  We describe optical characterisation of a Strained Silicon Cold Electron
Bolometer (CEB), operating on a $350~\mathrm{mK}$ stage, designed for
absorption of millimetre-wave radiation. The silicon Cold Electron Bolometer
utilises Schottky contacts between a superconductor and an n++ doped silicon
island to detect changes in the temperature of the charge carriers in the
silicon, due to variations in absorbed radiation. By using strained silicon as
the absorber, we decrease the electron-phonon coupling in the device and
increase the responsivity to incoming power. The strained silicon absorber is
coupled to a planar aluminium twin-slot antenna designed to couple to
$160~\mathrm{GHz}$ and that serves as the superconducting contacts. From the
measured optical responsivity and spectral response, we calculate a maximum
optical efficiency of $50~\%$ for radiation coupled into the device by the
planar antenna and an overall noise equivalent power (NEP), referred to
absorbed optical power, of $1.1 \times 10^{-16}~\mathrm{\mbox{W Hz}^{-1/2}}$
when the detector is observing a $300~\mathrm{K}$ source through a
$4~\mathrm{K}$ throughput limiting aperture. Even though this optical system is
not optimised we measure a system noise equivalent temperature difference
(NETD) of $6~\mathrm{\mbox{mK Hz}^{-1/2}}$. We measure the noise of the device
using a cross-correlation of time stream data measured simultaneously with two
junction field-effect transistor (JFET) amplifiers, with a base correlated
noise level of $300~\mathrm{\mbox{pV Hz}^{-1/2}}$ and find that the total noise
is consistent with a combination of photon noise, current shot noise and
electron-phonon thermal noise.
