Measuring the profile of a high power density beam with a small diameter can be tricky. Cameras are not very good at measuring beams with diameters of less than 50μm, and the attenuation required for the high power or energy densities can be substantial. The attenuationf can also be a source of beam distortion, which adds great uncertainty to the data. Proper attenuation of high power beams can be quite complex and generally requires multiple levels of attenuation provided by both reflective and absorptive filters. The first stages of attenuation need to be reflective attenuators, which in turn generate additional beams (reflections) that must be controlled or captured with beam dumps. It is not unusual to need four to six stages of attenuation to get a beam power to the level necessary to make camera measurements. It can be difficult to find space for this in the solar panel production modules.
In concert with several of the companies building photovoltaic manufacturing equipment, Photon has developed measurement instruments that are uniquely suited to making these measurements. The NanoScan slit-based profiler has the capability of measuring small beams directly with little or no attenuation, making it a logical choice for these types of analyses. However, some of these beams are operated as pulsed beams, which complicate the measurement somewhat. Although the NanoScan is capable of measuring pulsed beams, small diameter beams present a problem. Unless the repetition frequency of the pulses is very high, the nature of pulsed beam analysis limits the size that can accurately be measured.4 In addition, as the beam’s diameter decreases, the power or energy density increases dramatically, making damage to the profiler a possibility. By using a simple magnification system, it is possible to make direct measurements of the beams. Photon has coupled a high power 10x objective into the NanoScan Near-Field Profiler system to create an instrument specifically designed to measure the typical laser output used in the solar panel manufacturing process. Expanding the beam 10-fold reduces the power or energy density by two orders of magnitude (1/100). It also makes the measurement of pulsed beams ossible at lower repetition rates. The minimum beam diameter that can be measured with the NanoScan for a 20 kHz pulsed laser is ~90μm—well above the 30μm beam size required for this application.5 Expanding the beam to 300μm makes it easy to measure at this pulse frequency.