CN114583538B - Off-axis pumping laser gain module - Google Patents
Off-axis pumping laser gain module Download PDFInfo
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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
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/0915—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light
- H01S3/0933—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light of a semiconductor, e.g. light emitting diode
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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
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/08072—Thermal lensing or thermally induced birefringence; Compensation thereof
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Abstract
The present disclosure relates to an off-axis pumped laser gain module comprising: the rod-shaped gain medium is provided with a central symmetry axis, an optical conduit and a pumping semiconductor linear array, wherein a preset off-axis quantity (delta D) exists between an optical axis of a normal line of a light emitting surface led out from the center of a pumping semiconductor linear array light emitting surface and a central symmetry ray, the central symmetry ray passes through the axis of the gain medium, and the preset off-axis quantity delta D is used for adjusting the pumping semiconductor linear array and carrying out off-axis pumping on the rod-shaped laser gain medium so as to enable laser gain distribution in the rod-shaped laser gain medium to be more uniform. The off-axis pumping laser gain module and the off-axis pumping laser gain device can effectively solve the problem of uneven extraction caused by uneven gain distribution due to excessively concentrated spatial distribution of pumping light, and can improve the intrinsic beam quality of the laser gain module.
Description
Technical Field
The disclosure relates to the field of laser technology, and in particular, to a laser gain module and device for off-axis pumping.
Background
The existing semiconductor side pumping laser generally adopts a centering pumping structure that pumping light in different directions is incident to the geometric center of a rod-shaped gain medium.
The gain intensity distribution within the laser medium is gaussian-like from the center of the medium to the edges, the laser medium has a high center gain, low edge gain, and non-uniform gain distribution at the edges of the medium. Uneven absorption of the pump light results in varying waste heat generation rates from location to location in the lasing medium. Uneven distribution of temperature can lead to thermal stress in the laser medium. Both the unevenly distributed temperature and the thermal stress of the lasing medium cause a change in the refractive index of the lasing medium, thereby creating a thermal lens effect and a thermal stress birefringence effect. When a laser beam propagates through such a laser medium, wavefront distortion occurs, and the beam quality of the laser beam decreases. In addition, if the thermal stress in the laser medium exceeds the stress limit that the laser medium can withstand, the thermal stress may cause damage to the laser medium. Therefore, the method effectively reduces the stress in the laser medium and is an important way for improving the quality of the laser beam.
In the prior art, there are three general ways to optimize the design of the side pump gain module: firstly, the distance L from the luminous surface of the semiconductor laser array to the center of the rod-shaped gain medium and the pumping dimension n of the pumping module surrounding the laser medium are increased in a proper amount, the method can change the gain distribution at the edge of the laser medium, but the influence on the range of the strong gain distribution area at the center of the laser medium and the gain gradient between the center and the edge of the laser medium is not great; the method can obtain gain intensity distribution from the center to the edge of the laser medium, which is similar to flat-top Gaussian distribution or crater distribution, but gain medium with good optical performance and high doping concentration is difficult to grow, and the increase of the pumping dimension makes the geometric structure of the gain module more complex and increases the integration difficulty; the method effectively increases the heat exchange capacity of the surface of the laser medium and reduces the overall temperature of the laser medium, but the improvement on the temperature gradient in the laser medium is limited, and the fluid pressure of a laser cooling system can be increased and the reliability of the laser gain module can be reduced.
Disclosure of Invention
Object of the invention
The purpose of the present disclosure is to provide a laser gain module with off-axis pumping, which makes gain distribution uniform when a gain medium works in an off-axis pumping mode, improves the problem of uneven temperature distribution in the laser gain medium, and improves the beam quality of laser.
