The high-speed hybrid photodetector (HS-HPD) is the optimum photodetector for photoluminescence lifetime measurements.
It achieves this by uniting the benefits of a photomultiplier tube, such as wide spectral coverage and a wavelength-independent temporal response, and the advantages of a solid-state avalanche photodiode, such as high quantum efficiency and no afterpulsing.
The HS-HPD is the detector of choice for fluorescence lifetime imaging (FLIM) on the RMS1000 Confocal Microscope and short-lifetime measurements on the FLS1000 Photoluminescence Spectrometer.
Figure 1. Operating Principle of the HS-HPD. The first stage operates like a photomultiplier tube where photons are converted to photoelectrons by the photocathode and the photoelectrons are accelerated by a voltage difference. In the second stage, the photoelectrons strike the avalanche diode where they are multiplied in a two-step gain process to create the electrical pulse for photon counting. Image Credit: Edinburgh Instruments
Picosecond Lifetime Measurements
The HS-HPD is the ideal detector for examining fast photoluminescence lifetimes that can resolve lifetimes down to 5 ps when combined with a suitable laser source. The fluorescence decay of 4-DASPI was measured in water and ethanol to exhibit the ability of the HS‑HPD, as shown in Figure 2.
Lifetimes of 11 ps in water and 57 ps in ethanol were obtained utilizing a reconvolution fitting with the Edinburgh Instruments FAST advanced lifetime analysis software’s instrument response function (IRF).
Figure 2. Fluorescence decay of 4-DASPI in ethanol (A) and water (B) was measured using the FLS1000 with the HS‑HPD‑870 detector and a femtosecond laser with a pulse width of 150 fs. Image Credit: Edinburgh Instruments
HS-HPD Specifications
The HS-HPD detector is offered in a variety of models that are optimized for different applications. The standard model, the HS-HPD-870, has the fastest temporal response (shown by the lowest TTS in Table 1) and the broadest wavelength coverage, making it the best option for most applications.
The HS‑HPD‑860 and the HS‑HPD‑-910 have the highest QE in the NIR and are recommended for measurement of weak emission in the NIR, while the HS-HPD-670 has the highest QE in the UV-Blue region.
The HS-HPD-760 has the highest QE in the visible region and is recommended for high throughput applications, e.g. FLIM.
Figure 3. Quantum efficiency curves the HS-HPD models. Image Credit: Edinburgh Instruments
Table 1. Specifications of the HS-HPD models. Source: Edinburgh Instruments
HS-HPD versus MCP-PMT
For short-lifetime TCSPC measurements, the historical detector of choice is the microchannel plate PMT (MCP-PMT).
When assessed with a femtosecond laser, the HS‑HPD (FWHM = 28 ps) has a marginally narrower IRF than the MCP-PMT (FWHM = 33 ps), as shown in Figure 4a, and both detectors can theoretically resolve lifetimes down to 5 ps.
The HS-HPD has a cleaner IRF than the MCP-PMT (see Figure 4b). The MCP‑PMT IRF contains a pronounced afterpulse (circled in red) that can cause it to become challenging to reconvolution fit short lifetimes. Meanwhile, the afterpulse is insignificant in the HS-HPD.
A more robust detector, the HS‑HPD can be exposed to >1×107 photons/s, whereas the MCP-PMT is relatively fragile, with a maximum exposure rate of 1×105 photon/s.
These advantages have resulted in the HS-HPD being the detector of choice for short fluorescence lifetime measurements on the RMS1000 and FLS1000.
Figure 4. Comparison of the IRF of the HS-HPD-870 and MCP-PMT. (a) IRF measured with a femtosecond laser (150 fs) and shown on a linear y-scale. (b) IRF measured with an EPL-375 (70 ps) and shown on a logarithmic y‑scale. The afterpulse of the MCP is circled in red. Image Credit: Edinburgh Instruments
Conclusion
The HS-HPD is the ideal detector for short-lifetime measurements on the RMS1000 Confocal Microscope and FLS1000 Photoluminescence Spectrometer due to its negligible afterpulse and narrow IRF.
The HS-HPD is available in various models with different response times and wavelength coverage to suit different applications.
This information has been sourced, reviewed and adapted from materials provided by Edinburgh Instruments.
For more information on this source, please visit Edinburgh Instruments.