CN101465512B - Symmetrical polarized light laser for novel pole - Google Patents

Abstract

Translated fromChinese

一种新型柱对称偏振光激光器，属光电子领域。柱对称偏振光激光包括径向偏振激光和切向偏振激光。本激光器是以Nd:YAG为激光增益介质，利用Nd:YAG晶体的热致双折射效应，采取特殊非对称的谐振腔设计抑制其中一种偏振光的起振，而另一种偏振光则可以单独运转，从而输出径向偏振激光或切向偏振激光。本激光器中可应用于激光加工方面。

The invention discloses a novel cylindrical symmetric polarized light laser, which belongs to the field of optoelectronics. Cylindrical polarized lasers include radially polarized lasers and tangentially polarized lasers. This laser uses Nd:YAG as the laser gain medium, uses the thermally induced birefringence effect of Nd:YAG crystal, and adopts a special asymmetric resonator design to suppress the vibration of one polarized light, while the other polarized light can Operate independently to output radially polarized laser or tangentially polarized laser. The laser can be used in laser processing.

Description

Translated fromChinese

一种新型柱对称偏振光激光器A Novel Cylindrical Polarized Laser

技术领域technical field

本发明一种新型柱对称偏振光激光器，属光电子领域。本激光器中可以输出柱对称偏振光激光，可应用于激光加工方面。The invention relates to a novel cylindrical symmetric polarized light laser, which belongs to the field of optoelectronics. The laser can output cylindrically symmetrical polarized light laser, which can be applied to laser processing.

背景技术Background technique

柱对称偏振激光分为两种，一种是径向偏振激光(图1)，另一种是切向偏振激光(图2)，图上箭头方向为激光电矢量方向。There are two types of cylindrically symmetric polarized lasers, one is radially polarized laser (Figure 1), and the other is tangentially polarized laser (Figure 2). The direction of the arrow in the figure is the direction of the laser electric vector.

在光泵浦激光增益介质Nd:YAG的过程中，增益介质除输出激光能量外，不可避免地会产生热量，对于棒状增益介质来说，通常采用外围通水冷却的方案对其进行冷却。这种泵浦及冷却结构导致了在增益介质的截面上温度呈梯度分布，使得径向偏振光和切向偏振光产生两个不同的聚焦点，这就是Nd:YAG增益介质的热致双折射效应。光学谐振腔内径向偏振光或切向偏振光如单独运转，激光器则输出径向偏振激光或切向偏振激光。In the process of optically pumping the laser gain medium Nd:YAG, the gain medium will inevitably generate heat in addition to outputting laser energy. For the rod-shaped gain medium, it is usually cooled by peripheral water cooling. This pumping and cooling structure leads to a gradient temperature distribution on the cross-section of the gain medium, so that radially polarized light and tangentially polarized light produce two different focal points, which is the thermally induced birefringence of the Nd:YAG gain medium effect. If the radially polarized light or tangentially polarized light in the optical resonator operates independently, the laser will output radially polarized laser or tangentially polarized laser.

根据国外大量研究结果表明：在激光切割和钻孔方面，柱对称偏振光比其它偏振光，如线偏振光和圆偏振光，具有更好的加工效果。目前，圆偏振激光通常用于激光切割，而径向偏振激光的切割效果是圆偏振激光的两倍；对于激光钻孔来说，在某些特定情况下，切向偏振激光有最佳的加工效果。According to a large number of foreign research results, in terms of laser cutting and drilling, cylindrically symmetrical polarized light has better processing effects than other polarized light, such as linearly polarized light and circularly polarized light. At present, circularly polarized lasers are usually used for laser cutting, and the cutting effect of radially polarized lasers is twice that of circularly polarized lasers; for laser drilling, in some specific cases, tangentially polarized lasers have the best processing Effect.

