Patent ID: 7639348
Filing Date: 2009-12-29
Classification: G01L

Abstract:
1. A method of measuring stress using laser photoelasticity, wherein an infrared laser beam from a laser source is impinged upon a polarizer in which the laser beam is converted into a linear polarized light wave that oscillates in a fixed direction on a plane perpendicular to the light path axis; the linear polarized light wave is impinged upon a photoelastic modulator, such that the optical axis matches the light path axis, in which a linear polarized light wave is converted into a modulation polarized wave that changes continuously from linearly polarized light to circularly polarized light with a predetermined frequency; the modulation polarized wave is passed through a first quarter-wave plate and a second quarter-wave plate in this order and impinged upon an analyzer in which the modulation polarized wave is converted into a linear modulation polarized wave that oscillates in another direction; the linear modulation polarized wave is impinged upon a photodetector in which an electric signal corresponding to the physical property of the linear modulation polarized wave is generated; then, a test sample is disposed between the first quarter-wave plate and the second quarter-wave plate; the modulation polarized wave is passed there through; and the electric signal generated at the photodetector when the test sample is not disposed between the first quarter-wave plate and the second quarter-wave plate is compared with the transmission electric signal when the test sample is disposed between the first quarter-wave plate and the second quarter-wave plate and the stress of the test sample is determined, wherein the method comprising: input of the electric signal in a DC-voltage indicator to cause the indicator to indicate the detected value; rotating the polarizer about the light path axis such that the transmission principal axis S perpendicular to the light path is positioned orthogonally to the oscillation direction F of the linear modulation polarized wave and the minimum value that the DC-voltage indicator indicates becomes M; then, rotating the polarizer +45 degrees such that the DC-voltage indicator indicates a predetermined increased value M rotating the analyzer such that the principal axis S then, rotating the polarizer such that the principal axis S thereof is positioned orthogonally to the principal axis S repeating these operations such that the value that the DC-voltage indicator indicates gradually decreases to Mmn (Mm rotating the photoelastic modulator such that the principal axis W thereof matches the principal axis S of the polarizer whereby the minimum value that the DC-voltage indicator indicates becomes Mx; rotating the first quarter-wave plate such that the principal axis H thereof matches the principal axis S of the polarizer whereby the minimum value that the DC-voltage indicator indicates decreases to Mxm; then, rotating the first quarter-wave plate +45 degrees such that the value that the DC-voltage indicator indicates becomes a predetermined increased value Mx rotating the second quarter-wave plate such that the principal axis J thereof is positioned orthogonally to the principal axis H of the first quarter-wave plate whereby the minimum value that the DC-voltage indicator indicates decreases to Mx finally rotating the polarizer +45 degrees such that the principal axis S thereof and the principal axis S supplying the reference electric signal to the DC-voltage indicator and an amplifier, wherein the amplifier amplifies the reference electric signal and supplies the amplified signal to a signal processor, and the signal processor generates reference signal data; then, disposing a test sample between the first quarter-wave plate and the second quarter-wave plate, passing the modulation polarized wave there through, at this time the photodetector generates a transmission electric signal and supplies the transmission electric signal to the DC-voltage indicator and the amplifier, wherein the amplifier amplifies the transmission electric signal and supplies the amplified signal to the signal processor, and the signal processor generates transmission signal data; and then, comparing the reference signal data with the transmission signal data and determining the stress of the test sample.