Study on mechanics and key technologies of laser nondestructive mirror-separation for KDP crystal

• A laser nondestructive mirror-separation technology for KDP crystal has been developed.
• A nondestructive mirror-separated sidewall of KDP crystal with 4.7 nm (p-v) and 2.1 nm (RMS) roughness, 5.433 μm flatness and an angular precision of about 0.06° is achieved for the first time.
• A separating speed 200 times faster than that of conventional method was achieved.
• A numerical simulation to analyze the mechanisms of LNMS separating KDP crystal was developed.

KDP crystal is an important electro-optic material in various laser systems. At present, the greatest difficulty is the cutting and polishing of large-scale crystals. In this study, a laser nondestructive mirror-separation technology (LNMS) for KDP crystal has been developed for the first time by skillfully adopting femtosecond laser pretreating and fiber laser separating. The separating efficiency of LNMS is at least 200 times faster than that of traditional mechanical cutting, and a nondestructive mirror-separated crystal sidewall with surface roughness (Sa) of 4.7 nm (P−V) and 2.1 nm (RMS), flatness of 5.433 μm and an angular precision about 0.06° could be obtained using the LNMS method. The effects of laser separating parameters, including laser power, laser moving speed and internal stress release on separating accuracy and quality, were investigated and optimized; meanwhile its principle was expounded as well as its mechanism was discussed. The experimental and analyzed results show that the LNMS technology may also have a prospect in the analysis of residual stress distribution inside KDP crystal. A numerical simulation on the thermal stress in the LNMS separating process of KDP crystal was developed to analyze the separating mechanism, which is in good agreement with the theoretical analysis and experimental results.

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