Optical Quality Laser Polishing of CVD Diamond by UV Pulsed Laser Irradiation

Abstract

It is a great technical challenge to precisely polish diamond substrates due to their extremely high hardness, especially for micro‐optics fabrication. Here, a simple laser polishing process is demonstrated for the optical quality surface finish of chemical vapor deposition diamond using a 355 nm nanosecond laser. Raman spectroscopy and surface profile analyses reveal that the laser polishing is an ablation‐based process that consists of laser graphitization and the subsequent laser ablation of the graphitized layer. An optimized strategy is proposed to realize the high‐quality polishing by combining the ablation effect and defocusing laser irradiation. The polishing strategy can effectively reduce the peak‐to‐valley height difference of a rough surface and automatically enables the laser fluence at a low level close to the ablation threshold. Laser polishing at such critical laser fluence can greatly avoid harmful effects caused by high laser fluence and achieve precision materials’ removal while maintaining optical surface quality. The approach is capable of delivering an average roughness Ra down to 8.02 nm and a high transmittance up to 80% of mechanically polished diamond in the visible spectrum. High optical performances make it possible to directly fabricate micro‐optical components on diamond substrates using this novel laser polishing approach.

Energy beam-based direct and assisted polishing techniques for diamond: A review

“…Even for the same crystal plane, there are harder or softer polishing directions. For example, the <100> direction, along which a higher removal rate and better surface quality can be obtained, is considered to be a soft direction on the (001) plane, Energy beam polishing techniques of diamond [8,39,46,48,[50][51][52][53]. Reproduced from [8] with permission from the Royal Society of Chemistry.…”

“…With the rapid industrial revolution, diamond grinding and polishing technologies have continuously advanced, and many innovative diamond polishing techniques have been established. Mechanical polishing (MP) [30,31], chemical-mechanical polishing (CMP) [32,33], thermochemical polishing (TCP) [34,35], dynamic friction polishing (DFP) [36,37], laser polishing (LP) [38,39], ion beam polishing (IBP) [7,40], electrical discharge machining (EDM) [41,42], ultrasonic-assisted polishing (UAP) [43,44], plasma-assisted polishing (PAP) [45,46], and laser-assisted polishing (LAP) [47,48] are some of the commonly used techniques, each with its own advantages and limitations. Among them, MP has simple equipment and low processing costs, DFP has high polishing efficiency, and CMP and TCP have high polishing accuracy.…”

Progress in diamond polishing with light source assistance

“…The UV laser (λ=355nm, τ=50ns) polishing of diamond was studied by Liu et al [27] in 2021. The result evaluated by AFM showed the average roughness Ra of 8.02 nm could be achieved in an area of 20 μm × 20 μm.…”

“…Figure 5 Schematic of the laser polishing which consists of: (a) laser graphitization and (b) laser ablation of the graphitized layer by 355 nm nanosecond laser [27]. …”

Novel Laser Crystal Nd:LiY(MoO4)2: Crystal Growth, Characterization, and Orthogonally Polarized Dual-Wavelength Laser

“…Lasers have been widely used in military, medical, and scientific research fields due to their advantages of large energy density, high directionality, and coherence, which have greatly promoted societal development and scientific progress. − All-solid-state lasers have attracted increasing attention due to their compact structure, small size, and low maintenance cost. , Usually, the all-solid-state laser can only produce a single-wavelength laser because of the limitation of active ion energy level transitions in the laser medium. With the continuous expansion of laser applications, orthogonal polarized dual-wavelength lasers generated by a single laser are required in laser medical treatment, differential absorption lidar, fine laser spectroscopy, terahertz fields, etc. − Therefore, the all-solid-state orthogonal polarized dual-wavelength laser has become a hot topic of research in the fields of laser and laser crystal research.…”