Laser heterodyne surface profiler

Patent · Sun Jan 01 00:00:00 EST 1984

OSTI ID:865065

Sommargren, Gary E ^[1]

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1. Livermore, CA

Method and apparatus for testing the deviation of the face of an object from a flat smooth surface using a laser beam having two plane-polarized components, one of a frequency greater than the other to produce a difference frequency with a phase to be used as a reference. The beam also is split into its two components which are directed onto spaced apart points on the face of the object. The object is rotated on an axis coincident with one component as a reference. The other component follows a circular track on the face of the object as the object is rotated. The two components are recombined after reflection to produce a difference frequency having a phase that is shifted in an amount that is proportional to the difference in path length as compared to the reference phase to produce an electrical output signal proportional to the deviation of the height of the surface along the circular track. The output signal is generated by means of a phase detector that includes a first photodetector in the path of the recombined components and a second photodetector in the path of the reference phase. The output signal is dependent on the phase difference of the two photodetector signals. A polarizer, a quarter-wave plate and a half-wave plate are in series in the path of the reference phase. Rotation of the half-wave plate can be used for phase adjustment over a full 360.degree. range for initial calibration of the apparatus.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• DOE Contract Number: W-7405-ENG-48
• Assignee: United States of America as represented by United States (Washington, DC)
• Patent Number(s): US 4456339
• OSTI ID: 865065
• Country of Publication: United States
• Language: English

Related Subjects

laser
heterodyne
surface
profiler
method
apparatus
testing
deviation
flat
smooth
beam
plane-polarized
components
frequency
produce
difference
phase
reference
split
directed
spaced
apart
rotated
axis
coincident
component
follows
circular
track
recombined
reflection
shifted
amount
proportional
path
length
compared
electrical
output
signal
height
generated
means
detector
photodetector
dependent
signals
polarizer
quarter-wave
plate
half-wave
series
rotation
adjustment
360
degree
range
initial
calibration
circular track
laser heterodyne
surface profile
phase difference
signal proportional
smooth surface
path length
laser beam
output signal
spaced apart
electrical output
difference frequency
surface profiler
detector signal
flat smooth
heterodyne surface
wave plate
plane-polarized components
/359/