Waveguided illumination

The ODMR spectrometer resembles the PA spectrometer shown in Figure 7-1, with the sample placed in a microwave cavity between the pole pieces of an electromagnet. The sample is constantly illuminated by the pump and probe beams amplitude-modulated microwaves arc coupled into the cavity through a waveguide. Changes Si in PL or ST in probe transmission are delected by lock-in am-... 

Occasionally, arrangements with a fibre as sensing element (Figure 7-c) are used, in particular for SERS measurements (the fibre is then coated with the SERS substrate). When using such a layout, it must be taken into account that also the Raman scattering caused by the waveguide material is recorded and must be filtered out. The same applies to arrangements where a window or any other optical element illuminated by the excitation radiation is in the field of view of the collection optics. 

When a grating is used to excite the modes, usually the waveguide film is periodically modulated at the film/cover or film/substrate (or at both) interface (Fig. 15.4b). The incident beam illuminates this grating and one of the diffraction orders will excite the modes. The mode s effective refractive index can be calculated from the so-called grating equation10,30. 

In the decade since these first reports, various advances in blood serum Raman spectroscopy have been reported. As mentioned above, Qu developed a system with a waveguiding sample-filled capillary tube and two linear arrays of abutting fibers, with 100 mW sample illumination at 745 nm. On synthetic mixtures that simulated human serum, they obtained prediction errors for glucose and urea of 0.5 and 0.4mM, respectively [4]. 

Recently, Qi et al. made measurements on approximately 70 serum samples using an epi-illuminated waveguiding sample chamber, 160 mW of 830 nm excitation, up to 150 s of spectral integration, and PLS leave-one-out... 

The semiconductor wafer is mounted at the end of an X-band microwave waveguide so that microwave radiation probes the reflectivity of the sample. The ohmic contact is applied as a grid of thin lines in order to minimise microwave losses. The front of the wafer is in contact with an electrolyte solution, and a modulated light source (for example a light emitting diode) illuminates the sample. The changes in... 

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