Methods and Research Progress for High-Quality Laser Processing of Diamond Materials

As an ultra-wide bandgap semiconductor, diamond stands out with its exceptional properties: Mohs hardness up to 10, thermal conductivity exceeding 2000 W/(m·K), a 5.47 eV bandgap, and chemical inertness. These attributes make diamond indispensable in high-power electronics, optoelectronics, quantum computing, and aerospace engineering. With the rapid growth of diamond synthesis technology, traditional mechanical machining faces insurmountable limitations in achieving sub-micron precision and fabricating complex micro-nano structures. Laser processing, leveraging non-contact ablation, localized energy deposition, and precise parameter control, has emerged as a transformative solution for diamond machining.

The mechanism of laser interaction with diamond involves two primary steps. Initially, diamond is transformed into the graphite phase through laser induction. After that, the graphitized layer is removed via vaporization and chemical etching to complete the material processing. Surface graphitization occurs as a result of photon energy exciting the transition of sp³ bonds between carbon atoms to sp² bonds. This process is influenced and directed to a certain extent by laser parameters and the thermal gradients in the laser - irradiated area. Regarding the mechanism of laser - induced graphite removal, lasers with different pulse widths, ranging from continuous lasers to extremely short femtosecond pulses, behave differently. Laser pulses having pulse width exceeding one picosecond can heat both the lattice and electrons simultaneously. In contrast, laser pulses with a width less than 1 ps mainly excite electrons through nonlinear ionization. Nanosecond or longer - pulse lasers typically cause lattice heating, which can induce solid - solid phase transitions, amorphization, melting, or evaporation. On the other hand, femtosecond lasers remove material through expanding plasma, which helps reduce damage to the remaining surface. Based on these differences, each type of laser has its own set of advantages and limitations in specific applications.

Regarding surface treatment and polishing, while laser processing outperforms mechanical methods in efficiency and material loss, its final surface roughness traditionally lagged behind mechanical polishing. Recent advancements in multi-laser source polishing, laser-assisted polishing, and pulse burst mode have demonstrated transformative potential. High-power lasers with pulse burst mode (energy density <5 J/cm²) reduced surface roughness by 50% while maintaining minimal HAZ (<3 μm). Furthermore, a hybrid process combining laser trimming and plasma-assisted polishing (PAP) achieved atomic-scale flatness (R_a <10 nm). This method uses laser pretreatment to remove macroscopic defects followed by plasma etching for nanoscale smoothing.

In surface treatment and polishing, while laser processing outperforms mechanical methods in efficiency and material loss, its final surface roughness traditionally lags behind conventional mechanical polishing. Recent advancements in multi-laser source polishing, laser-assisted polishing, and pulse burst mode have demonstrated transformative potential. Sequential polishing with hybrid laser sources (e.g., nanosecond + femtosecond lasers) combines ablation effects and defocused beam strategies to reduce peak-valley height differences while maintaining laser energy near the ablation threshold (<5 J/cm²). This approach minimizes thermal damage, ensures optical surface quality, and enables precision material removal. High-power lasers with pulse burst mode achieve 50% roughness reduction (e.g., from 0.41 μm to 0.2 μm S_a) through energy density optimization (<5 J/cm²), resulting in minimal heat-affected zones (<3 μm). Additionally, a hybrid process integrating laser trimming and plasma-assisted polishing (PAP) achieves atomic-scale flatness (R_a <10 nm). This method uses laser pretreatment to eliminate macroscopic defects followed by plasma etching for nanoscale smoothing.

Laser processing has demonstrated transformative potential in diamond machining. However, current technologies face several challenges. Laser polishing of diamond requires further roughness reduction, with sequential multi-laser polishing, pulse burst mode processing, and laser-assisted polishing representing viable next steps. Mitigating thermal damage from long-pulse lasers and improving efficiency of short-pulse lasers are critical for widespread adoption. Future research should integrate short- and long-pulse laser advantages through process design or source selection to achieve high-precision, high-quality, and low-defect machining. In recent years, innovative technologies such as Bessel beam shaping, femtosecond laser direct writing, and laser microjet have further broken through the limitations of traditional processes, providing brand new solutions for the manufacturing of quantum devices, optical components, and high-precision microstructures. In conclusion, while challenges persist, continuous advancements in laser technology promise to address these bottlenecks, enabling scalable diamond machining for next-generation applications.