CN108004593B - Method for improving fluorescence output efficiency of erbium-ytterbium co-doped laser crystal - Google Patents

Abstract

The invention belongs to the technical field of laser crystals, and relates to a method for improving the fluorescence output efficiency of an erbium-ytterbium co-doped laser crystal by utilizing OH^‑The easy incorporation of ions into the rare earth borate host crystal, and OH^‑Vibration frequency and Er of ion³⁺Of ions⁴I_11/2And⁴I_13/2the fact that the energy levels are closely spaced allows OH^‑Ion transfer through radiationless energy to Er³⁺Ion from⁴I_11/2Energy level and other particles which are transited to higher energy level through excited state absorption and the like are rapidly transferred to⁴I_13/2Energy level, effective reduction of Er³⁺Is/are as follows⁴I_11/2Life of energy level, increase⁴I_13/2The population ratio of the energy level is increased, thereby effectively increasing Er³⁺/Yb³⁺The fluorescence output intensity and efficiency of the co-doped rare earth borate crystal in the wave band of 1.5-1.6 mu m lay a foundation for the high-efficiency laser output of the crystal.

Description

Method for improving fluorescence output efficiency of erbium-ytterbium co-doped laser crystal

The technical field is as follows:

the invention belongs to the technical field of laser crystals, and relates to a method for improving the fluorescence output efficiency of an erbium-ytterbium co-doped laser crystal, in particular to a method for improving the fluorescence output efficiency of a laser crystal of erbium-ytterbium co-doped rare earth borate in a waveband of 1.5-1.6 mu m, wherein OH in the rare earth borate crystal is utilized^-The vibration frequency of the ions (about 2500-3600 cm)^-1) And Er³⁺Of ions⁴I_11/2And⁴I_13/2energy level separation (energy difference about 3300 cm)^-1) Close to, OH^-Ions can transfer energy through radiationless energy to Er³⁺Ion from⁴I_11/2Energy level is rapidly transferred to⁴I_13/2Energy level, effective reduction of Er³⁺Is/are as follows⁴I_11/2Life of energy level, increase⁴I_13/2The population ratio of the energy level, and then the Er content is effectively improved³⁺/Yb³⁺The fluorescence output intensity and efficiency of the co-doped rare earth borate crystal in the wave band of 1.5-1.6 mu m lay a foundation for the high-efficiency laser output of the crystal.

Background art:

the 1.5-1.6 mu m wave band laser has important application value in various fields due to the unique physical properties. Firstly, the wave band is far away from the absorption peak of the main components of the atmosphere, and has strong penetration capacity to smoke and fog, and the transmission ranging effect has obvious advantages. Secondly, the band corresponds to the lowest loss window in the optical fiber and can be well matched and compatible with the current communication network system. In addition, the wave band laser is highly safe to human eyes and is easy to realize high-sensitivity signal guidance and detection. Based on the characteristics and advantages, the laser with the wave band of 1.5-1.6 microns has important application value in the fields of remote sensing detection, optical communication, laser radar, medical treatment, military and the like.

At present, laser operation with a wave band of 1.5-1.6 μm is obtained, and the most effective technical scheme is a laser with a 0.98 μm wave band LD (laser diode) pumping erbium-ytterbium co-doped solid medium. Using Yb³⁺And Er³⁺The characteristic of energy level interval matching enables the particles to be effectively distributed to Er through resonance energy transfer and radiationless transition^3+_4I_13/2And (3) realizing particle number turnover by multiple states, and directly obtaining laser output with a wave band of 1.5-1.6 mu m. At present, only a 1.5-1.6 mu m solid laser based on phosphate glass has higher product level in erbium-ytterbium co-doped laser medium. However, the glass matrix generally has the significant defects of low laser damage resistance threshold, poor thermal conductivity and the like, and the high-energy laser output is difficult to realize, which seriously limits the application of the laser with the wave band of 1.5-1.6 μm. Compared with glass substrates, single crystal substrates have more advantages in terms of thermal properties, but have the disadvantage thatThe phonon energy of the crystal is small.

In the erbium-ytterbium co-doped laser host crystal, the rare earth borate crystal has higher effective phonon energy, and is the most promising 1.5-1.6 mu m laser crystal for realizing industrial application at present. But because of Er³⁺The ion has rich energy level structure, when Er^{3 +}/Yb³⁺When the co-doping is carried out in a high phonon energy matrix, complex energy transfer and energy level transition processes exist in the system. Er³⁺/Yb³⁺In co-doping systems other than Yb^3+_2F_5/2To Er^3+_4I_11/2Energy transfer of energy level and reverse energy transfer, secondary energy transfer, excited state absorption, co-ordinated up-conversion, multiphoton relaxation processes and the like also exist. Transition of energy levels makes erbium ion⁴I_11/2Relatively long energy level lifetime, resulting from Yb³⁺Ion direction Er³⁺The reverse energy transfer process of the ions is enhanced, and⁴I_11/2long energy level lifetime of Er also enhances Er³⁺The up-conversion process of (2) can obviously reduce the pumping efficiency of the pumping source, so that the slope efficiency of the crystal outputting 1.5-1.6 mu m laser is reduced, and the practical requirement is difficult to meet.

