Debugging-free composite cavity flat-top laser

Abstract

The invention provides a debugging-free composite cavity flat-top laser, and relates to the technical field of laser. According to the technical key points, a cat eye reflector, a gain medium, a pumping source, a polaroid, a half-wave plate, a polarization beam splitter and a first plane mirror form a first resonant cavity; the cat eye reflector, the gain medium, the pumping source, the polarizing film, the half-wave plate, the polarization beam splitter, the quarter-wave plate, the small-hole diaphragm and the second plane mirror form a second resonant cavity; a debugging-free composite cavity is constructed based on the cat eye reflector; gains and loss distribution in the second resonant cavity are controlled through the polarization element, and the center gain of the gain medium is extracted; the polarization state of the light beam is adjusted by rotating the quarter-wave plate, so that mode competition in the composite cavity is adjusted and controlled, the flat-topped light beam is excited in the first resonant cavity, the flat-topped light beam with uniform energy distribution is generated, and shaping loss inside and outside the cavity is avoided. According to the invention, no additional optical shaping device is needed, and flat-topped beam output can be directly realized in the resonant cavity.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, in particular to an adjustment-free composite cavity flat-top laser. Background Art

[0002] In applications such as high-power laser processing, optical capture, and precision measurement, the intensity distribution of the laser beam has a significant impact on system performance. Traditional Gaussian beams, characterized by high energy at the center and exponentially decreasing energy at the edges, can lead to problems such as uneven heat-affected zones in material processing, lateral force fluctuations in optical capture, and speckle noise in precision measurement. In contrast, flat-top beams, with their flat center intensity, steep edges, and uniform energy distribution, can overcome these issues.

[0003] There are two main approaches to generating flat-top beams: extracavity shaping and intracavity shaping. Extracavity shaping uses external optical elements such as phase plates, lens arrays, dual-lens systems, and diffractive optical elements to shape a traditional Gaussian beam into a flat-top beam. This method has the advantages of wide applicability and ease of integration, but is accompanied by additional optical losses and is limited to fixed input parameters. Intracavity shaping generates a flat-top beam through amplitude and phase control, but requires complex custom optical devices such as deformable mirrors, aspheric optical devices, gradient phase mirrors, diffractive optical devices, and spatial light modulators, resulting in high system complexity and cost. More importantly, traditional laser resonators are extremely sensitive to cavity mirror angle deviations (allowable deviation <0.1 mrad), and the assembly and adjustment process requires repeated iterative adjustments to the cavity mirror angle, which is both complex and difficult to maintain long-term stability. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a debugging-free composite cavity flat-top laser.

[0005] A debugging-free composite cavity flat-top laser comprises: a cat's eye reflector 1, a gain medium 2, a pump source 3, a polarizer 4, a half-wave plate 5, a polarization beam splitter 6, a first plane mirror 8, a quarter-wave plate 9, a pinhole aperture 10, a second plane mirror 11, and a detection assembly; wherein the cat's eye reflector 1, the gain medium 2, the pump source 3, the polarizer 4, the half-wave plate 5, the polarization beam splitter 6, and the first plane mirror 8 constitute a first resonant cavity; and the cat's eye reflector 1, the gain medium 2, the pump source 3, the polarizer 4, the half-wave plate 5, the polarization beam splitter 6, the quarter-wave plate 9, the pinhole aperture 10, and the second plane mirror 11 constitute a second resonant cavity;

[0006] The cat's eye reflector 1 and the first plane mirror 8 serve as two cavity end reflectors of the first resonant cavity; the cat's eye reflector 1 and the second plane mirror 11 serve as two cavity end reflectors of the second resonant cavity;

[0007] The pump source 3 emits pump light which is incident on the gain medium 2 to generate oscillating light. The oscillating light passes through the polarizer 4 and the half-wave plate 5 successively and then enters the polarization beam splitter 6 to be split. The horizontally polarized light is transmitted to the first resonant cavity, and then outputs a flat-top beam to the detection component; the vertically polarized light is reflected to the second resonant cavity, and the optical axis angle of the quarter-wave plate 9 is adjusted according to the light intensity distribution information fed back by the detection component, thereby changing the vertical polarization state of the vertically polarized light, so that part of the oscillating light is converted into horizontally polarized light. The converted horizontally polarized light is transmitted out of the second resonant cavity along the polarization beam splitter 6, thereby adjusting the intra-cavity loss; the small aperture 10 is used to selectively suppress high-order transverse modes so that the Gaussian base mode forms a stable resonance.