(II) technical scheme
In order to solve the above problems, the present invention provides an off-axis pumped laser gain module, which includes three components: gain component, pumping component and beam homogenizing component; the gain component comprises: a rod-shaped laser gain medium for generating a laser gain; the gain component further comprises an optical conduit arranged at the outer side of the rod-shaped laser gain medium, a cooling working medium is filled in a gap between the rod-shaped laser gain medium and the optical conduit, and the cooling working medium is used for sealing and cooling the rod-shaped laser gain medium; the rod-shaped laser gain medium is in a round rod shape and has a central symmetry axis; the diameter of the rod-shaped laser gain medium is not smaller than 5mm;
the pump assembly includes: the number of the pumping semiconductor linear arrays is N, the value range of N is 3-9, each pumping semiconductor linear array surrounds the rod-shaped laser gain medium in a rotationally symmetrical mode, each pumping semiconductor linear array is circumferentially distributed along the rod-shaped laser gain medium and is rotationally arranged at an angle alpha, wherein alpha=360 degrees/N, so that the rod-shaped laser gain medium can effectively absorb pumping light; the pumping assembly further comprises a heat sink, wherein the heat sink adopts a macro-channel or micro-channel cooling structure and is used for radiating the semiconductor laser array; the optical homogenizing component comprises a diffuse reflection cavity, wherein the diffuse reflection cavity is provided with a light passing window, and the size and the position of the light passing window correspond to those of the pumping light spot; the rod-shaped laser gain medium is provided with N central symmetry rays, and the central symmetry rays pass through the axis of the rod-shaped laser gain medium; the optical axis of the normal line of the luminous surface passes through the center of the semiconductor luminous surface and along the normal direction of the luminous surface; a preset off-axis quantity exists between the optical axis of the normal line of the pumping semiconductor linear array light emitting surface and the central symmetry ray, the preset off-axis quantity is expressed as delta D, and the delta D is used for adjusting the off-axis pumping distance of the pumping semiconductor linear array to the rod-shaped laser gain medium so as to ensure even gain distribution; the vertical distance from the center point of the light emitting surface of the pumping semiconductor linear array to the center point of the rod-shaped laser gain medium is expressed as a preset distance L; the specific quantitative relationship can be given by:
tan(θ)＝δD/L,
the off-axis angle theta is an included angle between a connecting line from the axis of the rod-shaped laser gain medium to the center of the pumping semiconductor linear array light emitting surface and the normal line of the center of the pumping semiconductor linear array light emitting surface, and the theta is adjusted by adjusting the preset distance L and the preset off-axis quantity delta D.
Further, the divergence angle of the pump semiconductor linear array in the cross section is omega; the off-axis angle theta is matched with the divergence angle omega of the pumping semiconductor linear array; has the following relationship:
θ<1/3ω；
further, the relationship between the preset off-axis amount δD and the radius of the rod-shaped laser gain medium satisfies the following relationship
δD＝μR；
Wherein mu is a correction factor, generally the mu value is between 0.4 and 1.0, R is the radius of the rod-shaped laser gain medium, and the radius is used for ensuring the uniformity of crystal absorption;
the off-axis angle θ has the following relationship:
when the number of the pumping semiconductor linear arrays is increased to 3 or more, the off-axis angle theta can be adjusted according to the above formula in combination with the simulation result of the ray tracing.
Further, the rod-shaped laser gain medium comprises the following materials: and one or more of laser crystal, ceramic and glass doped with active ions, wherein the rod end face of the rod-shaped laser gain medium adopts a bonding structure so as to eliminate the influence of thermal lens effect.
Furthermore, the optical conduit is made of quartz glass and used for transmitting pump light and forming an effective convection heat exchange channel, and can also be made of transparent ceramics, sapphire and other materials with good optical transmission capacity and mechanical strength.
Further, the pumping semiconductor linear array includes: a vertical cavity surface emitting semiconductor laser array or an edge emitting semiconductor laser array, the edge emitting semiconductor laser comprising one or more of a non-collimated semiconductor laser, a semiconductor laser with a slow axis collimator, and a semiconductor laser with a fast axis collimator.
Further, the diffuse reflection cavity is structurally designed by adopting a metal gold plating or ceramic diffuse reflection cavity.
Furthermore, the light-transmitting window can adopt a structure of directly grooving the side wall of the diffuse reflection cavity or a quartz cylindrical mirror structure with curvature, and is used for realizing secondary shaping of pump light. (III) beneficial effects
The method solves the problem of uneven gain distribution of the laser gain medium during operation in an off-axis pumping mode, reduces the thermal stress degree of the laser gain medium caused by uneven temperature distribution, and relieves the wave front distortion generated by laser propagation in the gain medium. Therefore, the off-axis pumping laser gain module has more uniform gain and temperature distribution, and improves the beam quality of laser.
Drawings
FIG. 1 is a schematic diagram of a five-dimensional vertical cavity surface emitting semiconductor laser array off-axis pumped laser gain module according to an alternative embodiment of the present disclosure;
FIG. 2 is a schematic diagram of a laser gain module for off-axis pumping of a three-dimensional edge-emitting semiconductor laser array according to an alternative embodiment of the present disclosure;
FIG. 3 is a schematic diagram of a centered pumping state of a five-dimensional vertical cavity surface emitting semiconductor laser array pumped laser gain module according to a related embodiment of the present disclosure;
FIG. 4 is a graph of the centered pumping state of a five-dimensional vertical cavity surface emitting semiconductor laser array pumped laser gain module according to a related embodiment of the present disclosure;
FIG. 5 is an off-axis pumping state diagram of a five-dimensional vertical cavity surface emitting semiconductor laser array pumped laser gain module according to an alternative embodiment of the present disclosure;
FIG. 6 is an off-axis pumping state diagram of a five-dimensional vertical cavity surface emitting semiconductor laser array pumped laser gain module according to an alternative embodiment of the present disclosure;
FIG. 7 is a schematic diagram of a centered pumping state of a five-dimensional edge-emitting semiconductor laser array pumped laser gain module according to a related embodiment of the present disclosure;
FIG. 8 is a graph of a centered pumping state of a five-dimensional edge-emitting semiconductor laser array pumped laser gain module according to a related embodiment of the present disclosure;
FIG. 9 is an off-axis pumping state diagram of a five-dimensional edge-emitting semiconductor laser array pumped laser gain module according to an alternative embodiment of the present disclosure;
FIG. 10 is an off-axis pumping state diagram of a five-dimensional edge-emitting semiconductor laser array pumped laser gain module according to an alternative embodiment of the present disclosure;
FIG. 11 is a top view of a vertical cavity surface emitting semiconductor laser array according to an alternative embodiment of the present disclosure;
fig. 12 is a front view of a vertical cavity surface emitting semiconductor laser array according to an alternative embodiment of the present disclosure.
