Method for generating a 266 nm laser and device therefor

Abstract

This invention discloses a method and apparatus for generating 266nm laser. The method includes the following steps: S1, shaping an incident 532nm laser into an elliptical spot; S2, incidenting the elliptical spot onto a BBO crystal under controlled temperature, generating 266nm ultraviolet laser through fourth harmonic generation; wherein the major and minor axes of the elliptical spot are aligned with the ordinary and extraordinary beam directions of the BBO crystal, respectively, and the dimensions of the major and minor axes of the elliptical spot are adapted to the lateral dimensions of the BBO crystal in the corresponding directions. The apparatus includes a laser source, a spot shaping module, a temperature control module, a BBO crystal module, and a detection module. This invention effectively solves the problem of beam quality degradation and conversion efficiency reduction caused by the thermal effect of the BBO crystal during high-power fourth harmonic generation, meeting the urgent need for high-power and high-stability 266nm lasers in fields such as semiconductor wafer micromachining, biomedical imaging, and environmental monitoring.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and specifically to a method and apparatus for generating 266nm laser. Background Technology

[0002] As the fourth harmonic of the 1064 nm near-infrared laser, the 266 nm ultraviolet laser possesses irreplaceable application value in fields such as semiconductor microfabrication, cell fluorescence imaging, and trace pollutant detection due to its advantages such as short wavelength, high photon energy, and strong spatial coherence. In recent years, the demand for 266 nm laser output power in industrial and scientific research fields has continued to rise; however, current technology still faces a key bottleneck.

[0003] Currently, barium borate (BBO) crystals are the core nonlinear optical element for generating 266 nm lasers, used to achieve fourth harmonic conversion. However, in this process, the BBO crystal absorbs some energy from the incident 1064 nm fundamental frequency light and 532 nm second harmonic light, thus triggering a thermal effect. This thermal effect leads to the formation of a non-uniform temperature field and thermal stress within the crystal, resulting in two major problems: first, the output beam spot is distorted from the designed elliptical shape to a quasi-star shape, severely degrading the beam quality; second, the fourth harmonic conversion efficiency decreases significantly.

[0004] Existing research often focuses on the local optimization of single parameters, such as using the finite element method to analyze crystal temperature distribution, without delving into the impact of thermal stress on beam quality; or it only focuses on optimizing temperature control parameters, neglecting the matching relationship between beam spot morphology and crystal physical properties. These local optimization strategies fail to systematically address the performance degradation problem caused by thermal effects from the perspective of multi-physics synergistic control, making it difficult to achieve both high power output and high beam quality, thus hindering the further development and promotion of 266nm lasers in industrial applications. Summary of the Invention

[0005] To address the bottleneck in existing technologies where the thermal effect during fourth harmonic generation of BBO crystals causes multi-physics coupling, resulting in a trade-off between output power and beam quality, this application proposes a method and apparatus for generating 266nm lasers through a multi-physics synergistic modulation approach.

[0006] According to a first aspect of the present invention, a method for generating a 266nm laser is provided, comprising the following steps: S1. Shape the incident 532nm laser into an elliptical spot; S2. The elliptical light spot is incident on the BBO crystal to be incident under a controlled temperature, and 266nm ultraviolet laser is generated by frequency doubling. The major and minor axes of the elliptical light spot are aligned with the ordinary and extraordinary light directions of the BBO crystal to be incident on, respectively, and the dimensions of the major and minor axes of the elliptical light spot are adapted to the lateral dimensions of the BBO crystal to be incident on in the corresponding directions.

[0007] Furthermore, the ratio of the major axis to the minor axis of the elliptical light spot is (2~20):1, and the controlled temperature is 10~25℃.

[0008] Furthermore, the BBO crystal to be incident is a uniform crystal under dry conditions, and the region with a power output difference of ≤5% on its light-transmitting surface is used as the laser incident region.

[0009] Furthermore, the lateral dimension of the BBO crystal to be incident on is 1.5~3mm in the non-optical direction.

