Tham khảo tài liệu 'frontiers in guided wave optics and optoelectronics part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Polarization Properties of Laser-Diode-Pumped Microchip Nd YAG Ceramic Lasers 545 be pm. An SEM surface image of the micro-grained sample used in this experiment is shown in Fig. 17 b together with that of large-grain sample. The collimated linearly-polarized LD beam was passed through an anamorphic prism pair and it was focused onto the sample by a microscope objective lens of NA where the focused beam diameter was about 80 pm. The laser exhibited a single-frequency TEM00-mode oscillation which is linearly polarized along the LD pump-beam polarization direction due to the reduced thermal birefringence for mode-matched on-axis pumping condition as mentioned in section 3. By shifting or tilting the laser cavity slightly as depicted by arrows in Fig. 17 a a variety of MG mode operations were observed instead of Ince-Gauss IG modes depending on the degree of effective off-axis pumping. Typical far-field patterns including BG modes are shown in Fig. 18. For the higher-order BG modes BG1 BG2 an optical vortex having a topological charge of 1 and 2 was formed in the center. Pump power p 220 mW 196 mW 205 mW 173 mW Fig. 18. Observed far-field lasing patterns. a Mathieu-Gauss laser beam. b Bessel-Gauss laser beam. Numerically reproduced intensity patterns corresponding to Fig. 18 and the phase portraits are shown in Fig. 19. Here the complex amplitude of the m-th order even and odd MG beams propagating along the positive z of an elliptic coordinate system r ệ n z is given by Gutierrez-Vega Bandres 2007 MGem r exp - GB r Jem ệ q cem n q 2kp. 9 10 MGOm r exp -k Z GB r Jom ệ q sem n q . 2kjU Here Jem and Jom are the m-th order even and odd radial Mathieu functions cem and sem are the m-th order even and odd angular Mathieu functions GB r p-1exp -r2 pwo2 is 546 Frontiers in Guided Wave Optics and Optoelectronics the fundamental Gaussian beam p z 1 iz kw02 w0 is the Gaussian width at the waist plane z 0 and k 2n X is the longitudinal wave number. q kt2f02 4 is the .
