As part of its portfolio, Lambert Instruments designs and manufactures ICCD cameras based on modulated image intensifiers for frequency domain imaging techniques such as FLIM. Standard products such as the new TRiCAM M ICCD camera, the TRiCATT M modulated intensifier attachment, and the LIFA system are all based on a proximity-focused modulated Gen II or Gen III image intensifier.

Figure 1. Schematic representation of a proximity-focused image intensifier, showing its photocathode, micro-channel plate and anode, fiber-optically coupled to a sensor.

Figure 1. Schematic representation of a proximity-focused image intensifier, showing its photocathode, micro-channel plate and anode, fiber-optically coupled to a sensor.

Figure 2. Modulated detector gain (green), pulsed excitation (blue) and fluorescence emission (red) in a homodyne FLIM system. The phase and duty cycle of the detector gain is controllable.

Figure 2. Modulated detector gain (green), pulsed excitation (blue) and fluorescence emission (red) in a homodyne FLIM system. The phase and duty cycle of the detector gain is controllable.

The modulated sensitivity of an image intensifier is produced by high-frequency switching of its photocathode voltage. In this modulation mode the temporal and also the spatial characteristics of the image intensifier are different from the nominal characteristics under continuous operation.

The following table lists the nominal characteristics for the Gen II and Gen III intensifiers provided.

 

Gen II S20 & S25

Gen III GaAs

Gen III GaAsP

Spatial resolution
Photocathode QE at 550 nm

28 lp/mm
14%

17 lp/mm
28%

7 lp/mm
48%

The increased sensitivity of the Gen III image intensifier results in a better lifetime accuracy, although the amount further depends on the model and the modulated light source used. For a LIFA Gen III GaAs compared to a LIFA Gen II S25 at 550nm, both using the same Multi-LED light source, the increased sensitivity results in an increased lifetime accuracy of 40% at the same acquisition speed and fluorescence intensity.

For phosphorescence lifetime imaging with the TRiCAM GM and the LIFA-P the image intensifier is operated at lower frequencies spatial resolution is higher, reaching values in excess of 35 lp/mm for a Gen III GaAs image intensifier.

Please note that the characteristics of an image intensifier are unique and are known to vary between units.

Figure 3. Image intensifier spectral response.

Figure 3. Image intensifier spectral response.