Spectrometer optical principles

In the mid-IR, routine infrared spectroscopy nowadays almost exclusively uses Fourier-transform (FT) spectrometers. This principle is a standard method in modem analytical chemistry45. Although some efforts have been made to design ultra-compact FT-IR spectrometers for use under real-world conditions, standard systems are still too bulky for many applications. A new approach is the use of micro-fabrication techniques. As an example for this technology, a miniature single-pass Fourier transform spectrometer integrated on a 10 x 5 cm optical bench has been demonstrated to be feasible. Based upon a classical Michelson interferometer design, all... 

To establish a quantitative basis for comparing the performance of dispersive and FT spectrometers, it is necessary to review first the optical principles governing the operation of each type of instrument. The primary purpose here will be to... 

Conventional IR spectrometers follow the same principles as described for UV/vis spectrometers, but, bearing in mind that IR radiation is basically radiant heat, the detectors are usually sensitive thermocouples and the monochromator/spectrometer optics must be adapted to transmit in this spectral region. Samples are frequently prepared as thin films or solid dispersions between IR transparent optical surfaces (KBr discs, etc.). 

When recording excitation and fluorescence spectra it must be ensured that monochromatic light falls on the detector This can best be verified in instruments built up on the kit principle or in those equipped with two monochromators (spectrofluonmeters) The majority of scanners commercially available at the moment do not allow of such an optical train, which was realized in the KM3 chromatogram spectrometer (Zeiss) So such units are not able to generate direct absorption or fluorescence spectra for the charactenzation of fluorescent components... 

Using the same PAbs an optical biosensor system has been developed for 2,4,6-TCP [224]. The principle is the detection of laser-induced fluorescence (LIF) in single microdroplets by a homogeneous quenching fluorescence immunoassay (QFIA). The competitive immunoassay occurs in microdroplets (d=58.4 mm) produced by a piezoelectric generator system. A continuous Ar ion laser (488 nm) excites the fluorescent tracer and its fluorescence is detected by a spectrometer attached to a cooled, charge-coupled device (CCD) camera... 

Conversely, we may observe an exceedingly narrow spectral line, so that o(x ) is approximated by <5(x ). Now the data i(x) represent the response function. This principle can, in fact, be used to determine the response function of a spectrometer. The laser, for example, is a tempting source of monochromatic radiation for measuring the response function of an optical spectrometer. Coherence effects, however, complicate the issue. We present further detail in Section II of Chapter 2. 

Raman microspectroscopy results from coupling of an optical microscope to a Raman spectrometer. The high spatial resolution of the confocal Raman microspectrometry allows the characterization of the structure of food sample at a micrometer scale. The principle of this imaging technique is based on specific vibration bands as markers of Raman technique, which permit the reconstruction of spectral images by surface scanning on an area. 

High resolution mass spectrometers used in dioxin/furan analyses (EPA Method 8290 and EPA Method 1613) offer supreme sensitivity, down to parts per quadrillion concentration levels in purified samples. These are research grade instruments with a principle of operation that is based on the separation of ions in a magnetic field followed by ion optics detection. Dioxin/furan analysis is a unique application... 

R 18] [A 1] Each module is equipped with a heater (H3-H8) and a fluidic cooling (C03-C06). Temperature sensors integrated in the modules deliver the sensor signals for the heater control. Fluidic data such as flow and pressure are measured integrally outside the micro structured devices by laboratory-made flow sensors manufactured by silicon machining. The micro structured pressure sensor can tolerate up to 10 bar at 200 °C with a small dead volume of only 0.5 pi. The micro structured mass flow sensor relies on the Coriolis principle and is positioned behind the pumps in Figure 4.59 (FIC). For more detailed information about the product quality it was recommended to use optical flow cells inline with the chemical process combined with an NIR analytic or a Raman spectrometer. 

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