YAG Focal Spot Analyzer

  • 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 10-10attenuation available (without external filters)

Setup Program for YAG FSA and Beam Cube

Ordering Info
Download Data Sheet.
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.
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.
Focal Spot Assembly Looking from camera mounting position
Focal Spot Assembly showing various beam paths
Examples of Usage
65µm diameter focal spot Focal spot shape changing with laser power level
Model YAG Focal Spot Analyzer
Wavelength 1064nm
Wedge Material BK7
Wedge Coating AR ≤1%
Clear aperture 17.5mm
Wedge ND value, each ND ≥2
ND Filters Bulk ND
ND Values, nominal 0.3, .7, 1.0, 2.0, 3.0, 4.0 (Red holders)
Filter Slides 3
Filter Damage (1) 50 W/cm²
1J/cm², 10ns pulse
Negative Lens FSA-50Y
To add FSA capability -50mm YAG
  -100mm YAG
  -125mm YAG
  -150mm YAG
  -200mm YAG
Variable Wedge ND Filter kit WVF-300
Beam Dumps BD-040-A,    40 Watts Max Power, Air Cooled
  BD-500-W,    500 Watts Max Power, Water Cooled
Note: (1) ND bulk absorbing filters damage threshold is 50W/cm² but should be used at <5W/cm² to avoid thermal lensing effects.

YAG Focal Spot Analyzer assembly requires 1 each LBS-300-NIR and 1 each Negative Lens
      Item Description P/N  
  YAG Focal Spot Analyzer  
  LBS-300-NIR Beam splitter and attenuators; beam split 2 times SP90185  
  FSA-50Y Negative lens; -50 mm YAG SP90187  
  FSA-100Y Negative lens; -100 mm YAG SP90188  
  FSA-125Y Negative lens; -125 mm YAG SP90189  
  FSA-150Y Negative lens; -150 mm YAG SP90190  
  FSA-200Y Negative lens; -200 mm YAG SP90191  
  WVF-300 ND filters; variable wedge. Replaces fixed value filter slides SP90195  
  BD-040-A Beam Dump; 40 Watts max. power, air cooled SP90192
  BD-500-W Beam Dump; 500 Watts max. power, water cooled SP90193  
  Beam Profilers Beam Profilers Catalog
129 pages (6.46 MB )
  Beam Profilers YAG Focal Spot Analysis Adapter
7 pages (245 KB )