A thulium-aluminum co-doped calcium fluoride near-mid-infrared waveband laser crystal, a preparation method and application thereof

Abstract

The application relates to a thulium-aluminum co-doped calcium fluoride near-mid-infrared waveband laser crystal and a preparation method and application thereof. x Al y Ca 1‑x‑y F2, wherein 0.001<=x<=0.01, 0.05<=y<=0.5; the preparation method comprises the following steps: uniformly mixing and grinding TmF3, AlF3 and CaF2, and processing through a temperature rising-temperature keeping-slow temperature falling-cooling procedure in a protective gas atmosphere, so that the obtained crystal is a thulium-aluminum co-doped calcium fluoride near-mid-infrared waveband laser crystal. Compared with the prior art, the prepared near-mid-infrared waveband laser crystal can realize higher output power than that of existing fluorides, and has good application potential in aspects of 1.5 mu m and 2 mu m laser output laser materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of laser materials technology, and relates to a near-mid-infrared laser crystal and its preparation method, particularly to a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal, its preparation method, and its application. Background Technology

[0002] With the advancement of information technology, the demand for lasers in specific wavelengths is increasing. This has prompted research in related fields to shift towards high-performance lasers in new wavelength bands. Among them, near-infrared lasers have received widespread attention due to their broad applications in daily life. The infrared spectrum is generally divided into three regions: near-infrared (0.75–2.5 μm), mid-infrared (2.5–25 μm), and far-infrared (25–300 μm). Due to different application requirements, different fields have different definitions for the range of infrared wavelengths. In the laser field, the near-infrared wavelength range is generally defined as 1–5 μm. Near-infrared lasers have important applications in medicine, military, communication, and detection.

[0003] Currently, there are three main methods for realizing near-mid-infrared lasers:

[0004] 1) Activated ion-doped lasers utilize specific near-mid-infrared transitions in activated ions to prepare ion-doped laser materials such as crystals, glasses, ceramics, and optical fibers. These lasers are important choices in fields such as medicine and environmental monitoring due to their small size, high stability, and excellent beam quality.

[0005] 2) Optical parametric technology utilizes nonlinear techniques such as optical parametric oscillation, optical parametric amplification, difference frequency conversion, and sum frequency conversion to tune mature short-wavelength lasers using nonlinear materials, thereby obtaining mid-infrared lasers. For example, patent CN119395896A provides a spatial optical structure mid-infrared supercontinuum light source that uses gratings to compress pulses and combines them with fluoride optical fibers to broaden the supercontinuum spectrum. This technology extends the mid-infrared laser wavelength range through nonlinear effects (such as supercontinuum generation) and is suitable for fields such as optical communication and environmental monitoring.

[0006] 3) Semiconductor lasers achieve population inversion between the conduction and valence bands through excitation. Stimulated emission occurs when electrons at the bottom of the conduction band recombine with holes at the top of the valence band. Commonly used semiconductor lasers include InGaAsSb and AlGaAsS. For example, patent CN119354919A provides a method for detecting ethane and ethane dual gases based on a mid-infrared laser. This invention uses a DAC pin of a microcontroller to output a sawtooth scanning signal superimposed with a sinusoidal wave modulation. By adjusting the amplitude of the sawtooth scanning signal, the wavelength of the laser emission is controlled between 3344.4 nm and 3345.8 nm, simultaneously covering the absorption peaks of ethane and methane, thus achieving simultaneous detection of both ethane and ethane components. Patent CN118905417B provides a data processing system for a black phosphorus-based mid-infrared laser, relating to the field of infrared laser technology. By integrating emission, control, detection, processing, feedback, and interaction modules, it realizes the manipulation and intelligent analysis of mid-infrared laser pulses.

[0007] While optical parametric technology can utilize readily available lasers, it is costly and inconvenient to apply; semiconductor lasers also suffer from low power and poor beam quality; however, doped activated ion solid-state or fiber lasers, especially rare-earth ion doped lasers, are not only small in size and easy to use, but also stable in operation, with high output beam quality and high efficiency, and are attracting increasing attention from researchers in modern society. Summary of the Invention

[0008] Based on the deficiencies in the existing technology, the purpose of this invention is to provide a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal, its preparation method and application, wherein the laser crystal can generate new fluorescence peaks after co-doping with ions.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] One of the technical solutions of this invention provides a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal, the chemical composition of which is represented as Tm. x Al y Ca 1-x-y F2, where 0.001≤x≤0.01, 0.05≤y≤0.5; Tm represents thulium, Al represents aluminum, Ca represents calcium, and F represents fluorine.

