Photodiode, photodiode or photomultiplier?
Photodiode, photodiode or photomultiplier?
(OP)
I know one could write a thesis on this topic all the time....but quick answers would really help before I delve into the elaborate books like Building Electro-Optic Systems (which I'm reading slowly...)
Silicone photodiodes are easier to use and I have had very good experience with Hamamatsu silicone S8745 which gives 0.3V/nW for the wavelength I am concerned with: 633 nm (He-Ne). However, this was when my signal was around 1 nW when hitting the diode window. And I was using a SRS chopper + lock-in amplifier to enhance the SNR (which I will continue to use).
Now I will detect some weaker signals perhaps on the order of 0.1 nW (10^-10 W) or less, so I will definitely need a more sensitive detector. I get quite lost looking at Hamamatsu TE-cooled photodiode S2592 (0.3A/W@630 nm) and photomultiplier R9647 (3mA/W @630nm); how to compare their sensitivities with the previous S8745?
Thanks!
Silicone photodiodes are easier to use and I have had very good experience with Hamamatsu silicone S8745 which gives 0.3V/nW for the wavelength I am concerned with: 633 nm (He-Ne). However, this was when my signal was around 1 nW when hitting the diode window. And I was using a SRS chopper + lock-in amplifier to enhance the SNR (which I will continue to use).
Now I will detect some weaker signals perhaps on the order of 0.1 nW (10^-10 W) or less, so I will definitely need a more sensitive detector. I get quite lost looking at Hamamatsu TE-cooled photodiode S2592 (0.3A/W@630 nm) and photomultiplier R9647 (3mA/W @630nm); how to compare their sensitivities with the previous S8745?
Thanks!





RE: Photodiode, photodiode or photomultiplier?
A more useful quantity to look at is the noise equivalent power (NEP), which tells you what external illumination power is the same amplitude as the rms noise of the detector. Once you have this, you know that an input signal about 6.3 times the NEP will get you about 99% probability of detection.
TTFN
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RE: Photodiode, photodiode or photomultiplier?
Since you need about 6 times that to get reliable detection, you need to figure out how to get more signal, or spend more time detecting.
TTFN
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RE: Photodiode, photodiode or photomultiplier?
Is the noise equivalent power the power that matches the rms noise of a single pixel or on the entire chip? Or is it the power/pixel?
The reason that I am asking is that on some cameras there is a Noise Equivalent Irradiance specification instead.
RE: Photodiode, photodiode or photomultiplier?
TTFN
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RE: Photodiode, photodiode or photomultiplier?
Harold
SW2010 SP1.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600
www.lumenflow.com
RE: Photodiode, photodiode or photomultiplier?
If you do not otherwise have volume constraints, some of Hamamatsu's other detectors might have substantially higher performance, i.e., their photomultipliers and intensifiers.
TTFN
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RE: Photodiode, photodiode or photomultiplier?
Let me first improve my design by increasing the laser power and the detector aperture trying to bring up the signal level...then I'll bug the forum again :)
RE: Photodiode, photodiode or photomultiplier?
Harold
SW2010 SP1.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600
www.lumenflow.com
RE: Photodiode, photodiode or photomultiplier?
So the NEP listed in spec sheets is on a pixel basis then right?
RE: Photodiode, photodiode or photomultiplier?
It SHOULD be, but obviously, I can't speak for every datasheet writer.
As mentioned earlier, sometimes neither NEP nor NEI is directly specified, and you have to infer it from other parameters.
Next time, please start a separate thread for your questions; it makes it very difficult to follow a thread when there are multiple discussions going on.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Photodiode, photodiode or photomultiplier?