[OPTICAL REVIEW Vol. 4, No. 2 (1997) 288-292]
Small Deformation Measurements of Diffuse Objects: Phase Stepping by Frequency Drift of a He-Ne Laser*
Tina L. HELG,1 Tom H. BARNES1 and Tim G. HASKELL2
1Physics Department, University of Auckland, Private Bag 92019, Auckland New Zealand, 2New Zealand Institute for Industrial Research, Private Box 31-310, Lower Hutt, New Zealand
(Received October 3, 1996; Accepted December 6, 1996)
We describe a simple phase-stepping speckle interferometer with large path difference, in which phase modulation is achieved by thermal frequency drift of the He-Ne light source. This system is easy to set up, requires no specialised components, is immune from the effects of piezo actuator hysteresis, and is capable of producing phase maps in which the noise is less than 1/20λ.
Key words : interferometry, phase stepping, deformation measurement
*Presented at 1996 International Workshop on Interferometory (IWI '96), August 27-29, Wako, Saitama, Japan.