Mid-infrared laser-induced fluorescence with nanosecond time resolution using a superconducting nanowire single-photon detector: New technology for molecular science
Li Chen, Dirk Schwarzer, Varun Verma, Marty Stevens, Francesco F. Marsili, Richard Mirin, Sae Woo Nam, Alec M. Wodtke
In contrast to UV photomultiplier tubes widely used in physical chemistry, mid- infrared detectors are notorious for poor sensitivity and slow time response. This helps explain why, despite the importance of infrared spectroscopy in molecular science, mid-infrared fluorescence is not more widely used. We present an example of what is now possible using superconducting nanowire single photon detectors (SNSPDs), which have recently demonstrated single photon detection sensitivity in the mid-infrared. SNSPDs are fabricated from a thin film of superconducting metal, patterned into a meandering nanowire. The nanowire is cooled below its superconducting temperature, Tc, and held in a constant current circuit below the critical current necessary to destroy superconductivity, Ic. Upon absorption of a photon, the resulting heat is sufficient to destroy superconductivity across the entire width of the nanowire, an event that can be detected as a voltage pulse. In contrast to semiconductor-based detectors, which have a long wavelength cutoff determined by the band gap, the SNSPD will absorb light across the entire mid-IR spectrum. We demonstrate the advantages of these detectors in a time- resolved laser-induced infrared fluorescence experiment on the energy pooling in crystalline CO over-layers formed on a NaCl (100) surface. We present dispersed fluorescence spectra recorded from 1.9-7.0 um obtained by single-photon counting. We also estimate the sensitivity of this WSi-based detection system at 3 um - the system's Noise Equivalent Power (NEP) value is 10^-3^ of a conventional InSb photovoltaic device. Straightforward modifications are expected to provide at least a further 100-fold improvement. We demonstrate that the temporal resolution of the experiment is limited only by the pulse duration of the laser used in this work (FWHM = 3.7 ns). The use of SNSPDs enables dramatically improved observations of energy pooling in cryogenic molecular cr
, Schwarzer, D.
, Verma, V.
, Stevens, M.
, Marsili, F.
, Mirin, R.
, Nam, S.
and Wodtke, A.
Mid-infrared laser-induced fluorescence with nanosecond time resolution using a superconducting nanowire single-photon detector: New technology for molecular science, Accounts of Chemical Research, [online], https://doi.org/10.1021/acs.accounts.7b00071
(Accessed December 10, 2023)