SUPERCONDUCTING TRANSITION EDGE BOLOMETERS
Abstract
This report describes the development of a servo-controlled
superconducting transition edge bolometer (STEB) intended for use as
a sensitive broadband far infra-red (FIR), i. e. =1 mm to 100 μm
wavelength, detector.
A STEB uses a constant current biased superconducting film held
on its superconducting transition, where it has a very high temperature
coefficient of resistance, as a temperature sensing element for the
absorbing substrate. Radiation absorbed by the substrate can be
detected by measuring the change in voltage across the superconductor.
The STEB's described in this thesis have in addition a resistive
heater mounted on the substrate which is used as part of a servoregulating
system maintaining the temperature of the bolometer at a
fixed point on the superconducting transition. The potential advantages
of this arrangement are higher frequency response, greater
dynamic range, improved linearity and a STEB which can be more easily
held on the superconducting transition. The STEB's described in this
thesis used Sn films mounted on sapphire substrates as temperature
sensors.
Following a general introduction and review of previous work, the
principles of operation of the servo system are described together
with the theory of the system response, noise and the radiation
performance of the detector. A detailed description is given of the
construction of the bolometer, the bolometer optics, cryogenic
apparatus and the servo circuitry. Optimisation of-the absorption
of radiation by the bolometer substrate is studied using a transmission
line analogue model. Experiments establishing the validity of the
model are also included.
The measured performance of the constructed STEB's is given and
compared with theoretical predictions. The measured noise performance
was found to be considerably better than predicted. Finally,
suggestions are made for future improvements in detector-performance.
Authors
Dunn, Michael Sidney FrancisCollections
- Theses [4125]