Most of them are manufactured from UV-grade fused silica.  They can be manufactured in a variety of focal length options. There are two main configurations used, the fly’s eye condenser and the square lens.  Both of them are often used in pairs. 

• Fly’s Eye Condenser Arrays: A fly’s eye condenser array is formed of dual-surface cylindrical micro lenses mounted in a close-packed configuration, and are used for flat-top and line generation. They are ideal for situations in which one must work with a short working distance and also a large illuminated field.
• Square Microlens Arrays: They have a high ratio of active refracting area to total continuous area of the microlens array.  This tight packing is known as a high fill factor and means zero-order hot spots in the illuminated field are eliminated.  They are often used to homogenize and shape beams and can produce a square flat-top or spot pattern.