Reference numerals:
1: a rod-shaped laser gain medium; 2: an optical conduit; 3: pumping the semiconductor linear array; 4: a heat sink; 5: a diffuse reflection cavity; 6: a light-transmitting window; 7: gain medium axis; 8: a first straight line; 9: an optical axis of a center normal line of the light emitting surface; θ: off-axis angle; l: a preset distance; δD, preset off-axis amount.
Detailed Description
For the purposes of promoting an understanding of the principles and advantages of the disclosure, reference will now be made to the drawings and specific language will be used to describe the same. It should be understood that the description is only exemplary and is not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and techniques are omitted so as not to unnecessarily obscure the concepts of the present disclosure.
A layer structure schematic diagram according to an embodiment of the present disclosure is shown in the drawings. The figures are not drawn to scale, wherein certain details may be exaggerated and some details may be omitted for clarity. The shapes of the various regions, layers and relative sizes, positional relationships between them shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.
It will be apparent that the described embodiments are some, but not all, of the embodiments of the present disclosure. Based on the embodiments in this disclosure, all other embodiments that a person of ordinary skill in the art would obtain without making any inventive effort are within the scope of protection of this disclosure.
In addition, technical features related to different embodiments of the present disclosure described below may be combined with each other as long as they do not make a conflict with each other.
Fig. 1 is a schematic diagram of a side pump laser gain module of a five-dimensional vertical cavity surface emitting semiconductor laser array off-axis pump according to an alternative embodiment of the present disclosure.
As shown in fig. 2 and 1, an off-axis pumped laser gain module according to an embodiment of the present disclosure includes three components: gain component, pumping component and beam homogenizing component; the gain component comprises: a rod-shaped laser gain medium 1 for generating a laser gain; the gain component further comprises an optical conduit 2 which is arranged at the outer side of the rod-shaped laser gain medium 1, a cooling working medium is filled in a gap between the rod-shaped laser gain medium 1 and the optical conduit 2, and the cooling working medium is used for sealing and cooling the rod-shaped laser gain medium 1; the rod-shaped laser gain medium 1 is in a round rod shape and has a central symmetry axis 7; to ensure the effectiveness of the present invention, the module design is only aimed at a rod-shaped laser gain medium with a larger diameter, and the diameter of the rod-shaped laser gain medium 1 is not less than 5mm. In the embodiment of the disclosure, the optical conduit 2 is used for forming a flow channel, the flow channel enables the cooling working medium to be in contact with the rod-shaped laser gain medium 1, and the pumping light reaches the rod-shaped laser gain medium 1 through the optical conduit 2, so that optical pumping is realized. The material of the optical conduit 2 is typically a molten glass, such as one or more of quartz, sapphire, and transparent ceramics. The cooling working medium is heat-conducting liquid or gas, and is generally one or more of water, heavy water, glycol, freon, organic liquid, air, carbon dioxide gas, helium and nitrogen. In some embodiments, the rod shape of the rod-shaped laser gain medium 1 is understood to be cylindrical, and fig. 1, 2, 3, 5, 7, and 9 illustrate cross-sectional structures of the rod-shaped laser gain medium 1 of the present disclosure, and the rod-shaped laser gain medium 1 of the present disclosure may be gain media of other shapes, so long as the gain media are suitable for the off-axis pumping principles of the present disclosure.
In some embodiments, the pump assembly comprises: the number of the pumping semiconductor linear arrays 3 is N, the value range of N is 3-9, each pumping semiconductor linear array 3 surrounds the rod-shaped laser gain medium 1 in a rotationally symmetrical mode, each pumping semiconductor linear array 3 is circumferentially distributed along the rod-shaped laser gain medium 1, and each pumping semiconductor linear array 3 is rotationally arranged at an angle alpha, wherein alpha=360 degrees/N, so that the rod-shaped laser gain medium 1 effectively absorbs pumping light; the pump assembly further comprises a heat sink 4, the heat sink 4 employing a macro-channel or micro-channel cooling structure for dissipating heat from the semiconductor laser array 3. In some embodiments, the number of the pump semiconductor linear arrays 3 is 3-9, each pump semiconductor linear array 3 surrounds the rod-shaped laser gain medium 1 in a rotating manner, each pump semiconductor linear array 3 is circumferentially distributed along the rod-shaped laser gain medium 1 and each pump semiconductor linear array 3 is rotationally arranged at an angle α, so that the rod-shaped laser gain medium 1 effectively absorbs pump light. In some embodiments, the pump semiconductor line 3 may be understood as a pump source.