The invention content is as follows:

the invention aims to overcome the defects in the prior art and seeks to design and provide a method for improving the fluorescence output efficiency of an erbium-ytterbium co-doped laser crystal by utilizing OH^-The easy incorporation of ions into the rare earth borate host crystal, and OH^-The vibration frequency of the ions (about 2500-3600 cm)^-1) And Er³⁺Of ions⁴I_11/2And⁴I_13/2energy level separation (energy difference about 3300 cm)^-1) Close facts to the fact that OH^-Ion transfer through radiationless energy to Er³⁺Ion from⁴I_11/2Energy levels and other transitions to higher energy levels (e.g. via excited state absorption, etc.)⁴F_9/2、⁴S_3/2、⁴F_7/2Etc.) to be rapidly transferred to⁴I_13/2Energy level, effective reduction of Er³⁺Is/are as follows⁴I_11/2Life of energy level, increase⁴I_13/2The population ratio of the energy level is increased, thereby effectively increasing Er³⁺/Yb³⁺The fluorescence output intensity and efficiency of the co-doped rare earth borate crystal in the wave band of 1.5-1.6 mu m lay a foundation for the high-efficiency laser output of the crystal.

In order to achieve the purpose, the specific process of the invention is as follows:

(1) growing erbium ytterbium codoped borate laser crystal, controlling OH in the crystal^-Ion content:

firstly, Er is synthesized by adopting a standard high-temperature solid-phase reaction method_xYb_yCa₄Re_1-x-yO(BO₃)₃Crystal growth raw material, in which Re is Y, Gd or Lu, x is 0.01-0.03, Y is 0.18-0.25, in the synthesis process of crystal growth raw material, H is used₃BO₃Replace B in the prior art₂O₃To increase OH content in the crystal growth raw material^-The content of Er is 99.99 percent of the purity of the raw material₂O₃(erbium oxide) Yb₂O₃Ytterbium (O) and H₃BO₃(boric acid), CaCO₃(calcium carbonate) and Re₂O₃The solid-phase reaction formula is as follows:

xEr₂O₃+yYb₂O₃+(1-x-y)Re₂O₃+6H₃BO₃+8CaCO₃→2 Er_xYb_yCa₄Re_1-x-yO(BO₃)₃+8CO₂+9H₂O

the raw materials are fully mixed, then are placed in a platinum crucible to be sintered for 10 hours in a vacuum atmosphere at 950 ℃, are fully ground again and then are tabletted,

calcining for 8 hours at 1050 ℃ in a vacuum atmosphere to finish the preparation of the crystal growth raw material;

secondly, the crystal growth is carried out by using a standard Czochralski method (Czochralski method) crystal growth furnace and an iraurite crucible, high-purity nitrogen is adopted as the protective gas of the crystal growth, the crystal growth speed is 0.6mm/h, the crystal growth rotating speed is 12rpm, and the final size of the crystal growth is phi 20 multiplied by 60mm³Cutting and polishing the grown crystal into a crystal sample for spectrum test, and annealing the crystal sample for spectrum test at 1000 ℃ for 12 hours in a tubular furnace simultaneously filled with nitrogen and water vapor;

(2) testing the infrared spectrum of the crystal sample obtained in the step (1) by using a Fourier transform infrared spectrometer, and calculating OH in the crystal by using the following formula^-Absorption coefficient alpha of ion at infrared characteristic peak_OHTo analyze OH in the crystal^-Content of ions:

wherein l is the sample thickness (in cm), T₀The maximum infrared transmittance of the crystal sample, and T is the transmittance of the crystal sample at a characteristic peak.

The invention utilizes OH^-The ion-regulated erbium-ytterbium co-doped laser crystal has fluorescence output intensity and efficiency in a wave band of 1.5-1.6 microns, and the specific process is as follows: first use Yb³⁺The absorption band of the ions is in the 900-fold 1100nm wave band, and the ions can be effectively coupled with the emission wavelength of the current commercial high-power InGaAs LD pumping source through the Yb^3+_2F_5/2Energy level and Er^3+_4I_15/2Energy transfer between energy stages (Yb)^3+_2F_5/2+Er^3+_4I_15/2→Yb^3+_2F_7/2+Er^3_4I_11/2) Indirectly improve the pumping efficiency; then based on OH^-And Er^{3 +_4}I_11/2Phonon-assisted energy transfer between energy levels to improve Er³⁺From pump energy level⁴I_11/2Returning to metastable energy level⁴I_13/2The non-radiative transition rate is increased, so that the excited state absorption is inhibited, the fluorescence emission intensity and efficiency of the 1.5-1.6 mu m wave band are effectively improved, and high-efficiency laser output is realized.

