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

Method for optimizing heat-related transient response of high-power fiber laser Download PDF

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CN110277723B
CN110277723B CN201910529635.3A CN201910529635A CN110277723B CN 110277723 B CN110277723 B CN 110277723B CN 201910529635 A CN201910529635 A CN 201910529635A CN 110277723 B CN110277723 B CN 110277723B
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韩志刚
闫明鉴
沈华
朱日宏
李思宇
郑云瀚
梁慧生
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Nanjing University of Science and Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
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Abstract

The invention discloses a method for optimizing heat-related transient response of a high-power fiber laser, which utilizes a transient heat conduction equation to simulate and calculate a time curve of the temperature of a semiconductor laser under certain output power; calculating to obtain a function of the output central wavelength of the semiconductor laser to time by considering the temperature drift of the output central wavelength of the semiconductor laser; then, according to the calculated function of the output wavelength of the semiconductor laser to time, correcting a classical fiber laser rate equation set, and calculating a time curve of the output power of the high-power fiber laser with given relevant parameters to obtain transient response time; and optimizing and modifying the relevant parameters and calculating to shorten the transient response time of the output power of the high-power fiber laser.

Description

Method for optimizing heat-related transient response of high-power fiber laser
Technical Field
The invention belongs to the field of high-power fiber lasers, and particularly relates to a method for optimizing heat-related transient response of a high-power fiber laser.
Background
The high-power optical fiber laser has the advantages of compact structure, high conversion efficiency, good beam quality and the like, and is widely applied to the fields of medical treatment, industrial processing, military, national defense and the like. In practical application, the transient response of the high-power fiber laser often affects the use performance of the fiber laser. For example, in the laser welding process, the laser power is insufficient in the initial period, so that the penetration of the welded material is insufficient, and the defective rate of welding is increased.
Wei T, Li J, Zhu J, in the text of the Theoretical and experimental study of the Yb-doped fiber amplifier [ J ] (Chinese Optics Letters,2012,10(4):040605.), studied the transient response problem with respect to the output laser pulses of ytterbium-doped fiber amplifiers. Zhu, T.Yang et al in the Reliability study of high brightness multiple emitter Diode lasers [ C ] (Diode Laser technologies & Applications XIII,2015.) studied the thermal effect of semiconductor lasers and the shift of the output center wavelength. No relevant research has been seen on the problem of optimizing the transient response of a continuous fiber laser caused by the temperature drift of the pump wavelength.
Disclosure of Invention
The invention aims to provide a method for optimizing heat-related transient response of a high-power fiber laser, which solves the problem of optimizing the transient response of a continuous fiber laser caused by temperature drift of a pumping wavelength.
The technical solution for realizing the purpose of the invention is as follows: the method for optimizing the thermal correlation transient response of the high-power fiber laser comprises the following steps:
step 1, simulating and calculating a time curve of the temperature of the semiconductor laser under given output power by using a transient heat conduction equation;
step 2, considering the temperature drift of the output central wavelength of the semiconductor laser, and obtaining a function of the output central wavelength of the semiconductor laser to time;
step 3, correcting a classical fiber laser rate equation set according to a function of the output center wavelength of the semiconductor laser to time, and calculating a time curve of the output power of the high-power fiber laser with given relevant parameters to obtain transient response time;
and 4, optimizing and modifying the relevant parameters and calculating, thereby shortening the transient response time of the output power of the high-power fiber laser.
Compared with the prior art, the invention has the remarkable advantages that:
(1) the transient response optimization problem of the continuous fiber laser caused by the temperature drift of the pump wavelength is put forward for the first time.
(2) The method for optimizing the relevant parameters is put forward for the first time, and the transient response time of the continuous fiber laser caused by the temperature drift of the pumping wavelength is effectively shortened.
Drawings
FIG. 1 is a flow chart of the method for optimizing the thermal-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 chart of the output power of the high power fiber laser after independently optimizing the cooling temperature in embodiment 1 of the present invention.
Fig. 4 is a time curve diagram of the output power of the high power fiber laser after the doping concentration of the core of the gain fiber is optimized separately in the embodiment 1 of the present invention.
Fig. 5 is a time chart of the output power of the high power fiber laser after the gain fiber length is optimized separately in embodiment 1 of the present invention.
Detailed Description
The present invention is described in further detail below with reference to the attached drawing figures.
For the semiconductor pump ytterbium-doped fiber laser with 976nm wavelength, the output wavelength of the semiconductor pump source will drift with the temperature, thereby affecting the absorption of the pump light by the ytterbium-doped fiber (YDF). Because ytterbium ion has an absorption peak at 976nm, the output central wavelength of the semiconductor laser is generally less than 976nm at room temperature (20 ℃), and gradually shifts to the vicinity of 976nm of the absorption peak with the gradual rise of the internal temperature of the semiconductor laser in the working process. In the process, the absorptivity of the YDF to the pump light is gradually increased, so that the output power of the fiber laser shows a gradually rising trend, namely the transient response of the fiber laser is slow.
With reference to fig. 1, the method for optimizing the thermal-related transient response of the high-power fiber laser solves the problem of optimizing the transient response of the continuous fiber laser caused by the temperature drift of the pump wavelength, and comprises the following specific steps:
step 1, simulating and calculating a time curve of the temperature of the semiconductor laser under given output power by using a transient heat conduction equation;
step 2, considering the temperature drift of the output central wavelength of the semiconductor laser, and obtaining a function lambda of the output central wavelength of the semiconductor laser to timeP(t)：
λP(t)＝λ0+(T(t)-T0)β.
Wherein, T0For cooling the temperature, λ0For semiconductor lasers at cooling temperature T0Output wavelength of time, beta being the output center of the semiconductor laserThe temperature drift coefficient of the wavelength, t (t), is the temperature of the semiconductor laser.
And 3, correcting the classical fiber laser rate equation set according to a function of the output center wavelength of the semiconductor laser to time, and calculating a time curve of the output power of the high-power fiber laser given relevant parameters to obtain transient response time.
The classical fiber laser rate equation set is corrected, and the corrected fiber laser rate equation set is as follows:
Figure BDA0002099318360000031
Figure BDA0002099318360000032
Figure BDA0002099318360000033
Figure BDA0002099318360000034
Figure BDA0002099318360000035
in the formula (I), the compound is shown in the specification,
Figure BDA0002099318360000036
and
Figure BDA0002099318360000037
forward and reverse transmitted cladding optical powers respectively,
Figure BDA0002099318360000038
and
Figure BDA0002099318360000039
forward and reverse transmitted signal optical powers, respectively; n is a radical of2(z, t) is the upper-level population density, and N is Yb in the core of the gain fiber3+The doping concentration of (a); gamma-shapedpAnd ΓsFill factors of the pump light and the signal light, respectively; sigmaap(t) and σep(t) absorption and emission cross-sectional areas of the pump light, respectively; sigmaasAnd σesAbsorption and emission cross-sectional areas of the signal light, respectively; alpha is alphaPAnd alphaPLoss coefficients of the pump light and the signal light, respectively; τ is upper level particle lifetime; lambda [ alpha ]sIs the signal light wavelength; lambda [ alpha ]p(t) is a function of semiconductor laser output center wavelength versus time; h is the Planck constant; c is the speed of light in vacuum, AcIs the core cross-sectional area;
for a fiber laser oscillator having a gain fiber length of L, the boundary condition is expressed as
Figure BDA0002099318360000041
Figure BDA0002099318360000043
Ps +(0)＝R1·Ps -(0)，
Ps -(L)＝R2·Ps +(L).
Wherein the content of the first and second substances,
Figure BDA0002099318360000042
is the total pump power; r1And R2Respectively, the reflectivity of the high and low inverse gratings.
The transient response in step 3 is caused by the temperature drift of the semiconductor laser output center wavelength.
And 4, optimizing and modifying the relevant parameters and calculating, thereby shortening the transient response time of the output power of the high-power fiber laser. Relevant parameters include the cooling temperature T0Length L of gain fiber and Yb in core of gain fiber3+The doping concentration of (c).
Increasing the cooling temperature T0And observing an output power curve of the fiber laser, and recording the transient response time of the output power of the high-power fiber laser when the output power of the fiber laser is increased to more than 95% of the stable power.
And increasing the length L of the gain optical fiber, observing an output power curve of the optical fiber laser, and recording the transient response time of the output power of the high-power optical fiber laser when the output power of the optical fiber laser is increased to more than 95% of the stable power.
Raising Yb in the core of a gain fiber3+And (3) observing an output power curve of the fiber laser, and recording the transient response time of the output power of the high-power fiber laser when the output power of the fiber laser is increased to more than 95% of the stable power.
Example 1
The invention discloses a method for optimizing heat-related transient response of a high-power fiber laser, which comprises the following steps:
step 1, simulating and calculating a time curve of the temperature of the semiconductor laser under 100W output power by using a transient heat conduction equation;
step 2, considering the temperature drift of the output central wavelength of the semiconductor laser, and obtaining a function of the output central wavelength of the semiconductor laser to time;
step 3, correcting a classical fiber laser rate equation set according to a function of the output center wavelength of the semiconductor laser to time, and calculating a time curve of the output power of the high-power fiber laser with given relevant parameters to obtain transient response time;
and 4, optimizing and modifying the relevant parameters and calculating, thereby shortening the transient response time of the output power of the high-power fiber laser.
Before parameter optimization: cooling temperature T 020 ℃ is set; gain optical fiber core doping concentration N is 4.5 multiplied by 1025m-3(ii) a The gain fiber length L is 20 m. The output light intensity time curve of the high-power optical fiber laser is shown in figure 2,the time required for the power to increase to 95% and 97% of the steady power was 4.6s and 8.5s, respectively.
Cooling temperature was optimized separately: changing the cooling temperature to T0When the other parameters are kept unchanged at 25 ℃, the output light intensity time curve of the high-power fiber laser is shown in fig. 3, and the time required for the power to increase to 95% and 97% of the stable power is respectively 0.22s and 1.1 s.
Doping concentration of single gain optical fiber core: the doping concentration of the fiber core of the gain fiber is changed, other parameters are kept unchanged, the time curve of the output light intensity of the high-power fiber laser is shown in figure 4, the time required for increasing to 95% of the stable power is less than 0.1s, and the time required for increasing to 97% of the stable power is 0.22s respectively.
Optimization of gain fiber length alone: the length of the gain fiber is changed to be L which is 30m, other parameters are kept unchanged, the time curve of the output light intensity of the fiber laser is shown in figure 5, and the time required by the power to increase to 95% and 97% of the stable power is less than 0.1 s.
In conclusion, the invention can effectively shorten the transient response time of the high-power continuous fiber laser caused by the temperature drift of the pumping wavelength.

