CN110277723B - Method for optimizing heat-related transient response of high-power fiber laser - Google Patents

Abstract

The invention discloses a method for optimizing the thermal-related transient response of a high-power fiber laser. The transient heat conduction equation is used to simulate and calculate the time curve of the temperature of a semiconductor laser under a certain output power; considering the temperature drift of the output center wavelength of the semiconductor laser, the output of the semiconductor laser is calculated to obtain the output of the semiconductor laser. The function of the center wavelength versus time; then, according to the calculated function of the output wavelength of the semiconductor laser versus time, the classical fiber laser rate equations are modified, and the time curve of the output power of the high-power fiber laser given the relevant parameters is calculated to obtain Transient response time; optimize and modify relevant parameters and calculate to shorten the transient response time of high-power fiber laser output power.

Description

A method for optimizing the thermally dependent transient response of high-power fiber lasers

technical field

The invention belongs to the field of high-power fiber lasers, and in particular relates to a method for optimizing the thermal-related transient response of high-power fiber lasers.

Background technique

High-power fiber lasers are widely used in medical, industrial processing, and military and defense fields due to their compact structure, high conversion efficiency, and good beam quality. In practical applications, the transient response of high-power fiber lasers often affects the performance of fiber lasers. For example, in the laser welding process, due to insufficient laser power in the initial period, the penetration of the welded material is insufficient, which increases the defective rate of welding.

Wei T, Li J, Zhu J in "Theoretical and experimental study of transientresponse of the Yb-doped fiber amplifier[J]" (Chinese Optics Letters, 2012, 10(4):040605.) researched about Yb-doped fiber Transient response problem of amplifier output laser pulse. J.Zhu, T.Yang et al. studied the thermal effect of semiconductor lasers and their output center wavelength shift in the article "Reliability study of high brightness multiple single emitterdiode lasers[C]" (Diode Laser Technology&Applications XIII, 2015.). Regarding the optimization of the transient response of the continuous fiber laser caused by the temperature drift of the pump wavelength, no relevant research has been seen yet.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for optimizing the thermal-related transient response of a high-power fiber laser, which solves the problem of optimizing the transient response of the continuous fiber laser caused by the temperature drift of the pump wavelength.

The technical solution for realizing the purpose of the present invention is: a method for optimizing the thermally related transient response of a high-power fiber laser, the steps are as follows:

Step 1. Use the transient heat conduction equation to simulate and calculate the time curve of the temperature of the semiconductor laser under a given output power;

Step 2. Considering the temperature drift of the output center wavelength of the semiconductor laser, the function of the output center wavelength of the semiconductor laser versus time is obtained;

Step 3. According to the function of the output center wavelength of the semiconductor laser versus time, correct the classical fiber laser rate equations, and calculate the time curve of the output power of the high-power fiber laser given the relevant parameters to obtain the transient response time;

Step 4: Optimize and modify relevant parameters and calculate, thereby shortening the transient response time of the output power of the high-power fiber laser.

Compared with the prior art, the present invention has the following significant advantages:

(1) For the first time, the optimization problem of transient response of CW fiber lasers caused by the temperature drift of pump wavelength is proposed.

(2) For the first time, a method to optimize the relevant parameters is proposed, and the transient response time of the continuous fiber laser caused by the temperature drift of the pump wavelength is effectively shortened.

Description of drawings

FIG. 1 is a flow chart of the method for optimizing the thermally related transient response of a high-power fiber laser according to the present invention.

FIG. 2 is a time curve diagram of the output power of the high-power fiber laser before parameter optimization in Embodiment 1 of the present invention.

FIG. 3 is a time curve diagram of the output power of the high-power fiber laser after the cooling temperature is individually optimized in Embodiment 1 of the present invention.

4 is a time curve diagram of the output power of the high-power fiber laser after individually optimizing the doping concentration of the gain fiber core in Embodiment 1 of the present invention.

FIG. 5 is a time curve diagram of the output power of the high-power fiber laser after the length of the gain fiber is individually optimized in Embodiment 1 of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

For the 976nm wavelength semiconductor-pumped ytterbium-doped fiber laser, the output wavelength of the semiconductor pump source will drift with its temperature, which affects the absorption of the pump light by the ytterbium-doped fiber (YDF). Since ytterbium ions have an absorption peak at 976 nm, at room temperature (20°C), the output center wavelength of the semiconductor laser is generally less than 976 nm. With the gradual increase of the internal temperature of the semiconductor laser during operation, the output center wavelength of the semiconductor laser gradually drifts to the absorption peak. around 976nm. During this process, the absorption rate of YDF to the pump light gradually increased, resulting in a gradual increase in the output power of the fiber laser, that is, a slow transient response of the fiber laser.

