The conventional separation of complex microstructure optical components leveraging mechanical contact has the problems of low separation efficiency and serious chipping at the edge of the separation. Ultra-fast laser separation technology offers the advantages of high separation quality, fast speed, and contact-free separation. However, laser distortion is caused when microstructure optical components are cut using the laser . Analyzing the causes of distortion and developing a method to eliminate it is the focus of high-quality and high-efficiency separation of complex microstructure optical components using ultrafast lasers. It has implications for the extended use of ultrafast lasers to separate optical lenses with non-planar structures.

This study utilizes the optical software Zemax to model the optical system and processing environment and analyzes the light path to reveal the underlying reason for the distortion of the laser light incident on the microstructure optical components. A liquid-phase matching medium-assisted ultrafast laser separation manufacturing technology is employed. A compound system is formed by placing the optical component into the liquid medium with a refractive index matching its own. This method reduces the distortion of the operating laser at the microstructures of the optical component, thereby enabling the establish of the modified surface inside the component. This study adopts a heat bath to supply a constant thermal environment for the entire optical component. The four sides of the modified surface of the optical component are heated uniformly at the same time, the thermal stress induces the cracks to extend from the surface to the inside under the guidance of the microcracks, and the cracks are finally realized.

This study derives that the sudden change in the refractive index of the propagating medium during the propagation of the laser from the environment medium to the target medium is the underlying reason for the distortion of laser through the functional microstructures of optical components. It causes the laser to generate irregular dispersion and reflection, deviating from the original path. Liquid phase-assisted ultrafast laser separation of complex microstructure optical components is proposed (Fig. 1).

This study utilizes Sellmeier formula [formula(3)] and Cauchy dispersion formula [formula(4)] to derive the refractive index values of optical component materials and liquid-phase refractive index-matching media under the operating laser wavelength, respectively, and selects the liquid-phase matching liquid whose refractive index matches the refractive index of the optical materials under the operating laser wavelength, such that the solid-liquid compound with the same refractive indices can be obtained.

This study obtains the Bessel beam length [formula(1)] and displacement [formula(2)] control relationship in different liquid-phase matching media. This study simulates the optical field distribution of the laser as well as the energy distribution of the Bessel beam primary axis after the laser enters the optics under three different values of the matching deviation (Fig. 5), and the results show that the smaller the matching deviation, the better the quality of the separation. In the presence of large matching deviations, the separation surface will show defects consistent with the microstructural cycle of the lens surface, primarily natural cracks that result in a morphologically uncontrollable separation. The laser cannot process the continuous modified surfaces required for separation inside the microstructure optics when the matching deviation is greater (Fig. 8).

An ultrafast laser separation process window for H-BaK3 is experimentally obtained, and the irregular separation of a variety of microstructure optical components proves the effectiveness and wide applicability of the technique.

The laser separation of complex microstructure optical components is analyzed by optical simulation to determine the reason for the failure of laser separation, i.e., the operating laser produces distortion at the microstructures to obstruct the formation of the Bessel beam inside the components, which leads to the inability to process the modified surfaces that cover the cross section of the components. Liquid-phase refractive index matching media are used to suppress laser distortion. Following analysis of the distribution of the optical field and the quality of the separated facets under different matching deviations, it is concluded that the use of a refractive index matching liquid that matches the optical material at the operating laser wavelength can effectively suppress distortion and obtain an excellent modified surface. Adopting the heat bath method to conduct contactless and uniform heating on the modified surface guarantees excellent separation quality. Compared with the traditional mechanical separation of optical components, liquid-phase-assisted laser separation of complex microstructure optical components can realize rapid and high-quality separation of optical components in bulk. The separation speed for H-BaK3 can reach 100 mm/s, the cut surface roughness is as low as 2.4 μm, and the chipping size is less than 20 μm, which provides a reference window for the laser modification separation process. This technology expands the application of ultrafast laser separation and can fulfill the demand for the customized separation of optical components.