Diffusion-engineered single-photon spectrometer for UV/visible detection

Abstract

We present predictions for a diffusion-engineered, single-photon spectrometer in the UV-visible range using a superconducting tunnel junction. Quasiparticles are created by photoexcitation, with charge Q 0 . After tunneling through the junction, the quasiparticles can either backtunnel or diffuse away. With confinement by a higher gap or by narrow leads the quasiparticles in the counterelectrode dwell next to the junction and backtunnel, increasing the collected charge to Q ¼ pQ 0 ; p>1. For very narrow leads the dwell time is inversely proportional to the lead width, up to the recombination time of Al, 1 ms at 0.2 K. The new aspect of our work is the use of narrow leads to control the charge gain p, while minimizing self-heating. This charge gain will improve the energy resolution compared to the case p ¼ 1; where the electronic noise is dominant, and compared to much larger charge gain, pE50, where large self-heating resulted with extra noise. r

Enhancing the Energy Resolution of a Singles Photon STJ Spectrometer Using Diffusion Engineering

“…The loss mechanism is assumed to be uniform within the electrodes and the wire. Previously [7] we found that a good approximation to the 2-D simulation is the steady-state 1-D diffusion result, where the outdiffusion time is: (1) where is the effective Al area, and are the wire length and width, and is the quasiparticle diffusion constant in Al. This result diverges from the 2-D simulation as the time to reach steady-state in the wire becomes longer.…”

Experimental and theoretical response of distributed read-out imaging devices with imperfect charge confinement

“…Segall 10 and Savu et al 11 developed a model for DROIDs which included the processes inside the STJs but assumes perfect trapping. Den Hartog et al 12 produced a twodimensional diffusion model of a DROID without trapping but accounting for quasiparticle dynamics in the STJ using Rothwarf-Taylor equations.…”

Imaging spectroscopy with Ta/Al DROIDs: Performance for different absorber lengths

“…Superconducting Tunneling Junctions STJs are being developed as spectro-photometers in wavelengths ranging from the NIR to X-rays in different groups [1,2]. A pixelated 10 Â 12 array of STJs has already successfully been used as an optical imaging spectrometer, SCAM-3, for ground-based astronomy [3].…”