WO2016045218A1

WO2016045218A1 - Resonant cavity structure for generating radial polarized laser

Info

Publication number: WO2016045218A1
Application number: PCT/CN2014/095041
Authority: WO
Inventors: 王又青; 李波; 杨扬; 赵江; 贺昌玉
Original assignee: 武汉博问光电有限公司
Priority date: 2014-09-23
Filing date: 2014-12-26
Publication date: 2016-03-31

Abstract

Provided is a resonant cavity structure for generating radial polarized laser, comprising a tail mirror (1), a first equivalent 1/2 wave plate (17), a second equivalent 1/2 wave plate (18), a window mirror (6) and three sections of gain regions (7, 8, 9); the three sections of gain regions (7, 8, 9) are connected in series in space via the first equivalent 1/2 wave plate (17) and the second equivalent 1/2 wave plate (18) to form a complete resonant cavity optical path; the tail mirror (1) and the window mirror (6) are respectively located at the head end and tail end of the resonant cavity optical path; optical axes where the three sections of gain regions (7, 8, 9) are located along on the resonant cavity optical path are mutually parallel; and an included angle between an optical axis of the first equivalent 1/2 wave plate (17) and an optical axis of the second equivalent 1/2 wave plate (18) is 45 degrees. An initial polarization state of a light beam in the cavity is determined as an angular polarization via the tail mirror (1), and a plurality of gain regions are connected in series via a polarizing mirror, thus directly obtaining the output of radial polarized laser; in addition, the resonant cavity does not have any external optical conversion component, thus having a simple structure, and being easy to realize.

Description

A cavity structure for generating a radially polarized laser

Technical field

The invention belongs to the field of laser and optical technology, and in particular relates to a resonant cavity structure for generating a radially polarized laser.

Background technique

Recently, with the development of technologies such as holography, coherence, spectroscopy, photochemistry, and accelerators, there is an increasing demand for some special axisymmetric polarization lasers such as radially polarized lasers. In addition, in laser processing, especially in laser cutting processing, in order to ensure uniformity of processing quality of linear polarization (S-polarized or P-polarized) laser in different processing directions, it is usually necessary to convert linearly polarized laser into After the circularly polarized laser is processed, the method is more complicated. Therefore, a laser source with no directional selectivity and higher material absorption rate than the circularly polarized laser is sought, which is the pursuit of the laser processing industry. The target, and the radially polarized laser is the laser source with such characteristics.

There are currently two methods for directly generating an axisymmetric radial polarization laser output:

One is to directly generate a radially polarized laser output by introducing an optical element having polarization selection characteristics into the cavity of the laser, such as using a grating mirror having a radial polarization selection characteristic as a tail mirror of the laser. However, the grating mirror structure is complicated, it is difficult to manufacture, and its service life is difficult to guarantee under high-power working conditions.

The second is to obtain a linearly polarized laser or an angularly polarized laser output, and then use an extraluminal optical system to convert the polarization state to obtain a radially polarized laser. For the linearly polarized laser light generated by the laser, a rotating wave optical element is used outside the cavity to convert the linearly polarized beam into a radially polarized beam, but the special optical component such as the rotating wave plate is very complicated in structure, and its fabrication is also very difficult. .

Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned deficiencies of the prior art and to provide a resonant cavity structure for generating a radially polarized laser light which is simpler in structure and easy to implement.

The technical solution adopted by the invention is: a resonant cavity structure for generating a radially polarized laser, comprising a tail mirror, a first equivalent 1/2 wave plate, a second equivalent 1/2 wave plate, a window mirror and three a segment gain region, wherein the three gain regions are a first gain region, a second gain region, and a third gain region, respectively; the first equivalent 1/2 wave plate oscillates the first gain region The optical axis at the end of the cavity optical path is connected in series with the optical axis of the first end of the optical path of the cavity in which the second gain region is located; the second equivalent 1/2 wave plate is the optical path of the cavity in which the second gain region is located The optical axis of the tail end is connected in series with the optical axis of the first end of the optical path of the resonant cavity of the third gain region to form a complete cavity optical path; the tail mirror and the window mirror are respectively located at the beginning and the end of the optical path of the resonant cavity. The optical axes of the optical paths of the resonators in the three-stage gain region are parallel to each other, and the angle between the optical axis of the first equivalent 1/2 wave plate and the optical axis of the second equivalent 1/2 wave plate is 45 degrees. .

The tail mirror is used to determine the initial polarization state in the cavity as angular polarization, and two adjacent optical axes formed by the equivalent 1/2 wave plate form two intersecting planes with an angle of 45 degrees. This means that the angle between the optical axes of the two equivalent 1/2 wave plates is also exactly 45 degrees. In this case, when the beam sequentially passes through the equivalent 1/2 wave plate of the 45-degree intersection of the two optical axes, the polarization direction of the incident beam is just rotated by 90 degrees, since the incident beam is angularly polarized, then After the transformation, it becomes a radial polarization. After a partial beam of this polarization state is output through the window mirror, the polarization direction remains unchanged, and the output laser beam is a radially polarized laser.