[0010] Furthermore, the light transmission dimension of the BBO crystal to be incident is 3~12mm.

[0011] According to a second aspect of the present invention, a device for generating 266nm ultraviolet laser is provided, comprising a laser source, a spot shaping module, a temperature control module, a BBO crystal module, and a detection module; The laser source is used to output 532nm laser light; The spot shaping module is located downstream of the laser source's optical path and is used to shape the 532nm laser into an elliptical spot. The spot shaping module includes a cylindrical mirror group. The temperature control module is thermally coupled to the BBO crystal module to maintain the BBO crystal module at a stable temperature. The BBO crystal module is located downstream of the optical path of the spot shaping module and is used to generate 266nm ultraviolet laser through frequency quadruple harmonic processing. The detection module is located downstream of the optical path of the BBO crystal module and is used to monitor the output power and beam quality of the 266nm ultraviolet laser in real time. The major and minor axes of the elliptical light spot are aligned with the ordinary and extraordinary light directions of the BBO crystal module, respectively, and the major and minor axis dimensions of the elliptical light spot are adapted to the lateral dimensions of the BBO crystal module in the corresponding directions.

[0012] Furthermore, the ratio of the major axis to the minor axis of the elliptical light spot is (2~20):1, and the temperature control module is configured to maintain the temperature of the BBO crystal module at 10~25℃.

[0013] Furthermore, the BBO crystal module is a uniform crystal in a dry environment, and the region with a power output difference of ≤5% on the light-transmitting surface of the BBO crystal module is used as the laser incident region.

[0014] Furthermore, the lateral dimension of the BBO crystal module in the non-optical direction is 1.5~3mm.

[0015] Furthermore, the light transmission size of the BBO crystal module is 3~12mm.

[0016] The beneficial effects of this invention are: This invention effectively solves the problem of beam quality degradation and conversion efficiency reduction caused by thermal effects in BBO crystals during high-power fourth harmonic generation through a multi-dimensional synergistic design of beam spot morphology, crystal physical properties, and thermal management. The core of this design lies in shaping the incident 532nm laser into an elliptical beam spot, aligning its major and minor axes with the ordinary and extraordinary beam directions of the crystal, respectively, while precisely matching the dimensions of the major and minor axes of the beam spot with the transverse dimensions of the crystal in the corresponding directions. This proactive synergistic design disperses the laser energy along the crystal's vulnerable axes, significantly suppressing thermal stress concentration and preventing thermal distortion of the output beam spot from an elliptical to a quasi-star shape, thus ensuring stable beam quality at high power. This solution significantly improves the fourth harmonic conversion efficiency while ensuring the long-term stability and reliability of the system, ultimately achieving a synergistic breakthrough in key performance indicators such as high power and high beam quality for 266nm lasers, strongly supporting application needs in high-end fields such as semiconductor precision processing and biomedical imaging. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the 266nm ultraviolet laser generating device in a specific embodiment of the present invention; Figure 2 The above are the light output curves of 266 nm laser under different temperature control methods in a specific embodiment of the present invention. Figure 3 This is a schematic diagram showing the nine-square grid positions of the light-transmitting surface of the BBO crystal in a specific embodiment of the present invention; Figure 4 This is a graph showing the output laser power of BBO crystals of different sizes in a specific embodiment of the present invention; Figure labels: 1-Laser source; 2-Spot shaping module; 3-Temperature control module; 4-BBO crystal module; 5-Detection module. Detailed Implementation

[0018] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] In view of the problems of beam quality degradation and low conversion efficiency caused by thermal effects in existing technologies, the first objective of this invention is to propose a method for generating 266nm laser. Through the coordinated optimization of multiple parameters such as beam shaping, precise temperature control and crystal region selection, a high-power, high-beam-quality 266nm laser output is achieved.

[0021] The second objective of this invention is to propose a 266nm ultraviolet laser generation device. By integrating a spot shaping module, a high-precision temperature control module, and a preferred BBO crystal module, the bottlenecks of thermal stress distortion and efficiency reduction are systematically solved, providing a stable and reliable high-power ultraviolet laser source for applications such as microfabrication and bioimaging.