[0011] Preferably, x = 0.005, 0.1 ≤ y ≤ 0.5, that is, the preferred chemical composition of the thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal is expressed as Tm 0.005 Al y Ca 0.995-y F2;

[0012] Furthermore, when x = 0.005 and 0.1 ≤ y ≤ 0.5, the space group of the crystal is Fm-3m, belonging to the cubic crystal system, and possessing high symmetry. Here, "F" represents a face-centered cubic lattice, meaning that atoms are distributed at the eight vertices and the centers of the six faces of the unit cell; "m-3m" indicates that the crystal possesses multiple symmetry elements, including mirror planes (m), triple rotation axes (-3), and inversion centers. The combination of these symmetry elements determines the positional relationships of atoms in the crystal and the macroscopic symmetry of the crystal. Specifically, crystals of this space group exhibit specific symmetry operations along the crystal axis, face diagonal, and volume diagonal, causing the crystal to exhibit similar structures and properties in different directions.

[0013] The second technical solution of the present invention provides a method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal, comprising the following steps:

[0014] 1) Using TmF3, AlF3, and CaF2 as raw materials, according to the chemical formula Tm x Al y Ca 1-x-y F2 calculates and weighs the required mass of each raw material; grinds the weighed raw materials thoroughly, mixes them evenly, and then puts them into a container; adds the oxygen scavenger and covers the container; the mixture is obtained.

[0015] 2) Place the mixture from step 1) in a hot field and evacuate it until the vacuum level reaches below 8 Pa. Then fill it with protective gas until the positive bias is zero. Then process it through a process of heating-holding-slow cooling-cooling. The resulting crystal is a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal.

[0016] Furthermore, the TmF3, AlF3, and CaF2 raw materials mentioned in step 1) are in the form of single crystal particles or powder, and the purity of the TmF3, AlF3, and CaF2 single crystal particles or powder is 5N. The 5N purity has less impurity content than chemically analytical grade and 4N purity raw materials, which can avoid problems such as difficulty in obtaining crystals and poor crystal quality caused by impurities reacting with the container and raw materials during the growth process.

[0017] The grinding time in step 1) is 40-60 minutes, preferably 40 minutes;

[0018] The oxygen scavenger mentioned in step 1) is PbF2, which is used to prevent the calcium fluoride raw material from being oxidized; the amount of oxygen scavenger added is 1-3% of the total mass of TmF3, AlF3 and CaF2, preferably 1%;

[0019] The container mentioned in step 1) is preferably a porous graphite crucible, and the corresponding container lid is a graphite lid;

[0020] Furthermore, the vacuuming process described in step 2) includes coarse vacuuming using a mechanical pump and fine vacuuming using a molecular pump;

[0021] The protective gas mentioned in step 2) is preferably at least one of argon or a fluorine-containing gas; specifically, the fluorine-containing gas is at least one of CF4 or HF.

[0022] The heating in step 2) is as follows: heating to 1400-1700℃ at a rate of 200-300℃ / h; the holding time is 10-15 hours to ensure complete material melting and impurity removal; the slow cooling is as follows: slowly cooling to 1000-1200℃ at a rate of 1-3℃ / h for crystal growth; the cooling is as follows: after the slow cooling crystal growth is completed, cooling to room temperature at a rate of 50-60℃ / h.

[0023] Currently, the rare earth ions that produce laser output in the near-mid-infrared range of 1.5-3.5 μm mainly include thulium (Tm), holmium (Ho), erbium (Er), and dysprosium (Dy). Compared to other rare earth ions, Tm... 3+ The ion absorption energies in the 1.5 μm and 2 μm bands match those of commonly used pumps, and the wide gain bandwidth enables the laser to be tunable. Tm 3+ Ions are composed of Tm atoms (outer electron distribution 4f) 13 6s 2 The 4f electron shell loses one electron, and the 6s electron shell loses two electrons to form Tm. 3+ The main absorption band of the ion corresponds to 3 H6→ 3 The H4 transition, with a wavelength around 800 nm, closely matches the emission wavelength of GaAsAl laser diodes. Therefore, high-power GaAsAl lasers can be used as Tm... 3+ Ion-doped laser dielectric pump source. Tm 3+ The main luminescence of ions in the near-mid-infrared band includes transitions at 1.5 μm, 2 μm, and 2.3 μm, respectively. 3 H4→ 3 F4 3 F4→ 3 H6 3 H4→ 3 H5.