Further, the tail mirror and the window mirror are respectively located at a leading end of the optical path of the resonant cavity where the first gain region is located and a tail end of the optical path of the resonant cavity where the third gain region is located.

Further, the first equivalent 1/2 wave plate comprises two polarizers having high reflectivity and quarter wave plate phase delay characteristics, and the two polarizers are respectively located in the cavity of the cavity where the first gain region is located. At the head end of the optical path of the cavity where the tail end and the second gain region are located, the two polarizers are placed at an angular position of 45 degrees from the respective normal rays.

Further, the second equivalent 1/2 wave plate comprises two polarizers having high reflectivity and quarter wave plate phase delay characteristics, and the two polarizers are respectively located in the cavity of the cavity in the second gain region. At the head end of the optical path of the cavity where the tail end and the third gain region are located, the two polarizers are placed at an angular position of 45 degrees from the respective normal rays.

Four high-reflectance polarizers with quarter-wave retardation characteristics are placed at an incident angle of 45 degrees from the respective normals. When the gain length is connected in series, two groups are formed. Two equivalent 1/2 wave plates can both rotate the polarization direction of the beam passing through it.

Preferably, the tail mirror is a grating mirror that matches the output laser wavelength.

Preferably, the tail mirror is an inner cone mirror having a cone angle of 90 degrees.

When the tail mirror has an angular polarization selection characteristic, the radial polarization laser output can be directly obtained by the above technical solution, which has great economic value for greatly improving the speed or efficiency of laser cutting processing, and is also used for a particle accelerator or the like. Research has great scientific significance. Since metal mirrors or metal cone mirrors generally have higher reflectance for S-polarization than for P-polarization, angles can be easily achieved with a cone-shaped tail mirror with a cone angle of 90 degrees. Select for polarization.

In particular, the tail mirror of the present invention employs a laser tail mirror assembly for selecting angular polarization, including an inner cone mirror and an outer cone mirror that are fixed together in a rotationally symmetric manner about the optical axis, and the inner cone mirror is opened. There is an entrance hole, the outer cone mirror is provided with an outer cone reflection surface and an annular reflection surface, and the inner cone mirror is provided with an inner cone reflection surface, and the inner cone reflection surface is arranged opposite to the outer cone reflection surface, The inner cone reflecting surface, the annular reflecting surface and the outer cone reflecting surface are sequentially connected to form an inner hollow multiple reflection combined structure, and the inner cone reflecting surface and the outer cone reflecting surface have a taper angle of 90 degrees.

Further, the inner cone reflecting surface, the outer cone reflecting surface and the annular reflecting surface are respectively plated with a gold film. The gold film on the reflective surface can further increase the reflectivity of the laser.

Further, the annular reflecting surface is a plane perpendicular to the optical axis.

Further, the annular reflecting surface is a spherical surface or a concave surface with a large radius of curvature.

Further, the spherical or concave surface has a radius of curvature of 10-30 m.

Further, the inner cone mirror and the outer cone mirror are both metal bronze mirrors having high reflectivity.

The above-mentioned tail mirror (a laser tail mirror assembly for selecting angular polarization) makes full use of the metal cone mirror to reflect the S-polarized light higher than the reflectivity of the P-polarized light, through two The conical reflecting surface and the annular reflecting surface form a hollow multiple reflection combined structure. After the laser beam is injected into the combined mirror, it is reflected multiple times in the combined mirror and then returned to the outside by the original path, and passes through the combined mirror. After multiple cone reflections, the S-polarized light maintains a high reflectivity, while the P-polarized light has a large loss. Finally, the polarization state that can be oscillated in the laser cavity and maintained is only angular polarization. By using the combined mirror as a cavity tail mirror, it is possible to effectively suppress P-polarized light in the cavity, and only cause the S-polarized light to oscillate, thereby functioning as an angular polarization selection.

In particular, the tail mirror of the present invention also employs an inner cone W-shaped combination mirror structure for selecting angular polarization, including an inner cone mirror and a W-shaped cone mirror fixedly arranged in a rotationally symmetric manner about the optical axis. The center of the inner cone mirror is provided with an entrance hole, and the inner cone mirror is provided with an inner cone reflection surface, and the reflection surface of the W-shaped cone mirror is composed of an outer cone surface located at a central area and an inner cone surface of the outer circumference area, The inner cone reflecting surface is opposite to the outer cone surface, and the inner cone reflecting surface, the inner cone surface and the outer cone surface are sequentially connected to form an inner hollow multiple reflection combined structure, the inner cone reflecting surface and the outer cone surface The taper angle of the inner tapered surface is 90 degrees.

