In industrial processes, laser pulses are traditionally triggered temporally. However, time domain spacing produces inherent laser processing challenges when motion systems depart from continuous velocity operation. Process parameters such as energy density and power density vary wildly when pulses bunch together during slowdowns, which is unacceptable in many sensitive material processing applications (Figure 1).
Figure 1. Traditional temporal laser pulsing (shown at left) causes laser emission to bunch as beam steering elements depart from continuous velocity operation, such as during sharp features. Spatial laser pulsing through the PSO feature maintains pulse spacing regardless of velocity as laser emission is directly tied to distance traveled instead of elapsed time.
Aerotech’s Position Synchronized Output (PSO) feature alleviates many of these problems by enabling the user to control laser pulses in the spatial domain. Maintaining consistent pulse spacing, regardless of velocity, provides constant energy density delivery over the path. Additionally, the A3200 controller allows for the scaling of power output from the laser as a function of velocity and position to correct for repetition rate modulation and known optical distortions. Pairing these features with PSO gives the user explicit control over not only the energy density via pulse spacing, but also the power density via power scheduling. These features combined allow for the most explicit process control available for laser micromachining applications.
Figure 2. Example of PSO laser output when used in conjunction with a polygon scanner. Windowing is used to gate the laser while it traverses the polygon’s edges.
The PSO hardware is capable of triggering firing events at 10 MHz, and allows for the programming of nearly unlimited user-defined windows for real-time gating of laser emission output as a function of position (Figure 2). The PSO feature also includes user-created spacing arrays to produce laser pulses at varied positions throughout travel, allowing for the creation of any spatial pulse pattern desired. An added advantage to triggering based on feedback is that dynamic tracking errors do not affect pulse placement. Finally, an added value of the PSO feature is that it works based off of combined laser spot motion when used in conjunction with a multi-axis system. This means that laser output will be triggered as a function of vector distance traveled between up to three coordinated axes.
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