Demonstration of nonlinear absorption in Au semi-continuous film by electrical measurement.

We have demonstrated the nonlinear absorption at 532 nm wavelength in an Au semi-continuous film (SF) resulting from smearing of the Fermi distribution and diffusion of conduction electrons into the substrate. The Au SF was irradiated by a pulsed laser with 8 ns pulse width at 532 nm in near resonance with the interband transition of the Au. We determined the temperature increase in the SF for different intensities by electrical measurement. We calculated the temperature increase by using a 1D heat transport equation; comparing the results of the calculation with measured values for the temperature increase, revealed the nonlinear absorption in the Au SF. We employed this deviation from linear behaviour to determine the nonlinear absorption coefficient.

Distortion induced effects on the finesse of high-performance large-aperture Fabry-Perot etalon filters.

The effect of thickness uniformity and distortion on the performance of large-aperture Fabry-Perot etalon filters is investigated. It is shown that for etalons currently being used for solar observation it is important to consider the effect of distortion due to mounting and to gravity when in use. It is further shown that the effects of distortion can be largely avoided by operating the etalon at or near normal incidence.

Calibration of a 300-mm-aperture phase-shifting Fizeau interferometer.

A 300-mm-aperture digital phase-shifting Fizeau interferometer has been developed in-house for precision metrology of optical components fabricated by the optical workshop at Telecommunications and Industrial Physics, Commonwealth Scientific and Industrial Research Organization. We describe the procedures used in the calibration of the instrument. A reference data file representing the deviations from flatness of the reference surface is generated, measurement uncertainty estimated, and aberrations in the instrument assessed. Measurements on 250-mm-diameter uncoated optical surfaces have consistently shown short-term repeatability of 0.3-nm rms from measurement to measurement and allowed for absolute characterization of these surfaces to within a few nanometers.

Fabrication and measurement of optics for the laser interferometer gravitational wave observatory.

The manufacture and testing of high-precision optical surfaces for the Laser Interferometer Gravitational Wave Observatory is described. Through the use of carefully shaped polishing laps made of a nondeformable polymer material coated on a rigid base, surfaces 250 mm in diameter with radii of curvature between 7 and 15 km were polished to an accuracy of several hundred meters in the curvature and with low values of waviness and microroughness. Metrology instrumentation used to measure the optical finish included a large-aperture digital interferometer calibrated to nanometer-level accuracy for measurements of curvature, astigmatism, and waviness and an interference microscope for measurements of microroughness. The power spectra of the data from both instruments were in good agreement.

Measurement of transient deformations with dual-pulse addition electronic speckle-pattern interferometry.

We describe an electronic speckle-pattern interferometry system for analyzing addition fringes generated by the transient deformation of a test object. The system is based on a frequency-doubled twin Nd:YAG laser emitting dual pulses at a TV camera field rate (50 Hz). The main advance has been the automatic, quantitative analysis of dual-pulse addition electronic speckle-pattern interferometry data by the introduction of carrier fringes and the application of Fourier methods. The carrier fringes are introduced between dual pulses by a rotating mirror that tilts the reference beam. The resulting deformation-modulated addition fringes are enhanced with a deviation filter, giving fringe visibility close to that of subtraction fringes. The phase distribution is evaluated with a Fourier-transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructed with an iterative weighted least-squares unwrapper. Preliminary results for a thin plate excited by an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformation fields.

Simultaneous measurement of three orthogonal components of displacement by electronic speckle-pattern interferometry and the Fourier transform method.

The measurement of three-dimensional displacement by electronic speckle-pattern interferometry with three object beams and one reference beam is presented. Multiple interference fringes corresponding to different sensitivity vectors are recorded in a single interferogram and separated by means of the Fourier transform method to give three components of displacement. The relationship between the ratio of the speckle size to the pixel size of a TV camera and the measurement error is investigated experimentally and compared with the research of others. The optimum condition leading to a minimum measurement error occurs when the speckle size is approximately equal to the pixel size. With this condition satisfied, the measurement error varies from 1.5% to 6.0%.

Dynamic range of Ronchi test with a phase-shifted sinusoidal grating.

The dynamic range of a Ronchi test with a phase-shifted sinusoidal grating was investigated theoretically and experimentally. As the number of fringes in a Ronchi interferogram increases, the fringe visibility decreases, which results in a decrease of phase-measurement resolution. It is shown that in order to optimize the dynamic range the effective wavelength of the interferogram should be tuned to the characteristic wavelength of the object wave front. The maximum dynamic range achievable is estimated to be 16 times larger than that of a Fizeau interferometer. Suppressing higher-order diffraction components has achieved sheared interferograms with a signal-to-noise ratio in excess of 60:1. The effects of nonsinusoidal transmittance of the grating and the phase-shift errors were minimized by a seven-sample phase-shifting algorithm, and a phase measurement uncertainty of less than 1/700 has been achieved.