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115
))
sin(
1
)
5
sin(
5
1
)
3
sin(
3
1
)
(sin(
2
)
(
t
n
t
t
t
E
t
f
Where the n
th
harmonic is a sine wave:
)
sin(
2
)
(
t
n
n
E
t
f
Therefore, the valid value of the n
th
harmonic is :
n
E
R
2
We can verify that whether the measured result is close to the theoretical result. In this example, the peak-peak
value E is 160mV, and the calculated value of first harmonic is:
mV
mV
R
025
.
72
1
160
2
The calculated value of third harmonic is :
mV
mV
R
008
.
24
3
160
2
The calculated value of fifth harmonic is :
mV
mV
R
410
.
14
5
160
2
Compare the measured result with theoretical result according the above method.
7.3 Optical Spectral Measurements
This example will show how to measure a spectral diagram of any light source. You need an optical chopper (such
as SIGNAL RECOVERY MODEL 197 Light Chopper), a grating monochromator (such as WDG15-Z) and its
control system, a photoelectric detector (such as the S286 series photodiode of Japan Hamamatsu Company), a data
collection platform (such as NI cDAQ-9172) and a PC. You should control the monochromator to sweep
automatically in the spectral measurement range. Then measure the photo current by the SE1022D. The steps are as
follows:
1. Disconnect all cables from the lock-in. Connect the power source and then turn on the power switch. The system
is in default.
2. Set the corresponding parameters of SE1022D.