[0008] Furthermore, the cat's eye reflector 1 is composed of a concave reflector 1-1 and a convex lens 1-2, the concave surface of the concave reflector 1-1 and the convex surface of the convex lens 1-2 are opposite to each other; the light-transmitting surface of the concave reflector 1-1 is coated with a high-reflection film corresponding to the laser wavelength emitted by the pump source 3; the curvature radius of the concave reflector 1-1, the focal length of the convex lens 1-2 and the distance between the concave reflector 1-1 and the convex lens 1-2 are equal.

[0009] Furthermore, a Q-switching module 7 is placed between the polarization beam splitter 6 and the first plane mirror 8 to achieve high-power millijoule pulse output.

[0010] Furthermore, the gain medium 2 is a Nd:YAG crystal or a Nd:YVO4 crystal; and the Q-switching module 7 is a passive Q-switched crystal, an electro-optical Q-switched crystal or an acousto-optical Q-switched crystal.

[0011] Furthermore, the optical axis angle of the half-wave plate 5 is 22.5° relative to the horizontal, so as to control the reflection and transmission splitting ratio to be 1:1.

[0012] Furthermore, the detection component includes a CCD charge-coupled device 12 and a computer 13. The CCD charge-coupled device 12 is placed on the flat-top light output side of the first plane mirror 8, and is used to capture the light intensity distribution image of the flat-top light beam, and realize real-time display of the light intensity distribution of the flat-top light beam through the connected computer 13.

[0013] Furthermore, the first plane mirror 8 is replaced by a cat's eye reflector; and the second plane mirror 11 is replaced by a cat's eye reflector.

[0014] Furthermore, the transmittance of the first plane mirror 8 is 20%; and the transmittance of the second plane mirror 11 is 5%.

[0015] Furthermore, the pinhole diaphragm 10 is a continuously adjustable diaphragm with a diameter of 1 mm-12 mm.

[0016] Furthermore, the light-transmitting surfaces of all devices are coated with an anti-reflection film that matches the pump wavelength corresponding to the gain medium 2 .

[0017] The beneficial technical effects of the present invention are:

[0018] The present invention proposes an adjustment-free composite cavity flat-top laser. The adjustment-free composite cavity is constructed based on a cat's eye reflector. The unique beam self-collimation characteristics of the cat's eye reflector convert the critical alignment conditions of the traditional laser resonant cavity into a wide-range tolerance design, thereby improving the problem of complex adjustment of the traditional laser resonant cavity and improving the system stability. The gain and loss distribution in the second resonant cavity is controlled by a polarization element, the central gain of the gain medium is extracted, and the polarization state of the beam is adjusted by rotating the wave plate angle, thereby regulating the mode competition in the composite cavity, exciting a flat-top beam in the first resonant cavity, generating a flat-top beam with uniform energy distribution, and avoiding shaping losses inside and outside the cavity. Compared with traditional flat-top laser generation methods, no additional optical shaping devices are required, and flat-top beam output is directly realized in the resonant cavity. Combined with a Q-switching module, high-power pulse output can be achieved.

[0019] The present invention provides a low-complexity, high-stability, low-cost flat-top laser output solution for high-power laser processing, optical capture, precision measurement and other application fields requiring high-brightness uniform beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily apparent by reading the following detailed description with reference to the accompanying drawings, in which several embodiments of the present invention are shown by way of example and not limitation, in which:

[0021] Figure 1 This is a structural schematic diagram of a debugging-free composite cavity flat-top laser proposed by the present invention. DETAILED DESCRIPTION

[0022] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided solely to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the present invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0023] The purpose of the present invention is to provide a debugging-free composite cavity flat-top laser. The laser cavity mode has high stability, which can reduce the need for precise adjustment of optical components. At the same time, it has a simple structure and low cost. The cavity gain and loss are controlled only by polarization elements to output a flat-top beam. It can also be used for high-power laser systems.

