Hybrid detectors and multichannel-plate (MCP) PMTs achieve a timing resolution (IRF width) of less than 20 ps FWHM when operated with the new Becker and Hickl SPC-150NX TCSPC modules. As a test light source, Becker and Hickl used a Toptica FemtoFErb laser with a pulse width of 100 fs. The laser beam was directed through a package of ND filters to the photocathodes of a bh HPM-100-06 and a HPM-100-07 detector (based on Hamamatsu R10467-06 and 07 tubes) and a Hamamatsu R3809U-50 MCP PMT. In all cases, an IRF width around 20 ps FWHM and below was obtained. This is considerably shorter than previously reported for these detectors. We attribute the improvement to the superior bandwidth of the discriminators and the extremely low jitter of the timing electronics of the SPC-150NX modules.
Top to bottom: IRF of HPM-100-06, HPM-100-07, R3809U. Response to 100-fs pulse, Recorded with SPC-150NX TCSPC module. Time scale 100 ps/div, 405 fs / time channel.
So far, similar IRF widths have only be obtained with superconducting NbN detectors (see bh news 2015 / 10), and, in a few cases, with MCP PMTs operated at maximum voltage and a CFD threshold that detected only a small fraction of the photon pulses. However, NbN detectors have extremely small active areas, and MCP PMTs operated at high CFD threshold deliver poor efficiency and limited count rate. No such tradeoffs were made for the tests described here: The light was spread over an area of about 5 mm2 for the hybrid detectors, and 50 mm2 for the MCP PMT. The MCP PMT was operated at 3000 V (88% of the maximum), and at a CFD threshold that suppressed no more than 50% of the photon pulses. The maximum count rate under these conditions is several MHz. For the HPM detectors a CFD threshold was used that did not suppress any photon pulses at all.
We believe that the detector / SPC combinations described here deliver the best combination of time resolution, detection area, and sensitivity currently available.