Evaluating a Multimodal Beam: A Brief Tutorial Highlighting the Use of BeamGage® PRO Partitioning

Author: 
Mark Szorik, Sr. Sales Territory Manager, Ophir Products

Lasers have been around for over 65 years. Since they were first conceived, many different industries and institutions have actively and routinely pursued ways of embedding these unique devices into various processes, systems, and end use applications. One of the greatest strengths that lasers have over standard processing tools and other light sources is their capability to accomplish exotic tasks that are beyond those of tradition tools.

Initially, lasers were somewhat simple devices that generated just a fundamental Gaussian mode – TEM00 or a close derivation of this. Shortly thereafter, researchers began devising ways of generating and using more complex higher-order multimode formats, such as a TEM03 or TEM33. Some current examples are: telecommunications, analytical instrumentation (LIBS), medicine (endoscopic treatment, drug therapy and activation), multi-source welding, laser scanning, facial recognition, printing, and many more.

Evaluating a Multimodal Beam
Figure 1. Example of a Gaussian TEM00 Beam.

Evaluating a Multimodal Beam
Figure 2. Example of higher order Multimode Intensity Profiles. (Source: RP Photonics Encyclopedia)

Process and quality control drives the majority of today’s industries and as a result this has created a demand for effective and efficient tools which will help them to see, measure, and define various aspects of research and industrial processes.

All laser operators and end users clearly understand the importance of fine tuning the outputs of their lasers in order to understand and optimize the end result within their process. They also understand that because lasers are very dynamic and in a constant state of flux, variations in modal distribution can and do occur. Everything from process inputs to environmental conditions tend to impact modal distributions. As a result, we are often asked the following question:

“What type of tool does Ophir have that will allow me to collect real time qualitative and/or quantitative data about our beam or light source regardless of modal structure – i.e., single or multimode?”

In order to address this, Ophir-Spiricon developed a suite of camera-based profiling systems. These systems are relatively easy to use and allow the end user to evaluate the behavior of their source or target sample in real time – modal distribution, irradiance, power and energy density, etc. Each profiling system is comprised of a camera and software package (varies depending on which camera system is chosen).

Partitioning
This overview will focus specifically on a function within Ophir’s BeamGage® software, the primary engine that drives the laser beam profiling system.* There are two levels of BeamGage software available: Standard and Professional. Three distinct features differentiate BeamGage PRO from BeamGage Standard:

  • Partitioning
  • Custom Calculations
  • Automation Interface

In order to fully analyze a multimode source, we suggest the use of the partitioning feature contained within BeamGage PRO. This provides the necessary functionality allowing the user to isolate and fully evaluate various user defined regions of interest (ROI) for any modal array or chosen target source. Partitions essentially subdivide the camera image into separate regions, called partitions, and compute separate beam results for each partition.

When using partitioning, the results of independent partitions can be compared one to another; results are displayed either in the results window or delta centroid table. The results window can only display the computational results for one partition at a time, regardless of how many partitions have been established.

Common applications pertaining to partitioning include comparing the alignment of multiple beam spots or sample cells to either a fixed set of spatial coordinates and/or to each other. This is accomplished by using the Delta Centroid and Delta Peak tables. The following is an example of a multimodal beam that was generated using the BeamMaker® function, found in all levels of BeamGage software, and the partition feature.

Evaluating a Multimodal Beam
Figure 3. Example of the use of partitioning function of BeamGage PRO™ (simulated beam).

Evaluating a Multimodal Beam
Figure 4. Detailed view of 1D and 2D with ROI Partitions (BeamMaker generated beam).

Partition data can be customized and viewed within the Results Window, as shown below.

Evaluating a Multimodal Beam
Figure 5. Example of the Results Window.

Some end users also find it helpful to evaluate peak or centroid data for when comparing different regions of interest. Six variations are possible and can be displayed based on the user’s preference – see Delta Centroid Table below.

Six possible variations can be computed and displayed based on the user’s preference:

  1. Straight line centroid to centroid delta values
  2. X axial direction centroid to centroid delta values
  3. Y axial direction centroid to centroid delta values
  4. Straight line peak to peak delta values
  5. X axial direction peak to peak delta values
  6. Y axial direction peak to peak delta values

 

Evaluating a Multimodal Beam
Figure 6. Example of a Delta Centroid Table.

The example below is of an actual multi-array welled structure which is illuminated by a single source. Note that the cells are not equally or uniformly illuminated. This is where the partitioning function within BeamGage can provide valuable qualitative information in order to evaluate the exact difference between individual wells or regions of interest (ROI). This type of information can be valuable in “fine tuning,” or root causing, the specific differences between each well.

Evaluating a Multimodal Beam
Figure 7. Multi-cell cavity imaged with SP928 profiling system with & without partitioning.

The are many more creative ways of using the partitioning feature and numerous other features not discussed in the body of this review. Download the current version of BeamGage PRO directly from the Ophir web site. Try the BeamMaker application and experience, first hand, the capabilities of this feature.

If you are currently have a camera profiling system using a software license for BeamGage Standard, you can upgrade to BeamGage PRO for a nominal fee. All software and manuals located our web site are always free of charge.

If you would like a more immersive user experience using your in house laser or light source, please contact your regional Ophir sales represenative and we will schedule a visit or demo.

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