As shown in fig. 2 and 1, in some embodiments, the optical homogenizing component comprises a diffuse reflection cavity 5, wherein the diffuse reflection cavity 5 is provided with a light-passing window 6, and the size and position of the light-passing window 6 correspond to the size and position of the pumping light spot; the rod-shaped laser gain medium 1 is provided with N central symmetry rays 8, and the central symmetry rays 8 pass through the axis of the rod-shaped laser gain medium 1; the optical axis 9 of the normal line of the luminous surface passes through the center of the semiconductor luminous surface and along the normal direction of the luminous surface;
in some embodiments, the common side pump laser gain module adopts a coaxial design, and the central symmetry line 8 passes through the axis of the rod-shaped laser gain medium 1 and the center of the light emitting surface of the semiconductor, wherein the central symmetry line 8 is collinear with the optical axis 9 of the normal line of the light emitting surface.
In some embodiments, the off-axis pumping design is that a preset off-axis amount exists between an optical axis 9 of a normal line of a light emitting surface of the pumping semiconductor linear array 3 and the central symmetry ray 8, wherein the preset off-axis amount is denoted as δD, and δD is used for adjusting the off-axis pumping distance of the pumping semiconductor linear array 3 to the rod-shaped laser gain medium 1 so as to ensure uniform gain distribution; the vertical distance from the center point of the light emitting surface of the pumping semiconductor linear array 3 to the center point of the rod-shaped laser gain medium 1 is expressed as a preset distance L; the specific quantitative relationship can be given by:
tan (θ) =δd/L, equation (1)
The off-axis angle theta is an included angle between a connecting line from the axis of the rod-shaped laser gain medium 1 to the center of the light emitting surface of the pumping semiconductor linear array 3 and the normal line of the center of the light emitting surface of the pumping semiconductor linear array 3, and the theta is adjusted by adjusting the preset distance L and the preset off-axis amount delta D. In some embodiments, the off-axis angle θ may be understood as the angle at which the optical axis of the pump semiconductor linear array 3 deviates from the axis of the gain medium. In some embodiments, D may be understood as the vertical distance from the axis of the rod-shaped laser gain medium 1 to the optical axis of the pump semiconductor linear array 3; l is understood to be the vertical distance from the center of the light emitting surface of the pump semiconductor linear array 3 to a plane in which the axis of the rod-shaped laser gain medium 1 is located, wherein the plane is perpendicular to the optical axis of the pump semiconductor linear array 3. In some embodiments, the off-axis angle θ may be understood as an off-axis angle, that is, an angle at which the optical axis of the pump semiconductor array 3 deviates from the rod-shaped laser gain medium 1 during off-axis pumping of the pump semiconductor array 3. The magnitude of the off-axis angle theta is matched with the radius of the rod-shaped laser gain medium 1 and the divergence angle of the pumping semiconductor linear array 3. In one embodiment, the off-axis angle θ is preferably 3 ° to 30 °. In some embodiments, the included angle may be adjusted according to practical situations, and parameters that may be considered to be adjusted include: the degree of the off-axis angle θ is adjusted according to the radial dimension of the rod-shaped laser gain medium 1 and the degree of the off-axis angle θ is adjusted according to the degree of the divergence angle of the pump semiconductor linear array 3.
In a related embodiment, one of the optimal design modes of the opposite side pumping rod-shaped gain module is to increase the distance L from the light emitting surface of the semiconductor laser array to the center of the rod-shaped gain medium and the pumping dimension n of the pumping module surrounding the laser medium, and the method can change the gain distribution at the edge of the laser medium, but has little influence on the range of the strong gain distribution area at the center of the laser medium and the gain gradient between the center and the edge of the laser medium. If the pump profile of each pump semiconductor line is a gaussian beam, the superposition of multiple beams remains gaussian, except that the intensities at the edges and center are superimposed at the same time, but the relative magnitudes (the "gradient" in the expression) are unchanged.
The off-axis pumping is achieved through the first preset distance by adjusting the size of the preset distance. The gain medium is uniformly distributed when in operation by an off-axis pumping mode, so that the problem of uneven temperature distribution in the laser gain medium is solved, and the beam quality of laser is improved.
In some embodiments, the pump semiconductor linear array 3 has a divergence angle ω in cross section; the off-axis angle theta is matched with the divergence angle omega of the pumping semiconductor linear array 3; has the following relationship:
θ <1/3 ω, equation (2);
in some embodiments, the relationship of the preset off-axis amount δD and the radius of the rod-shaped laser gain medium 1 satisfies the following relationship
δd=μr, equation (3);
wherein mu is a correction factor, generally mu is 0.4-1.0, R is the radius of the rod-shaped laser gain medium 1, and the radius is used for ensuring the uniformity of crystal absorption;
the off-axis angle θ has the following relationship:
when the number of the pumping semiconductor linear arrays 3 is increased to 3 or more, the off-axis angle θ can be adjusted according to the above equation in combination with the simulation result of the ray tracing.