[0024] like Figure 1As shown, the present invention proposes a non-adjustable composite cavity flat-top laser comprising: a cat's eye reflector 1, a gain medium 2, a pump source 3, a polarizer 4, a half-wave plate 5, a polarization beam splitter 6, a Q-switching module 7, a first plane mirror 8, a quarter-wave plate 9, a pinhole aperture 10, a second plane mirror 11, a charge coupled device 12, and a computer 13; wherein the cat's eye reflector 1, the gain medium 2, the pump source 3, the polarizer 4, the half-wave plate 5, the polarization beam splitter 6, the Q-switching module 7, and the first plane mirror 8 constitute the first A resonant cavity; a cat's eye reflector 1, a gain medium 2, a pump source 3, a polarizer 4, a half-wave plate 5, a polarization beam splitter 6, a quarter-wave plate 9, a pinhole aperture 10, and a second plane mirror 11 constitute a second resonant cavity; the cat's eye reflector 1 and the first plane mirror 8 serve as two cavity end reflectors of the first resonant cavity; the cat's eye reflector 1 and the second plane mirror 11 serve as two cavity end reflectors of the second resonant cavity; a CCD charge coupled device 12 and a computer 13 constitute a detection assembly for detecting the light intensity distribution of the flat-top beam.

[0025] The cat's-eye reflector 1 consists of a concave reflector 1-1 and a convex lens 1-2. The concave surface of the concave reflector 1-1 faces the convex surface of the convex lens 1-2. The light-transmitting surface of the concave reflector 1-1 is coated with a highly reflective coating corresponding to the wavelength of the laser emitted by the pump source 3. The radius of curvature of the concave reflector 1-1 is equal to the focal length of the convex lens 1-2 and the distance between them. For example, the radius of curvature = focal length = 50 mm. The cat's-eye reflector achieves antiparallel reflection through the "cat's-eye effect": when the light beam is incident normally along the optical axis, the reflected light returns strictly along the original path. When the light beam is incident at a large angle and the principal ray passes through the center of the convex lens, the reflected light remains collinear with the original incident light beam. Compared to traditional flat total reflection mirrors, the cat's-eye reflector exhibits significant advantages in mechanical vibration conditions. It is used to form a highly stable reflective end within the resonant cavity, provides a small range of adjustment-free characteristics, and forms a self-collimating optical path, reducing assembly errors.

[0026] The laser gain medium 2 can be doped with a concentration of 0.6% and has a size of 3×3×8mm. 3 Nd:YAG crystal with a 1064nm anti-reflection coating on the transparent surface. Nd:YVO with the same doping concentration and size can also be used. 4 The pump source 3 is a side pump source with a wavelength of 808 nm, corresponding to the main absorption peak of the gain medium 2. Furthermore, gain media with other operating wavelengths and pump sources with corresponding absorption wavelengths can also be selected based on actual needs.

[0027] The pump source 3 emits pump light that is incident on the gain medium 2 to generate oscillating light. After the oscillating light passes through the polarizer 4, the half-wave plate 5, and the polarization beam splitter 6, the horizontally polarized light is transmitted to the first resonant cavity, and then a flat-top beam is output to the detection component; the vertically polarized light is reflected to the second resonant cavity for mode selection and gain control; according to the light intensity distribution information fed back by the detection component, the vertical polarization state is changed by rotating the optical axis angle of the quarter-wave plate 9, so that part of the oscillating light is converted into a horizontal polarization component. For example: the optical axis degree of the quarter-wave plate 9 is rotated clockwise, thereby gradually increasing the proportion of the vertical polarized light converted into the horizontal polarized light component. The converted horizontally polarized light is transmitted out of the second resonant cavity along the polarization beam splitter 6, thereby adjusting the intra-cavity loss and observing the detection component. The light intensity distribution is adjusted until the output laser energy distribution exhibits a flat-top structure with similar center and edge intensities, indicating that the system has entered a steady state. Polarizer 4 is positioned at a 56° angle with the optical path to allow horizontally polarized light to pass through. Half-wave plate 5 is used to tune the polarization state to control the ratio of reflected and transmitted energy. By rotating the optical axis of half-wave plate 5 to 22.5° relative to the horizontal, the angle of the linear polarization state is adjusted to 45° relative to the horizontal, thereby controlling the reflection-transmission splitting ratio to 1:1. This allows the first and second resonant cavities to oscillate simultaneously, helping to maintain the stable coexistence of the two modes. Polarization beam splitter 6 transmits horizontally polarized light and reflects vertically polarized light. Pinhole aperture 10 selectively suppresses high-order transverse modes, allowing the Gaussian fundamental mode to form a stable resonance. Because the oscillating light in the second resonant cavity extracts Gaussian fundamental mode energy from the central region of gain medium 2, the gain center of the first resonant cavity is weakened.

