KEYWORDS: Solar cells, Semiconductor lasers, Silicon, Laser applications, Thin films, Semiconducting wafers, Manufacturing, Crystals, Thin film solar cells, Solar energy
For semiconductor manufacturing, a mature industry, a number of laser techniques are employed in production. Diodepumped
solid-state (DPSS) lasers are used in applications that cannot be performed by mechanical, chemical, or other
laser fabrication methods as well as where they add value through increased throughput and/or improved process quality.
Applications such as edge isolation, wafer scribing/dicing, via formation, laser doping and annealing for Semicon are
being applied to crystalline silicon PV manufacture as well as research and development for the next generation of high
efficiency cells. Similarly, selective material removal for exposing underlying layers without thermal damage is vital in
the production of thin film PV panels. In this paper, some of the most important applications of lasers along with
experimental results will be reviewed to illustrate how laser methods can have a significant impact on the development
and productivity of the photovoltaic industry.
The distinction between exposure time and sample rate is often the first point raised in any discussion of high speed imaging. Many high speed events require exposure times considerably shorter than those that can be achieved solely by the sample rate of the camera, where exposure time equals 1/sample rate. Gating, a method of achieving short exposure times in digital cameras, is often difficult to achieve for exposure time requirements shorter than 100 microseconds. This paper discusses the advantages and limitations of using the short duration light pulse of a near infrared laser with high speed digital imaging systems. By closely matching the output wavelength of the pulsed laser to the peak near infrared response of current sensors, high speed image capture can be accomplished at very low (visible) light levels of illumination. By virtue of the short duration light pulse, adjustable to as short as two microseconds, image capture of very high speed events can be achieved at relatively low sample rates of less than 100 pictures per second, without image blur. For our initial investigations, we chose a ballistic subject. The results of early experimentation revealed the limitations of applying traditional ballistic imaging methods when using a pulsed infrared lightsource with a digital imaging system. These early disappointing results clarified the need to further identify the unique system characteristics of the digital imager and pulsed infrared combination. It was also necessary to investigate how the infrared reflectance and transmittance of common materials affects the imaging process. This experimental work yielded a surprising, successful methodology which will prove useful in imaging ballistic and weapons tests, as well as forensics, flow visualizations, spray pattern analyses, and nocturnal animal behavioral studies.
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