1, the method for optimizing the thermally related transient response of a high-power fiber laser according to the present invention solves the problem of optimizing the transient response of the continuous fiber laser caused by the temperature drift of the pump wavelength. The specific steps are as follows:

Step 1. Use the transient heat conduction equation to simulate and calculate the time curve of the temperature of the semiconductor laser under a given output power;

Step 2. Considering the temperature drift of the output center wavelength of the semiconductor laser, obtain the function λ _P (t) of the output center wavelength of the semiconductor laser against time:

λ _P (t)=λ ₀ +(T(t)-T ₀ )β.

Among them, T ₀ is the cooling temperature, λ ₀ is the output wavelength of the semiconductor laser at the cooling temperature T ₀ , β is the temperature drift coefficient of the output center wavelength of the semiconductor laser, and T(t) is the temperature of the semiconductor laser.

Step 3. According to the function of the output center wavelength of the semiconductor laser versus time, correct the classic fiber laser rate equations, and calculate the time curve of the output power of the high-power fiber laser given the relevant parameters to obtain the transient response time.

Among them, the classic fiber laser rate equations are modified, and the modified fiber laser rate equations are as follows:

和

分别为正向和反向传输的包层光功率，

和

分别为正向和反向传输的信号光功率；N₂(z，t)为上能级粒子数数密度，N是增益光纤纤芯中Yb³⁺的掺杂浓度；Γ_p和Γ_s分别是泵浦光和信号光的填充因子；σ_ap(t)和σ_ep(t)分别是泵浦光的吸收和发射截面面积；σ_as和σ_es分别是信号光的吸收和发射截面面积；α_P和α_P分别是泵浦光和信号光的损耗系数；τ是上能级粒子寿命；λ_s为信号光波长；λ_p(t)是半导体激光器输出中心波长对时间的函数；h是普朗克常量；c是真空中光速，A_c是纤芯截面积；In the formula,

and

are the cladding optical power of forward and reverse transmission, respectively,

and

are the signal optical powers transmitted in the forward and reverse directions, respectively; N ₂ (z, t) is the number density of the upper energy level, N is the doping concentration of Yb ³⁺ in the core of the gain fiber; Γ _p and Γ _s , respectively is the filling factor of pump light and signal light; σ _ap (t) and σ _ep (t) are the absorption and emission cross-sectional areas of pump light, respectively; σ _as and σ _es are the absorption and emission cross-sectional areas of signal light, respectively; α _P and α _P are the loss coefficients of pump light and signal light, respectively; τ is the lifetime of the upper-level particle; λ _s is the wavelength of the signal light; λ _p (t) is the function of the output center wavelength of the semiconductor laser against time; h is Planck's constant; c is the speed of light in vacuum, A _c is the core cross-sectional area;

For a fiber laser oscillator with a gain fiber length L, the boundary conditions are expressed as

P _s ⁺ (0)=R ₁ ·P _s ⁻ (0),

P _s ⁻ (L)=R ₂ ·P _s ⁺ (L).

为总泵浦功率；R₁和R₂分别是高反光栅和低反光栅的反射率。in,

is the total pump power; R ₁ and R ₂ are the reflectances of the high-inversion and low-inversion gratings, respectively.

The transient response in the step 3 is caused by the temperature drift of the output center wavelength of the semiconductor laser.

Step 4: Optimize and modify relevant parameters and calculate, thereby shortening the transient response time of the output power of the high-power fiber laser. The relevant parameters include the cooling temperature T ₀ , the gain fiber length L and the doping concentration of Yb ³⁺ in the gain fiber core.

Increase the cooling temperature T ₀ and observe the output power curve of the fiber laser. When the output power of the fiber laser increases to more than 95% of the stable power, record the transient response time of the output power of the high-power fiber laser at this time.

Increase the gain fiber length L and observe the output power curve of the fiber laser. When the output power of the fiber laser increases to more than 95% of the stable power, record the transient response time of the output power of the high-power fiber laser at this time.

Increase the doping concentration N of Yb ³⁺ in the core of the gain fiber, and observe the output power curve of the fiber laser. When the output power of the fiber laser increases to more than 95% of the stable power, record the transient response of the output power of the high-power fiber laser at this time. time.

Example 1

The method for optimizing the thermally related transient response of a high-power fiber laser according to the present invention, the steps are as follows:

Step 1. Use the transient heat conduction equation to simulate and calculate the time curve of the semiconductor laser temperature under 100W output power;

Step 2. Considering the temperature drift of the output center wavelength of the semiconductor laser, the function of the output center wavelength of the semiconductor laser versus time is obtained;

Step 3. According to the function of the output center wavelength of the semiconductor laser versus time, correct the classical fiber laser rate equations, and calculate the time curve of the output power of the high-power fiber laser given the relevant parameters to obtain the transient response time;

Step 4: Optimize and modify relevant parameters and calculate, thereby shortening the transient response time of the output power of the high-power fiber laser.

