Optical Linewidth Measuring Device
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
An optical linewidth measuring device can measure linewidths of both reflective and transparent films down to 0.5 mm with an accuracy of 1 nm or better. The system is based on making a precise measurement of the differential phase. In the figure, the linearly polarized output from a He-Ne laser 1 at frequency Wo is incident on a polarizing beam-splitter 2. This beam-splitter 2 splits the beam into two orthogonally polarized beams (A) and (B) which pass via quarter-wave plates 3 and 4 to two retro- reflectors 5 and 6. Beam (B) passes through a beam stop 7 which reduces its diameter to one half its initial value. The attenuator 8 placed in beam (A) is adjusted so that after reflection from the retro-reflectors, the optical power in beam (A) and beam (B) is equal.