Semrock Master Catalog 2018

Working with Optical Density
Optical Density – or OD, as it is commonly called – is a convenient tool to describe the transmission of light through a highly
blocking optical filter (when the transmission is extremely small). OD is simply defined as the negative of the logarithm (base
10) of the transmission, where the transmission varies between 0 and 1 (OD = – log 10
(T)). Therefore, the transmission is
simply 10 raised to the power of minus the OD (T = 10 – OD ). The graph below left demonstrates the power of OD: a
variation in transmission of six orders of magnitude (1,000,000 times) is described very simply by OD values ranging between
0 and 6. The table of examples below middle, and the list of “rules” below right, provide some handy tips for quickly
converting between OD and transmission. Multiplying and dividing the transmission by two and ten is equivalent to
subtracting and adding 0.3 and 1 in OD, respectively.
Optical Density
Optical Density
6
5
4
3
2
1
0
1E-6 1E-5 1E-4 1E-3 0.01 0.1 1
Transmission (0-1)
4
Edge 5 Filters vs. Notch Filters for Raman Instrumentation
6
RazorEdge ® Filter Advantages: Edge Design
7
Notch Design
Steepest possible edge for Laser looking Line at the smallest
8
Stokes 610 615 shifts 620 625 630 635 640 645 650 655 660
Wavelength (nm)
0
0
1
1
2
2
3
3
the laser 4 wavelength (on Semrock U-grade edge filters), these filters don’t need to be angle-tuned!
4
5
5
6
Edge Design
6
7
Notch Design
Edge Design
Laser Line
7
Notch Design
shift toward 8 shorter wavelengths as the angle of incidence is increased from Laser Line 0° up to about 14°.
610 615 620 625 630 635 640 645 650 655 660
8
610 615 620 625 630 635 640 645 650 655 660
Wavelength (nm)
Wavelength (nm)
Optical Density
Transmission (%)
TECHNICAL NOTE
100
90
80
70
60
50
40
30
20
10
0
0
1
2
TECHNICAL NOTE
3
Largest blocking of the laser line for maximum
laser rejection
Edge Measured
Notch Measured
Laser Line
550 600 650 700 750 800
Wavelength (nm)
Optical Density
Optical Density
0
1
2
3
4
5
Transmission OD
1 0
0.5 0.3
0.2 0.7
0.1 1.0
0.05 1.3
0.02 1.7
0.01 2.0
0.005 2.3
0.002 2.7
0.001 3.0
6
Edge Design
7
Notch Design
Laser Line
8
610 615 620 625 630 635 640 645 650 655 660
Wavelength (nm)
Optical Density
0
1
2
3
4
5
The “1” Rule
T = 1 → OD = 0
The “x 2” Rule
T x 2 → OD – 0.3
The “÷ 2” Rule
T ÷ 2 → OD + 0.3
The “x 10” Rule
T x 10 → OD – 1
The “÷ 10” Rule
T ÷ 10 → OD + 1
StopLine ® Notch Filter Advantages:
Measure Stokes and Anti-Stokes signals simultaneously
Greater angle-tunability and bandwidth for use with variable
laser lines
The graph below left illustrates the ability of a long-wave-pass (LWP) filter to get extremely close to the laser line. The graph
in the center compares the steepness of an edge filter to that of a notch filter. A steeper edge means a narrower transition
width from the laser line to the high-transmission region of the filter. With transition widths guaranteed to be below 1% of
The graph on the right shows the relative tuning ranges that can be achieved for edge filters and notch filters. Semrock edge
filters can be tuned up to 0.3% of the laser wavelength. The filters shift toward shorter wavelengths as the angle of incidence
is increased from 0° to about 8°. Semrock notch filters can be tuned up to 1.0% of the laser wavelength. These filters also
6
Edge Design
7
Notch Design
Laser Line
8
610 615 620 625 630 635 640 645 650 655 660
Wavelength (nm)
NIR Filters Mirrors Polarizers
Edge
Filters
Dichroic
Beamsplitters
Laser-line
Filters
Laser Diode
Filters
Notch
Filters
Lamp Clean-up
Filters
0
(%)
100
90
80
70
Density
1
2
3
107
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