Interference Filters & Special Filters
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glass made of ideas Interference Filters & Special Filters

SCHOTT is an international technology group with more than 125 years of experience in the areas of specialty glasses and materials and advanced technologies. With our high-quality products and i ­ntelligent solutions, we contribute to our customers’ success and make SCHOTT part of everyone’s life. SCHOTT Advanced Optics, with its deep technological expertise, is a valuable partner for its customers in developing products and customized solutions for applications in optics, lithography, astronomy, opto-electronics, life sciences, and research. With a product portfolio of more than 120...

Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Explanation of interference filter types . . . . . . . . . . . . . . . 6 ­ 1.4 Environmental aspects, hazardous substances, RoHS, ISO, REACh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Basic information on interference filters. . . . . . . . . . . . 7 2.1...

Interference filters are used in various industries and enable challenging applications. Leveraging the function of various substrate materials in combination with special coatings, SCHOTT has been developing such filters since 1939. While advancing its capabilities SCHOTT has continuously expanded its interference and special filter program. These developments are reflected in this brochure. The content has been updated and new products based on our latest technologies have been added. Thus, SCHOTT’s Interference Filters & Special Filters Brochure can be used as a reliable information...

SCHOTT Advanced Optics offers a wide variety of different interference filters for use in medical technology, analytics, consumer and security applications, whereby most of the offered filters are designed and manufactured according to customers’ specifications. SCHOTT first developed interference filters back in 1939, when Dr. Walter ­Geffcken, a SCHOTT researcher, filed a patent on “interference filters” (DE716153 and DE742463 – German patent office), a metal dielectric and all dielectric thin-film filter. In 1940, another patent was filed by Dr. Geffcken on “coatings with reduced surface...

1.3 Explanation of i ­nterference filter types The interference and special filter portfolio of SCHOTT includes the following types of filters: • Longpass interference filters that only permit longer wavelengths to pass through • Shortpass interference filters that only permit shorter wavelengths to pass through • Bandpass interference filters that only permit a certain wavelength band to pass through • Neutral density thin-film filters with a nearly constant transmission spectrum over the VIS spectrum to lower the light by a certain extent • Notch filters or bandblock filters that block a...

2. Basic information on interference filters Interference filters leverage (as the name implies) the physical effect of the interference of light waves. This is illustrated in Fig. 2.1 for the case of constructive and destructive interference. Destructive interference Constructive interference Light wave 2 λ/2 out of phase Fig. 2.1 Interference of two light waves for constructive interference (left): the two light waves are in phase and add to a superposition of both waves. In contrast, for destructive interference (right) one light wave is half a wavelength out of phase leading to light...

Incident light wave Reflection I Reflection II Thin-film layer: thickness: λ/4 Fig. 2.3 A thin-film layer of thickness λ/4 avoids any back reflection by destructive interference of the two reflected waves resulting in an anti-reflective (AR) coating. nsubstrate > n1 Transmitted light wave As shown in Fig. 2.3, an incident light wave is partly reflected at the interface airthin-film layer. A second partial reflection occurs at the interface thin-film layersubstrate. Due to the thin-film thickness of λ/4, the two light waves referred to as “Reflection I” and “Reflection II” are half a...

MgF2 with a refractive index of 1.38 is used and some back reflections are accepted. For this type of AR coating at 500 nm, a thin-film layer thickness of d = 500 nm/(4 ∙ 1.38) = 90.5 nm is needed. The wavelength dependency and r ­ esidual back reflection at 500 nm can be seen in Fig. 2.4. AR Reflection: substrate glass with n = 1.52 in air Design wavelength: 500 nm 10 9 8 Designs: (left: refractive index right: opt. thickness) λ/4 MgF2 layer = 1.38 AI2O3 layer = 1.60 Substrate Fig. 2.4 A single layer MgF2 AR coating reduces the airglass reflectance from 4.3 % to 1.3 % at 500 nm. A double...

(HL)n reflector building block (HL)2 Fig. 2.5 Reflectance spectrum of (HL) n layers from a simple (HL) building block towards an (HL)10 building block from 300 nm to 1200 nm. The design above shows the set-up of a (HL)2 layer design on a glass substrate with a refractive index of nsubstrate = 1.45. The H layer has a refractive index of 2.05 made out of Ta2O5 and the L layer a refractive index of 1.38 made out of ­ MgF2 at a design wavelength of 1000 nm. H layer Ta2O5 = 2.05 L layer MgF2 layer = 1.38 H layer Ta2O5 = 2.05 L layer MgF2 layer = 1.38 In order to visualize the interference filter...

A narrow bandpass ADI filter can be produced by adding a λ/2 layer (absentee layer) inside the bandblock. The absentee layer allows the design wavelength to pass through the filter and to generate a narrow bandpass filter. For example, a simple bandblock is generated from an (HL)8 design where a glass of refractive index nsubstrate = 1.52, H layer made of Ta2O5 and L layer made out of SiO2 at 550 nm design wavelength were used. The narrow bandpass filter design with 2H as the λ/2 narrow bandpass layer is: Air-(HL)4–2H–(LH)4 - glass. The design is illustrated in Fig. 2.7. Fig. 2.7...