Superconducting Bolometers
	We are developing antenna-coupled superconducting bolometers as fast and sensitive direct detectors for terahertz spectroscopy. The bolometer consists of a niobium microbridge electrically biased on its superconducting transition, where its resistance changes in proportion to absorbed terahertz power. This detector can record changes in terahertz transmission, reflection, or emission from a sample on nanosecond to millisecond timescales. Applications include studies of transient photoconductivity in molecules and semiconductor nanocrystals, as well as the rotational and vibrational modes of excited molecular species. This work is in collaboration with the group of Prof. C. Schmuttenmaer (Yale Chemistry) and is supported by NSF-CHE.
	Left: 2" silicon wafer after microfabrication of more than a hundered antenna-coupled bolometer devices. Top right: Optical micrograph of niobium bolometer with log spiral antenna. Bottom right: Measured frequency response of device with log spiral antenna.
	We are also developing infrared/terahertz single-photon detectors based on a superconducting titanium nanobridge. These devices have a lower superconducting critical temperature and a smaller volume than the niobium detectors, resulting in significantly greater sensitivity (but with a slower response time and lower saturation power). We have characterized these devices using a pulsed microwave technique, where the absorbed energy of a fast microwave pulse simulates the energy of a single terahertz photon. This work is in collaboration with Dr. B. Karasik at the Jet Propulsion Lab.
	Recent Publications: "Nanobolometers for THz photon detection," B.S. Karasik, A.V. Sergeev and D.E. Prober, IEEE Transactions on Terahertz Science and Technology 1, 97 (2011). "Proposal for a GHz count rate near-IR single-photon detector based on a nanoscale superconducting transition edge sensor," D.F. Santavicca, F.W. Carter, and D.E. Prober, Proc. SPIE 8033, 80330W (2011). "Energy resolution of terahertz single-photon-sensitive bolometric detectors," D.F. Santavicca, B. Reulet, B.S. Karasik, S.V. Pereverzev, D. Olaya, M.E. Gershenson, L. Frunzio and D.E. Prober, Appl. Phys. Lett. 96, 083505 (2010). "A far-infrared Fourier transform spectrometer with an antenna-coupled niobium bolometer," D.F. Santavicca, A.J. Annunziata, M.O. Reese, L. Frunzio and D.E. Prober, Supercond. Sci. Technol. 20, S398-S402 (2007). "Antenna-coupled niobium bolometers for terahertz spectroscopy," D.F. Santavicca, M.O. Reese, A.B. True, C.A. Schmuttenmaer and D.E. Prober, IEEE Trans. Appl. Supercond. 17(2), 412 (2007).
	Recent Talks: "Superconducting single photon detectors," a keynote talk given by Daniel Prober at the Keck Institute for Space Studies Workshop on Single Photon Counting Detectors (Caltech, 2010) [slides] [video] "Energy resolution of THz single-photon-sensitive bolometric detectors," an invited talk given by Daniel Santavicca at the Keck Institute for Space Studies Workshop on Single Photon Counting Detectors (Caltech, 2010) [slides]
	Earlier work in our lab focused on the development of superconducting bolometers as heterodyne mixers for applications in far-infrared astronomy. We developed niobium bolometers utilizing out-diffusion of hot electrons to achieve response times as fast as 20 ps, corresponding to output bandwidths approaching 10 GHz. We also investigated the use of lower critical temperature superconducting materials, including aluminium and niobium-gold bilayers, to improve device sensitivity. More information on this work can be found in the following publications: "Nb-Au bilayer hot-electron bolometers for low-noise THz heterodyne detection," I. Siddiqi and D.E. Prober, Appl. Phys. Lett. 84, 1404 (2004). "Heterodyne mixing in diffusion-cooled superconducting aluminum hot-electron bolometers," I. Siddiqi, A. Verevkin, D.E. Prober, A. Skalare, W.R. McGrath, P.M. Echternach and H.G. LeDuc, J. Appl. Phys. 91, 4646 (2002). "Length scaling of bandwidth and noise in hot-electron superconducting mixers," P.J. Burke, R.J. Schoelkopf, D.E. Prober, A. Skalare, W.R. McGrath, B.Bumble and H.G. LeDuc, Appl. Phys. Lett. 68, 3344 (1996). "Superconducting terahertz mixer using a transition-edge microbolometer," D.E. Prober, Appl. Phys. Lett. 62, 2119 (1993). more