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Optical Linewidth Measuring Device

IP.com Disclosure Number: IPCOM000062560D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Wickramasinghe, HK: AUTHOR

Abstract

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.

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Optical Linewidth Measuring Device

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. The Pockel Cell Modulator, placed between the laser and the polarizing beam-splitter can be used to control the laser polarization in such a way that only beam (A) or beam (B) exists at any given time. On reflection from the retro-reflectors and passing via the quarter-wave plates, the polarization of both beam (A) and beam (B) is rotated by 90OE, so that they propagate toward the Bragg cell 10. Part of the beam passes directly through at Wo and is incident via a beam expanding telescope 11 onto a microscope objective 12 which focuses it onto the line to be measured. The remainder of the beam is upshifted by the Bragg frequency Wb and diffracted toward the retro-reflector 13 where it is reflected back to the photodiode 14. The beam incident on the line to be measured on sample 15, is reflected t...