The Slit Diameter (Slit_D) is defined as the distance between the two slit positions having a certain amount of the beam peak energy.
Normally the reference value is agreed to be 86.5% of the peak energy of the laser beam.
One can define both Horizontal and vertical slit diameter in a following manner:
#1 Consider 1 pixel wide slit that is scanning across the image from left to right.
#2 If we calculate the peak energy through that slit at each position, then after full scan we can get Maximum energy (peak energy).
#3 Now we repeat the same scan until we reach 13.5% energy of the peak. The position found we mark as Point_1.
#4 Making scan from the right side to left of the image we can similarly find Point_2 at 13.5% peak energy.
The Slit Diameter
can be defined as the difference between Point_1 and Point_2.
Slit_D = P2 - P1
The profile in
the drawing below represents the energy contained in each pixel column of the
determine the Vertical Slit diameter, perform the same process with a slit that
scans from the top of the image to the bottom.
Knife Edge Width Measurement
The Knife Edge
Widths are widths in Horizontal (X) and vertical ( Y) axes. Using ISO
standard we can define these as follows:
#1 We calculate
total power of the beam.
#2 We start summing power in vertical laser profiles from left to right direction. When the sum reaches 16% of the total energy, we mark corresponding position Point_1.
#3 We start summing power in vertical laser profiles from right to left direction. When the sum reaches 16% of the total energy, we mark corresponding position Point_2.
#4 By ISO definition, the Knife Edge Widths are defines as:
K = 2 * (P2 - P1)
The profile in
the drawing below shows the energy contained in each pixel column of the image.
Vertical Knife width is we can determine in a similar manner summing horizontal profiles power.
refer to ISO documentation for more information.
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