[0024] In Tm 3+ In ions, 3 H4 and 3 The energy level spacing of F4 and 3 F4 and 3 The energy level spacing of H6 is relatively close, making it highly susceptible to cross relaxation (CR). The pump light then... 3H6 population pumping to 3 The H4 energy level, through a cross-relaxation process 3 H4(Tm 3+ )+ 3 H6(Tm 3+ → 3 F4(Tm 3+ )+ 3 F4(Tm 3+ ),exist 3 The F4 energy level receives twice the number of particles, and then through 3 F4→ 3 The H6 emission transition generates a 2μm laser. Through a cross-relaxation process, the theoretical quantum efficiency of the 2μm laser can reach 200%, meaning that one pump photon can generate two 2μm laser photons. Therefore, Tm 3+ High-power, high-slope-efficiency lasers have been achieved in the 2 μm wavelength range using ion-doped laser media, and these have been put into practical use. In 2007, researchers achieved similar results with Tm-doped lasers. 3+ A 1.9 μm continuous-wave laser output with an output power of 64 W and a slope efficiency of 68% was obtained in a Ge fiber containing ions. By 2010, Tm 3+ Ion-doped fiber lasers have achieved kilowatt-level output power.

[0025] Although cross-relaxation is very beneficial to Tm 3+ The laser output at 2μm ion emission has the opposite effect on 1.5μm and 2.3μm emission. Especially for 1.5μm, the lower energy level... 3 F4's lifetime relative to the upper energy level 3 H4 is an order of magnitude higher, which leads to self-termination of the 1.5μm laser. To achieve laser output at both 1.5μm and 2.3μm, a crucial approach is to suppress cross-relaxation and achieve population inversion. This is achieved by controlling the local coordination within the crystal, thereby modulating Tm. 3+ Near-mid-infrared luminescence of ions.

[0026] Disorderly distributed mixed type Tm 0.005 Al 0.1 Ca 0.895 F2 crystals, still belonging to the cubic crystal system, not only possess lower phonon energies but also allow for the modulation of Tm at the atomic, molecular, and group scales. 3+ The local coordination structure of ions introduces modulating ions Al into Tm:CaF2 crystals. 3+ When Al is an ion, 3+ and Tm 3+ All will replace Ca 2+ Grid position, on the one hand, Al 3+ Ion incorporation can improve Tm 3+The clustering state of ions enables efficient laser output; on the other hand, Al 3+ The incorporation of ions forms a mixed fluoride crystal with a disordered distribution of (Ca,Al)F2 in the form of compound components, creating a truly effective "disorder" of activating ions, which enhances the splitting between energy levels, thereby splitting new fluorescence peaks at 1.5 μm and 2 μm.

[0027] Based on the above theory, this invention develops a laser material that generates new laser wavelengths compared to existing fluorides and is more likely to achieve 1.5μm and 2μm laser output.

[0028] The third technical solution of the present invention provides an application of a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal, wherein the laser crystal serves as a gain medium for constructing a high-power near-mid-infrared laser.

[0029] Compared with the prior art, this application has at least the following improvements and beneficial effects:

[0030] Taking a specific embodiment of the present invention as an example, the present invention selects (Ca,Al)F2 as the laser crystal matrix material, and uses the temperature gradient method to increase Tm 3+ Ions are incorporated into the (Ca,Al)F2 lattice. The lower phonon energy of (Ca,Al)F2 helps reduce nonradiative transitions caused by multiphonon relaxation, which greatly improves the output efficiency of near-mid-infrared lasers. Furthermore, the disordered, mixed-type crystal structure allows for the modulation of Tm at the atomic, molecular, and group scales. 3+ The localized coordination structure of the ions forms a truly effective "disorder" activating ion, enhancing the splitting between energy levels and resulting in new fluorescence peaks at the 1.5 μm and 2 μm splitting points. Based on the above analysis, Tm 0.005 Al 0.5 Ca 0.915 F2 crystals can achieve higher output power than existing fluorides and have good application potential in laser materials for 1.5μm and 2μm laser output. Attached Figure Description

[0031] Figure 1 The thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm prepared in Example 1 0.005 Al 0.5 Ca 0.495 The room temperature absorption coefficient spectrum of F2;

[0032] Figure 2 The images show the room temperature fluorescence spectra of the thulium aluminum co-doped calcium fluoride laser crystals prepared in Examples 1-3 at (a) 1.5 μm and (b) 2 μm.

