Understanding optical thin films
Optical thin films are widely used in everyday optical systems, industrial products, and consumer electronics. Now, industrial production ushered in the laser era, and the optical film also has a wide range of application prospects, in the next 20 years, the optoelectronics industry is about to usher in a great era of development. Although the optical film is a small part, an accessory to optical components, it plays a huge value and can make the impossible possible.
1. Definition of optical thin film
A class of optical dielectric materials consisting of thin layered media that propagate a beam of light through an interface. The application of optical films began in the 1930s. Nowadays, optical thin film has been widely used in the field of optical and optoelectronic technology to manufacture various optical instruments.
The optical film is a thin and uniform dielectric film that adheres to the surface of optical devices in the course of light propagation. Optical film is everywhere in our life, from precision and optical equipment, and display equipment to the application of optical film in daily life.
For example, eyeglasses, digital cameras, various household appliances, or anti-counterfeiting technology on banknotes can be called an extension of optical film technology. Without optical thin-film technology as the development foundation, modern photoelectric, communication, or laser technology would not have made progress, which also shows the importance of optical thin-film technology research and development.
2. Optical film materials
(1) Metals and alloys
Metals and alloys are a wide range of films with high reflectivity, cutoff bandwidth, good neutrality, small polarization effect, variable absorption, etc. They play a particularly important role in some special film systems.
(2) Compound (dielectric)
Compounds are widely used optical films with important applications, including halides, oxides, sulfides, and selenides.
Semiconductor materials are transparent in near-infrared and far-infrared regions and are important optical thin film materials. The most common semiconductor materials used in optical thin films are silicon and germanium.
3. Characteristics of optical films
The characteristics of optical films are: smooth surface, the interface between the film layer is geometrically segmented; The refractive index of the film can change at the interface, but it is continuous in the film. Can be a transparent medium, and can also be an absorption medium; It could be normally homogeneous or it could be normally inhomogeneous. Practical films are much more complex than ideal films.
This is because: when preparing, the optical and physical properties of the film deviate from the bulk material, and its surface and interface are rough, resulting in diffuse scattering of a light beam; The interpenetration between the film layers forms a diffusion interface; Due to the growth, structure, and stress of the film, the anisotropy of the film is formed.
The film layer has a complex time effect.
4. Properties of optical thin films
The direct theoretical basis of the optical thin film is thin-film optics, which is based on the interference effect of light and discusses the propagation behavior of light in layered media. Even with the rapid development of science and technology today, the theory can still accurately describe the propagation behavior of light in tens of micron layer, nanometer layer, or even atomic layer thick film, thus designing optical thin-film elements with different wavelengths, different properties, and different requirements.
The traditional linear optical thin film is a kind of passive optical component, as some optical properties of active regulation of membrane materials were introduced into the design and application of optical thin film, optical thin film, and breakthrough the limitation of the traditional, development for a both can realize passive transfer function and can realize the active control or transformation of the functional optical beam element.
With the continuous development of science and technology and the deepening and widening of the demand for optical thin film, thin-film optics will also be constantly enriched and deepened, in the mutual penetration of a variety of disciplines to develop and broaden their subject content. In addition to the basic optical properties, modern optical thin films also involve the mechanics, structure, and nonlinear properties of optical thin films, as well as the photothermal, photoacoustic, photoelectric, photovoltaic effect and damage effects of thin films under the action of strong laser in the process of interaction between light and thin films. These problems involve more in-depth and extensive scientific content.