In its broadest sense, a beam expander is any optical system designed to increase the diameter of a laser beam. In most cases, the term is taken to mean a telescope designed to take a small-diameter collimated beam input beam and produce a larger diameter collimated output beam, thus reducing the divergence of the beam. The beam expander consists of a negative input lens and a positive objective. The expansion factor is the ratio of the focal length of the two lenses.

Wavelength Range: 532nm, 632.8nm
Recommended Beam Diameter: <0.14mm
Dimension Tolerance: ±0.2mm 
Surface Quality: 60/40 scratch and dig 
Coatings: AR-Coatings @ 532nm
Wavefront Distortion: l/2 (p-p, over clear aperture, @ 632.8 nm)