The feasibility study of beam propagation ratio (M2) measurement made by the two-point knife-edge method
| Autor: | Yu-Bin, Chang, 張育彬 |
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| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 The beam propagation ratio (or the beam quality factor, or the times-diffraction-limit number), M2, is the most fundamental parameter to describe the propagation of laser beams and their ability to be tightly focused. M2 is based on the second moments of real intensity profiles of laser beams. The ratio is also a key factor to evaluate the mode content of a multimode laser beam from a stable resonator. However, the nonlinear optical conversion efficiency is significantly influenced by the beam quality of the fundamental radiation. Therefore, it is vital to obtain the information about M2 of the fundamental laser beam before experiments on frequency-doubling are performed. For intensity profile measurements made using CCD cameras, there are several limitations, such as wavelength range, A/D resolution, array size, pixel size, and the saturation level. Fortunately, The ISO 11146-3:2004 standard specifies three alternative methods for measuring a beam radius to acquire M2. We prefer the moving knife-edge (or two-point knife-edge) method of alternatives because of its simplicity and manageability. Between the two-point knife-edge method and the standard method, there exists a correlation factor of 0.81, verified for gas laser beams with stable resonator. In our case, the laser beam came from a homemade end-diode-pumped Nd-YVO4 continuous-wave laser. When the pump power was increased to over 6 W (7-10 W), the correlation factors obtained range from 0.84 to 1.06 in x-direction and 0.80 to 1.11 in y-direction. The respective means are 0.94 and 0.97, both being a little larger than the correlation factor for gas lasers. Key word : moving knife-edge method, beam quality factor, beam width |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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