[0028] The Q-switching module 7 can be selected in the size of 3*3*4.2mm 3 A Cr:YAG passive Q-switched crystal with an initial transmittance of 70% for a laser with a central wavelength of 1064 nm can be optionally placed equidistantly between the polarization beam splitter 6 and the first plane mirror 8 to achieve high-power millijoule pulse output. Alternatively, the Q-switching module 7 can utilize other types of Q-switching elements, such as electro-optical Q-switching and acousto-optic Q-switching, to accommodate the repetition frequency, power, and modulation requirements of different scenarios.

[0029] A CCD (charge-coupled device) 12 is placed to the right of the first plane mirror 8 (i.e., on the flat-top beam output side). It is used to capture the intensity distribution image of the flat-top beam and, via a connected computer 13, to display the flat-top beam intensity distribution in real time. By adjusting the aperture diameter of the pinhole diaphragm 10 and the angle between the optical axis of the quarter-wave plate 9, the flat-top beam intensity distribution displayed on the computer 13 is observed until the final output beam energy range becomes uniform, exhibiting a flat-top distribution.

[0030] Optionally, the transmittance of the first plane mirror 8 is 20%; the transmittance of the second plane mirror 11 is 5%.

[0031] Optionally, the pinhole diaphragm 10 is a continuously adjustable diaphragm with a diameter of 1 mm to 12 mm.

[0032] Optionally, the light-transmitting surfaces of all devices are coated with an anti-reflection film that matches the pump wavelength corresponding to the gain medium 2 .

[0033] Optionally, the first plane mirror 8 and the second plane mirror 11 are placed at a distance of 120 mm from the gain medium 2 .

[0034] Optionally, both the first and second plane mirrors 8 and 11 can be replaced with cat's-eye reflectors to create a fully self-collimating composite cavity structure, enhancing the system's anti-interference capabilities. This full cat's-eye architecture further enhances the laser's stability and anti-interference capabilities, compensating for pitch, yaw, and axial displacement errors simultaneously.

[0035] The principle of the flat-top light generated by the debugging-free composite cavity flat-top laser proposed in the present invention is:

[0036] The first resonant cavity and the second resonant cavity share the gain medium 2, forming a spatially overlapping pump region in the gain medium 2. Subsequently, the oscillating light is separated by the polarization beam splitter 6. The first resonant cavity preferentially oscillates in the edge region of the gain medium, and part of the gain in the central region is extracted by the second resonant cavity. By rotating the optical axis angle of the quarter-wave plate 9 to control the extraction intensity, the energy distribution of the output beam of the first resonant cavity tends to be uniform, and its transverse intensity distribution changes from a typical Gaussian beam to a flat-top beam. The output light intensity distribution is approximately a super-Gaussian function, which can be expressed as:

[0037]

[0038] Where I(r) is the intensity distribution of the flat-top beam at radial position r, I0 is the peak intensity at the center of the beam, w0 is the beam waist radius, and n is the super-Gaussian index, which depends on the intracavity gain distribution. When n = 1, the distribution degenerates into a Gaussian distribution. As n increases, the central region of the beam becomes more uniform, and the attenuation at the edges becomes steeper. If the quarter-wave plate 9 rotates the optical axis by a small angle, insufficient vertically polarized light is converted into horizontally polarized light. The loss in the second resonant cavity is low, resulting in weak oscillations and a Gaussian output beam distribution. However, when the quarter-wave plate 9 is adjusted to a moderate angle, the second resonant cavity extracts an appropriate amount of central energy, and the energy distribution of the beam in the first resonant cavity becomes spatially uniform, forming an intensity distribution close to a flat-top. Simultaneously, a pinhole diaphragm 10 is placed in the second resonant cavity to selectively suppress the oscillation of high-order transverse modes and allow only the Gaussian base mode to pass. By adjusting its aperture size, combined with the adjustment of the optical axis angle of the quarter-wave plate 9, the n value can be further optimized, improving mode purity and coupling efficiency, thereby more precisely controlling the uniformity of the flat-top beam.