[0022] The method for generating this product provided by the present invention includes the following steps: S1. Shape the incident 532nm laser into an elliptical spot; S2. The elliptical light spot is incident on the BBO crystal to be incident under a controlled temperature, and 266nm ultraviolet laser is generated by frequency doubling. The major and minor axes of the elliptical light spot are aligned with the ordinary and extraordinary light directions of the BBO crystal to be incident on, respectively, and the dimensions of the major and minor axes of the elliptical light spot are adapted to the lateral dimensions of the BBO crystal to be incident on in the corresponding directions.

[0023] The ratio of the major axis to the minor axis of the elliptical beam spot is (2~20):1, such as 2:1, 5:1, 10:1, 15:1, 20:1, or any value between them. This ratio of elliptical beam spot effectively reduces the energy density of the BBO crystal in stress-sensitive non-polar light directions, thereby significantly suppressing thermal stress concentration, avoiding distortion of the output beam spot, and ensuring good beam quality.

[0024] The controlled temperature is 10~25℃, such as 10℃, 12℃, 14℃, 16℃, 18℃, 20℃, 22℃, 25℃, or any value between them. Preferably, the controlled temperature is 16~25℃, such as 16℃, 18℃, 20℃, 22℃, 25℃, or any value between them. Precise control of the controlled temperature can significantly improve the fourth harmonic conversion efficiency. The BBO crystal to be incident is a homogeneous crystal under dry conditions. The region with a power output difference ≤5% on its light-transmitting surface is used as the laser incident region. By selecting a newly prepared homogeneous dry crystal and prioritizing the light-transmitting region, the consistency of the laser-crystal interaction is ensured, reducing efficiency loss and beam inhomogeneity caused by local performance differences in the crystal from the source.

[0025] The transverse dimension of the BBO crystal to be incident on in the non-light direction is 1.5~3mm, such as 1.5mm, 2mm, 3mm or any value between them; the light transmission dimension of the BBO crystal to be incident on is 3~12mm, such as 3mm, 5mm, 7mm, 9mm, 12mm or any value between them.

[0026] like Figure 1 As shown, the generating device provided by the present invention includes a laser source, a spot shaping module, a temperature control module, a BBO crystal module, and a detection module; The laser source (pulse width 10ns, repetition frequency 50kHz, power adjustable range 10-70W) is used to output 532nm laser light. The beam shaping module is located downstream of the laser source's optical path and is used to shape the 532nm laser light into an elliptical beam. The temperature control module is thermally coupled to the BBO crystal module to maintain the BBO crystal module at a stable temperature. The BBO crystal module is located downstream of the beam shaping module's optical path and is used to generate 266nm ultraviolet laser light through fourth-harmonic generation. The detection module is located downstream of the BBO crystal module's optical path and is used to monitor the output power and beam quality of the 266nm ultraviolet laser light in real time. The beam shaping module includes a cylindrical mirror group, the temperature control module includes a water-cooling device or a semiconductor cooler, and the detection module includes a power meter (accuracy ±2%) and a beam quality analyzer (resolution 1280×1024 pixels). The major and minor axes of the elliptical light spot are aligned with the ordinary and extraordinary light directions of the BBO crystal module, respectively, and the major and minor axis dimensions of the elliptical light spot are adapted to the lateral dimensions of the BBO crystal module in the corresponding directions.

[0027] The ratio of the major axis to the minor axis of the elliptical light spot is (2~20):1, such as 2:1, 5:1, 10:1, 15:1, 20:1, or any value between them. The temperature control module is configured to maintain the temperature of the BBO crystal module at 10~25℃, such as 10℃, 12℃, 14℃, 16℃, 18℃, 20℃, 22℃, 25℃, or any value between them. Preferably, the temperature is maintained at 16~25℃, such as 16℃, 18℃, 20℃, 22℃, 25℃, or any value between them. The BBO crystal in the BBO crystal module is a homogeneous crystal grown under dry conditions, and the region with a power output difference ≤5% on the light-transmitting surface of the BBO crystal module is used as the laser incident region. The lateral dimension of the BBO crystal module in the non-light direction is 1.5~3mm, such as 1.5mm, 2mm, 3mm or any value between them; the light transmission dimension of the BBO crystal module is 3~12mm, such as 3mm, 5mm, 7mm, 9mm, 12mm or any value between them.

