为克服光腔衰荡高反射率测量过程中初始腔和测试腔结构转换导致的腔参数相对失调,提升调腔效率,提出一种基于衰荡腔透射光斑形态监测的调腔方法。以衰荡腔透射光斑外接矩形宽高比及光斑与其外接矩形面积的比率作为调腔依据,抑制腔参数失调导致的高阶横模激发,使初始腔和测试腔透射光斑均保持在基横模状态。实验结果显示:以宽高比和面积比作为调腔依据,不仅能够分辨不同的光斑模式,同时能有效应对模式间的特殊光斑形态(如椭圆光斑、多模跳变等)。当初始腔和测试腔光斑均调节至基横模状态时,测得的样片反射率均值最高且方均根最小。结果表明该方法有助于提高光腔衰荡高反射率测量技术的调腔效率。

This paper proposes a cavity adjustment method that corrects the relative misalignment of cavity parameters caused by the conversion of the initial cavity and test cavity structure during cavity ring-down high reflectance measurements. The proposed method monitors the shape of the ring-down cavity-transmission spot and also improves the efficiency of cavity adjustment. The cavity adjustment is based on the aspect ratio of the circumscribed rectangle and the area ratio of the spot to the circumscribed rectangle. The method suppresses the excitation of the high-order transverse mode caused by the misalignment of cavity parameters and maintains the transmission spot modes of the initial and test cavities in the TEM00 mode. In experimental tests, the adjustment based on the aspect ratio and area ratio not only distinguished different spot modes but also effectively dealt with special spot patterns between modes (such as elliptical spot and multimode jump). When the initial cavity and the test cavity spots were adjusted to the TEM00 mode, the measured mean reflectance of the sample was maximized and root mean square was minimized. Results show that this method can help to improve the cavity adjustment efficiency in cavity ring-down high-reflectance measurement technology.