THORLABS FDPS3X3, Руководство пользователя

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Chapter 3: Operation
24700-D02 Page 4
Figure 1: Photodiode Model
3.2. Frequency Response
Photoconductors must be used with a pulsed signal, to obtain AC signals. An
optical chopper, such as the Thorlabs MC2000, is recommended for use with CW
light. The detector responsivity (R
f
) when using a chopper can be calculated
using the equation below:
=
1 + 4
= !ℎ#$$%&' ()*+)&!,
= ()-$#&-) ./ 0 12
= 3)/)!/#( (%-) /%4)
3.3. Effects of Chopping Frequency
The photoconductor signal will remain constant up to the time constant response
limit. PbS and PbSe detectors have a typical 1/f noise spectrum (i.e., the noise
decreases as chopping frequency increases), which has a profound impact on the
time constant at lower frequencies.
The detector will exhibit lower responsivity at lower chopping frequencies. Frequency
response and detectivity are maximized at:
Ground
Load
Resistance
R
LOAD
Output
Signal
V
OUT
+
-
Active Area
Dark Resistance R
DARK
Bias Voltage
V
BIAS