Manufacturers of optical coatings and components

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Newport Thin Film Laboratory offers a full range of Schott^® optical filter glass in various shapes, sizes and thickness.  Please contact us with your specific requirements.

Schott^® filter glass operates by selectively absorbing various frequencies and transmitting others.   Their advantage over dielectric/dichroic filters is that they block energy over much larger wavelength regions.  Their disadvantage is that since they absorb the energy blocked, they are subject to thermal fracture.  Often times, the optimal filter will utilize a dielectric multilayer coating applied to a Schott^® filter glass.

When light passes through an absorbing filter glass, the amount absorbed in any unit volume is proportional to the intensity of the incident light times the absorption coefficient, which is wavelength dependent.  As a result, the intensity of an incident beam drops exponentially as it passes through the filter.  This can be expressed by Lambert's law:

                                    t_i = e^-acx

where t_i is the internal transmittance of the filter, a is the absorption coefficient, c is the absorber concentration, and x is the filter thickness.  Note that a is wavelength dependent, so the filter transmittance is wavelength dependent.

As a general rule, absorbing filter glass is heated unevenly during irradiation.  Due to its low thermal conductivity, absorbing filter glass reaches thermal equilibrium slowly.  The resulting temperature differences between the front and back side of a filter and the edge and center of a filter produce flexural stresses within the filter glass that can result in filter breakage.

For many applications, a combination of thermal tempering of the filter glass and application of a dielectric coating will greatly improve resistance to rapid temperature changes.