Fused Silica for Analytical Instruments

Applications

Optical Laboratory Equipment

Laboratory

Many analytical instruments rely on optical detection methods. Yet, optical laboratory equipment by itself is a very diverse field. Depending on the employed analytical methods, different optical equipment and corresponding optical elements with different performance levels are required. As the equipment design depends on the individual supplier, we discuss some basic components of optical lab equipment and spare parts or auxiliary equipment, that could make a difference in performance.

The performance of optical components of fused silica as view ports, windows or lenses depends foremost on the optical finishing and potentially on the coating. However, choosing the right fused silica can make a difference as well. Absorption in the ppm / cm range can be significant for sensitive measurements.

Optical diffusers:

Optical diffusers are used to homogenize the beam of a light source, as a cosine corrector for detectors or as an inner layer for integrating spheres. The ideal diffuser has a Lambertian scattering characteristic, that means the intensity of a reflected beam depends on the cosine of the viewed angle. For many applications optical diffusers need to be easy to clean in addition to their good optical properties. Fused silica diffusers have a good chemical stability, but some have an open porosity (which could lead to the introduction of contaminates, and therefore to a deteriorating signal).

Our HOD® is a volume diffuser of high purity fused silica. Volume diffuser means that the reflection and transmission intensity depend on the thickness of the diffuser. It has a very good Lambertian angular intensity dependence, and a closed porosity that allows for easy cleaning.

Want to find out which material is suitable for your application? Please use our Material Selection Guide .

Optical Metrology

Optical metrology is the technology to measure with light. The properties can be dimensions and shape as well as temperatures or other properties that interact with light. Dimensional measurements with light are contact free and often very precise, as they are mostly only limited by the wavelength of the light used.

Spectroscopy

Another important optical analytical method is spectroscopy. Spectroscopy is a wide field of optical analytics focused on the study of matter via electromagnetic (EM) radiation.

Fused silica optics and fiber optic bundles are used if the wavelength region ranges from UV-VIS-NIR (from 180nm to 3500nm). It can be the direct detection of absorption bands or include indirect detection schemes, like nuclear particle detection from blue emitted Cherenkov light or detection of emission from irradiation of other EM sources on scintillating or fluorescing materials.

Optics and optical fibers used in spectroscopy follow the same design considerations as commercial optical components (mirrors, windows, lenses, and substrates) with particular attention to zero fluorescence and minimal absorption. As it is very difficult to differentiate if absorption is due to the measurement apparatus or the substance investigated, the presence of either would complicate the measurement or even make it impossible.

For example, if certain areas of the EM spectrum are absorbed by the optic, it is difficult or impossible to observe any potential absorption by the investigated substance. A similar effect occurs if the optical material shows fluorescence. In this case, the optic may cover up any absorption of the investigated substance.

Despite its good chemical stability, fused silica may age or deteriorate under some hostile conditions. Some fused silica grades perform better or are more resistant to these conditions than others.

For the reasons given above, it is important to choose the substrate, an optical fiber, or a cuvette for spectroscopic investigations with care.

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