Appendix A: Calibration
64
PEM 100 User Manual
Calibration Theory
The optical setup for most calibration procedures is shown in figure A.1.
Figure A.1 Typical Optical Setup
The modulator is placed between crossed polarizers, each of which is oriented with
its passing axis at 45 degrees with respect to the modulator axis. For some
calibration procedures, a retarder is required. If so, it should be placed between one
polarizer and the modulator, with the fast axis parallel or perpendicular to the
modulator axis.
The space between the two polarizers should contain nothing but the modulator and
the waveplate (if needed). Mirror, prisms, filters, windows, lenses, monochromators
or other wavelength selecting devices should be located outside the polarizers, if
possible.
Kemp
1
has derived the equations for the intensity of the light reaching the detector,
as a function of time.
0
A
is the amplitude of the sinusoidal retardation function; B is
the retardation magnitude of the waveplate; and
Ω
is the angular frequency of the
modulator. The general expression for the intensity function is:
(
)
(
)
{
}
t
A
B
t
A
B
Ω
+
Ω
−
=
Ι
cos
sin
sin
cos
cos
cos
1
2
1
0
=
{
( )
(
) }
t
A
B
Ω
+
−
cos
cos
1
2
1
0
(1)
For the majority of applications, expansion of this expression using a Fourier Series
is very useful;
( ) ( )
{
}
0
0
cos
1
2
1
A
J
B
−
=
Ι
DC
(2)
( ) ( ) ( )
t
A
J
B
Ω
+
cos
sin
2
0
1
1f
( ) ( ) (
)
t
A
J
B
Ω
+
2
cos
cos
2
0
2
2f
higher
...
+
}
terms
Monochromatic
Light Source
+45°
Polarizer
Modulator
0°
Polarizer
W
aveplate 0°
(Some experiments)
Detector
-45°
Summary of Contents for PEM-100
Page 1: ...PEM 100 PHOTOELASTIC MODULATOR USER MANUAL Hinds Instruments Inc P N 010 0000 021 UM Rev H ...
Page 4: ......
Page 8: ...Table Of Contents viii PEM 100 User Manual ...
Page 12: ...Table of Tables xii PEM 100 User Manual ...
Page 22: ...Unpacking the PEM 100 10 PEM 100 User Manual ...
Page 46: ...Chapter 5 PEM 100 Controller Display 34 PEM 100 User Manual ...
Page 52: ...Chapter 6 Operating the PEM 100 Controller 40 PEM 100 User Manual ...
Page 68: ...Chapter 9 Troubleshooting 56 PEM 100 User Manual ...
Page 74: ...Chapter 10 Maintenance 62 PEM 100 User Manual ...
Page 88: ...Appendix A Calibration 76 PEM 100 User Manual ...
Page 92: ...Appendix C Optical HeadSpecifications 80 PEM 100 User Manual ...
Page 100: ......