Instrumentation Design and Technology

There are two ways to view instrumentation in terms of the method used to separate the infrared radiation into its component parts as used for the analysis, or in terms of the enabling technologies used to selectively capture the relevant radiation required to perform the analysis. The selection of the approach used for the measurement, in line with the techniques outlined in Table 6.1, tends to dictate which view is the most relevant. To explain this we can consider the following examples  

Broadband tunable filters (examples AOTF, LCTF) X  

Note that the examples above to some extent are oversimplifications, and other critical elements, such as 

The latter is particularly the case for laser instruments where attention to optical interfacing is essential, and often features specialized optical hber based optical coupling. 

when instrumentation is implemented in an industrial environment there are many other parameters associated with the final instrument packaging and the electrical and fire hazard safety that need to be addressed. Often these issues are not trivial and can have a profound impact on both the design and final performance of an instrument. In the following sections instrumentation and component technology will be reviewed, and where appropriate the impact of operation in an industrial environment will be addressed. 

There are several measurement techniques that can be considered for use in IR-based instrumentation in the NIR and the mid-IR spectral regions, and these are summarized in Table 4.1. Some of these techniques are classical, as in the case of optical filter-based instruments and scanning monochromators. Others, such as acousto-optically tunable filter (AOTF), have been considered for 15+ years, but are mainly applied to NIR 

An FTIR instrument The three critical components (excluding the sample) are the source, the detector, and the interferometer. In terms of enabling technology it is the interferometer that is critical to the measurement. 

A diode laser spectrometer. In this case, if the laser is a tunable laser, there are only two critical components the tunable laser and the detector. Typically, the enabling technology is the laser, which in this mode acts as the light source and the wavelength selection device. 

Note that the examples above are over-simplifications to some extent, and other critical elements, such as optics, the associated electronics and the sampling interfaces are also important for a final implementation. The latter is particularly the case for laser instruments, where attention to optical interfacing is essential and often features specialized optical fiber-based optical coupling. 

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