We describe a superconducting transition edge sensor based on a nanoscale niobium detector element. This device is
predicted to be capable of energy-resolved near-IR single-photon detection with a GHz count rate. The increased speed
and sensitivity of this device compared to traditional transition edge sensors result from the very small electronic heat
capacity of the nanoscale detector element. In the present work, we calculate the predicted thermal response time and
energy resolution. We also discuss approaches for achieving efficient optical coupling to the sub-wavelength detector
element using a resonant near-IR antenna.
We present an overview of the recent progress made in the development of a far-IR array of ultrasensitive hot-electron
nanobolometers (nano-HEB) made from thin titanium (Ti) films. We studied electrical noise, signal and noise
bandwidth, single-photon detection, optical noise equivalent power (NEP), and a microwave SQUID (MSQUID) based
frequency domain multiplexing (FDM) scheme. The obtained results demonstrate the very low electrical NEP down to
1.5×10-20 W/Hz1/2 at 50 mK determined by the dominating phonon noise. The NEP increases with temperature as ~ T3
reaching ~ 10-17 W/Hz1/2 at the device critical temperature TC = 330-360 mK. Optical NEP = 8.6×10-18 W/Hz1/2 at 357
mK and 1.4×10-18 W/Hz1/2 at 100 mK respectively, agree with thermal and electrical data. The optical coupling
efficiency provided by a planar antenna was greater than 50%. Single 8-μm photons have been detected for the first time
using a nano-HEB operating at 50-200 mK thus demonstrating a potential of these detectors for future photon-counting
applications in mid-IR and far-IR. In order to accommodate the relatively high detector speed (~ μs at 300 mK, ~ 100 μs
at 100 mK), an MSQUID based FDM multiplexed readout with GHz carrier frequencies has been built. Both the readout
noise ~ 2 pA/Hz1/2 and the bandwidth > 150 kHz are suitable for nano-HEB detectors.
We report the characterization of superconducting niobium microbolometers designed for time-resolved terahertz
spectroscopy on nanosecond to millisecond timescales. Coupling of the incident signal is achieved via a planar antenna
mounted on a hyperhemispherical silicon lens. We have integrated these detectors into a custom Fourier-transform
spectrometer. The spectrometer optics are frequency independent over the spectral range 0.1-3 terahertz and thus the
system bandwidth is set by the detector antenna. We have fabricated devices with two different antenna geometries, the
double-dipole and the log spiral, and have characterized the spectral response of each. This detector will enable a variety
of novel spectroscopy applications.
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