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**Slit
Diameter Measurement**

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
image.

To
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.

Please
refer to ISO documentation for more information.

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