[0033] Figure 3The thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm prepared in Example 1 0.005 Al 0.5 Ca 0.495 F2 under 808nm light excitation, (a) 3 H4 and (b) 3 Fluorescence lifetime spectrum corresponding to the F4 energy level;

[0034] Figure 4 The thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm prepared in Example 2 0.005 Al 0.1 Ca 0.895 F2 under 808nm light excitation, (a) 3 H4 and (b) 3 Fluorescence lifetime spectrum corresponding to the F4 energy level;

[0035] Figure 5 The thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm prepared in Example 3 0.005 Al 0.3 Ca 0.695 F2 under 808nm light excitation, (a) 3 H4 and (b) 3 Fluorescence lifetime spectrum corresponding to the F4 energy level.

[0036] Figure 6 The thulium-doped calcium fluoride near-mid-infrared laser crystal Tm prepared in Comparative Example 1 0.005 Ca 0.995 F2 at room temperature fluorescence spectra at (a) 1.5 μm and (b) 2 μm;

[0037] Figure 7 The thulium-doped calcium fluoride near-mid-infrared laser crystal Tm prepared in Comparative Example 1 0.005 Ca 0.995 F2 under 808nm light excitation, (a) 3 H4 and (b) 3 Fluorescence lifetime spectrum corresponding to the F4 energy level; Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0039] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0040] Example 1:

[0041] A thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm 0.005 Al 0.5 Ca 0.495 F2, the preparation method of which includes the following steps:

[0042] 1) Using TmF3, AlF3, and CaF2 single crystal particles as raw materials, according to the chemical formula Tm 0.005 Al 0.5 Ca 0.495 Weigh 25g of F2, grind it thoroughly for 60.0min until it is evenly mixed, and then put it into a porous graphite crucible; add 1.25g of PbF2 as an oxygen remover to the porous graphite crucible and cover it with a round graphite lid.

[0043] 2) Place the porous graphite crucible from step 1) into a calcining furnace, evacuate the furnace to a vacuum level below 8 Pa, and then fill the furnace with argon gas as a protective atmosphere to zero positive bias. Start the heating program, increasing the temperature to 1500℃ at a rate of 200.0℃ / h, and hold for 12 hours to ensure complete melting and impurity removal. Then, slowly decrease the temperature to 1100℃ at a rate of 2.0℃ / h for crystal growth. After growth, cool to room temperature at 50.0℃ / h. The resulting crystal has good optical quality. 0.005 Al 0.5 Ca 0.495 F2 crystal, namely the thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal.

[0044] The Tm prepared in this embodiment 0.005 Al 0.5 Ca 0.495 The F2 crystal was characterized, including the determination of its room-temperature absorption coefficient, room-temperature fluorescence spectroscopy, and fluorescence lifetime. The experiments were performed using a UV-Vis-NIR spectroscopy system (Cary 5000UV / VIS / NIR) and an Edinburgh FLS1000 fluorescence spectrometer, respectively. The operating methods were all common knowledge to those skilled in the art and could be performed according to the instrument's instruction manual. The results are as follows:

[0045] like Figure 1 The image shows the prepared Tm. 0.005 Al 0.5 Ca 0.495 The room temperature absorption coefficient spectrum of sample F2 shows that it is very consistent with the emission wavelength of GaAsAl laser diode.

[0046] like Figure 2 The image shows the prepared Tm. 0.005 Al 0.5 Ca 0.495 The room temperature fluorescence spectra of the F2 sample at 1.5 μm and 2 μm show that Tm 3+ New fluorescence peaks were split at around 1420 nm and 2050 nm. Combined with the results provided in Examples 2 and 3, it can be found that the emission intensity increases with the increase of Al ion concentration.

[0047] like Figure 3 The image shows the prepared Tm. 0.005 Al 0.5 Ca 0.495 The fluorescence lifetime spectra of sample F2 under 808nm light excitation, corresponding to the emission peaks at 1.5μm (corresponding to H, the same below) and 2μm (corresponding to F, the same below), show that the sample... 3 The lifetime of the H4 level is 1.55 ms. 3 The lifetime of the F4 level is 12.3 ms.

[0048] Example 2:

[0049] A thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm 0.005 Al 0.1 Ca 0.895 F2 is prepared in the same way as in Example 1.