[0028] Example 1: Elliptical Spot Optimization Experiment This embodiment uses a tunable power 532nm solid-state laser with a pulse width of 10ns and a repetition frequency of 50kHz as the light source. Two cylindrical mirrors shape the beam into an elliptical spot in the ordinary beam direction, with a major-to-minor axis ratio of (2~20):1. A newly fabricated 6×6×5.5mm laser was selected. 3 BBO crystals were used, and their temperature was precisely stabilized at 16°C using a water-cooled temperature control device.

[0029] To clarify the technical advantages of elliptical spot shaping, a rigorous control experiment was set up: under the same experimental conditions, only the incident spot was changed to a circular spot (keeping the light transmission area similar to that of an elliptical spot), while the other parameters remained unchanged.

[0030] The experimental results are compared below: Elliptical spot scheme: 5.32W output power at 266nm, 13.3% conversion efficiency, regular spot shape with no distortion. Circular spot scheme: 4.928W output power at 266nm, 12.32% conversion efficiency, but noticeable thermal distortion appears at the spot edges.

[0031] This embodiment demonstrates that, under the same experimental conditions, elliptical beam shaping can increase output power by approximately 8% while effectively suppressing thermally induced beam distortion, thus verifying the technical advantages of this invention in improving conversion efficiency and maintaining beam quality.

[0032] Example 2: Temperature Optimization Experiment Previous theoretical simulations have shown that 25℃ is a critical point for crystal temperature control; above 25℃, the internal stress of the crystal increases rapidly, causing severe compression deformation of the light spot morphology. To verify the simulation results, this embodiment conducts a temperature control experiment on a fourth-harmonic generation BBO crystal based on Example 1. The newly prepared BBO crystal (6×6×5.5mm) described in Example 1... 3 The fourth harmonic emission efficiency of the BBO crystal was obtained by using different temperature conditions at 40℃, 25℃ and 16℃.

[0033] Table 1. 266 nm laser emission efficiency under different temperature control methods ; Figure 2 The output curves of 266 nm laser under different temperature control methods are shown in the figure. Figure 2 As shown in Table 1, when the injected 532 nm laser power is less than 20 W, the three temperature control effects are not significantly different. However, when the injected power exceeds 20 W, a significant difference emerges between 40℃ and 16℃ and 25℃. With increasing injected power, the increase in fourth harmonic efficiency at 40℃ is smaller than at 16℃ and 25℃; when the power reaches 40 W, the efficiency at 40℃ is close to saturation. At 16℃ and 25℃, the fourth harmonic efficiency of the system is much higher than that at 40℃, and both continuously increase with increasing injected power. It is worth noting that the efficiency at 16℃ is better than at 25℃, which is mainly related to the actual temperature control accuracy of the system: the circulating cooling water is affected by the environment during transportation, and its temperature is already higher than the set value when it reaches the crystal, resulting in a higher actual operating temperature at 25℃. Theoretically, a lower temperature helps to improve conversion efficiency. For the hygroscopic BBO crystal, in a normal environment, when the temperature is below 16℃, its surface is prone to condensation and fogging. If the crystal module is sealed with a moisture-proof coating, moisture can be effectively isolated, preventing low-temperature condensation. Under these conditions, the crystal's operating temperature can be stabilized at a lower range of 10°C to 16°C, thus ensuring crystal safety while further exploring the possibility of efficiency improvements.

