PhotonPix User Manual
The PhotonPix is an integrated module for photon counting based on a microchannel-plate photomultiplier tube (MCP-PMT). It comprises an MCP-PMT detector, high-voltage power supply, constant fraction discriminator (CFD), cooling, overexposure and overheat protection circuits, and a microcontroller.
!!! warning "Sensitive equipment" PhotonPix is extremely sensitive equipment and must be handled with care to avoid detector damage. Always read the safety section before operating.
Introduction
The PhotonPix integrates the following components in a single housing:
- MCP-PMT detector — photocathode, MCP stack, and anode
- High-voltage power supply — independently controlled photocathode and MCP voltages
- RF amplifier — fast signal amplification from the anode
- Constant fraction discriminator (CFD) — converts analog pulses to logical NIM output
- Microcontroller — USB interface, protection logic, and HV control
The HV divider applies voltage to three main points: the photocathode, the MCP stack, and the anode. The photocathode can be quickly switched on or off by the overexposure protection circuit or by user command. The output of the anode is connected to a fast RF amplifier whose signal is split into two outputs:
- Anode Output — analog signal available at a 50 Ω SMA connector
- NIM Output — logical current signal (20 mA into 50 Ω → −1/−2 V amplitude)
The microcontroller allows the user to adjust MCP voltage and photocathode state via USB.
Output Signals
The NIM output has a finite dead time of approximately 1.6 ns due to the CFD electronic logic. Analog pulses arriving within this window are not converted to NIM pulses.
Before You Begin
Safety Measures
!!! danger "Always use the protective cap during storage" Even without high voltage applied, the photocathode can be damaged by ambient light. Never expose the photocathode to bright light during storage or handling. Always replace the protective lens cap when not actively measuring.
!!! warning "Avoid strong illumination changes" The overexposure protection circuit counts pulses every 1 ms and disables the photocathode HV once the count rate exceeds 110 MHz. However, rapid light changes (e.g. a photo flash) can exceed this limit within the 1 ms integration window, potentially damaging the photocathode.
Starting the First Measurement
- Install the PhotonPix software (see Software Installation & Configuration)
- Connect the PhotonPix to your computer via USB
- Connect the NIM output to your time tagger (e.g. LINTag) or counting electronics
- Open the PhotonPix control software
- Ramp the MCP voltage slowly to the operating point (the software handles this automatically — the ramp takes up to 5 seconds)
- Enable the photocathode only when the optical path is prepared
In the Box
| Item | Quantity |
|---|---|
| PhotonPix detector module | 1 |
| USB cable | 1 |
| SMA cable (anode output) | 1 |
| SMA cable (NIM output) | 1 |
| Protective lens cap | 1 |
| Quick-start guide | 1 |
Hardware
Features
| Specification | Value |
|---|---|
| Detector type | MCP-PMT |
| Output 1 | Anode analog, 50 Ω SMA |
| Output 2 | NIM logical, 50 Ω SMA |
| Interface | USB |
| CFD dead time | ~1.6 ns |
| Overexposure protection | 110 MHz count-rate threshold |
| Cooling | Active (integrated) |
Mechanical Drawings
Detailed mechanical drawings are available on request from Photonscore.
Software Installation & Configuration
Installation
The PhotonPix control software is distributed as part of the Photonscore software suite. See the Download page for the latest release.
Requirements: - Windows 10/11 or Linux (Ubuntu 22.04+) - USB 2.0 or higher port
Steps:
- Download the installer from the Download page
- Run the installer and follow the on-screen instructions
- Connect the PhotonPix via USB — the driver installs automatically on Windows
- Launch LINPix Control from the start menu
Configuration
On first launch, set the following parameters in the control software:
| Parameter | Typical value | Notes |
|---|---|---|
| MCP voltage | 2200–2400 V | Ramp from 0 V; takes ~5 s |
| CFD threshold | −50 to −200 mV | Adjust to suppress dark counts |
| CFD zero-cross | −10 to −30 mV | Minimise timing jitter |
The MCP voltage must be ramped slowly. The software automatically ramps from zero to the target voltage. Do not set the voltage in large steps.
Conducting the First Measurement
Overload Protection & Shutdown
The protection circuit monitors the count rate every 1 ms. If it exceeds 110 MHz, the photocathode HV is disabled immediately. To re-enable:
- Reduce the light flux to a safe level
- Click Enable Photocathode in the control software
Standard Operation
1. Start LINPix Control
2. Set MCP voltage → click Apply → wait for ramp to finish (~5 s)
3. Set CFD threshold and zero-cross
4. Enable photocathode
5. Monitor count rate — target <10 MHz for typical single-photon experiments
6. Connect NIM output to your time-tagging electronics
7. Begin data acquisition in your measurement software
The NIM output is compatible with standard LINTag channel inputs (NIM mode).
Warnings
!!! danger "High voltage present" The PhotonPix operates at voltages up to 2400 V internally. Do not open the housing. There are no user-serviceable parts inside.
!!! warning "Temperature" Allow 10 minutes warm-up time after powering on before taking calibrated measurements. The detector temperature is actively stabilised but requires thermal equilibration.
!!! note "Export control" MCP-PMT detectors may be subject to export control regulations in your country. Please verify compliance before shipping the device internationally.