[0050] like Figure 2 The image shows the prepared Tm. 0.005 Al 0.1 Ca 0.895 The room temperature fluorescence spectra of the F2 sample at 1.5 μm and 2 μm show that Tm 3+ New fluorescence peaks were split at around 1420 nm and 2050 nm. Combined with the results provided in Examples 1 and 3, it can be found that the emission intensity increases with the increase of Al ion concentration.

[0051] like Figure 4 The image shows the prepared Tm. 0.005 Al 0.1 Ca 0.895 The fluorescence lifetime spectra of sample F2 under 808nm light excitation, corresponding to the emission peaks at 1.5μm and 2.3μm, show that the sample... 3 The lifetime of the H4 level is 1.05 ms. 3 The lifetime of the F4 level is 16.9 ms.

[0052] Example 3:

[0053] A thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal Tm0.005 Al 0.3 Ca 0.695 F2 is prepared in the same way as in Example 1.

[0054] like Figure 2 The image shows the prepared Tm. 0.005 Al 0.1 Ca 0.895 The room temperature fluorescence spectra of the F2 sample at 1.5 μm and 2 μm show that Tm 3+ New fluorescence peaks were split at around 1420 nm and 2050 nm. Combined with the results provided in Examples 1 and 2, it can be found that the emission intensity increases with the increase of Al ion concentration.

[0055] like Figure 5 The image shows the prepared Tm. 0.005 Al 0.3 Ca 0.695 The fluorescence lifetime spectra of sample F2 under 808nm light excitation, corresponding to the emission peaks at 1.5μm and 2.3μm, show that the sample... 3 The lifetime of the H4 level is 1.36 ms. 3 The lifetime of the F4 level is 15.19 ms.

[0056] Comparative Example 1

[0057] A thulium-doped calcium fluoride near-mid-infrared laser crystal Tm 0.005 Ca 0.995 F2 is prepared in the same way as in Example 1.

[0058] like Figure 6 The image shows the prepared Tm. 0.005 Ca 0.995 The room temperature fluorescence spectra of the F2 sample at 1.5 μm and 2 μm show that Tm 3+ There were no splitting fluorescence peaks around 1420nm and 2050nm.

[0059] like Figure 7 The image shows the prepared Tm. 0.005 Ca 0.995 The fluorescence lifetime spectra of sample F2 under 808nm light excitation, corresponding to the emission peaks at 1.5μm and 2.3μm, show that the sample... 3 The lifetime of the H4 level is 1.05 ms. 3 The lifetime of the F4 level is 18.3 ms.

[0060] 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 thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal, characterized in that, The chemical composition of the laser crystal is represented as Tm. x Al y Ca 1-x-y F2, where 0.001≤x≤0.01, 0.05≤y≤0.

5.

2. The thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 1, characterized in that, x = 0.005, 0.1 ≤ y ≤ 0.

5.

3. The thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 2, characterized in that, The space group of the crystal is Fm-3m, belonging to the cubic crystal system.

4. A method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Using TmF3, AlF3, and CaF2 as raw materials, according to the chemical formula Tm x Al y Ca 1-x-y F2 calculates and weighs the required mass of each raw material; grinds thoroughly, mixes evenly, weighs the deoxidizer, mixes it with the raw materials, and obtains a mixture. The mixture from step 1) is placed in a protective gas; then it is processed through a process of heating-holding-slow cooling-cooling to obtain a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal.

5. The method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 4, characterized in that, The grinding time described in step 1) is 40-60 min.

6. The method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 4, characterized in that, The oxygen scavenger mentioned in step 1) is PbF2; the amount of oxygen scavenger added is 1 to 3% of the total mass of TmF3, AlF3 and CaF2.

7. The method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 4, characterized in that, The protective gas mentioned in step 2) is either argon or a fluorine-containing gas; the fluorine-containing gas is either CF4 or HF.

8. The method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 4, characterized in that, The heating in step 2) is as follows: the temperature is increased to 1400-1700℃ at a rate of 200-300℃ / h; the holding time is 10-15 hours.

9. The method for preparing a thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal according to claim 4, characterized in that, The slow cooling process involves slowly cooling the temperature to 1000-1200℃ at a rate of 1-3℃ / h for crystal growth; the cooling process involves reducing the temperature to room temperature at a rate of 50-60℃ / h after the slow cooling crystal growth is completed.

10. An application of the thulium aluminum co-doped calcium fluoride near-mid-infrared laser crystal as described in any one of claims 1 to 3, characterized in that, The laser crystal serves as the gain medium for constructing high-power near-mid-infrared lasers.

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