Further, the inner cone reflecting surface, the outer cone surface and the inner cone surface are respectively plated with a gold film.

Further, a transition region is provided at the intersection of the outer tapered surface and the inner tapered surface of the W-shaped cone mirror.

Further, the transition region is an annular plane perpendicular to the optical axis.

Further, the transition region is an annular curved surface that is tangent to the outer tapered surface and the inner tapered surface, respectively.

Further, the inner cone mirror and the W cone mirror are both metal bronze mirrors having high reflectivity.

The above-mentioned tail mirror (an inner cone W-shaped combination mirror structure for selecting an angular polarization) makes full use of a metal cone mirror to reflect the S-polarized light higher than that of the P-polarized light. A hollow multi-reflection combined structure is formed by three conical reflecting surfaces, and the laser beam is injected into the combined mirror, and is reflected multiple times in the combined mirror and then emitted outward in a direction parallel to the incident light, passing through the combined mirror. After multiple cone reflections, the S-polarized light maintains a high reflectivity, while the P-polarized light has a large loss. Finally, the polarization state that can be oscillated in the laser cavity and maintained is only angular polarization. By using the combined mirror as a cavity tail mirror, it is possible to effectively suppress P-polarized light in the cavity, and only cause the S-polarized light to oscillate, thereby functioning as an angular polarization selection.

The above two kinds of tail mirrors of the invention have simple structure, good polarization selectivity, high anti-damage threshold, good symmetry, strong anti-offset ability, excellent thermal stability and mechanical properties, simple fabrication, low cost, and can be widely applied. Gas, solid, and semiconductor lasers produce high power, high purity angularly polarized light.

The invention determines the initial polarization state of the intracavity beam as the angular polarization by the tail mirror, and then uses the polarizer having the phase delay characteristic to connect the plurality of gain regions in series, thereby realizing the polarization while achieving the gain length concatenation. The rotation of the direction is transformed to directly obtain the output of the radially polarized laser. The cavity has no external switching optics and is simple in structure and easy to implement.

DRAWINGS

Figure 1 is a schematic view of the structure of the present invention.

2 is a schematic structural view of another perspective of the present invention.

Figure 3 is a schematic view of the end face of the present invention.

4 is a schematic view of an equivalent 1/2 wave plate 17 composed of

polarizers

2 and 3 of the present invention.

Figure 5 is a schematic illustration of an equivalent 1/2 wave plate 18 of

polarizers

4 and 5 of the present invention.

FIG. 6 is a schematic structural view showing the optical axes of two equivalent 1/2 wave plates formed by four polarizers intersecting 45 degrees according to the present invention.

FIG. 7 is a schematic diagram showing the axisymmetric polarization conversion of the optical axes of two equivalent 1/2 wave plates of the present invention intersecting 45 degrees.

FIG. 8 is a schematic diagram showing the orthogonal transformation of the axisymmetric polarization directions by the optical axes of the two equivalent 1/2 wave plates of the present invention intersecting 45 degrees.

Figure 9 is a block diagram showing the structure of a laser tail mirror assembly for selecting angular polarization.

Figure 10 is an axial cross-sectional view of the inner cone mirror of the tailgate assembly of Figure 9.

Figure 11 is a front elevational view of the inner cone mirror of the tailgate assembly of Figure 9.

Figure 12 is an axial cross-sectional view of the outer cone mirror of the tailgate assembly of Figure 9.

Figure 13 is a front elevational view of the outer cone mirror of the tailgate assembly of Figure 9.

Figure 14 is a schematic view showing the structure of an inner cone W-shaped combination mirror for selecting angular polarization.

Figure 15 is an axial cross-sectional view of the inner cone mirror of the combination mirror of Figure 14.

Figure 16 is a front elevational view of the inner cone mirror of the combination mirror of Figure 14.

Figure 17 is an axial cross-sectional view of the W-cone mirror of the combination mirror of Figure 14.

Figure 18 is a front elevational view of the W-cone mirror of the combination mirror of Figure 14.

Fig. 19 is a graph showing the relationship between the reflectance of S-polarized light and P-polarized light and the incident angle by a metallic copper mirror.

