Enhancing the Linear Dynamic Range in Multi-Channel Single Photon Detector beyond 7OD

Abstract

We present design, implementation, and characterization of a single photon detector based on 32-channel PMT sensor [model H7260-20, Hamamatsu]. The developed high speed electronics enables the photon counting with linear dynamic range (LDR) up to 10⁸count/s per detector's channel. The experimental characterization and Monte-Carlo simulations showed that in the single photon counting mode the LDR of the PMT sensor is limited by (i) "photon" pulse width (current pulse) of 900ps and (ii) substantial decrease of amplitudes of current pulses for count rates exceeding 10⁸ count/s. The multi-channel architecture of the detector and the developed firm/software allow further expansion of the dynamic range of the device by 32-fold by using appropriate beam shaping. The developed single photon counting detector was tested for the detection of fluorescence labeled microbeads in capillary flow.

Keywords: fluorescence detection; photomultipliers; single photon counting.

Fig. 1

Schematic of the amplifier/comparator circuit.

Fig. 2

One stage amplifier and comparator pulses for different light attenuations. From left to right: dark counts, −2OD, −1OD, −0.3OD.

Fig. 3

Block diagram of the measurement setup.

Fig. 4

PMT pulses in the range from darkness to very high light (from left to right: dark current pulses, light attenuation: −6OD, −5OD, −4OD, −3OD, −2OD, −1OD, 0 OD).

Fig. 5

Dark count versus comparator threshold voltage.

Fig. 6

Crosstalk of neighboring channels.

Fig. 7

Photon count versus illumination for 32 channels of the PMT. The comparator response time is 2.5ns. Circled and squared curves present results of the Monte-Carlo simulation for 1ns and 2.5ns comparator pulses correspondingly. Dashed curve is the ideal linear response.

Fig. 8

Simulated distributions of photon arrival times for photocount rates from 2×10⁵/s through 2×10⁹/s.

Fig. 9

Light/Count characteristics measured for three comparator thresholds Vth. Dashed line presents simulated incident (true) photon count, and white circles are Monte-Carlo simulated photon count as detected by comparator.

Fig. 10

Photo-count rate, mean photon count accumulated during 25ms and its variance.

Fig. 11

Fluorescence of three types of quantum dots.

Fig. 12

Fluorescence detected from 250 individual beads colored with three quantum dot types.

Fig. 13

3D bead map of color codes of 1500 beads encoded with three types of quantum dots.