Before parameter optimization: cooling temperature T ₀ =20°C; gain fiber core doping concentration N=4.5×10 ²⁵ m ^-3 ; gain fiber length L=20m. The time curve of the output light intensity of the high-power fiber laser is shown in Figure 2. The time required for the power to increase to 95% and 97% of the stable power is 4.6s and 8.5s, respectively.

Optimize the cooling temperature individually: change the cooling temperature to T ₀ =25°C, other parameters remain unchanged, the output light intensity time curve of the high-power fiber laser is shown in Figure 3, and the power is required to increase to 95% and 97% of the stable power The times are 0.22s and 1.1s, respectively.

Doping concentration of individual gain fiber core: Change the doping concentration of gain fiber core to other parameters unchanged. The output light intensity time curve of high-power fiber laser is shown in Figure 4. It is required to increase to 95% of the stable power. The time is less than 0.1s, and the time required to reach 97% of the stable power is 0.22s, respectively.

Optimize the length of the gain fiber separately: change the length of the gain fiber to L=30m, and keep other parameters unchanged. The time curve of the output light intensity of the fiber laser is shown in Figure 5. The time required for the power to increase to 95% and 97% of the stable power is both. less than 0.1s.

To sum up, the present invention can effectively shorten the transient response time of the high-power continuous fiber laser caused by the temperature drift of the pump wavelength.

Claims (6)

1. a method for optimizing the thermally related transient response of a high-power fiber laser, characterized in that the steps of the method are as follows: Step 1. Use the transient heat conduction equation to simulate and calculate the time curve of the temperature of the semiconductor laser under a given output power; Step 2. Considering the temperature drift of the output center wavelength of the semiconductor laser, the function of the output center wavelength of the semiconductor laser versus time is obtained; Step 3. According to the function of the output center wavelength of the semiconductor laser versus time, correct the classical fiber laser rate equations, and calculate the time curve of the output power of the high-power fiber laser given the relevant parameters to obtain the transient response time; Step 4. Optimize and modify relevant parameters and calculate, thereby shortening the transient response time of the output power of the high-power fiber laser; In step 2, the function λ _P (t) of the output center wavelength of the semiconductor laser to time is expressed as λ _P (t)=λ ₀ +(T(t)-T ₀ )β Among them, T ₀ is the cooling temperature, λ ₀ is the output wavelength of the semiconductor laser at the cooling temperature T ₀ , β is the temperature drift coefficient of the output center wavelength of the semiconductor laser, and T(t) is the temperature of the semiconductor laser; In step 3, the classic fiber laser rate equations are modified, and the modified fiber laser rate equations are as follows:

In the formula,

and

are the cladding optical power of forward and reverse transmission, respectively,

and

are the signal optical powers transmitted in the forward and reverse directions, respectively; N ₂ (z,t) is the number density of the upper energy level, N is the doping concentration of Yb ³⁺ in the core of the gain fiber; Γ _p and Γ _s are respectively Fill factor of pump light and signal light; σ _ap (t) and σ _ep (t) are the absorption and emission cross-sectional areas of pump light, respectively; σ _as and σ _es are the absorption and emission cross-sectional areas of signal light, respectively; α _P and α _s are the loss coefficients of pump light and signal light, respectively; τ is the lifetime of the upper-level particle; λ _s is the wavelength of the signal light; λ _P (t) is the function of the output center wavelength of the semiconductor laser against time; Runck's constant; c is the speed of light in vacuum, A _c is the core cross-sectional area; For a fiber laser oscillator with a gain fiber length L, the boundary conditions are expressed as

in,

is the total pump power; R ₁ and R ₂ are the reflectances of the high-inversion and low-inversion gratings, respectively. 2 . The method for optimizing the thermally related transient response of a high-power fiber laser according to claim 1 , wherein the transient response in the step 3 is caused by the temperature drift of the output center wavelength of the semiconductor laser. 3 . 3. The method for optimizing the thermal-related transient response of a high-power fiber laser according to claim 1, wherein the relevant parameters in step 4 include cooling temperature T ₀ , gain fiber length L and Yb ³⁺ in the gain fiber core The doping concentration N. 4. The method for optimizing the thermally related transient response of a high-power fiber laser according to claim 3, wherein the cooling temperature T ₀ is increased, and when the output power of the fiber laser increases to more than 95% of the stable power, the recording is performed at this time. Transient response time of high power fiber laser output power. 5. the method for optimizing high-power fiber laser thermal-related transient response according to claim 3, is characterized in that: increase gain fiber length L, when fiber laser output power increases to more than 95% of stable power, record this time Transient response time of high power fiber laser output power. 6. The method for optimizing the thermally related transient response of a high-power fiber laser according to claim 3, wherein: the doping concentration N of ^Yb in the core of the gain fiber is improved, and when the output power of the fiber laser increases to a stable power 95% or more, record the transient response time of the output power of the high-power fiber laser at this time.

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