Sources for Mid-Infrared Microspectroscopy

Provided that samples can be removed from the laboratory, there are two alternative sources of infrared radiation that are far better than incandescent sources for mid-IR microspectroscopy, namely the synchrotron and the free electron laser (FEE) [16]. 

Depending on the position along the undulator, the oscillation of the electrons is either in-phase or out-of-phase with the radiation introduced from the outside. The light either tries to accelerate or decelerate these electrons, thereby gaining or losing kinetic energy, and so moves faster or slower along the undulator. This causes the electrons to form bunches when they are synchronized they will in turn emit synchronized (i.e., coherent) radiation. 

Prom a spectroscopic standpoint, the main difference between a synchrotron and an FEE is that a synchrotron emits broadband radiation, while the FEL emits monochromatic radiation with several orders of magnitude higher brUUance than a synchrotron. Thus, radiation from a synchrotron can be expanded and passed into a FT-IR spectrometer, for which the interferometer and aU the subsequent optics are no different from those in a conventional FT-IR spectrometer (or microspectrometer.) When a FEL is used for spectroscopy, the monochromatic radiation generated can be modulated in any appropriate manner (e.g., by a tuning fork chopper) before being passed onto the sample and detector. In principle, FELs can 

In a typical cyclotron, the maximum radius is quite limited as the particles start at the center and spiral outward thus, the entire path must be a self-supporting disk-shaped evacuated chamber. Since the radius is limited, the power of the 

Steiner et al. [14] have reported the measurement of maps of octadecanephos-phonic acid (OPA) molecules deposited on a microstructured aluminum oxide/gold surface using an PEL source that was modulated by a rapid-scanning interferometer. The beam was then passed through a wire-grid polarizer and a photoelastic modulator so that the polarization was switched at a rate of 75 kHz. 

The effective diameter of the beam from a synchrotron is typically about 100 pm and light is emitted into a narrow range of angles, making this an almost perfect radiation source for mid-infrared microspectroscopy. Not all synchtrotrons are equipped with infrared beam lines, but as the importance of the results that are being obtained continues to increase, this situation is changing. Beam time on 

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