In some embodiments, the divergence angle ω of the pump semiconductor line array 3 in the cross section corresponds to half of the 95% energy angle; in order to ensure uniformity of the pump light distribution, the problem of matching the off-axis angle with the divergence angle of the pump semiconductor linear array 3 needs to be considered, and the off-axis angle θ is matched with the divergence angle ω of the pump semiconductor linear array 3.
In some embodiments, the materials of the rod-shaped laser gain medium 1 include: the rod end face of the rod-shaped laser gain medium 1 adopts a bonding structure to eliminate the influence of thermal lens effect by doping one or more of laser crystal, ceramic and glass with active ions.
In some embodiments, the optical conduit 2 is made of quartz glass, is used for transmitting pump light and forming an effective convective heat exchange channel, and may also be made of transparent ceramics, sapphire and other materials with good optical transmission capability and mechanical strength.
In some embodiments, pumping the semiconductor line array 3 comprises: a vertical cavity surface emitting semiconductor laser array or an edge emitting semiconductor laser array, the edge emitting semiconductor laser comprising one or more of a non-collimated semiconductor laser, a semiconductor laser with a slow axis collimator, and a semiconductor laser with a fast axis collimator.
In some embodiments, the diffuse reflective cavity 5 is structurally designed with gold plating or ceramic diffuse reflective cavities.
In some embodiments, the light-transmitting window 6 may adopt a structure of directly grooving the side wall of the diffuse reflection cavity 5, or adopt a quartz cylindrical mirror structure with curvature, so as to realize secondary shaping of the pump light.
As shown in fig. 2 and 1, in an alternative embodiment, a laser gain module is related, wherein the laser array includes: a vertical cavity surface emitting laser array or an edge emitting semiconductor laser array, the edge emitting semiconductor laser comprising one or more of a semiconductor laser, a semiconductor laser with a fast axis collimator and a semiconductor laser with a slow axis collimator.
As further shown in FIG. 1, in an alternative embodiment, the degree of the preset off-axis angle θ is adjusted according to the magnitude of D.
In an alternative embodiment, the degree of off-axis angle θ is adjusted according to the magnitude of L.
In an alternative embodiment, the degree of off-axis angle θ is adjusted according to the radial dimension of the rod-shaped laser gain medium 1.
In an alternative embodiment, the degree of the angle θ is adjusted according to the degree of the divergence angle of the pump semiconductor line 3.
In one embodiment, a laser gain module is provided, comprising: the rod-shaped laser gain medium 1, the optical conduit 2, the pumping semiconductor linear array 3, the heat sink 4, the diffuse reflection cavity 5 and the light transmission window 6, in some embodiments, the number of the pumping semiconductor linear arrays 3 is n, and the n pumping semiconductor linear arrays 3 are pumped around the rod-shaped laser gain medium 1 in a rotationally symmetrical manner. The rotation angle alpha=360°/n, wherein the value of n is preferably 3-9; the positional relationship between the pumping semiconductor linear array 3 and the rod-shaped laser gain medium 1 can be determined by the included angle θ of the pumping light:
tan (θ) =d/L, equation (5)
θ can also be understood that the optical axis of the pump semiconductor linear array 3 deviates from the included angle of the rod-shaped laser gain medium 1 during off-axis pumping of the pump semiconductor linear array 3. The magnitude of the off-axis angle theta is matched with the radius of the rod-shaped laser gain medium 1 and the divergence angle of the pumping semiconductor linear array 3. In one embodiment, the off-axis angle θ is preferably 3 ° to 30 °. In some embodiments, the off-axis angle θ may be adjusted according to the actual situation, and parameters that may be considered for adjustment include: the degree of the off-axis angle θ is adjusted according to the radial dimension of the rod-shaped laser gain medium 1 and the degree of the off-axis angle θ is adjusted according to the degree of the divergence angle of the pump semiconductor linear array 3.
In this embodiment, the off-axis pumping laser gain module can effectively improve the uniformity of the pumping light in the gain medium, effectively compensate for a larger temperature gradient in the rod-shaped gain medium, and reduce the wavefront distortion of the output laser. And in the stress range which can be borne by the laser medium, the upper limit of the pumping power is effectively improved, and finally, the laser output with high power and high beam quality is realized.
With continued reference to FIG. 1, as shown in FIG. 1, in an alternative embodiment, a side pump laser gain module is involved that is five-dimensional off-axis pumping. In combination with the above embodiments, n in the present embodiment has a value of 5, α is an angle at which several semiconductor laser arrays are rotationally arranged, and in the present embodiment, the n is an angle at which the semiconductor laser arrays are equiangularly arranged, so that the number n divided by 360 degrees in one circle is the rotation angle in the expression. The rotation angle α=360°/5=72° is known from the rotation angle α=360°/n. The pump semiconductor line 3 will pump the rod-shaped laser gain medium 1 with a rotation angle of 72 deg..
