Evaluation of composite bolometers at 0.4 kelvin

Conclusions

In this study we have screened some ten different material coules and tested approximately fifty individual bolometer elements. A number of important empirical conclusions can be made for fabricating reasonable optimum bolometers for operation at 0.4K. We summaraize the results as follows:

• 1. The load curve data or electrical properties do not provide a reliable estimate of the radiative or optical NEP. The electrical NEP can overestimate the true radiative sensitivity by several orders of magnitude.

• 2. Helium-3 cooled bolometers can achieve sensitivities near to the fundamental limits in many applications. For composite detector #2 the optical NEP achieved is equivalent to the photon noise limit for an f/6, 6.4mm diam detector, viewing room temperature rediation with emissivity 0.25 over the spectral range zero to thirty wave numbers (incident power ∼5nW corresponding to a photon noise limit of 7×10⁻¹⁵ Whz^−1/2).

• 3. Singly doped Ge:Sb exhibits the highest resistance-temperature coefficient of all the samples tested, including Ge:InSb. The largest band gap temperature is displayed by the most sensitive bolometer #1.

• 4. The increase in NEP obtained by using a composite structure is less than expected based upon detector area considerations only. This indicates that the integrating cavity efficiencies are quite good at near millimeter wavelengths.