Compared with the prior art, the invention makes full use of the easy bonding of borate crystal into OH^-The characteristics of ions only need to reasonably control the synthesis, growth and annealing processes of crystal raw materials to control OH^-Of ionsContent, no need of additionally introducing other deactivation ions, effective guarantee of crystal quality not affected, low preparation cost, simple process, convenient operation, and effective reduction of Er³⁺Ion(s)⁴I_11/2Energy level lifetime, and then due to⁴I_11/2Long energy level lifetime, resulting from Yb³⁺Ion direction Er³⁺Enhanced reverse energy transfer process of ions, and Er³⁺The up-conversion process of (a) enhances the problem, significantly enhancing the pumping efficiency of the pump source.

Description of the drawings:

FIG. 1 is the OH of the present invention^-Ion-regulated enhanced Er³⁺/Yb³⁺A principle schematic diagram of a fluorescence output operation mechanism of a 1.5-1.6 mu m waveband of the co-doped rare earth borate crystal.

FIG. 2 is OH in the IR spectrum of a sample of Er, Yb: YCOB crystals according to an example of the present invention^-The change chart of the ion absorption coefficient, wherein X is the infrared spectrum of the crystal sample grown by adopting the embodiment; y is the infrared spectrum of the crystal sample grown without the example.

FIG. 3 is a fluorescence property test chart of a sample of Er, Yb: YCOB crystal of the present invention at a wavelength band of 1.5-1.6 μm, wherein the insets are a fluorescence decay curve and a fluorescence lifetime of the crystal at 1530nm, and X is an infrared spectrum of the crystal sample grown by using the example; y is the infrared spectrum of the crystal sample grown without the example.

The specific implementation mode is as follows:

the invention is further illustrated by the following examples in conjunction with the accompanying drawings.

Example (b):

in this example, Er is used to form Er: Yb: YCa₄O(BO₃)₄Taking the crystal as an example, firstly, according to the molar ratio: nEr₂O₃: nYb₂O₃:nY₂O₃:nH₃BO₃:nCaCO₃Weighing erbium oxide, ytterbium oxide, yttrium oxide, boric acid and calcium carbonate with the purity of 99.99 percent according to the weight ratio of 0.03:0.2:0.77:6:8, fully mixing the raw materials, placing the mixture into a platinum crucible, sintering the mixture for 10 hours at 950 ℃ in a vacuum atmosphere, fully grinding the mixture again, and tabletting the ground mixtureCalcining for 8 hours at 1000 ℃ in vacuum atmosphere to finish the preparation of the crystal growth raw material, wherein the high-temperature solid-phase chemical reaction equation is as follows: 0.03Er₂O₃+0.2Yb₂O₃+0.77 Y₂O₃+6H₃BO₃+8CaCO₃→2Er_0.03Yb_0.2Ca₄Y_0.77O(BO₃)₃+8CO₂+9H₂O; then utilizing a crystal growth furnace and an iraurite crucible in a Czochralski method to carry out crystal growth, adopting high-purity nitrogen as crystal growth protective gas, wherein the crystal growth speed is 0.6mm/h, the crystal growth rotating speed is 12rpm, and the final crystal growth size is phi 20 multiplied by 60mm³Cutting and polishing the crystal sample for the spectrum test, and annealing the crystal sample for the test at 1000 ℃ for 12 hours in a tube furnace simultaneously filled with nitrogen and water vapor; then, a Fourier transform infrared spectrometer is used for testing the infrared spectrum of the crystal sample, and the OH in the crystal is calculated and calculated by the following formula^-Absorption coefficient alpha of ion at infrared characteristic peak_OH：

Wherein l is the sample thickness (in cm), T₀The maximum infrared transmittance of the crystal sample is shown, T is the transmittance of the crystal sample at a characteristic peak, the test result is shown in figure 2, and the infrared spectrum is 3550cm as can be seen from figure 2^-1The characteristic absorption peak of O-H exists nearby, particularly, the characteristic absorption peak of O-H is very obvious when the crystal sample grown by the embodiment is adopted, and the strength of the characteristic absorption peak of O-H is obviously reduced in the infrared spectrum of the crystal sample grown by the embodiment without being adopted; through calculation, OH in the crystal samples adopting the scheme and the crystal samples not adopting the scheme is found^-The absorption coefficients of the ions at the infrared characteristic peak are respectively alpha_OH＝0.31cm^-1And alpha_OH＝0.18cm^-1The OH in the rare earth borate crystal grown by the scheme is explained^-The concentration of ions increases and the absorption coefficient increases significantly.

