非异常区TM偏振波宽波段特性在激光器调谐光栅设计中的应用

通过刻划工艺控制光栅槽形零级面宽度,使-1级和0级衍射效率同时达到期望值是激光器调谐光栅研制中的技术难题。基于光栅电磁场理论,利用光栅非异常区入射波长与光栅周期之比λ/d≈1.414附近较宽波段范围内TM偏振波的衍射效率变化梯度小,而且同一波长的衍射效率随闪耀角增大呈单调递增或随槽顶角增大呈单调递减趋势的特性,给出了-1级振荡0级输出激光器调谐光栅的全三角槽形模型及设计方法。该方法用常规三角槽形光栅即可实现任意比值的-1级与0级衍射能量分布,避免了以往通过控制类梯形槽形零级面宽度来制作此类光栅的工艺不确定性,降低了制作难度。应用该模型设计并制作了-1级衍射效率为65%的0级输出激光器调谐光栅,其在10.6μm处的衍射效率误差为0.6%。该方法还适用于-1级振荡-1级输出激光器调谐光栅的设计,实现了两类激光器谐振光栅在设计方法以及制作工艺上的统一。

Application of broadband characteristics of TM polarized wave in non-anomaly region to designing laser resonator gratings

It is a technical difficulty of fabricating laser resonator gratings that the -1 and 0 order diffraction efficiencies of the gratings are equal to expectation values synchronously in controlling zero plane width of grating groove by ruling technology. Based on the electromagnetic theory of gratings, the triangle model and design method of laser resonator gratings with 0 order coupling-out and -1 order oscillation are proposed according to the characteristics of TM polarization in non-anomaly region. The characteristics are that the change gradient of diffraction efficiency of the TM polarized wave in the region close to λ/d≈1.414 is small,and the diffraction efficiency is increased with a blazed angle and decreased with an apex angle monotonically. This model can realize the random energy distributions of 0 and -1 order diffraction efficiencies and can avoid the uncertainty of technique coming from old methods and reduce the fabricating difficulty.The model is used to fabricate a grating with diffraction efficiency of 65% and its efficiency error is only 0.6% at 10.6 μm. Moreover, the method can also be applied to design a grating with -1 order oscillation and -1 order coupling-out, so that the design method and fabrication technology of two kinds of gratings are unified.