以色列人Inon Moshe等以半导体侧面泵浦Nd:YAG增益介质，通过在腔内插入衍射小孔，在半对称腔和对称腔两种谐振腔结构上都实现了径向偏振光或切向偏振光独立运转。采用半对称腔结构，全反腔镜尽量贴近增益介质，输出腔镜取一定腔长，衍射小孔位于腔内靠近输出腔镜的位置，其工作区域位于谐振腔ω0-D曲线(ω0为增益介质基模半径，D为光焦度)第一稳定区的上边界(上边界为泵浦功率大的边界，下边界为泵浦功率小的边界)，如图3所示；采用对称腔结构，衍射小孔位于腔内靠近输出腔镜的位置，其工作区域位于谐振腔ω0-D曲线第二稳定区的上边界，如图4所示。当径向偏振光处于稳定区边界时，图3中1所处区域以及图4中3所处区域，径向偏振光模体积远大于切向偏振光模体积，谐振腔输出径向偏振激光；而当切向偏振光处于稳定区边界时，图3中2所处区域以及图4中4所处区域，切向偏振光有大的模体积而径向偏振光处于非稳定区无法起振，此时谐振腔输出切向激光。Israeli Inon Moshe et al. pumped the Nd:YAG gain medium on the side of the semiconductor, and by inserting diffraction holes in the cavity, they realized radially polarized light or tangentially polarized light in both semi-symmetric cavity and symmetric cavity resonator structures. operate independently. The semi-symmetrical cavity structure is adopted, the total anti-cavity mirror is as close as possible to the gain medium, the output cavity mirror has a certain cavity length, the diffraction pinhole is located in the cavity close to the output cavity mirror, and its working area is located on the ω0-D curve of the resonant cavity (ω0 is the gain Radius of the fundamental mode of the medium, D is the optical power) of the upper boundary of the first stable zone (the upper boundary is the boundary with high pump power, and the lower boundary is the boundary with small pump power), as shown in Figure 3; a symmetrical cavity structure is adopted , the diffraction pinhole is located in the cavity close to the output cavity mirror, and its working area is located at the upper boundary of the second stable region of the ω0-D curve of the resonator, as shown in Figure 4. When the radially polarized light is at the boundary of the stable region, the area where 1 is located in Figure 3 and the area where 3 is located in Figure 4, the radially polarized light mode volume is much larger than the tangentially polarized light mode volume, and the resonant cavity outputs radially polarized laser light; However, when the tangentially polarized light is at the boundary of the stable region, the area where 2 is located in Figure 3 and the area where 4 is located in Figure 4, the tangentially polarized light has a large mode volume and the radially polarized light cannot start to vibrate when it is in the unstable area. At this time, the resonator outputs tangential laser light.

发明内容Contents of the invention

本发明提出一种新的实现柱对称偏振光激光运转方案，该方案以Nd:YAG为增益介质，采用特殊设计的非对称腔结构可以实现径向偏振光或切向偏振光运转。The present invention proposes a new scheme for realizing cylindrically symmetric polarized laser operation. The scheme uses Nd:YAG as a gain medium and adopts a specially designed asymmetric cavity structure to realize radially polarized light or tangentially polarized light operation.

本发明谐振腔的两臂腔长或两个腔镜采取特殊的非对称设计，使得切向偏振光第一稳定区上边界对着径向偏振光非稳定区的最小值，此时切向偏振光模体积极大而径向偏振光模体积极小或者通过设计使得径向偏振光第二稳定区的下边界对着切向偏振光非稳区最小值，此时径向偏振光模体积极大而切向偏振光模体积极小，切向偏振光无法起振，从而实现径向偏振激光运转。The two-arm cavity length or the two cavity mirrors of the resonator cavity of the present invention adopt a special asymmetric design, so that the upper boundary of the first stable region of the tangentially polarized light faces the minimum value of the unstable region of the radially polarized light. The volume of the optical mode is extremely large and the modulus of the radially polarized light is extremely small, or the lower boundary of the second stable region of the radially polarized light is designed to face the minimum value of the unstable region of the tangentially polarized light, and the modulus of the radially polarized light is positively The large and tangentially polarized light modulus is extremely small, and the tangentially polarized light cannot be oscillated, thereby realizing radially polarized laser operation.

众所周知，在以Nd:YAG为增益介质的谐振腔中，热致双折射效应导致径向偏振光和切向偏振光产生两个不同的聚焦点，切向偏振光焦距f_θ和径向偏振光焦距f_r的理论比值f_θ/f_r为1.2，实际测量值为1.35～1.5之间。这种不同的热焦距导致径向偏振光和切向偏振光产生两个不同的稳定区曲线。另外，谐振腔中两臂腔长的不一致或两个腔镜参数的不一致都会使谐振腔随泵浦功率变化出现两个分离的稳定区。As we all know, in the resonant cavity with Nd:YAG as the gain medium, the thermally induced birefringence effect leads to two different focal points for radially polarized light and tangentially polarized light, and the focal length f_θ of tangentially polarized light and radially polarized light The theoretical ratio f_θ /_fr of the focal length f_r is 1.2, and the actual measured value is between 1.35 and 1.5. This different thermal focal length results in two different stability zone curves for radially polarized light and tangentially polarized light. In addition, the inconsistency of the cavity lengths of the two arms in the resonator or the inconsistency of the parameters of the two cavity mirrors will cause two separate stable regions to appear in the resonator as the pump power changes.