In this example, a 980nm LD was used as an excitation source, and a near field was usedThe infrared fluorescence spectrometer tests the fluorescence spectrum of the grown crystal at 1400-1650nm band, the result is shown in figure 3, a digital storage oscilloscope is adopted to test the fluorescence lifetime of the crystal sample at 1530nm wavelength, and the oscilloscope records the fluorescence attenuation signal of the sample; comparison of FIG. 2 with different OH groups^-Fluorescence properties of crystal samples with an absorption coefficient of ions, fluorescence near 1550nm corresponding to Er³⁺Ion(s)⁴I_13/2→⁴I_15/2Transition of energy level, OH^-Ion absorption coefficient of alpha_OH＝0.31cm^-1The fluorescence intensity and fluorescence lifetime of the crystal sample are obviously higher than alpha near 1550nm_OH＝0.18cm^-1The above experimental results show that due to OH^-Vibration frequency and Er³⁺Is/are as follows⁴I_11/2And⁴I_13/2the energy level intervals are very close, and Er can be effectively promoted³⁺Ion(s)⁴I_11/2→⁴I_13/2Radiationless transition rate between energy levels, realization of⁴I_11/2Deactivation, lowering of energy level⁴I_11/2Energy level lifetime to allow population of more particles⁴I_13/2Energy level, and further improve the fluorescence emission intensity and efficiency of the crystal in a 1.5-1.6 mu m wave band.

Claims (2)

1. A method for improving the fluorescence output efficiency of an erbium-ytterbium co-doped laser crystal is characterized by comprising the following specific processes:

(1) growth of Er: Yb: YCa₄O(BO₃)₄Crystal: firstly, according to the molar ratio: nEr₂O₃:nYb₂O₃:nY₂O₃:nH₃BO₃:nCaCO₃Weighing erbium oxide, ytterbium oxide, yttrium oxide, boric acid and calcium carbonate with the purity of 99.99 percent according to the ratio of 0.03:0.2:0.77:6:8, fully mixing the raw materials, placing the raw materials in a platinum crucible, sintering the raw materials for 10 hours at 950 ℃ in a vacuum atmosphere, fully grinding the raw materials again, tabletting the raw materials, and calcining the raw materials for 8 hours at 1000 ℃ in the vacuum atmosphere to finish the preparation of crystal growth raw materials, wherein the high-temperature solid-phase chemical reaction equation is as follows: 0.03Er₂O₃+0.2Yb₂O₃+0.77Y₂O₃+6H₃BO₃+8CaCO₃→2Er_0.03Yb_0.2Ca₄Y_0.77O(BO₃)₃+8CO₂+9H₂O; then utilizing a crystal growth furnace and an iraurite crucible in a Czochralski method to carry out crystal growth, adopting high-purity nitrogen as crystal growth protective gas, wherein the crystal growth speed is 0.6mm/h, the crystal growth rotating speed is 12rpm, and the final crystal growth size is phi 20 multiplied by 60mm³Cutting and polishing the crystal sample for the spectrum test, and annealing the crystal sample for the test at 1000 ℃ for 12 hours in a tube furnace simultaneously filled with nitrogen and water vapor;

(2) testing the infrared spectrum of the crystal sample obtained in the step (1) by using a Fourier transform infrared spectrometer, and calculating OH in the crystal by using the following formula^-Absorption coefficient alpha of ion at infrared characteristic peak_OHTo analyze OH in the crystal^-Content of ions:

wherein l is the sample thickness in cm, T₀The maximum infrared transmittance of the crystal sample is shown, and T is the transmittance of the crystal sample at a characteristic peak; infrared spectrum of 3550cm^-1Having a characteristic absorption peak of O-H, OH^-The absorption coefficient of the ion at the infrared characteristic peak is alpha_OH＝0.31cm^-1。

2. The method of claim 1, wherein OH is utilized to improve the fluorescence output efficiency of the erbium ytterbium co-doped laser crystal^-The ion-regulated erbium-ytterbium co-doped laser crystal has fluorescence output intensity and efficiency in a wave band of 1.5-1.6 microns, and the specific principle is as follows: due to OH^-Vibration frequency and Er³⁺Is/are as follows⁴I_11/2And⁴I_13/2the energy level intervals are very close, and Er can be effectively promoted³⁺Ion(s)⁴I_11/2→⁴I_13/2Radiationless transition rate between energy levels, realization of⁴I_11/2Deactivation, lowering of energy level⁴I_11/2Energy level lifetime to allow population of more particles⁴I_13/2Energy level, and further improve the fluorescence emission intensity and efficiency of the crystal in a 1.5-1.6 mu m wave band.

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