detailed description

The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1, the axisymmetric polarization laser cavity structure of the present invention has a high reflectivity tail mirror 1 having a characteristic of axisymmetric polarization (angular polarization or radial polarization), and has a quarter wave phase. The

high reflectivity polarizers

2, 3, 4, 5 of the delay characteristic and the output window mirror 6 having a partially reflective partial transmission characteristic, and three parallel gain regions which are parallel to each other. The three gain regions are respectively the first gain region 7, the second gain region 8, and the third gain region 9, and the optical axes of the respective optical paths are respectively 10, 11, and 12, and the

optical axes

10, 11, and 12 are mutually parallel. The angle between the incident beam and the reflected beam of the

polarizers

2, 3, 4, 5 having high reflectivity and their respective normals is 45 degrees, and the first gain region 7, the second gain region 8 and the third The optical path of the cavity in which the gain region 9 is located is effectively connected in series to form a complete cavity optical path. The tail mirror 1 and the window mirror 6 are respectively located at the beginning and the end of the optical path of the cavity, and their respective central axes are respectively located The optical axis of the cavity of the cavity is coaxial, and the positions of the tail mirror 1 and the window mirror 6 can be interchanged, and the effect is the same, except that the position and direction of the output laser are changed. The specific serial connection manner is: the first equivalent 1/2 wave plate 17 composed of the

polarizers

2 and 3 sets the optical axis of the end of the cavity of the cavity in which the first gain region 7 is located and the cavity light of the second gain region 8 The optical axes of the head end of the process are connected in series; the second equivalent 1/2 wave plate 18 composed of the

polarizers

4 and 5 sets the optical axis of the end of the cavity of the cavity in which the second gain region 8 is located and the third gain region 9 The optical axes at the head end of the optical path of the resonant cavity are connected in series to form a complete resonant cavity optical path; that is, the

polarizers

2 and 3 are respectively located at the end of the optical path of the resonant cavity where the first gain region 7 is located. And the first end of the optical path of the cavity where the second gain region 8 is located, the

polarizers

4 and 5 are respectively located at the end of the optical path of the cavity where the second gain region 8 is located and the first end of the optical path of the cavity where the third gain region 9 is located, The tail mirror 1 and the window mirror 6 are respectively located at the end of the optical path of the cavity where the first gain region 7 is located and the end of the optical path of the cavity where the third gain region 9 is located, forming a spatially multi-folded laser cavity. The laser oscillates within the cavity and is amplified in the first gain region 7, the second gain region 8, and the third gain region 9, and then a portion of the laser light is transmitted through the window mirror 6 to form an output laser 13. The medium in the three-stage gain region can be a variety of laser gain materials, and the cross-sectional density distribution has axisymmetric uniformity.

As shown in FIG. 2, in the axisymmetric polarization laser cavity structure of the present invention, the tail mirror 1 is used to determine the initial polarization state in the cavity as angular polarization, and the high reflectivity polarization polarization having a quarter wave plate phase delay characteristic. The incident and reflected beams of

mirrors

2 and 3 are placed at 45 degrees to their respective normals to form a first equivalent 1/2 wave plate, which can rotate the polarization direction of the beam passing through the wave plate by a certain angle. Similarly, the

high reflectance polarizers

4 and 5 having a quarter-wave phase retardation characteristic form a second equivalent 1/2 wave plate, which will also produce the same polarization direction rotation effect. The equivalent half-wave plate can be composed of two polarizers with 1/4 wave plate phase delay characteristics mentioned above, and can also be composed of multiple 1/8 wave plates or other wave plates. .

As shown in FIGS. 2 and 3, in the "∠" shaped space multi-fold laser cavity of the present invention, the plane 15 formed by the

optical axes

10 and 11 connected in series by the

polarizers

2 and 3 and the passing

polarizers

4 and 5 The planes 16 formed by the series of

optical axes

11 and 12 intersect at the optical axis 11, and the two planes are distributed in a "∠" shape, and the angle 14 between the two planes is 45 degrees. This means that the angle between the first equivalent 1/2 wave plate composed of the

polarizers

2 and 3 and the optical axis of the second equivalent 1/2 wave plate composed of the

polarizers

4 and 5 is exactly 45 degrees. In this case, when the beam sequentially passes through the equivalent 1/2 wave plate of the 45-degree intersection of the two optical axes, the polarization direction of the incident beam is just rotated by 90 degrees, since the incident beam is angularly polarized, then After the transformation, it becomes a radial polarization. After a partial beam of this polarization state is output through the window mirror 6, the polarization direction remains unchanged, that is, the output laser beam is a radial polarization characteristic.

As shown in FIG. 4, the

polarizers

2 and 3 having the quarter-wave retardation characteristic of the quarter-wavelength are placed at a 45-degree position with respect to their normals 2' and 3', respectively, thereby forming a reflective inverted line. The first equivalent 1/2 wave plate 17 is. When the incident beam 19 passes through the wave plate, the polarization direction of the exit beam 20 will rotate at a certain angle.

Similarly, as shown in FIG. 5, when the incident beam 20 passes through the second equivalent 1/ which consists of the

polarizers

4 and 5 having a phase retardation characteristic of 1/4 wave plate (the normals thereof are 4' and 5', respectively) After the wave plate 18, the polarization direction of the outgoing beam 21 will also rotate at a certain angle.