In some embodiments, the pumping semiconductor linear array 3 is in an angular symmetric state when surrounding the rod-shaped laser gain medium 1, and the symmetric rotation angle α is more beneficial to the absorption of the pumping light by the rod-shaped laser gain medium 1. The value of n determines the degree of the rotation angle α. In some embodiments, the value of n is typically an odd number, e.g., 3 or 5 or 7 laser arrays 1, and preferably 3-9 of the arrays are eligible. When the number of the laser arrays 1 is selected, the value of n should be avoided as much as 1 or 2, because the power generated by the pump is very small due to the fact that the value of n is too small, and meanwhile, the value of n should be also avoided to be too large, and when the value of n is too large, the pump semiconductor linear array cannot be arranged. In general, n=3 or n=5 is the best pumping effect, and next n=7 or n=9 is also preferable.
As shown in fig. 2 and 1, in an alternative embodiment, a laser gain module is provided, where the material of the rod-shaped laser gain medium 1 includes: one or more of crystals, ceramics and glass. In a related embodiment, the semiconductor pump laser has the advantages of small volume, high efficiency, simple structure, long service life and the like, and is widely applied. In some embodiments, the structure of the gain medium includes: non-bonding material and bonding material. The bonding material comprises: matrix materials for lasers, e.g. YAG crystals, frequency doubling materials for lasers, e.g. crystals, e.g. KTP crystals, and passive Q-switching materials for lasers, e.g. Cr 4+ One or more of YAG crystals.
As shown in fig. 2 and 1, in an alternative embodiment, a laser gain apparatus is provided, comprising: the laser gain module is described above.
Please refer to fig. 3-12, as shown in fig. 3-12.
Fig. 11 is a top view of a vertical cavity surface emitting semiconductor laser array according to an alternative embodiment of the present disclosure, and fig. 12 is a front view of a vertical cavity surface emitting semiconductor laser array according to an alternative embodiment of the present disclosure. As shown in fig. 11 and 12, a schematic diagram of a vertical cavity surface emitting semiconductor laser array is specifically applied to an off-axis pumping rod-shaped gain medium. The laser array is a 15X 1 linear array, each chip has a size of 4.7mm multiplied by 4.7mm, the light emitting surface of the array has a size of 140mm multiplied by 4.7mm, and the divergence angle is 14 degrees.
Fig. 3 is a schematic diagram of the centering pumping state of a five-dimensional vcsels array gain module according to a related embodiment of the present disclosure, and fig. 4 is a graph of the centering pumping state of the five-dimensional vcsels array gain module according to a related embodiment of the present disclosure. As shown in fig. 3 and 4, simulation results of the absorption flux distribution of the pumping light by the gain medium in the array-centered pump rod laser gain module are shown. The absorption flux distribution of the gain medium for the pump light is directly related to the gain distribution of the gain medium when in operation. The structure adopts a five-dimensional centering side pump rod-shaped gain medium structure, and parameters are as follows: the pumping semiconductor linear array is a laser array shown in fig. 3, the off-axis angle θ=0°, l=25 mm, and the size of the rod-shaped gain medium is the same as that of the pumping semiconductor linear arrayThe inner diameter of the optical catheter is +.>The outer diameter is->The cooling working medium is water, and the radius of the diffuse reflection cavity is 20mm. Simulation results show that for a rod-shaped laser gain module adopting a laser array for central pumping, gain intensity distribution in a laser medium is similar to Gaussian distribution from the center to the edge of the medium, the gain of the center of the laser medium is high, the gain of the edge is low, and the gain distribution at the edge of the medium is uneven.
Fig. 5 is a schematic diagram of off-axis pumping states of a five-dimensional vertical cavity surface emitting semiconductor laser array gain module according to an alternative embodiment of the present disclosure, and fig. 6 is a graph of off-axis pumping states of a five-dimensional vertical cavity surface emitting semiconductor laser array gain module according to an alternative embodiment of the present disclosure. As shown in fig. 5 and 6, an array off-axis side pump rod is shownSimulation results of the laser gain module and energy absorption intensity distribution of the cross section of the gain module. The structure adopts a five-dimensional off-axis side pump rod-shaped gain medium structure as shown in figure 1, and parameters are as follows: the pumping semiconductor linear array is a laser array shown in fig. 2, the off-axis angle θ=5.71°, l=25 mm, d=2.5 mm, and the size of the rod-shaped gain medium is the same as that of the pumping semiconductor linear arrayThe inner diameter of the optical catheter is +.>An outer diameter ofThe cooling working medium is water, and the radius of the diffuse reflection cavity is 20mm. Simulation results show that for a rod-shaped laser gain module adopting laser array off-axis pumping, the off-axis pumping structure remarkably improves the uniformity of the gain medium on pump light absorption; the temperature gradient existing in the rod-shaped gain medium can be effectively compensated, and the wave front distortion of the output laser is reduced; the upper limit of pumping power is effectively improved within the stress range which can be born by the laser medium; finally, the laser output with high power and high beam quality is realized.
