Models bolometers

Up to now, in the formulation of a bolometer model, only the heat capacity of itinerant carriers was considered [57], However, our measurements show that, even at 24 mK, the presence of a spurious heat capacity in the thermometer increases the expected value of the pulse rise time. We expect that the spurious contribution in Fig. 12.17 increases down to the temperature of the Schottky peak at T = k.E/khT about 10 mK. Since gc decreases at low temperatures, the total effect on pulse rise time and pulse amplitude can be dramatic at lowest temperatures. In reality, the measured rise time of CUORICINO pulses is about three times longer than that obtained from a model which neglects the spurious heat capacity of the thermistor. For the same reason, also the pulse amplitude is by a factor two smaller than the expected value (see Section 15.3.2). 

Carbon resistor First bolometer Historical Easy to model Easy to make Need LHe (4 K)... 

The first bolometers are of interest for historical reasons and because the first-order models that describe their performance also apply to modern microbolometers. The first bolometers were made from thin chips cut from a carbon resistor, connected to a plate at near-liquid-helium temperatures by 2-mil-diameter gold wires (Putley, 1963). The gold wires provided a path for the bias current, and also provided thermal impedance between the active element and the helium bath - see Figure 3.2. 

We can model the performance of a bolometer (and microbolometer) using basic thermal physics and a knowledge of how the resistance varies with temperature. The dependence of resistance on temperature is captured in the thermal coefficient of resistance (TCR). The electrical resistor is connected to a heat sink through thermal... 

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