As shown in FIG. 6, the plane 15 of the optical axis of the first equivalent 1/2 wave plate 17 in FIG. 4 is composed of the

optical axes

10 and 11. It is determined that the normals 2' and 3' of the

polarizers

2 and 3 also fall on the plane 15. Similarly, the plane 16 of the optical axis of the second equivalent 1/2 wave plate 18 in FIG. 5 is determined by the

optical axes

11 and 12, and the normals 4' and 5' of the

polarizers

4 and 5 also fall on the plane. On the 16th, the angle 14 between the plane 15 and the plane 16 is 45 degrees.

Figure 7 is an equivalent schematic view of the system of Figure 6. When the beam 19 (the illustrated polarization state is the angular polarization 19') passes through the first equivalent 1/2 wave plate 17, the polarization direction of the corresponding outgoing beam 20 is a certain angular rotation. Similarly, when the beam 20 passes through the second equivalent 1/2 wave plate 18, the polarization direction of the corresponding outgoing beam 21 also rotates at a certain angle. Since the angle 14 between the optical axes 17' and 18' of the first equivalent 1/2 wave plate 17 and the second equivalent 1/2 wave plate 18 is exactly 45 degrees, this means that when the light beam 19 is in turn After passing through the first equivalent 1/2 wave plate 17 and the second equivalent 1/2 wave plate 18 placed in such a space, the polarization direction of the outgoing beam 20 is just rotated by 90 degrees, that is, the polarization direction thereof is angularly polarized 18 ' becomes radial polarization 20'. In the same way, the above-mentioned polarization direction conversion process is reversible, such as a radially polarized beam that is reflected back into the cavity by the window mirror portion, and after passing through the system again, it is reduced to an angularly polarized beam.

Fig. 8 is a schematic diagram showing the mutual conversion of angular polarization and radial polarization between two 1/2 wave plates having an optical axis angle of 45 degrees. In the xoy coordinate system, the optical axis 17' of the first equivalent 1/2 wave plate 17 is first selected to be parallel to the y axis, and the polarization direction at any point A of the incident beam cross section is angularly polarized.

And when the angle between the optical axis 17' of the first equivalent 1/2 wave plate 17 is α, the polarization direction of the first equivalent 1/2 wave plate 17 is changed by the rotation of the 2α angle. The angle between E', E' and the optical axis 17' is α. Similarly, when E' passes through the second equivalent 1/2 wave plate 18, its polarization direction will also change from 2θ angle rotation, where θ is E' and the second equivalent 1/2 wave plate An angle between the optical axes 18' of 18; then, the angle between the optical axes 17' and 18' of the first equivalent 1/2 wave plate 17 and the second equivalent 1/2 wave plate 18 is (α + θ). It can be seen that after the incident beam passes through the first equivalent 1/2 wave plate 17 and the second equivalent 1/2 wave plate 18 in sequence, the rotation angle between the polarization direction of the outgoing beam and the polarization direction of the incident beam is 2 (α). +θ). Obviously, when the angle (α + θ) between the optical axes 17' and 18' of the first equivalent 1/2 wave plate 17 and the second equivalent 1/2 wave plate 18 is selected to be 45 degrees, There is just a 90 degree rotation between them, which is the angular polarization.

The incident beam becomes the outgoing beam of the radial polarization E _r . Similarly, the conversion process of the polarization state of an equivalent 1/2 wave plate with an axisymmetric polarization (angular or radial) beam passing through the optical axis at 45 degrees is reciprocal, that is, when the tail mirror selects the initial polarization state. For radial polarization, the cavity can also output an angularly polarized laser.

Preferably, the tail mirror of the embodiment may select a laser tail mirror assembly for selecting angular polarization, as shown in FIG. 9-13, the tail mirror assembly includes a fixed rotationally symmetric arrangement centered on the optical axis. Inner cone mirror 1.1.1 and The outer cone mirror 1.1.2, the inner cone mirror 1.1.1 center has an entrance hole 1.1.3. Wherein, the inner cone mirror 1.1.1 has only one inner cone reflecting surface 1.1.4, and the outer cone mirror 1.1.2 is composed of an outer cone reflecting surface 1.1.5 and a circular reflecting surface 1.1.6, and the inner cone reflecting surface 1.1.4 And the outer cone reflecting surface 1.1.5 is respectively connected to the outer edge and the inner edge of the annular reflecting surface 1.1.6. The inner cone reflecting surface 1.1.4, the outer cone reflecting surface 1.1.5 and the annular reflecting surface 1.1.6 are all planes having high reflectivity, and the three are rotationally symmetric about the optical axis 1.1.7. The inner cone reflecting surface 1.1.4 and the outer cone reflecting surface 1.1.5 are mounted together in an opposing manner to form an inner hollow multiple reflection combining structure. In order to ensure that the incident light can be returned outward along the original path, the cone angle of the inner cone reflecting surface 1.1.4 and the outer cone reflecting surface 1.1.5 are both 90°, that is, the incident light and the inner cone reflecting surface are 1.1.4 and The angle of the conical reflecting surface 1.1.5 is 45°, and the reflectance of S-polarized light and P-polarized light incident at 45° is slightly higher. The taper angle of the inner cone reflecting surface 1.1.4 and the outer cone reflecting surface 1.1.5 is not limited to 90 degrees, and the same effect can be achieved by the same.