Fig. 7 is a schematic diagram of a centered pumping state of a five-dimensional edge-emitting semiconductor laser array gain module according to a related embodiment of the present disclosure, and fig. 8 is a graph of a centered pumping state of a five-dimensional edge-emitting semiconductor laser array gain module according to a related embodiment of the present disclosure. As shown in fig. 7 and 8, simulation results of a pumping rod-shaped laser gain module of an edge-emitting semiconductor laser array on the center side and energy absorption intensity distribution of a cross section of the gain module are shown. The structure adopts a five-dimensional centering side pump rod-shaped gain medium structure, and parameters are as follows: the pumping semiconductor linear array is an edge-emitting semiconductor laser array, the fast axis diverges by a full angle of 60 degrees, the off-axis angle theta=0°, l=8 mm, and the size of the rod-shaped gain medium is equal to that of the rod-shaped gain mediumThe inner diameter of the optical conduit isThe outer diameter is->The cooling working medium is water, and the radius of the diffuse reflection cavity is 8.5mm. Simulation results show that for a rod-shaped laser gain module adopting edge-emitting semiconductor laser array centering pumping, gain intensity distribution in a laser medium is similar to Gaussian distribution from the center to the edge of the medium, the gain of the center of the laser medium is high, the gain of the edge is low, and the gain distribution at the edge of the medium is uneven.
Fig. 9 is an off-axis pumping state diagram of a five-dimensional edge-emitting semiconductor laser array gain module according to an alternative embodiment of the present disclosure, and fig. 10 is an off-axis pumping state diagram of a five-dimensional edge-emitting semiconductor laser array gain module according to an alternative embodiment of the present disclosure. As shown in fig. 9 and 10, simulation results of a centrifugal side pump rod-like laser gain module of an edge-emitting semiconductor laser array and energy absorption intensity distribution of a gain module cross section are shown. The structure adopts a five-dimensional off-axis side pump rod-shaped gain medium structure as shown in figure 1, and parameters are as follows: the pumping semiconductor linear array is an edge-emitting semiconductor laser array, the fast axis diverges by a full angle of 60 degrees, the off-axis angle theta=5.71 degrees, l=8mm, d=2.5 mm, and the size of the rod-shaped gain medium is the same as that of the pumping semiconductor linear arrayThe inner diameter of the optical catheter is +.>The outer diameter is->The cooling working medium is water, and the radius of the diffuse reflection cavity is 8.5mm. Simulation results show that for a rod-shaped laser gain module adopting side-emitting semiconductor laser array for center pumping, the off-axis pumping structure also obviously improves the uniformity of the gain medium for pumping light absorption. This means that the off-axis pumping structure can be realized either with a vertical cavity surface emitting semiconductor laser orImplemented using edge-emitting semiconductor lasers.
The method solves the problem of uneven gain distribution of the laser gain medium during operation in an off-axis pumping mode, reduces the thermal stress degree of the laser gain medium caused by uneven temperature distribution, and relieves the wave front distortion generated by laser propagation in the gain medium. Therefore, the off-axis pumping laser gain module has more uniform gain and temperature distribution, and improves the beam quality of laser.
In this embodiment, the off-axis pumping laser gain module can effectively improve the uniformity of the pumping light in the gain medium, effectively compensate for a larger temperature gradient in the rod-shaped gain medium, and reduce the wavefront distortion of the output laser. And in the stress range which can be borne by the laser medium, the upper limit of the pumping power is effectively improved, and finally, the laser output with high power and high beam quality is realized.
It is to be understood that the above-described embodiments of the present disclosure are merely illustrative or explanatory of the principles of the disclosure and are not restrictive of the disclosure. Accordingly, any modifications, equivalent substitutions, improvements, or the like, which do not depart from the spirit and scope of the present disclosure, are intended to be included within the scope of the present disclosure. Furthermore, the appended claims of this disclosure are intended to cover all such changes and modifications that fall within the scope and boundary of the appended claims, or the equivalents of such scope and boundary.
