NIR Optical Probe Instrumentation

Commercially available instrumentation for absorbance and fluorescence measurements in the NIR region is scarce. Conventional absorbance spectrophotometers 

The design and operation of an NIR probe is similar to that of conventional UV-visible OFCD reported in the literature.(21) These probes consist of a light source, a bifurcated fiber, an NIR dye, a polymer matrix, a detector, and other optical components. 

Additional laser diode technologies recently reported include a continuous-wave rhodamine 700 dye laser with a maximum wavelength output at 758 nm, powered by two laser diodes each operated with two standard AA batteries (RDT E division of the US Naval Command, Control, and Ocean Surveillance Center, San Diego, California), and a tunable laser diode with output laser wavelengths of 650, 780, 850, and 1320 nm (New Focus, Mountain View, California). 

Some of the typical parameters or properties utilized for NIR detection are potentiometry,(5) absorbance,(52 54) refractometry/18,19) or fluorescence spectros-copy.(55) Of these, has proven to be the most valuable detection method in fiber optic applications/2,56) In standard spectroscopic techniques, the detection limits of a method are greatly determined by the instrument and by the chemical method used for the analysis. However, in OFCD research the detection limits are governed by a series of other variables including the dye, the matrix, and the instrument. By optimizing these variables, low detection limits can be obtained with this technique. 

At room temperature, normally 99% of the molecules are in the ground state. On radiant excitation, the absorbed energy promotes electrons to a higher energy state of the chromophore. In chromophores with acceptable quantum yields, the fluorescence emission can be measured as the electrons return to the ground state. 

---