[0039] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division into various aspects does not mean that the features of these aspects cannot be combined to benefit. Such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A debugging-free composite cavity flat-top laser, characterized in that: include: A cat's eye reflector (1), a gain medium (2), a pump source (3), a polarizer (4), a half-wave plate (5), a polarization beam splitter (6), a first plane mirror (8), a quarter-wave plate (9), a pinhole aperture (10), a second plane mirror (11), and a detection component; wherein the cat's eye reflector (1), the gain medium (2), the pump source (3), the polarizer (4), the half-wave plate (5), the polarization beam splitter (6), and the first plane mirror (8) constitute a first resonant cavity; and the cat's eye reflector (1), the gain medium (2), the pump source (3), the polarizer (4), the half-wave plate (5), the polarization beam splitter (6), the quarter-wave plate (9), the pinhole aperture (10), and the second plane mirror (11) constitute a second resonant cavity; The cat's eye reflector (1) and the first plane mirror (8) serve as two cavity end reflectors of the first resonant cavity; the cat's eye reflector (1) and the second plane mirror (11) serve as two cavity end reflectors of the second resonant cavity; A pump source (3) emits pump light incident on a gain medium (2) to generate oscillating light, which successively passes through a polarizer (4) and a half-wave plate (5) and then enters a polarization beam splitter (6) to be split, wherein the horizontally polarized light is transmitted to the first resonant cavity, and then a flat-top beam is output to a detection component; the vertically polarized light is reflected to the second resonant cavity, and the optical axis angle of the quarter-wave plate (9) is adjusted according to the light intensity distribution information fed back by the detection component, thereby changing the vertical polarization state of the vertically polarized light, so that part of the oscillating light is converted into horizontally polarized light, and the converted horizontally polarized light is transmitted out of the second resonant cavity along the polarization beam splitter (6), thereby adjusting the intra-cavity loss; a pinhole aperture (10) is used to selectively suppress high-order transverse modes, so that the Gaussian base mode forms a stable resonance.

2. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The cat's eye reflector (1) is composed of a concave reflector (1-1) and a convex lens (1-2), wherein the concave surface of the concave reflector (1-1) and the convex surface of the convex lens (1-2) are opposite to each other; the light-transmitting surface of the concave reflector (1-1) is plated with a high-reflection film corresponding to the wavelength of the laser emitted by the pump source (3); the curvature radius of the concave reflector (1-1), the focal length of the convex lens (1-2) and the distance between the concave reflector (1-1) and the convex lens (1-2) are equal.

3. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: A Q-switching module (7) is placed between the polarization beam splitter (6) and the first plane mirror (8) to achieve high-power millijoule-level pulse output.

4. The adjustment-free composite cavity flat-top laser according to claim 3, characterized in that: The gain medium (2) is a Nd:YAG crystal or a Nd:YVO4 crystal; and the Q-switching module (7) is a passive Q-switching crystal, an electro-optical Q-switching crystal or an acousto-optical Q-switching crystal.

5. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The optical axis angle of the half-wave plate (5) is 22.5° relative to the horizontal, so as to control the reflection and transmission splitting ratio to be 1:

1.

6. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The detection component comprises a CCD charge coupled device (12) and a computer (13). The CCD charge coupled device (12) is placed on the flat top light output side of the first plane mirror (8) and is used to capture the light intensity distribution image of the flat top light beam and realize real-time display of the light intensity distribution of the flat top light beam through the connected computer (13).

7. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The first plane mirror (8) is replaced by a cat's eye reflector; the second plane mirror (11) is replaced by a cat's eye reflector.

8. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The transmittance of the first plane mirror (8) is 20%; the transmittance of the second plane mirror (11) is 5%.

9. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The pinhole diaphragm (10) is a continuously adjustable diaphragm with a diameter of 1 mm to 12 mm.

10. The adjustment-free composite cavity flat-top laser according to claim 1, characterized in that: The light-transmitting surfaces of all devices are coated with an anti-reflection film that matches the pump wavelength corresponding to the gain medium (2).

Images