1. What is chemical imaging?
Chemical imaging is a method for spatially resolving the chemical properties of a sample in 2D or 3D images. With this technique it is possible to obtain information about the material properties, the structure and the origin of the examined samples.
2. What is FT-IR imaging?
FT-IR imaging is one way to create said spatially resolved chemical images. Each pixel of these images consists of a whole IR spectrum. By interpreting the individual spectra, interesting sample regions can be detected and evaluated.
3. How do you create FT-IR images?
Common methods are sequential single point or line array measurements, as well as the direct acquisition of 2D images by a focal-plane array (FPA) detector. While FPA detectors offer the superior solution, highly automated single-point measurements are an economical alternative.
4. How does an FPA detector work?
The principle of an FPA detector is analogous to that of a digital camera. Instead of visible light, however, a defined array of pixels is illuminated by infrared light, with each detector pixel recording an independent, spatially resolved IR spectrum.
5. Do FPA detectors require apertures?
No, an FPA detector does not require any apertures. Each pixel of the detector functions as an aperture and thus records a spatially IR information directly. This allows much faster and higher resolution measurements compared other detector techniques.
6. Is it possible to adjust the spatial resolution of an FPA?
The spatial resolution of an FPA detector depends on the size of the individual detector pixels. However, adjacent pixels can be combined to form a "larger pixel" and thus the spatial resolution is reduced, also improving spectral quality.
7. Are there different FPA sizes?
FPA detectors are available in different array sizes. Size should be selected according to the optical system (microscope). For example, the LUMOS II is optimized for a 32x32 pixel array, while the HYPERION 3000 is designed for a 64x64 or 128x128 pixel arrays. With the latter it is possible to record an impressive number of more than 16,000 spatially resolved spectra in one scan.
8. Is a larger FPA better?
No, because the size of the FPA detector depends exclusively on the optimal illumination provided by the microscope. A homogeneous illumination of the detector array is important to ensure a consistently high spectral sensitivity both in the center and at the edges of the detector.
9. When does a larger FPA have advantages?
The larger the FPA detector area, the more spectra are recorded simultaneously. Since the spatial resolution is independent of the array size, this means that a 128x128 FPA detector covers an area 16 times larger than a 32x32 detector array in a single measurement.
10. Can FPA be combined with any measurement technique?
Yes they can. FPA detectors offer advantages in transmission, reflection and attenuated total reflection (ATR). Especially when used with ATR technology, this type of detector achieves an exceptionally high spatial resolution.
11. Why is the resolution of FPA measurements in ATR increased?
The combination of a high refractive solid-state lens (germanium ATR crystal) and an "aperture-free" FPA detector increases spatial resolution by a factor of 4 compared to transmission measurements. This effect is also called an immersion lens.
12. Are FPA measurements applicable to all samples?
Since FPA measurements can be combined with all measurement techniques, in principle all types of samples can be analyzed this way. Gases, liquids and other volatile substances cannot be analyzed microscopically due to their kinetic properties.
13. What are typical applications of an FPA?
Typical applications can be found in all areas of industry and research. Starting with the analysis of microplastics, particles and contaminations over the characterization of complex chemical structures, such as biological tissue, pharmaceutical products up to multilayer laminates and lacquers. In short, this detector technology is used wherever very high spatial resolution and the analysis of large sample areas are indispensable.