TECHSPEC® Unmounted Hollow Roof Retroreflectors are constructed by cementing two coated prisms together to form a hollow roof. The hollow design enables these retroreflectors to be used over wide spectral ranges without loss due to dispersion or absorption. Incident light is reflected 180° back towards the source with great accuracy due to the 90° ± 10 arcsec roof tolerance. TECHSPEC Unmounted Hollow Roof Retroreflectors feature a 17.7 x 17.7mm footprint and can be mounted with #17-242 and #18-537. These retroreflectors are ideal for applications such as interferometry and optical delay lines.