Claims (6)
1. An off-axis pumped laser gain module comprising three major components: gain component, pumping component and beam homogenizing component;
the gain component comprises: a rod-shaped laser gain medium (1) for generating a laser gain; the gain component further comprises an optical conduit (2) which is arranged at the outer side of the rod-shaped laser gain medium (1), a cooling working medium is filled in a gap between the rod-shaped laser gain medium (1) and the optical conduit (2), and the cooling working medium is used for sealing and cooling the rod-shaped laser gain medium (1); the rod-shaped laser gain medium (1) is in a round rod shape and is provided with a central symmetry axis (7); the diameter of the rod-shaped laser gain medium (1) is not smaller than 5mm;
the pump assembly includes: the number of the pumping semiconductor linear arrays (3) is N, the value range of N is 3-9, each pumping semiconductor linear array (3) surrounds the rod-shaped laser gain medium (1) in a rotationally symmetrical mode, each pumping semiconductor linear array (3) is circumferentially distributed along the rod-shaped laser gain medium (1) and each pumping semiconductor linear array (3) is rotationally arranged at an angle alpha, wherein alpha=360 degrees/N, so that the rod-shaped laser gain medium (1) effectively absorbs pumping light; the pumping assembly further comprises a heat sink (4), wherein the heat sink (4) adopts a macro-channel or micro-channel cooling structure and is used for radiating the pumping semiconductor linear array (3);
the optical homogenizing component comprises a diffuse reflection cavity (5), wherein the diffuse reflection cavity (5) is provided with a light-passing window (6), and the size and the position of the light-passing window (6) correspond to the size and the position of a pumping light spot;
the rod-shaped laser gain medium (1) is provided with N central symmetry rays (8), and the central symmetry rays (8) pass through the axis of the rod-shaped laser gain medium (1); an optical axis (9) of the normal line of the light emitting surface passes through the center of the semiconductor light emitting surface and along the normal line direction of the light emitting surface;
a preset off-axis quantity is arranged between an optical axis (9) of a normal line of a light emitting surface of the pumping semiconductor linear array (3) and the central symmetry ray (8), the preset off-axis quantity is expressed as delta D, and the delta D is used for adjusting the off-axis pumping distance of the pumping semiconductor linear array (3) to the rod-shaped laser gain medium (1) so as to ensure even gain distribution; the vertical distance from the center point of the light emitting surface of the pumping semiconductor linear array (3) to the center point of the rod-shaped laser gain medium (1) is expressed as a preset distance L; the specific quantitative relationship can be given by:
tan(θ)＝δD/L，
the off-axis angle theta is an included angle between a connecting line from the axis of the rod-shaped laser gain medium (1) to the center of the light emitting surface of the pumping semiconductor linear array (3) and the normal line of the center of the light emitting surface of the pumping semiconductor linear array (3), and the theta is adjusted by adjusting the preset distance L and the preset off-axis quantity delta D;
the divergence angle of the pumping semiconductor linear array (3) in the cross section is omega; the off-axis angle theta is matched with the divergence angle omega of the pumping semiconductor linear array (3); has the following relationship:
θ＜1/3ω；
the relationship between the preset off-axis quantity delta D and the radius of the rod-shaped laser gain medium (1) satisfies the following relationship
δD＝μR；
Wherein mu is a correction factor, generally the mu value is O.4-1. O, R is the radius of the rod-shaped laser gain medium (1) and is used for ensuring the uniformity of crystal absorption;
the off-axis angle θ has the following relationship:
when the number of the pumping semiconductor linear arrays (3) is increased to 3 or more, the off-axis angle theta can be adjusted according to the above formula by combining simulation results of ray tracing.
2. The module according to claim 1, wherein the material of the rod-shaped laser gain medium (1) comprises: and one or more of laser crystal, ceramic and glass doped with active ions, wherein the rod end face of the rod-shaped laser gain medium (1) adopts a bonding structure so as to eliminate the influence of thermal lens effect.
3. The module according to claim 1, wherein the optical conduit (2) is made of quartz glass for transmitting pump light and forming an effective convective heat transfer channel, and is made of transparent ceramics, sapphire or other materials with good optical transmission capacity and mechanical strength.
4. The module according to claim 1, wherein the pump semiconductor linear array (3) comprises: a vertical cavity surface emitting semiconductor laser array or an edge emitting semiconductor laser array, the edge emitting semiconductor laser comprising one or more of a non-collimated semiconductor laser, a semiconductor laser with a slow axis collimator, and a semiconductor laser with a fast axis collimator.
5. The module according to claim 1, wherein the diffuse reflecting cavity (5) is structurally designed with gold metal plating or ceramic diffuse reflecting cavities.
6. The module according to claim 1, wherein the light-passing window (6) can adopt a structure of directly grooving the side wall of the diffuse reflection cavity (5) or a quartz cylindrical mirror structure with curvature for realizing secondary shaping of the pump light.
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| CN102545034A (en) * | 2011-04-21 | 2012-07-04 | 北京国科世纪激光技术有限公司 | Lateral pump module of semiconductor module |
| CN112864787A (en) * | 2019-11-26 | 2021-05-28 | 中国科学院大连化学物理研究所 | Solid laser gain module |
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| CN102545034A (en) * | 2011-04-21 | 2012-07-04 | 北京国科世纪激光技术有限公司 | Lateral pump module of semiconductor module |
| CN112864787A (en) * | 2019-11-26 | 2021-05-28 | 中国科学院大连化学物理研究所 | Solid laser gain module |
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