| 摘要 |
PURPOSE:To compensate the phase difference caused by birefringence by providing plural crystals for producing second harmonic within a resonator, and orientating them at a specified angle. CONSTITUTION:The straight polarized light in I direction, which has passed through a polarizer 18, enters an SHG (crystal for producing second harmonic) crystal 20 wherein two optical axes D and E are oriented at 45 deg.. A fundamental wave, which is polarized straight in I direction within this crystal, is decomposed in the directions of two optical axes O and E of the SHG crystal 20, and they advance at respective phase speed, and produce the second harmonic polarized straight in E direction. Since the fundamental wave is birefrigent by penetrating the SHG crystal 20, phase difference occurs between the polarized IO and IE polarized in E direction, and in general it become elliptic polarized light. Furthermore, the fundamental waves IO and IE enter an SHG crystal 22, which has two optical axis O' and E' being oriented 90 deg. with the optical axes of the SHG crystal 20. Since the SHG crystal 22 is made in such shape that the optical axes O and E are exchanged, the phase principles of IO and IE are compensated. Moreover, the second harmonic at the time of fundamental waves penetrating the SHG crystal 22 become the composite waves of the second harmonics which have occurred on both sides of the SHG crystals 20 and 22. While producing the second harmonic with both SHG crystals 20 and 20, the phase difference compensation of fundamental waves is done at the same. |
