was increased to ~1400℃ at a rate of 100℃ / h and held at this temperature for 12 hours until the raw material was completely melted and impurities were thoroughly removed. Then, crystal growth was carried out according to a pre-set slow cooling program of 1.5℃ / h with a cooling gradient of 150℃. After the slow cooling growth was completed, the temperature was lowered to room temperature at a rate of 15℃ / h, and the crystal was then removed. The obtained sample was cut and polished to obtain a 0.6% Pr:LaScCaSrBaF crystal with good optical quality. 12 Crystals are used for spectral testing.

[0055] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal, characterized in that, Including X:M1M2CaSrBaF 12 Wherein, X is one of Pr, Yb, Nd, Er, Ho, Tm, Dy, Tb ions, with a doping range of 0.003-0.05, M1 is La ion, and M2 is Y ion.

2. The rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal according to claim 1, characterized in that, X is a Pr ion.

3. A method for preparing a rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal as described in any one of claims 1 to 2, characterized in that, Growth was achieved using a temperature gradient method.

4. The method for preparing rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal according to claim 3, characterized in that, Includes the following steps: (1) Using single crystal particles or powders of PrF3, YF3, LaF3, CaF2, SrF2 and BaF2 as raw materials, calculate the required mass of each raw material according to the chemical formula based on the doping concentration of praseodymium ions of 0.003~0.05 and weigh them accurately. (2) Grind the weighed raw materials thoroughly to make them evenly mixed, then put them into a graphite crucible and cover the crucible with the lid; (3) Place the graphite crucible filled with material in the hot field and evacuate it. Fill the furnace with inert gas and raise the temperature to ensure complete melting and impurity removal. Then slowly lower the temperature to grow the crystal. After the growth is complete, lower the temperature to room temperature and then take out the crystal.

5. The method for preparing rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal according to claim 4, characterized in that, The heating rate in step (3) to ensure complete material processing and impurity removal is 100-200℃ / h, and the temperature is raised to 1350-1400℃, with a holding time of 8-12 h.

6. The method for preparing rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal according to claim 4, characterized in that, The slow cooling in step (3) is a slow cooling at a rate of 1.5℃ / h, with a cooling gradient of 150℃.

7. The method for preparing rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal according to claim 4, characterized in that, After the growth described in step (3) is completed, the temperature is lowered to room temperature at a rate of 5-20℃ / h.

8. The method for preparing rare-earth ion-doped disordered high-entropy fluoride ultrafast laser crystal according to claim 4, characterized in that, The vacuuming in step (3) involves coarse vacuuming with a mechanical pump and fine vacuuming with a molecular pump, achieving a vacuum level of less than 8 Pa.

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