Antireflection films

Modem displays have a variety of surface coatings, such as antireflection film, antistatic film, insulator film, and protection film. Si02 thin film is widely used as a functional surface coating film for displays. This chapter describes surface coatings for displays by the sol-gel method using photoirradiation. 

Part of the incident light will be reflected at the top and bottom surfaces of the antireflection film, and in both cases the reflection will take place in a medium of lower refractive index than the adjoining medium. Thus, to ensure that the relative phase shift is 180°, the optical thickness of the film should be made one quarter wavelength so that the total difference in phase between the two beams will correspond to twice one quarter wavelength, that is 180°. This is the phase condition ... 

The most widely used antireflection film is 4 layer of magnesium fluoride nD = 1.38. It can be coated on either glass or acrylic substrates. 

Measured curves for germanium samples coated with the broadband antireflection films INFRALIN 211 (Balzers). 

For glass, s is about 1.5, so the antireflecting film must have a refractive index ... 

Figure 5.45 (a) Transmission measurement of polycrystalline silicon. Since the UV-2600 system is capable of measurement to 1400 nm, the transmission characteristics of the bandgap region near 1000 nm are evident, (b) Reflection measurement of an antireflective film. The suppressed reflectance in the visible region is clearly seen. ( 2014 Shimadzu Scientific Instruments, www.ssi.shimadzu.com. Used with permission.)... 

Interference and coherence refer to the interactions between light rays. Both interference and coherence are often discussed in the context of a single wavelength or a narrow band of wavelengths from a light source. Interference can result either in an increased intensity of light or a reduction of intensity to zero. The optical phenomenon of interference is used in the creation of antireflective films. 

Lenses are coated with antireflecting films to increase the optical beam s energy through the instrument. These films are thickness and refractive index specific. IF they are touched, residual skin oils will adversely affect both film thickness and refractive index. The lens will then reflect more and transmit less. Dirty lenses should be cleaned with a fresh cotton-tip swab saturated with a 3 1 mixture of denatured alcohol and ether. Touch the swab to the lens center and then wipe in a spirUng motion to the edge. Rinse with denatured alcohol and allow to dry by evaporation. Do not attempt to clean coated lenses with silicon-coated lens tissues or cloths. The silicone will react with the antireflecting film to create a permanently clouded coating. 

Modem CRTs have been provided with better performance and higher functions. Recently, they have been coated with an antireflective film as well. This film provides two functions that are intended to make CRTs more user-friendly by preventing reflections from appearing on the CRT display screen. The antireflection function prevents external light from being reflected from the display screen. This makes it easier to watch the screen reducing eye fatigue for VDT operators and other viewers. 

Reflection characteristics can be controlled by controlling the thickness and the reflective index of the fihn layers. For CRTs which have no such film, the reflection rate about 4% in the range of visible lights. The CRTs which have the antireflective films show reflection of 0.5-1.2% at a wavelength of 550 nm (Ohishi, 1997). 

For single-layer quarter-wavelength homogeneous antireflection film, the condition of reflection minimum can be calculated as... 

The condition of reflection minimum for a double-layer quarter-wavelength antireflection film made from homogeneous strata is... 

Fig. 2.20 Multilayer antireflection film consisting of discrete and homogeneous all-dielectric strata...

For multilayer quarter-wavelength antireflection films with homogeneous strata (step-down refiactive index film) [156, 157], the amplimde reflection coefificient determined for the whole structure in the aforementioned manner is made equal to zero (the condition of reflection minimum) and numerical optimization is further performed to obtain the strata parameters. In that case, the above-mentioned step-down condition is applied that refractive index decreases in steps from the value at the substrate surface to the no value of the surrounding medium [155]. 

M.J. Minot, Single-layer, gradient refractive index antireflection films eflective from 0.35 to 2.5 (t. JOSA 66(6), 515-519 (1976)... 

Industrial Applications Organic photodetectors memory devices solar cells semiconductor film imaging method optical filters antireflection films as polymerization photoinitiators recording materi-... 

Yabuki, Y. Optical filters and antireflection films. Jpn. Kokai Tokkyo Koho JP 2000352613, 2000 Chem. 

The refractive index is one of the important optical properties in focus for nanocomposite research at present. Most of the conventional polymers show refractive indices between 1.3 and 1.7 only few polymers exhibit higher refractive indices such as polythiophene with n = 2.12. With the current development of optoelectronic applications the need to adjust the refractive index of polymeric materials is higher than ever before. Potential applications range from creating novel composite lenses for charged coupled devices, optical filters, or reflectors to optical waveguides, optical adhesives or encapsulants, antireflection films, or integration in improved efficiency solar cells. 

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