[0034] Example 3: Laser Incident Area Optimization Experiment Based on the optimized spot and temperature conditions in Examples 1 and 2, this example further optimizes the laser incident area. Figure 3 The BBO crystal (newly prepared 6×6×5.5mm) is shown. 3 The light transmission surface of the BBO crystal is divided into nine grid positions. A fourth harmonic emission experiment is conducted at nine different positions to test the surface quality of the BBO crystal and the internal uniformity of the BBO crystal.

[0035] Table 2. Laser output power at 266 nm at different positions on the same BBO crystal. ; Table 2 shows the 266 nm output power at nine different locations on the same BBO crystal surface at 532 nm laser powers of 3 W, 5 W, 7 W, and 10 W. The results indicate that, at the same incident power, the maximum and minimum output power differ by approximately 5%, suggesting a certain degree of efficiency inhomogeneity on the BBO crystal surface. Furthermore, locations exhibiting higher output power at low power show relatively higher fourth-harmonic efficiency as the incident power increases. Therefore, to ensure the consistency of laser-crystal interaction and reduce efficiency loss and beam inhomogeneity caused by local crystal performance differences at the source, this embodiment uses a newly prepared uniform BBO crystal, and the region with a power output difference ≤5% on its light-transmitting surface is used as the laser incident region.

[0036] Example 4: Output Experiments of BBO Crystals of Different Sizes Based on the optimized conditions of the above embodiments, this embodiment further explores the influence of the lateral size and optical transmission size of the BBO crystal on the output power and beam quality of the 266 nm fourth-harmonic laser. We selected and tested four different crystal specifications and conducted comparative experiments under the same experimental conditions. Higher output power is better, and the beam quality factor (M) is also more important. 2 The closer M is to 1, the better, where M 2 X and M 2 Y represents the mass of the beam in the X and Y directions, respectively. Specific experimental data are as follows: 3 mm × 10 mm × 3 mm crystal: output power 8.1 W, beam quality M 2 X: 1.768, M 2 Y: 1.379.

[0037] 3 mm × 10 mm × 4 mm crystal: output power 10.6 W, beam quality M 2 X: 2.946, M 2 Y: 3.447.

[0038] 1.5 mm × 10 mm × 4 mm crystal: output power 10.5 W, beam quality M 2 X: 2.335, M 2 Y: 2.881.

[0039] 3 mm × 12 mm × 8 mm crystal: output power 14.2 W, beam quality M 2 X: 3.746, M 2 Y: 5.300.

[0040] Combining the above results with Figure 4 It can be seen that the 3 mm × 12 mm × 8 mm crystal has a significant advantage in output power, with its 14.2 W output power being the highest among the four. This is mainly due to its larger light transmission cross-section and length, which allows for better matching with the elliptical pump spot. This effectively enhances the length of the fourth harmonic nonlinear interaction while avoiding internal stress overload caused by excessive power density, thus achieving stable high-power output. Although the 1.5 mm × 10 mm × 4 mm crystal has a slightly lower output power (10.5 W) than the 3 mm wide crystal of the same length, its beam quality (M... 2 X≤2.335, M 2 Y≤2.881) was significantly improved, achieving M 2 Good beam quality ≤3. This may be attributed to the superposition effect of its narrower beam width (1.5 mm) and elliptical spot. This design effectively reduces heat deposition and thermal gradient in the transverse direction of the crystal, significantly alleviates the thermal lensing effect and wavefront distortion caused by thermal stress, thereby achieving a better balance between power and beam quality while obtaining higher power.