Both the inner cone mirror 1.1.1 and the outer cone mirror 1.1.2 are metal bronze mirrors with high reflectivity, and the inner cone reflection surface 1.1.4 and the outer cone reflection surface 1.1.5 have a slightly higher reflectance for S-polarized light. Reflectivity of P-polarized light. The gold film may be plated on the inner cone reflecting surface 1.1.4, the outer cone reflecting surface 1.1.5 and the annular reflecting surface 1.1.6 to further improve the laser reflectivity, or may be plated with other special polarization selective films to increase the S-polarization. The difference in reflectance between light and P-polarized light to improve polarization selection. The annular reflecting surface 1.1.6 has high reflectivity for different polarization states, and may be a plane perpendicular to the optical axis, or a spherical or annular concave surface having a large radius of curvature. When it is spherical or concave, the radius of curvature ranges from Choose within 10-30m, with good stability.

The difference in reflectance between S-polarized light and P-polarized light will increase as the number of conical reflections in the combined mirror increases. The number of cone reflections can be adjusted by the structural parameters A, B, and C of the combined mirror, where A is the height of the inner cone reflecting surface 1.1.4, B is the width of the annular reflecting surface 1.1.6, and C is the outer cone reflection. The height of the surface 1.1.5. In the example of this scheme, any one of the laser beams 1.1.8 enters the combined mirror, and will be sequentially in the internal reflecting surface (1.1.5, 1.1.4, 1.1.5, 1.1.4, 1.1.6, 1.1. 4. 9 reflections occur on 1.1.5, 1.1.4, 1.1.5), and then return to the outside as originally. Among them, the number of reflections on the inner cone reflecting surface 1.1.4 and the outer cone reflecting surface 1.1.5 is 8 times, which will directly affect the difference in reflectance between the S-polarized light and the P-polarized light.

Preferably, the tail mirror of the embodiment may also select an inner cone W-shaped combination mirror for selecting an angular polarization, as shown in FIGS. 14-18, including an inner cone mirror fixedly arranged in a centrally symmetric manner. 1 and W-shaped cone mirror 1.2.2, wherein the inner cone mirror 1.2.1 is an inner cone structure, only one inner cone reflecting surface 1.2.4, the central region has an entrance hole 1.2.3, as a laser beam 1.2.8 The entrance of the W-cone mirror 1.2.2 is the outer cone structure, the outer peripheral part is the inner cone structure, and the reflection surface is composed of the outer cone surface 1.2.5 located in the central area and the inner cone surface 1.2.6 of the outer circumference area. , outer cone 1.2.5 An intersection with the inner cone surface 1.2.6 is provided with an excessive region 1.2.9 of width D, the transition region 1.2.9 may be an annular plane perpendicular to the optical axis, or may be respectively associated with the outer cone surface 1.2.5 and Inner cone surface 1.2.6 Tangent annular arc surface. The setting of this area is mainly to reduce the difficulty of processing, and the width of the transition area can be appropriately adjusted according to the processing requirements to facilitate the production. The inner cone reflecting surface 1.2.4, the outer cone surface 1.2.5 and the inner cone surface 1.2.6 are all planes having high reflectivity, and the inner cone reflecting surface 1.2.4 and the outer cone surface 1.2.5 are arranged in a relatively parallel manner. The method is installed together, the inner cone reflecting surface 1.2.4, the outer cone surface 1.2.5 and the inner cone surface 1.2.6 form an internal hollow multiple reflection combined structure, and the three are rotationally symmetric about the optical axis 1.2.7. In order to ensure that the incident light can be emitted parallel to the incident light, the cone angle α of the inner cone reflecting surface 1.2.4, the outer cone surface 1.2.5 and the inner cone surface 1.2.6 are both 90°, that is, the incident light and the inside The angle between the cone reflecting surface 1.2.4, the outer cone surface 1.2.5 and the inner cone surface 1.2.6 is 45°. The taper angle of the inner cone reflecting surface 1.2.4, the outer cone surface 1.2.5 and the inner cone surface 1.2.6 is not limited to 90°, and when the inner cone reflecting surface 1.2.4 and the inner cone surface 1.2.6 have the same taper angle, The same effect can be achieved when the taper angles of the outer tapered surface 1.2.5 and the inner tapered surface 1.2.6 are complementary angles.

