Will the TECHSPEC Monolithic Reflective Beam Expanders (Mark I) work in reverse (to reduce the size of a beam)?

Fundamentally, these laser beam expanders can work in reverse. However, the specified wavefront values are not guaranteed for reverse operation, and care should be taken to ensure that the input beam diameter is no greater than the specified maximum exit aperture. Also, note that divergence will increase proportionally with the laser beam expander’s magnification.