Coatings

Whenever light passes from one medium into another medium with different optical properties, most notably refractive index, part of the light is reflected and part of the light is transmitted. The intensity ratio of the reflected and refracted components is a function mainly of the difference in refractive index among the materials, the polarization of the incident light and the angle incidence.

According to Fresnel's law, it is convenient to think of incident radiation as the superposition of two plane-polarized beams, p-polarized which electric field paralled to plane of incidence and s-polarized which electric field perpendicular to the plane of incidence. Frenel? laws can be summarized the following two equation:

Specially when reflected and refracted rays are perpendicular to each othere(q1+q2= 90), the reflected light is completely s-polarized. This angle is called Brewster? angle.

Optical coatings are used to alter the reflectance, transmittance, absorbance, or polarizer properties of optical components. The optics being coated is usually called the substrate. The coating is deposited in high vacuum using the process of evaporation on substrate. Coating material include metal (Au, Al, Ag, Ni-Cr, Cr and so on), dieletrics(Oxides, Fluorides and Sulfides) and semiconductors(Si, Ge).

Optical interference coatings respond differently to s and p polarized light. For this reason, it is essential to specify s, p, or random (the average of the s and p performance) polarization when the angle of incidence exceeds 20 degrees.

l RS: Reflectance for s-plane polarization RP: Reflectance for p-plane polarization

l TS: Transmittance for s-plane polarization TP: Transmittance for p-plane polarization

Please contact CASIX, if our standard coatings described in this chapter can? meet your requirement. Our engineers will design special coating for you.

Coating Type		Properties and Application
Anti- reflection	Single Layer MgF₂	Applied to materials with refractive indices from 1.45 to 2.4. The most popular antireflection coating for visible. They are insensitive to change in incidence angles.
	Multilayer “V”	Used to provide lowest reflectance with narrow wave band for most laser application. Minimum reflection less than 0.1%
	Broadband Multilayer	They have excellent performance in broadband. Coating performance is sensitive to angle of incidence.
	Dual Wavelength Band	Offer very low reflectance at two widely spaced wavelengths, such as Nd:YAG Laser (1064) and its second harmonic (532) . CASIX makes it on dual wavelength waveplates.
Partial Reflection	Single Wavelength Band	Provide 50% reflection and transmission at 45° angle of incidence in single wavelength. Perfect for beamsplitters application. Transmission/reflection (T/R) ratio of 20/80, or others for Beamsplitter is available upon request.
Partial Reflection	Broadband	In wide bandwidth provide 50% reflection and transmission. CASIX can also partial coating with different R/T ratios at any angle of incident.
Beam -splitter	Laser Line Polarization Beamsplitter	High reflection to s-polarized and antireflection to p-polarized for laser application.
	Broadband Polarization Beamsplitter	In wide wavelength bandwidth provide high reflection to s-polarized and antiflection to p-polarized
	Dichroic Beamsplitters Mirrors	These coatings can separate the laser fundamental and the pump wavelength, or the fundamental and the second harmonic. They specifically applied to laser mirror.
DPSS Laser		These coatings are specifically designed to diode laser pumped laser. They can be deposited on a variety of substrates and have high damage threshold.
High Reflection	Dielectric High Reflective Coatings	Provide high reflectance over a broad bandwidth, it is ideal for tunable laser and white light application.
High Reflection	Metallic High Reflective Coatings	Metallic coatings have low peak reflectance, mechanical durability and damage threshold, but they have extremely broadband and low cost, specially they are insensitivity to angle of incident light and polarization.