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Diamond Processing
How can an unassuming rough diamond be transformed into the sparkling finished diamond we see today? As the hardest substance in nature (with a Mohs hardness of 10), diamond processing has always posed significant technical challenges. The introduction of laser technology has completely revolutionized traditional diamond processing methods, enabling high-precision, high-efficiency, and non-contact machining.
1. The basic principle of laser diamond processing
The core of laser diamond processing lies in utilizing the nonlinear interaction between high-energy photons and carbon atoms to achieve material removal. As a wide-bandgap semiconductor (with a bandgap width of 5.5 eV), diamond exhibits high transparency to visible light and near-infrared lasers, making traditional thermal processing mechanisms inefficient. Laser diamond processing primarily relies on the following physical mechanisms:
Multiphoton absorption effect:
When the laser power density exceeds 10⁹ W/cm², electrons in the diamond valence band can transition to the conduction band by simultaneously absorbing multiple photons. Ultraviolet lasers (such as 355 nm) have photon energies of 3.5 eV, which are close to the diamond bandgap, making it easier to induce electron transitions. The free electrons then absorb additional photon energy via inverse bremsstrahlung, forming a plasma.
Photochemical decomposition:
Ultraviolet laser photons directly break C-C bonds (bond energy approximately 3.7 eV), triggering a phase transition from sp³ (diamond) to sp² (graphite) in localized areas. The absorption rate in the graphitized region increases by a factor of 100, thereby facilitating subsequent material removal.
Plasma-assisted ablation:
High-power-density lasers ionize surface materials to form a plasma. The plasma absorbs laser energy and expands, generating a shock wave that removes material. This process avoids the heat-affected zone, enabling "cold processing."
2. The process of diamond processing
The process of diamond processing generally consists of seven steps: sorting rough stones, designing, cleaving, sawing, turning, grinding, and cleaning. This article provides a detailed introduction only to the laser-related processing steps—laser diamond planning and cutting.
Based on four aspects—size, color, clarity, and crystal shape—we can initially sort rough diamonds. From a design perspective, when examining the rough stones, we primarily consider two factors: crystal shape and clarity.
Crystal form: By convention, the crystal forms of raw stones are classified into six categories: regular crystals (Stones), deformed crystals (Shapes), cleavage crystals (Cleavages), twins (Macles), flats (Flats), and cubes (Cubes). Objectively speaking, there is no strict and uniform criterion for distinguishing between these crystal forms; to some extent, they must be judged based on experience.
Clarity: If crystal form primarily affects yield, then clarity directly impacts the value of the finished diamond. From a design perspective, when examining a rough diamond, one should first identify the types, sizes, numbers, locations, and contrast levels of inclusions. Next, determine which blemishes can be removed through cutting and polishing. Finally, for blemishes that cannot or cannot be completely removed, try as much as possible to position them in inconspicuous areas that do not reflect light.
2.1 Laser Diamond Planning
How can we scientifically plan to preserve the maximum finished weight while reasonably avoiding areas containing inclusions and defects? Here, we introduce the concept of laser planning. Diamond planning is a critical step in the diamond processing procedure, involving stages such as rough stone evaluation, line marking, cutting scheme design, and laser pre-shaping. Thanks to its non-contact, high-precision, and highly efficient characteristics, laser planning technology has become a core process in modern diamond processing.
Diamond planning uses a 1064nm short-pulse laser. | |
The Core Role of Laser Technology in Planning
Traditional methods | Laser Technology | Technical Advantages |
Manual visual assessment | 3D laser scanning | Accuracy up to ±0.01mm, fully digitized parameters |
Hand-drawn lines | Laser Preforming | Accuracy ±5μm, complex 3D path |
Mechanical sawing | Laser cutting | No tool wear, cut seam <50μm |
Empirical judgment | AI optimization algorithm | Considering over 100 parameters, the solution is more scientific. |
2.2 Laser Diamond Cutting
Compared to traditional mechanical methods, laser cutting offers unique advantages: it enables non-contact processing, boasts high efficiency, produces narrow kerfs, and minimizes the heat-affected zone, making it an ideal method for diamond processing. The high hardness and high thermal conductivity of diamonds pose significant challenges for laser cutting. Therefore, the future development of laser cutting technology for diamonds will focus on adopting short-pulse and ultrashort-pulse laser technologies, while ensuring precise control over the laser beam’s focal point and its movement trajectory, as well as developing new laser processing methods.
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Laser for Laser Diamond Cutting (AO-532W-LP) | |
Comparison of Laser Processing with Traditional Processing
Parameters | Laser processing | Mechanical Processing |
Processing Principle | Photothermal/Photochemical Effects | Mechanical stress fracture |
Tool wear | None | Diamond tools suffer severe wear. |
Processing power | Non-contact (zero stress) | High contact stress (prone to cracking) |
Accuracy | ±1μm | ±10 μm |
Minimum feature size | 5 μm | 50μm |
Complex Shape Capability | Arbitrary three-dimensional structure | Limited to two-dimensional profiles |
Processing efficiency | High (Automation) | Low (primarily manual operation) |
3. Laser Diamond Marking
The diamond symbols engraved on jewelry provide crucial information about the diamond's characteristics. Here are some common symbols and their meanings:
Weight: Indicates the carat weight of the diamond.
Color: Represents the diamond's color grade, ranging from colorless to light yellow or light brown.
Clarity: Displays the clarity grade and assesses the presence of inclusions or blemishes.
Cut: Refers to the quality of a diamond's cut, which affects its brilliance and sparkle.
Number: A unique identifier that can be used to verify the diamond’s certificate and authenticity.
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CNI UV Diamond Micro-engraving Machine | |
4. Diamond authenticity verification
Raman spectroscopy is a technique that provides molecular vibrational fingerprint information. It has advantages such as short detection time, strong specificity, no need for pretreatment, and non-destructive sampling. Natural diamonds exhibit a strong Raman characteristic peak around 1332 cm⁻¹. In contrast, synthetic diamonds show peaks of varying intensities in other regions.
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CNI's Raman spectrometer is used to distinguish between real and fake diamonds |
Diamonds are mainly classified into natural diamonds, CVD diamonds, HTHP diamonds, and others. They are primarily composed of carbon and cannot be distinguished by their appearance alone. Based on the characteristic that natural diamonds have a different internal structure from other imitation diamonds, we can easily identify them using Raman spectroscopy.
Raman spectra of genuine diamonds, HPHV, and CVD tested by the CNI Raman spectrometer
With the continuous advancement of laser technology, laser diamond processing is evolving toward higher precision, greater efficiency, and broader applications. In the future, ultraviolet picosecond laser systems are expected to become standard equipment in the industry, and the widespread adoption of intelligent processing systems will enable laser diamond processing technology to be applied more extensively across various fields, from industrial manufacturing to high-end customization.
Changchun New Industries Optoelectronics Technology Co., Ltd.
Address: No. 888 Jinhu Road, High-Tech Zone, Changchun, 130103, P.R.China
International Tel:+86-431-85603799
Email: sales@cnilaser.com
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