Table of Contents
Advertisement
2-6
SE955 Integration Guide
Collection Clear Aperture
As shown in
Figure
2-4, the collection clear aperture is the area on the exit window which intersects the collection beam envelope.
In both cases, ensure that the paths are free of obstructions. Also incorporate a minimum of a 0.020" to 0.040" spacing between the
clear apertures and the window borders.
Exit Window Materials
Many window materials that look perfectly clear to the eye can contain stresses and distortions which affect the laser beam and
reduce scan engine performance. For this reason, only optical glass or cell cast plastics are recommended. Following are descriptions
of three popular exit window materials:
• Poly-methyl Methacrylic (PMMA)
Allyl Diglycol Carbonate
•
• Chemically tempered float glass.
Cell Cast Acrylic (ASTM: PMMA)
Cell Cast Acrylic, or Poly-methyl Methacrylic is fabricated by casting acrylic between two precision sheets of glass. This material has
very good optical quality, but is relatively soft and susceptible to attack by chemicals, mechanical stress and UV light. It is strongly
recommended to have acrylic hard-coated with Polysiloxane to provide abrasion resistance and protection from environmental
factors. Acrylic can be laser-cut into odd shapes and ultrasonically welded.
Cell Cast ADC, Allyl Diglycol Carbonate (ASTM: ADC)
Also known as CR-39™, ADC, a thermal setting plastic widely used for plastic eyeglasses, has excellent chemical and environmental
resistance. It also has an inherently moderate surface hardness and therefore does not require hard-coating. This material cannot be
ultrasonically welded.
Chemically Tempered Float Glass
Glass is a hard material which provides excellent scratch and abrasion resistance. However, unannealed glass is brittle. Increased
flexibility strength with minimal optical distortion requires chemical tempering. Glass cannot be ultrasonically welded and is difficult
to cut into odd shapes.
Figure 2-4. Entrance Beam Envelope
(ADC)
Advertisement
Table of Contents