Claims (6)

1. A method of optimizing a thermally-related transient response of a high power fiber laser, the method comprising the steps of:
step 1, simulating and calculating a time curve of the temperature of the semiconductor laser under given output power by using a transient heat conduction equation;
step 2, considering the temperature drift of the output central wavelength of the semiconductor laser, and obtaining a function of the output central wavelength of the semiconductor laser to time;
step 3, correcting a classical fiber laser rate equation set according to a function of the output center wavelength of the semiconductor laser to time, and calculating a time curve of the output power of the high-power fiber laser with given relevant parameters to obtain transient response time;
step 4, optimizing and modifying relevant parameters and calculating, thereby shortening the transient response time of the output power of the high-power fiber laser;
in step 2, the semiconductor laser outputs a function lambda of the central wavelength to the timeP(t) is represented by
λP(t)＝λ0+(T(t)-T0)β
Wherein, T0For cooling the temperature, λ0For semiconductor lasers at cooling temperature T0The output wavelength of the time, beta is the temperature drift coefficient of the output central wavelength of the semiconductor laser, and T (t) is the temperature of the semiconductor laser;
in step 3, correcting the classical fiber laser rate equation set, wherein the corrected fiber laser rate equation set is as follows:
Figure FDA0002802502690000011
Figure FDA0002802502690000012
Figure FDA0002802502690000013
Figure FDA0002802502690000014
Figure FDA0002802502690000021
in the formula (I), the compound is shown in the specification,
Figure FDA0002802502690000022
and
Figure FDA0002802502690000023
forward and reverse transmitted cladding optical powers respectively,
Figure FDA0002802502690000024
and
Figure FDA0002802502690000025
forward and reverse transmitted signal optical powers, respectively; n is a radical of2(z, t) is the upper-level population density, and N is Yb in the core of the gain fiber3+The doping concentration of (a); gamma-shapedpAnd ΓsFill factors of the pump light and the signal light, respectively; sigmaap(t) and σep(t) absorption and emission cross-sectional areas of the pump light, respectively; sigmaasAnd σesAbsorption and emission cross-sectional areas of the signal light, respectively; alpha is alphaPAnd alphasLoss coefficients of the pump light and the signal light, respectively; τ is upper level particle lifetime; lambda [ alpha ]sIs the signal light wavelength; lambda [ alpha ]P(t) is a function of semiconductor laser output center wavelength versus time; h is the Planck constant; c is the speed of light in vacuum, AcIs the core cross-sectional area;
for a fiber laser oscillator having a gain fiber length of L, the boundary condition is expressed as
Figure FDA0002802502690000026
Figure FDA0002802502690000027
Figure FDA0002802502690000028
Figure FDA0002802502690000029
Wherein the content of the first and second substances,
Figure FDA00028025026900000210
is the total pump power; r1And R2Respectively, the reflectivity of the high and low inverse gratings.
2. The method of optimizing the thermal-related transient response of a high power fiber laser of claim 1, wherein: the transient response in step 3 is caused by the temperature drift of the semiconductor laser output center wavelength.
3. The method of optimizing the thermal-related transient response of a high power fiber laser of claim 1, wherein: the relevant parameter in step 4 comprises the cooling temperature T0Length L of gain fiber and Yb in core of gain fiber3+Doping concentration N of (a).
4. A method of optimizing the thermal-related transient response of a high power fiber laser as in claim 3 wherein: increasing the cooling temperature T0And when the output power of the fiber laser is increased to more than 95% of the stable power, recording the transient response time of the output power of the high-power fiber laser.
5. A method of optimizing the thermal-related transient response of a high power fiber laser as in claim 3 wherein: and increasing the length L of the gain fiber, and recording the transient response time of the output power of the high-power fiber laser when the output power of the fiber laser is increased to more than 95% of the stable power.
6. A method of optimizing the thermal-related transient response of a high power fiber laser as in claim 3 wherein: raising Yb in the core of a gain fiber3+When the output power of the fiber laser is increased to more than 95% of the stable power, the transient response time of the output power of the high-power fiber laser is recorded.
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