Abstract
Market of digital dentistry is growing fast in recent years. Dental CAD/CAM system uses an intra-oral scanner to acquire the digital surface profile of the teeth, which is also called digital impression, and modify or design a 3D dental model with the simulation software. After the contour of the teeth is scanned, send the digital files to the following CAD/CAM process of making artificial teeth like a 5-axis CNC milling machine for the dental restoration. The digital impression method not only has the advantages of less required scanning time, high scanning accuracy, but also can ease the discomfort or distress of patients who undergo the dental impression. The intra-oral scanner is especially the key hardware for taking the digital impression. A commonly used approach is to project a line laser beam on the teeth and make the laser beam move back and forth with the assembled scanning mechanism. The image sensor detects and reconstructs the real-time 3D teeth profile from the distortion of the reflected line beam image with the algorithm behind. In order to acquire the accurate teeth model detected from the distorted line laser beam pattern, the quality of the line laser beam is supposed to meet the requirement in beam length, beam width, depth of focus, uniformity, etc. The topic of my thesis is to design some different kinds of laser module that generates a line laser beam and evaluate the possibility, applicability and commercialization of the laser module for the application of the intra-oral scanner. Currently there are several kinds of line laser beam shaping systems widely used, including refractive beam shapers, reflective beam shapers, diffractive beam shapers, etc. The research proposed designs containing both the refractive line laser beam shaper and the diffractive line laser beam shaper. A refractive beam shaper utilizes the refraction property, which happens when the light propagates through an optical lens because of the refractive index and the curvature of the lens, so as to have a laser beam shaped into a laser stripe. Each component of the refractive beam shaper is availably selected. Since the embodiment is relatively simple, it is flexible to adjust its configuration for different design requirements. The diffractive optical elements provide the incident light waves with the phase modulation to redistribute the light field. The research utilize a pure phase type liquid crystal on silicon (LCoS) SLM as the holographic recording of the interference pattern of dynamic line laser beam (object beam) and reference beam. The LCOS-SLM projective system is able to combine the function of line laser beam shaping with the one of scanning. Therefore, there will be a potential to minimize much more the volume of the intra-oral scanner. The required phase distribution information for generating a line laser beam pattern, called hologram, can be obtained by computer generated holography technique and calculated by the iterative Fourier transform algorithm. In addition, quantize and optimize the acquired continuous phase distribution into several levels, as well as analyze the performance of the line laser beam in different levels. The results can be treated as an evaluation for manufacturing the diffractive optical elements.