Detection source signal representations

The simplest representation of the thermal circuit of an infrared detector is shown in Fig. 3.1. The detector is represented by a thermal mass H coupled via a conductance Gto a heat sink at a constant temperature T. In the absence of a radiation input the average temperature of the detector will also be T, although it will exhibit a fluctuation about this value. This fluctuation gives rise to a source of detector noise ( temperature noise ) which sets the ultimate limit to the minimum signal detected by a perfect thermal detector. When a radiation input is received by the detector, the rise in temperature is found by solving the equation ... 

A method that has shown to be quite satisfactory and relatively straightforward is described in Protocol 2. In this method a diffuser plate or an MgO scatterer plate is placed in the sample holder and then both ExM and EmM are scanned synchronously from 250-600 mn. This will produce a spectrum of the xenon arc source that has been distorted by the sensitivity variation of the emission detection system. The reflector is replaced by a concentrated sample of rhodamine B in a triangular cuvette. The cuvette is oriented so that the hypotenuse is on the face opposite to EmM. This is a similar configuration to the cell in the reference channel of the instrument. A red cut-oflf filter is placed in front of the entrance slit to EmM and Xem is set to 620 ran. Then ExM is scanned from 250-600 nm and the spectrum is recorded. This spectrum is a close representation of the true xenon lamp intensity profile. Often neutral density filters will have to be placed in the emission beam in order to prevent signal saturation of the PMT. The two curves thus generated can be compared and the correction fector curve, C(X), calculated ... 

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