附图5为本发明的谐振腔结构图，R1、R2分别为腔镜5、腔镜6的曲率半径，L1、L2分别为腔镜5、腔镜6距离Nd:YAG增益介质7主平面的长度。对于径向偏振光，根据V.Magni的理论，谐振腔ω0-D曲线中第一稳定区的上边界位于X1_r＝1/u1，第二稳定区的下边界位于X2_r＝1/u2，其中：u1＝L1×(1-L1/R1)，u2＝L2×(1-L2/R2)。而中间非稳区模体积最小值位于X3_r＝(1/u1+1/u2)/2。对于切向偏振光来说，假设切向偏振光焦距f_θ和径向偏振光焦距f_r的实验测量比值f_θ/f_r为k，则切向偏振光第一稳定区的上边界位于X1_θ＝k/u1，第二稳定区的下边界位于X2_θ＝k/u2。而中间非稳区模体积最小值位于X3_θ＝k×(1/u1+1/u2)/2。Accompanying drawing 5 is the structural diagram of resonant cavity of the present invention, R1, R2 are respectively the radius of curvature ofcavity mirror 5,cavity mirror 6, L1, L2 are respectivelycavity mirror 5,cavity mirror 6 distance Nd:YAG gain medium 7 main planes length. For radially polarized light, according to V. Magni's theory, the upper boundary of the first stable region in the resonator ω0-D curve is located at X1_r =1/u1, and the lower boundary of the second stable region is located at X2_r =1/u2, Among them: u1=L1×(1-L1/R1), u2=L2×(1-L2/R2). And the minimum value of the mode volume in the intermediate unstable zone is located at X3_r =(1/u1+1/u2)/2. For tangentially polarized light, assuming that the experimentally measured ratio f_θ /f_r of the focal length_f θ of tangentially polarized light and the focal length f_r of radially polarized light is k, the upper boundary of the first stable region of tangentially polarized light is located at X1_θ =k/u1, the lower boundary of the second stable region is located at X2_θ =k/u2. And the minimum value of the mode volume in the intermediate unstable region is located at X3_θ =k×(1/u1+1/u2)/2.

谐振腔设计时，首先使X1_θ＝X3_r，得到u1/u2＝2k一1，此时切向偏振光第一稳定区的上边界最大值与径向偏振光中间非稳区模体积最小值对应，实验中减小两臂腔长差别，可以使切向偏振光第一稳定区的上边界与径向偏振光中间非稳区模体积最小值对应，切向偏振光模体积极大而径向偏振光极小且无法起振，从而实现切向偏振激光运转，如图6所示区域。而如设计谐振腔，使X2_r＝X3_θ，得到u1/u2＝k/(2-k)，此时径向偏振光第二稳定区的下边界最大值与切向偏振光中间非稳区模体积最小值对应，实验中同时减小两臂腔长差别，可以使径向偏振光第二稳定区的下边界与切向偏振光中间非稳区模体积最小值对应，径向偏振光模体积极大而切向偏振光极小且无法起振，从而实现切向偏振激光运转，如图7所示区域。When designing the resonant cavity, first set X1_θ = X3_r , get u1/u2 = 2k-1, at this time the maximum value of the upper boundary of the first stable region of tangentially polarized light and the minimum value of the mode volume of the middle unstable region of radially polarized light Correspondingly, reducing the difference in the cavity lengths of the two arms in the experiment can make the upper boundary of the first stable region of the tangentially polarized light correspond to the minimum value of the mode volume of the middle unstable region of the radially polarized light. The mode volume of the tangentially polarized light is extremely large and radial The polarized light is extremely small and cannot be oscillated, so that the tangentially polarized laser operation is realized, as shown in the area shown in Figure 6. However, if the resonant cavity is designed, X2_r =X3_θ , and u1/u2=k/(2-k) is obtained. At this time, the lower boundary maximum value of the second stable region of radially polarized light and the middle unstable region of tangentially polarized light The minimum value of the mode volume corresponds to the minimum value of the mode volume. In the experiment, the difference in the cavity length of the two arms is reduced at the same time, so that the lower boundary of the second stable region of the radially polarized light corresponds to the minimum value of the mode volume of the unstable region in the middle of the tangentially polarized light. The radially polarized light mode The volume is extremely large, but the tangentially polarized light is extremely small and cannot be oscillated, so that the tangentially polarized laser operation is realized, as shown in the area shown in Figure 7.

本发明不同于以色列人Inon Moshe的谐振腔设计，由于处于非稳定区的偏振光模体积接近零，则腔内无需插入衍射小孔即可实现柱对称偏振光激光运转。The present invention is different from the resonant cavity design of the Israeli Inon Moshe. Since the polarized light mode volume in the unstable region is close to zero, the cylindrically symmetrical polarized light laser operation can be realized without inserting diffraction holes in the cavity.

