1. Yongjin Shin Sohee Park, Youngseop Kim, Jangwoen Lee, Woonggyu Jung, Zhongping Chen, and J. Stuart Nelson 1

2. Outline Introduction to Laser Engraving Experiment - Sample preparation (Crystal & PMMA) - Procedure Results - Optical microscopy (OM) - Optical coherence tomography (OCT) Conclusions 2

3. Introduction to Laser Engraving Producing grooves on the substrate by evaporation of the substrate surface where laser is irradiated free of the surface residues does not require post process polishing PMMA (Polymethyl Methacryslate) has comparable refractive index (1.495) 3

4. Sample preparation (Crystal & PMMA) PMMA is strong, light, and transparent. Its durability and surface hardness are superior to other alternative material. 4

5. Procedure Laser 3D Engraving System - Q-switched 2nd harmonic Nd:YAG laser (wavelength = 532 nm, pulse energy=26.9 mJ, frequency=50~60 Hz) - Windows™-based software Sculptor biconvex focusing lens (f = 43 mm) 6×3 mm 2D image was engraved 1 mm inside the sample by irradiating the laser at 100~150 μm spatial resolution The analysis of the dot image on the sample was performed every 10 μm axially using OCT and the surface images were analyzed with the OM (x140). 5

6. OCT system (Optical Coherence Tomography) 6

7. Results (OM images) Changes in crystal / PMMA as a function of laser power crystal: cracks around the dots size of the dots diminished fast with lower laser output power PMMA: nearly circular shape less cracks around the dots produced smaller but clear dot engraving with low laser power The size of the dots and the distance between dots were consistent. 7

8. Results (OCT images) Changes in crystal / PMMA as a function of laser power crystal: more cracks ghost images with lower laser output power PMMA: otherwise 8

9. 3D laser engraving image 3D laser engraving image inside crystal and PMMA The comparably clear images can be produced with PMMA with simple manipulation of production parameters: the use of longer wavelength (1064 nm) reduction of laser power other adjustments with the software. 9

10. Conclusions PMMA can be used as an alternative to crystal for the laser engraving - less prone to the crack formation - The low laser output power did not affect the image formation inside PMMA as much as inside crystal. - free of the ghost images 10