The inner cone mirror 1.2.1 and the W-cone mirror 1.2.2 are both metallic copper mirrors with high reflectivity, inner cone reflecting surface 1.2.4, outer cone surface 1.2.5 and inner cone surface 1.2.6 pair S-polarization The reflectivity of light is slightly higher than the reflectivity of P-polarized light. The gold film may be plated on the inner cone reflecting surface 1.2.4, the outer tapered surface 1.2.5 and the inner tapered surface 1.2.6 to further increase the laser reflectivity, or may be plated with other special polarization selective films to increase the S-polarized light. And the reflectance difference of P-polarized light to improve the polarization selection ability.

The difference in reflectance between S-polarized light and P-polarized light will increase as the number of conical reflections in the combined mirror increases. The number of cone reflections can be adjusted by the structural parameters A, H, C, and D of the combined mirror, where A is the height of the inner cone reflecting surface 1.2.4, H is the height of the inner cone surface 1.2.6, and C is the outer The height of the cone 1.2.5, D is the width of the annular plane 1.2.9. In this embodiment, any one of the laser beams 1.2.8 enters the combined mirror, and then performs five reflections on the side of the optical axis 1.2.7, and then enters the other side of the symmetry to complete another five reflections. 10 occurs on the internal reflection cone (1.2.5, 1.2.4, 1.2.6, 1.2.5, 1.2.4, 1.2.4, 1.2.5, 1.2.6, 1.2.4, 1.2.5) The secondary reflection is then parallel to the incident light and is emitted outwardly from the other side symmetrical about the optical axis 1.2.7.

The reflectance of the reflectance of the metallic copper mirror to the S-polarized light and the P-polarized light as a function of the incident angle. The mathematical expressions of the reflectance of the two polarized light are: R _s =((n-cosθ) ² +k ² / ((n + cos θ) ² + k ² ) and R _p = ((n - sec θ) ² + k ² ) / ((n + sec θ) ² + k ² ), where θ is the incident angle, n and k is the real part and the imaginary part of the refractive index of the reflective surface material, respectively. For the plane reflection bronze mirror, when the incident angle θ = 0°, there is no difference in reflectance between the S-polarized light and the P-polarized light. For the inner cone mirror and the outer cone mirror of the same metal copper, when the incident angle θ=45°, it is apparent from Fig. 19 that the reflectance of the S-polarized light is higher than that of the P-polarization. The reflectivity of light, ie R _s >R _p . Therefore, when the S-polarized light and the P-polarized light are reflected by the metal cone of the combined mirror m times, the total reflectance is

with

That is, the difference in reflectance between the two polarized lights will increase as the number of reflections increases. The two combined mirrors (a laser tail mirror assembly for selecting an angular polarization and an inner cone W-shaped combination mirror for selecting an angular polarization) according to an embodiment of the present invention are used as a cavity tail mirror. It is possible to effectively suppress P-polarized light in the cavity, and only cause the S-polarized light to oscillate, thereby functioning as an angular polarization selection.

The contents not described in detail in the present specification belong to the prior art well known to those skilled in the art.

