This section provides an overview for infrared microscopes as well as their applications and principles. Also, please take a look at the list of 10 infrared microscope manufacturers and their company rankings.
Table of Contents
An infrared microscope is a type of optical microscope that uses infrared light to measure objects nondestructively and without contact. The microscopic functionality is the same as that of a general optical microscope, but since infrared light with a long wavelength is used as the light source, the spatial resolution is limited by the diffraction limit. However, materials often show unique responses to infrared light, and spectroscopic analysis can be used to analyze the components that make up the material.
Many infrared microscopes currently available on the market combine the functions of general infrared spectrometers such as Fourier transform infrared spectroscopy (FTIR) and total reflection spectroscopy.
Infrared microscopes can perform FTIR imaging, which can acquire two-dimensional chemical information because they have the microscope function to capture images and the spectrometer function to perform spectral analysis. Such FTIR imaging contributes to in vivo histological evaluation and pathological observation. It is also used in the industrial field to inspect foreign matter in solids or to inspect defective products by taking advantage of differences in infrared absorption rates.
Like an optical microscope, it is composed of a light source, mirror, lens, and detector. However, instead of a lens that uses refraction, as is common, infrared microscopes use an objective lens that uses the reflection of light, called Cassegrain optics, which is used in reflecting telescopes.
When such optics are used, the spatial resolution is known to be about the same as the wavelength of the light source and is limited to a few micrometers to a few dozen micrometers. Infrared light in the 2.5 to 25-micrometer wavelength range is typically used in infrared microscopy to perform FTIR imaging.
This wavelength band is modulated by molecular vibrations and rotations so that a material-specific spectrum is obtained when the wavelength is scanned. As with FTIR, this can be Fourier analyzed to obtain chemical information, such as the components that make up the substance, which can then be superimposed on a two-dimensional image acquired with a microscope for mapping.
There are two types of detectors for spectrum measurement: one that detects only one point and another that can be placed over this or that to acquire the spectrum in a single shot without scanning.
This is one method used to measure the thickness of semiconductors. Semiconductors have a high refractive index in addition to a transmission range in the infrared region. Because of this feature, optical measurement using infrared light instead of visible light is required.
Infrared light has the disadvantage of being affected by the high refractive index, which reduces accuracy, but it also has the advantage of being less affected by the uneven surface of the object being measured.
One method for measuring the thickness of semiconductors with an infrared microscope is the interferometry method, which determines thickness from optical path differences obtained from the interference of light reflected from the front and back surfaces of the object to be measured.
Unlike the dispersive type, the Fourier transform type (FT-IR) uses an interferometer to detect all wavelengths simultaneously. The obtained data is Fourier transformed, and each wavelength component is calculated.
There are four main advantages of the Fourier transform type.
There are two types of Fourier transform type measuring instruments commonly used.
High-performance infrared microscopes capable of measurement with a two-dimensional array detector need to be cooled with liquid nitrogen because of the heat generated. Failure to cool the microscope will result in a partial inability to measure due to heat damage to the elements. The amount of liquid nitrogen must be constantly controlled to avoid this situation. Liquid nitrogen cooling is also required for common MCT detectors.
Although the measurable thickness and accuracy differ from those when liquid nitrogen is used, there are infrared microscopes that can perform measurements without liquid nitrogen.
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