YAG Focal Spot Analyzer0 pages

3.2.2.1 YAG Focal Spot Analyzer
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Image focal spots down to 25µm in size
For laser powers up to 400W (additional external ND filters required)
Measure how focal distance shifts with power
Can measure systems with focal length as short as 50mm
Modular design allows flexibility in use
C-mount, compact laser beam sampler/attenuator for camera based laser beam profiling systems
High damage threshold optics for measuring energetic sources
Produces undistorted sample of laser under test
Adjustable attenuation maximizes system dynamic range
Up to 1 x 10-10 attenuation available (without external filters)
Measure the focal spot of a relatively high power laser, in particular a YAG laser. The average power can be from <1 to 400 Watts and the
focal spot can be as small as 25µm. The FSA can also be used to measure how the focal spot shifts with power.
The lasers focal length from the lens to the focal spot is usually on the order of 70 to 120mm. The YAG FSA assembly adds a negative lens
to the LBS-300 beam splitter assembly to increase the focal path and at the same time enlarge the image. Several focal length lenses are
available to accommodate different host system focal paths. The FSA includes; user selectable negative lens, 2 beam splitters, a removable
beam block on the 2nd splitter, and user selectable attenuation filters prior to the beam entering the camera. An excel spreadsheet is
downloadable from our website that calculates which lenses are available to use for your application, how far to mount the FSA from your
focusing lens in order to see the focal spot and what the magnification of the image will be.
3.2.2.1 Beam Profile
Operation:
The FSA is mounted to the camera as shown. Then the assembly is placed below the final focusing lens of the laser at the recommended
distance. The focal spot is found by moving the assembly closer and farther from the beam until the smallest spot size is seen. The exact
magnification factor (usually 2-3 times) is calculated by moving the stage holding the FSA assembly a given lateral distance and seeing
how far the centroid of the focal spot moves in the beam profiling software. This scaling factor is then entered into the software. In order
to find focal spot shift with laser power, simply find focal spot at one power, change the power and measure how far the stage has to be
moved up or down to get to the smallest beam size again.
Incoming Beam
Camera
Negative lens
LBS-300
2nd Output
Beam; built-in
beam block
Focal Spot Assembly Looking
from camera mounting position
1st Output Beam; either to power
meter or to Beam Dump
User selectable ND filters
for attenuating input to the
camera
Focal Spot Assembly showing
various beam paths
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01.01.2012
For latest updates please visit our website: www.ophiropt.com/photonics