Mid-infrared Laser-Induced Fluorescence with Nanosecond Time Resolution Using a Superconducting Nanowire Single-Photon Detector: New Technology for Molecular Science

Abstract

In contrast to UV photomultiplier tubes that are 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. In recent years, several new technologies have been developed that open new experimental possibilities for research in the mid-infrared. In this Account, we present one of the more promising technologies, superconducting nanowire single photon detectors (SNSPDs) by sharing our experience with its use in a typical experiment carried out by physical chemists (laser-induced fluorescence) and comparing the SNSPD to a detector commonly used by physical chemists (InSb at LN Temperature). SNSPDs are fabricated from a thin film of superconducting metal, patterned into a meandering nanowire. The nanowire is cooled below its superconducting temperature, T, and held in a constant current circuit below the critical current necessary to destroy superconductivity, I. 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 exhibits single-photon sensitivity across the entire mid-IR spectrum. As these devices have not been used extensively outside the field of light detection technology research, one important goal of this Account is to provide practical details for the implementation of these devices in a physical chemistry laboratory. We provide extensive Supporting Information describing what is needed. This includes information on a liquid nitrogen cooled monochromator, the optical collection system including mid-infrared fibers, as well as a closed-cycle cryogenic cooler that reaches 0.3 K. We demonstrate the advantages of these detectors in a time-resolved laser-induced infrared fluorescence experiment on the energy pooling in crystalline CO overlayers formed on a NaCl(100) surface. We present dispersed fluorescence spectra recorded from 1.9 to 7.0 μm obtained by single-photon counting. We also estimate the sensitivity of this WSi-based detection system at 3 μm; the system's noise equivalent power (NEP) value is ∼10 of a conventional InSb photovoltaic device. Straightforward modifications are expected to provide another 100 000-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 crystals.

Detecting Sub-GeV Dark Matter with Superconducting Nanowires

“…Superconducting nanowires are a rapidly developing technology with applications ranging from space communications [24,25], to LIDAR [26,27], to quantum-information science [28]. With sub-eV energy sensitivity [23], ∼ 10 −4 counts per second (cps) dark count rates [22], and spatial discrimination ability [29], superconducting-nanowire single-photon detectors (SNSPDs) provide an excellent candidate for detecting DM.…”

Circuit designs for superconducting optoelectronic loop neurons

“…SOENs are also well-suited to operate in conjunction with other cryogenic technologies. Many of the most advanced imaging systems used for medical applications, astronomical observation, and particle detectors use cryogenic sensors [55][56][57][58][59][60][61][62]. Integrated image processing and data communication in and out of the cryostat are central challenges for such technologies.…”

Perspectives for Applications of Quantum Imaging

“…Thus, the nanowires become normal conductors and an electrical signal can be measured. This way single photons in the VIS and NIR can be detected with detection efficiency . However, SNSPDs can also be used for much longer wavelengths up to 5 µm although the efficiency still needs to be optimized.…”