Optical Laboratory Equipment
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 require corresponding optical components with different performance levels. 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 fused silica optical components such 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.
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Optical Metrology
Optical metrology is the technology of measuring with light. The properties that can be measured are either dimensions or shapes of objects, as well as temperatures and other properties that result from the interaction of light and matter. Dimensional measurements done with light are contact free and often very precise, since they are usually only limited by the wavelength of the light being used.
Industrial Metrology
Many industrial processes light use light to measure the progress of production. The positioning on a conveyor is typically done with simple cameras. Cooling heated parts, UV inspection of cleanliness or laser-based positioning are a few examples of optical metrology in industrial applications. As the applications are numerous, so are the challenges. Challenges that fused silica optical components made of fused silica can help address are: Sensitivity (lower absorption of the bulk glass, high transmission); Accuracy (low wavefront distortion which leads to high optical homogeneity, excellent surface finish and coating, low absorption); Lifetime (even in hostile environments, low to no aging under UV irradiation); Usable over a broad wavelength range (UV to NIR)
Semiconductor Metrology
In chip production optical metrology is a very common technology. Optical systems position the wafer in many processes, as well as monitor the lithography steps. As the node sizes on computer chips get smaller and smaller, the precision of the metrology needs to improve. Fused silica is the material of choice due to its broad transmission window, very low thermal expansion and, for the highest resolution, very good optical homogeneity of the refractive index.
Medical Metrology
Today, medical metrology is key for the efficient treatment of diseases. From tissue analysis prior to cancer treatment, to optical remote sensing and analysis of the composition of kidney or bladder stones, and characterization of calcification in the arteries- metrology is a success factor in selecting the right surgical method or laser source for treatment. Optical fibers guide the light from the laser source to the point of use and back to the analyzing unit. But not only that, an optic fiber bundle can transmit a picture to the surgeon and in parallel act as a beam splitter to guide a fraction of the light from the tissue which needs to be analyzed to an analyzing unit. Although synthetic fused silica has a broad spectral transmission range, the transmission performance is wavelength dependent, which affects the sensitivity of the instrument. Heraeus Conamic offers materials tailored for all wavelength ranges from ultraviolet to visible and infrared.
Spectroscopy
Spectroscopy is another important and broad field of optical analysis that focuses on the study of matter by electromagnetic radiation - light.
Fused silica optics and optical fiber bundles can be used in the UV-vis-NIR wavelength range from (from 80nm to 3500nm). Spectroscopy can be performed through the direct detection of absorption bands in the source light, or can incorporate an indirect detection schemes, such as nuclear particle detection via Cherenkov light, or detection of other light sources like scintillating or fluorescent 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. Because it is very difficult to distinguish whether the absorption is due to the instrument or the substance being measured, a material that absorbs light in the wavelength range of interest complicates and may render measurements impossible.
For example, if certain regions of the electromagnetic spectrum are absorbed by the optics or optical fiber, it is difficult or impossible to observe any possible absorption by the investigated substance in that region. A similar effect occurs when the optical material shows fluorescence. In this case, the instrument material may obscure any absorption of the substance being measured
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 these reasons, it is important to carefully select the substrate, optical fiber material, or cuvette for spectroscopic investigations.
Cuvettes
For analyzing liquids in optical spectroscopy, the cuvette used should be chemically stable and absorb as little as possible. Fused silica is ideal for this application due to its very broad transmission spectrum from the UV to the NIR. As a result a large part of the optical spectrum investigating with the same cuvette is possible. To reduce illumination by back scattering use a highly absorbing fused silica grade named Nerasil®. Some cuvettes can partly consist of diffusing material to optimize the illumination.
Spectroscopy Lamps
Analysis and measurement of gases, liquids and solids must be as precise as possible to obtain exact results. Typical processes are absorption, reflection, transmission, fluorescence and ionization. In high-quality analytical instruments for these processes, the light source needs to fit the instrument and the measured part of the optical spectrum. Different specialty lamps are in use for this broad portfolio of spectroscopy lamps. However, one component applies for all analytics applications: the quartz glass for the lamp. It must be of the highest purity, homogenous and visually perfect. The Heraeus lamp tubing process is ensures the high requested quality, independent of the fusion method or quartz glass grade. Wavelength and intensity determine whether a natural quartz glass such as HLQ 200 or even a fully synthetic material as Suprasil 130 is the best choice.
Fiber Optic Bundles for Remote Sensing
When the object or substance of interest cannot be placed inside the spectrometer, because of its size, shape or harsh environment condition (e.g. for in-process control), fiber optic bundles enable flexible optical remote sensing of materials. They can act as beam splitter, beam combiners, or even deliver light and collect the signal within the same fiber optic bundle. The optical fibers within a fiber optic bundle can also convert the beam cross section, for example, from a line profile to a circular spot. Synthetic fused silica is of the highest purity and the fibers manufactured with this material have the best transmission performance in optical spectroscopy. However, there are differences between the different grades of fused silica. High power UV light can damage the material, causing the formation of color centers and decreased performance over time. A similar degradation can occur in power plants as a result of the nuclear radiation found in these environments. Degradation can also occur under moderate UV light or radiation exposure, but over long distances and over long periods of time. On the other hand, materials that have a higher resistance against UV radiation may have a poor performance in the infrared region - an important consideration when selecting the material for an optical fiber. In addition to material grade, other factors that affect fiber performance and must be considered in fiber design are size and geometry of the optical fiber core, and the choice of cladding material. Heraeus Conamic has a broad product portfolio with customized solutions for all wavelength ranges and can support you in determining the best design for your application.
