In applications in which single photons must be detected, such as in spectroscopy, confocal or Stimulated Emission Depletion (STED) microscopy, single molecule detection, and quantum cryptography, it is not only important to achieve an extremely low dark count rate of the detector, but a detection efficiency that is as high as possible. Each percent counts. Depending on the version, the COUNT modules exhibit efficiencies of >80% at 670 nm and >50% at 405 nm.
These very good detection rates should not be compromised by additional optical elements such as those required in fibre coupling. In modules with FC connectors a special GRIN lens is integrated that images single photons from the fibre onto the detector chip.
The lenses have been optimised with a double-sided AR coating using our in-house IBS coater. This broadband coating from 400-1100 nm has a reflection of less than 1.5%, and has thus led to a reduction in losses in detection efficiency.
Because the coating process is performed in house, we are able to provide further optimisation for special spectral ranges. Reflections of <1% with AR coatings in the range from 400 nm to 900 nm or from 600 nm to 1100 nm can be implemented according to customer specifications.
For COUNTblue modules with increased sensitivity in the blue to yellow spectral range, we designed a special AR coating option that has a reflection of under 1% from 350 nm to 700 nm. Starting the end of 2011, this coating will be routinely available.