[0041] In summary, the lateral dimension of the crystal in the non-optical direction is the core variable controlling thermal stress distortion and determining beam quality. When this dimension is 3 mm, the system achieves high power output; while when this dimension is optimized to 1.5 mm and matched to the minor axis of the elliptical beam, the system maintains >10 W power while achieving a beam quality factor M. 2 A significant improvement of ≤3 mm. This demonstrates that limiting the lateral dimension to the range of 1.5~3 mm is a common and necessary structural basis for achieving both high power output and high beam quality optimization goals. A dimension larger than 3 mm weakens thermal management capabilities and degrades beam quality; a dimension smaller than 1.5 mm is insufficient to support a high-power beam, leading to a decrease in light transmission efficiency. Simultaneously, the light transmission size is the dominant parameter for linearly controlling nonlinear conversion efficiency and the final output power. Under the same optimization conditions, increasing the light transmission size from 10 mm to 12 mm significantly increases the output power from approximately 10.5 W to 14.2 W. This proves that within the aforementioned collaborative design framework, a light transmission size range of 3~12 mm provides the possibility for achieving continuous performance expansion from basic efficiency to extremely high power output. A dimension smaller than 3 mm results in insufficient operational length and excessively low conversion efficiency; a dimension larger than 12 mm, under current technological conditions, faces bottlenecks such as excessively high overall thermal load, increased crystal processing difficulty, and soaring costs. The protection of the lateral dimension (1.5~3mm) and the light transmission dimension (3~12mm) is not an arbitrary limitation on the crystal size, but rather a preferred length range that can be effectively utilized and achieve the best results by the method of the present invention.

[0042] The specific embodiments of this application have been described above, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for generating a 266nm laser, characterized in that, Includes the following steps: S1. Shape the incident 532nm laser into an elliptical spot; S2. The elliptical light spot is incident on the BBO crystal to be incident under a controlled temperature, and 266nm ultraviolet laser is generated by frequency doubling. The major and minor axes of the elliptical light spot are aligned with the ordinary and extraordinary light directions of the BBO crystal to be incident on, respectively, and the dimensions of the major and minor axes of the elliptical light spot are adapted to the lateral dimensions of the BBO crystal to be incident on in the corresponding directions.

2. The generation method according to claim 1, characterized in that, The ratio of the major axis to the minor axis of the elliptical light spot is (2~20):1, and the controlled temperature is 10~25℃.

3. The generation method according to claim 1, characterized in that, The BBO crystal to be incident on is a uniform crystal under dry conditions, and the region with a power output difference of ≤5% on its light-transmitting surface is used as the laser incident region.

4. The generation method according to claim 1, characterized in that, The lateral dimension of the BBO crystal to be incident on is 1.5~3mm in the non-light direction.

5. The generation method according to claim 4, characterized in that, The light transmission size of the BBO crystal to be incident is 3~12mm.

6. A device for generating 266nm ultraviolet laser, characterized in that, It includes a laser source, a spot shaping module, a temperature control module, a BBO crystal module, and a detection module; The laser source is used to output 532nm laser light; The spot shaping module is located downstream of the laser source's optical path and is used to shape the 532nm laser into an elliptical spot. The spot shaping module includes a cylindrical mirror group. The temperature control module is thermally coupled to the BBO crystal module to maintain the BBO crystal module at a stable temperature. The BBO crystal module is located downstream of the optical path of the spot shaping module and is used to generate 266nm ultraviolet laser through frequency quadruple harmonic processing. The detection module is located downstream of the optical path of the BBO crystal module and is used to monitor the output power and beam quality of the 266nm ultraviolet laser in real time. The major and minor axes of the elliptical light spot are aligned with the ordinary and extraordinary light directions of the BBO crystal module, respectively, and the major and minor axis dimensions of the elliptical light spot are adapted to the lateral dimensions of the BBO crystal module in the corresponding directions.

7. The generating apparatus according to claim 6, characterized in that, The ratio of the major axis to the minor axis of the elliptical light spot is (2~20):1, and the temperature control module is configured to maintain the temperature of the BBO crystal module at 10~25℃.

8. The generating apparatus according to claim 6, characterized in that, The BBO crystal module is a uniform crystal in a dry environment, and the region with a power output difference of ≤5% on the light-transmitting surface of the BBO crystal module is used as the laser incident region.

9. The generating apparatus according to claim 6, characterized in that, The lateral dimension of the BBO crystal module in the non-light direction is 1.5~3mm.

10. The generating apparatus according to claim 9, characterized in that, The light transmission size of the BBO crystal module is 3~12mm.

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