附图说明Description of drawings

图1为径向偏振激光电矢量方向示意图；图2为切向偏振激光电矢量方向示意图；图3为半对称腔柱对称偏振激光工作区域ω0-D曲线图，1为径向偏振光工作区域，2为切向偏振光工作区域；图4为对称腔柱对称偏振激光工作区域ω0-D曲线图，3为径向偏振光工作区域，4为切向偏振光工作区域；图5为柱对称偏振激光器谐振腔结构图，R1、R2分别为腔镜5、腔镜6曲率半径，L1、L2分别为腔镜5、腔镜6距离Nd:YAG增益介质7主平面的长度；图6为非对称腔切向偏振激光工作区域ω0-D曲线图；图7为非对称腔径向偏振激光工作区域ω0-D曲线图。Figure 1 is a schematic diagram of the electric vector direction of the radially polarized laser; Figure 2 is a schematic diagram of the electric vector direction of the tangentially polarized laser; Figure 3 is the ω0-D curve diagram of the working area of the semi-symmetric cavity cylindrically symmetrically polarized laser, and 1 is the working area of the radially polarized light , 2 is the working area of tangentially polarized light; Fig. 4 is the ω0-D curve diagram of the working area of symmetric polarized laser in a symmetrical cavity; 3 is the working area of radially polarized light; 4 is the working area of tangentially polarized light; Fig. 5 is the working area of cylindrically symmetric Structural diagram of the polarized laser resonator, R1 and R2 are the curvature radii of thecavity mirror 5 and thecavity mirror 6 respectively, L1 and L2 are the distances from thecavity mirror 5 and thecavity mirror 6 to the main plane of the Nd:YAG gain medium 7 respectively; FIG. The ω0-D curve of the working area of the symmetric cavity tangentially polarized laser; Figure 7 is the ω0-D curve of the working area of the asymmetric cavity radially polarized laser.

具体实施方式：Detailed ways:

以下结合附图5对本发明的实施方式作进一步说明。The embodiment of the present invention will be further described below in conjunction with FIG. 5 .

设定通过实验测得的f_θ/f_r＝1.3，腔镜5、腔镜6为平面镜，即R1＝∞、R20＝∞，则当L1/L2＝1.6时，此时切向偏振光模体积最大值与径向偏振光模体积最小值对应，实验中缩小L1/L2比值到约1.5时，获得切向偏振激光输出，激光功率约12.7W。而当L1/L2＝1.86时，径向偏振光第二稳定区下边界模体积最大值与切向偏振光非稳区模体积极小值对应，实验中缩小L1/L2比值到约1.78时，获得径向偏振激光运转，激光功率约14.1W。Set f_θ /f_r = 1.3 measured through experiments,cavity mirror 5 andcavity mirror 6 are plane mirrors, that is, R1 = ∞, R20 = ∞, then when L1/L2 = 1.6, the tangentially polarized light mode The maximum volume corresponds to the minimum volume of the radially polarized light mode. In the experiment, when the L1/L2 ratio is reduced to about 1.5, the tangentially polarized laser output is obtained, and the laser power is about 12.7W. And when L1/L2=1.86, the maximum value of the lower boundary mode volume in the second stable region of radially polarized light corresponds to the positive minimum value of the mode volume in the unstable region of tangentially polarized light. When the ratio of L1/L2 is reduced to about 1.78 in the experiment, Obtain radially polarized laser operation, the laser power is about 14.1W.

Claims (1)

1. post symmetrical polarized light laser device, its resonant cavity is made up of gain medium Nd:YAG crystal and resonator mirror, and the long or resonator mirror radius of curvature of resonant cavity adopts asymmetric design; Make radial polarisation light or tangential polarization light independent operation; Outputting radial polarization laser or tangential polarization laser, the two is referred to as post symmetry polarization laser, and it is characterized in that: the long ratio in two arm chambeies of resonant cavity is about at 1.5 o'clock; Coboundary, tangential polarization light first stable region is facing to the minimum value of radial polarisation light unstable region; This moment tangential polarization optical mode volume greatly and radial polarisation optical mode volume is minimum, radial polarisation light can't starting of oscillation, thereby realizes the tangential polarization laser operation; Perhaps the long ratio in two arm chambeies of resonant cavity is about at 1.78 o'clock; Make the lower boundary of radial polarisation light second stable region face toward the non-steady district of tangential polarization light minimum value; This moment radial polarisation optical mode volume greatly and tangential polarization optical mode volume is minimum; Tangential polarization light can't starting of oscillation, thereby realizes the radial polarisation laser operation.

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