Claims

A resonant cavity structure for generating a radially polarized laser, comprising: a tail mirror (1), a first equivalent 1/2 wave plate, a second equivalent 1/2 wave plate, and a window mirror (6) And a three-segment gain region; the three-segment gain region is a first gain region (7), a second gain region (8), and a third gain region (9), respectively, and the first equivalent 1/2 wave plate will The optical axis at the end of the optical path of the cavity in which the first gain region (7) is located is connected in series with the optical axis at the head end of the optical path of the cavity in which the second gain region (8) is located; the second equivalent 1/2 wave The slice connects the optical axis at the end of the optical path of the cavity in which the second gain region (8) is located and the optical axis at the head end of the optical path of the cavity in which the third gain region (9) is located to form a complete cavity optical path; The tail mirror and the window mirror are respectively located at the first and the last ends of the optical path of the resonant cavity, and the optical axes of the optical paths of the resonant cavity of the three-stage gain region are parallel to each other, and the optical axis of the first equivalent 1/2 wave plate and the second The angle between the optical axes of the equivalent 1/2 wave plates is 45 degrees.
A resonant cavity structure for generating a radially polarized laser according to claim 1, wherein said tail mirror (1) and window mirror (8) are respectively located in a cavity in which said first gain region (7) is located The end of the optical path and the third gain region (9) are located at the end of the optical path of the cavity.
A resonant cavity structure for generating a radially polarized laser according to claim 1, wherein said first equivalent 1/2 wave plate comprises a high reflectivity and a quarter wave plate phase retardation characteristic Two polarizers, the two polarizers are respectively located at the end of the optical path of the cavity where the first gain region is located and the first end of the cavity of the cavity where the second gain region is located, and the two polarizers are in accordance with the incident beam and the respective normal lines. Place at a 45 degree angular position.
A resonator structure for generating a radially polarized laser according to claim 1, wherein said second equivalent 1/2 wave plate comprises a high reflectivity and a quarter wave plate phase retardation characteristic Two polarizers, the two polarizers are respectively located at the end of the optical path of the cavity where the second gain region is located and the first end of the optical path of the cavity where the third gain region is located, and the two polarizers are in accordance with the incident beam and the respective normal lines. Place at a 45 degree angular position.
A resonant cavity structure for generating a radially polarized laser according to any of claims 1-4, wherein the tail mirror is a grating mirror that matches the output laser wavelength.
A resonant cavity structure for generating a radially polarized laser according to any one of claims 1-4, characterized in that The tail mirror is an inner cone mirror with a cone angle of 90 degrees.
A resonant cavity structure for generating a radially polarized laser according to any of claims 1-4, wherein said tail mirror is a laser tail mirror assembly for selecting angular polarization, including fixing An inner cone mirror (1.1.1) and an outer cone mirror (1.1.2) are arranged symmetrically about the optical axis, and the inner cone mirror (1.1.1) has an entrance hole (1.1.3) at the center thereof. The outer cone mirror (1.1.2) is provided with an outer cone reflecting surface (1.1.5) and an annular reflecting surface (1.1.6), and the inner cone mirror (1.1.1) is provided with an inner cone reflecting surface (1.1. 4), the inner cone reflecting surface (1.1.4) is arranged opposite to the outer cone reflecting surface (1.1.5), the inner cone reflecting surface (1.1.4), the annular reflecting surface (1.1.6), the outer cone The reflecting surfaces (1.1.5) are sequentially connected to form an internal hollow multiple reflection combined structure, and the cone angles of the inner cone reflecting surface (1.1.4) and the outer cone reflecting surface (1.1.5) are both 90 degrees.
A resonator structure for generating a radially polarized laser according to claim 7, wherein said inner cone reflecting surface (1.1.4), outer cone reflecting surface (1.1.5), and annular reflecting surface (1.1.6) are respectively plated with a gold film.
A resonator structure for generating a radially polarized laser according to claim 7, wherein said annular reflecting surface (1.1.6) is a plane perpendicular to the optical axis.
A resonant cavity structure for generating a radially polarized laser according to claim 7, wherein said annular reflecting surface (1.1.6) is a spherical or concave surface having a large radius of curvature.
A resonator structure for generating a radially polarized laser according to claim 10, wherein said spherical or concave surface has a radius of curvature of 10 to 30 m.
A resonator structure for generating a radially polarized laser according to claim 7, wherein said inner cone mirror (1.1.1) and outer cone mirror (1.1.2) both have high reflectance Metal bronze mirror.
A resonator structure for generating a radially polarized laser according to any one of claims 1 to 4, wherein said tail mirror is an inner cone W-shaped combination mirror for selecting an angular polarization. The inner cone mirror (1.2.1) and the W-cone mirror (1.2.2) are fixedly arranged in a rotationally symmetric manner around the optical axis, and the inner cone mirror (1.2.1) is opened at the center. An entrance hole (1.2.3), the inner cone mirror (1.2.1) is provided with an inner cone reflecting surface (1.2.4), and the reflecting surface of the W-shaped cone mirror (1.2.2) is located at a central area The outer tapered surface (1.2.5) and the inner tapered surface (1.2.6) of the outer peripheral region, the inner tapered reflecting surface (1.2.4) is arranged opposite to the outer tapered surface (1.2.5), the inner cone reflecting The surface (1.2.4), the inner tapered surface (1.2.6) and the outer tapered surface (1.2.5) are sequentially connected to form an inner hollow multiple reflection combined structure, the inner cone reflecting surface (1.2.4), and the outer surface The taper angles of the tapered surface (1.2.5) and the inner tapered surface (1.2.6) are both 90°.
A resonant cavity structure for generating a radially polarized laser according to claim 13, wherein said inner cone reflecting surface (1.2.4), outer tapered surface (1.2.5) and inner tapered surface ( 1.2.6) The gold film is plated separately.
A resonant cavity structure for generating a radially polarized laser according to claim 13, characterized in that the outer tapered surface (1.2.5) and the inner tapered surface of the W-shaped cone mirror (1.2.2) The intersection of 1.2.6) has an excessive area (1.2.9).
A resonant cavity structure for generating a radially polarized laser according to claim 15, wherein said transition region (1.2.9) is an annular plane perpendicular to the optical axis.
A resonant cavity structure for generating a radially polarized laser according to claim 15, wherein said transition region (1.2.9) is respectively opposite to the outer tapered surface (1.2.5) and the inner tapered surface ( 1.2.6) Tangent circular arc surface.
A resonant cavity structure for generating a radially polarized laser according to claim 13, wherein said inner cone mirror (1.2.1) and W-shaped cone mirror (1.2.2) both have high reflection The rate of metal bronze mirror.