Argo series are single-photon detector array cameras based on Single-Photon Avalanche Diodes (SPADs). The SPAD is a p–n junction which is reverse-biased well above its breakdown voltage. Under this operating condition, the absorption of a single photon triggers a macroscopic avalanche current able to mark very precisely photon detection and arrival time. The SPAD biasing electronics, namely the Active Quenching Circuit (AQC), is integrated on the same silicon chip. The AQC senses the avalanche current, quenches it and resets the diode to its initial state. Synchronously with the avalanche detection, an output pulse is generated. The total time, which is required to restore the initial state of the SPAD after the detection of a photon, is named dead-time. During the dead-time, no photons can be detected.

Peculiar of the Argo Series cameras is the fact that all AQC’s output pulses are directly routed outside and made available to the user, through a high-speed, high-density connector. In other words, the Argo cameras do not have on board counting or timing electronics and, thus, it is mandatory for the end user to connect an acquisition system to the camera. The high-density connector is placed on the back of the camera and LVDS electrical levels are used to minimize crosstalk between different outputs. The detector arrays used in the Argo series are square arrays of 7×7 or 8×8 pixels, to be selected before purchase (product part numbers listed at the end of this datasheet).

SPAD pixel performance is defined by noise levels, detection efficiency and photon timing jitter. Primary noise sources for Argo’s SPADs are dark-counting rates (DCR), after-pulses and optical crosstalk. As shown in the Specifications sheet, Argo cameras offer excellent noise performance, with low DCR and afterpulsing probability and negligible optical crosstalk. Photon Detection Efficiency (PDE) is defined as the probability to measure an output pulse, given an impinging photon. SPAD-PDE is the native PDE of the detector inside the active area and is very uniform across an array, with pixels in the 7×7 array slightly better than those inside the 8×8 arrays (see first page of this datasheet). Finally, Argo cameras offer excellent timing resolution with uniform IRF across the entire array and FWHM of just few hundreds of picoseconds. The AQC deadtime can be user-selected (for all the pixels of the array) with values from few tens to few hundreds of nanoseconds. The selection can be performed by setting high or low two specific pins the high-speed connector (see user manual for details). 

Argo can be powered by supplying a DC voltage through the side power connector and the provided power supply. Argo can be also easily integrated into common optical setups thanks to the direct compatibility with Thorlabs® SM1 system. A C-mount adapter further expands its integration capabilities. The imaging array inside Argo is available in two versions: (1) without a micro-lens array, i.e., with the native imager fill factor of 12.6%; (2) with a micro-lens array (MLA) able to recover the fill factor up to 76%, while being still optimal for microscope use. Indeed, MLA performance depends slightly on the incoming beam wavelength and greatly on its aperture as shown here. The reported imager fill factor is a simulation whose data has been averaged over three different wavelengths (400 nm, 600 nm and 800 nm).