Browse Prior Art Database

Electro-Optical Line Measurement

IP.com Disclosure Number: IPCOM000101089D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

Kallmeyer, M: AUTHOR [+2]

Abstract

An opto-electronic arrangement for detecting the center of lines, which are smaller than the resolution limit of the optical system, and for measuring the width of broad lines with high accuracy comprises a digital signal processing section to avoid the inaccuracies of conventional analog signal evaluation methods.

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Electro-Optical Line Measurement

       An opto-electronic arrangement for detecting the center
of lines, which are smaller than the resolution limit of the optical
system, and for measuring the width of broad lines with high accuracy
comprises a digital signal processing section to avoid the
inaccuracies of conventional analog signal evaluation methods.

      In Fig. 1, a laser beam 3 is focussed on sample 13 which is
scanned by x-y stage 12 with an associated interferometric position
control 11.  Light reflected from sample 13 is directed by
semitransparent mirror 9 to photodetector 10.  A fast switching
amplifier 7 activates electro-optical modulator EOM 8 such that the
laser focus oscillates rapidly between two adjacent positions (some
micrometers) on sample 13.

      The switching frequency (of the order of MHz) may be derived
from the clock frequency of position control 6. Selective
photodetector 10 is tuned to this switching frequency; the output of
selective photodetector 10 is sent via line 10a to sample-and-hold
circuit 2 which is activated by the switching frequency through delay
gate 5 such that the peak value of each output pulse from detector 10
is sampled.  This peak value is then digitized by analog/digital
transducer 1 after a further delay (in delay gate 4 to account for
the setting time of sample-and- hold circuit 2).  A fast digital
processor 6 receives both the digitized peak values and the position
signals from x-y table 12 during the...