# 光学镀膜简介

This is Sections 4.1, 4.2, and 4.7 of the Laser Optics Resource Guide.

Thin film optical coatings are typically created by depositing dielectric and metallic materials, such as Tantalum Pentoxide (Ta2O5) and/or Aluminum Oxide (Al2O3), in alternating thin layers. 为了最大程度地提高或降低干涉，它们的光学厚度通常为应用中所使用的光的波长的 λ/4 光学厚度 (QWOT) 或 λ/2 光学厚度 (HWOT)。这些薄膜由高折射率和低折射率交替而成，从而诱发需要的干涉效应（图 1）。

## 光学镀膜理论

(1)$$n_1 \sin \theta_1 = n_2 \sin \theta_2$$

##### 图 2: 光线从低折射率介质向高折射率介质移动，导致光线向界面法线方向折射

(2)$$n_1 \sin \theta_1 = n_2 \sin \theta_2 = n_3 \sin \theta_3 = n_4 \sin \theta_4$$
##### 图 3: 利用斯涅尔定律，可以找到由与层顺序无关的平面平行表面组成的多层薄膜镀膜任何层的光线折射角度

(3)$$\theta_1 = -\theta_2$$

(4)$$\theta_C = \frac {n_2}{n_1}$$
##### 图 4: 显示入射角大于 θc 的全反射 (TIR)

(5)$$t_s = \frac {2n_1 \cos \theta_1}{n_1 \cos \theta_1 + n_2 \cos \theta_2}$$
(6)$$r_s = \frac {n_1 \cos \theta_1 - n_2 \cos \theta_2}{n_1 \cos \theta_1 + n_2 \cos \theta_2}$$
(7)$$t_p = \frac {2n_1 \cos \theta_1}{n_1 \cos \theta_2 + n_2 \cos \theta_1}$$
(8)$$r_p = \frac {n_1 \cos \theta_2 - n_2 \cos \theta_1}{n_1 \cos \theta_2 + n_2 \cos \theta_1}$$

Where ts and tp are the amplitude transmission coefficients for s- and p-polarization, rs and rp are the amplitude reflection coefficients for s- and p-polarization, n1 and n2 are the refractive indices of the two optical media, θ1 is the incident angle, and θ2 is the transmitted or reflected angle. 在正入射时，θ1 和 θ2 为 0，使两种偏振状态的所有余弦项 1 和振幅系数都相同。这很直观，因为在正入射下，s 和 p 偏振状态没有区别。

## 镀膜技术

 Evaporative Evaporative with IAD Plasma Sputtering IBS ALD Spectral Performance Low Medium High High-Very High Very High Coating Stress Low Medium High Very High High Repeatability Medium Medium High Very High Very High Process Time Slow Slow Intermediate Very Slow Very Slow Non-Flat Geometry Capabilities Better Better Good Bad Best Relative Price  

### 原子层沉积 (ALD)

##### Figure 6: 在原子层沉积 (ALD) 过程中，通过将光学材料暴露于不同的气体前体来沉积单个薄膜层，从而在不依赖于光学表面几何形状的情况下对膜层厚度进行高水平的控制

1. Willey, Ronald R. Field Guide to Optical Thin Films. SPIE Optical Engineering Press, 2006.
2. Greivenkamp, John E. Field Guide to Geometrical Optics. SPIE Optical Engineering Press, 2004.
3. Paschotta, Rüdiger. Encyclopedia of Laser Physics and Technology, RP Photonics, October 2017, www.rp-photonics.com/encyclopedia.html.
4. Vandendriessche, Stefaan. “No One-Size-Fits-All Approach to Optical Coatings.” Photonics Spectra, Photonics Media, December 2016.
5. “IBS Mirror Coatings for Highly Demanding Applications.” Photonics News, Laser Components Group, August 2016, www.lasercomponents.com/uk/news/ibs-mirror-coatings-for-highly-demanding-applications

## 相关产品

EO 可提供波长为 250nm 到超过 10μm 的高反射金属镀膜。了解哪种镀膜最适合您的光学系统。

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