A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

The visualisation of living tissues at microscopic resolution is attracting attention in several fields. In medicine, the goals are to image healthy and diseased tissue with the aim of providing information previously only available from biopsy samples. In basic biology, the goal may be to image biological models of human disease or to conduct longitudinal studies of small-animal development. High-frequency ultrasonic imaging (ultrasound biomicroscopy) offers unique advantages for these applications. In this paper, the development of ultrasound biomicroscopy is reviewed. Aspects of transducer development, systems design and tissue properties are pre- sented to provide a foundation for medical and biological applications. The majority of applications appear to be developing in the 40 - 60-MHz frequency range, where resolution on the order of 50 mm can be achieved. Doppler processing in this frequency range is beginning to emerge and some examples of current achievements will be highlighted. The current state of the art is reviewed for medical applications in ophthalmology, intravascular ultrasound, dermatology, and cartilage imaging. Ultrasound biomicroscopic studies of mouse embryonic devel- opment and tumour biology are presented. Speculation on the continuing evolution of ultrasound biomicroscopy will be discussed. © 2000 World Federation for Ultrasound in Medicine & Biology.

Advances in ultrasound biomicroscopy

On propose une nouvelle methode de caracterisation tres precise des materiaux. On mesure les caracteristiques de propagation des ondes de fuite a la limite entre l'eau et l'echantillon; la vitesse de phase et l'attenuation sont determinees a travers des mesures de la courbe V(z). On presente une methode d'analyse spectrale pour obtenir les proprietes acoustiques a partir des courbes V(z). Description des mesures effectuees en utilisant des materiaux isotropes ou anisotropes pour lesquels les vitesses s'etendent de 2000 a 11000 m/s. On examine tous les modes d'ondes de fuite impliques dans les phenomenes d'interferences dans les courbes V(z). Resultats experimentaux confirmant les resultats theoriques. Application a l'analyse de la structure des materiaux polycristallins

Material Characterization by Line-Focus-Beam Acoustic Microscope

Relaxor-based ferroelectric single crystals: growth, domain engineering, characterization and applications.

The elastic constants of single‐crystal NbN, VN, and TiN films were determined from surface acoustic wave (SAW) dispersion curves obtained by the use of an acoustic microscope with a line‐focus beam. Measurements were carried out for single‐crystal nitride films grown on the (001) plane of single‐crystal cubic‐symmetric MgO substrates. The phase velocities measured as functions of the angle of propagation display the expected anisotropy. Dispersion curves of SAWs propagating along the symmetry axes were obtained by measuring the wave velocities for various film thicknesses and frequencies. Using a modified simplex method, an inversion of the SAW dispersion data yielded the elastic constants of cubic symmetry, namely c11, c12, and c44. The Rayleigh surface wave velocities calculated from the determined elastic constants and known mass densities agree well with a result measured by Brillouin scattering spectroscopy reported elsewhere.

Elastic constants of single‐crystal transition‐metal nitride films measured by line‐focus acoustic microscopy

The acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercial surface acoustic wave (SAW)-grade LiNbO/sub 3/ and LiTaO/sub 3/ single crystals were determined by measuring the bulk acoustic wave velocities, dielectric constants, and densities of many plate specimens prepared from the ingots. The maximum probable error in each constant was examined by considering the dependence of each constant on the measured acoustic velocities. By comparing the measured values of longitudinal velocities that were not used to determine the constants with the calculated values using the previously mentioned constants, we found that the differences between the measured and calculated values were 1 m/s or less for both LiNbO/sub 3/ and LiTaO/sub 3/ crystals. These results suggest that the acoustical physical constants determined in this paper can give the values of bulk acoustic wave velocities with four significant digits.

Accurate measurements of the acoustical physical constants of LiNbO/sub 3/ and LiTaO/sub 3/ single crystals

A line-focus-beam ultrasonic material characterization (LFB-UMC) system has been developed to evaluate large diameter crystals and wafers currently used in electronic devices. The system enables highly accurate detection of slight changes in the physical and chemical properties in and among specimens. Material characterization proceeds by measuring the propagation characteristics, viz., phase velocity and attenuation, of Rayleigh-type leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface. The measurement accuracy depends mainly upon the translation accuracy of the mechanical stages used in the system and the stability of the temperature environment. New precision mechanical translation stages have been developed, and the mechanical system, including the ultrasonic device and the specimen, has been installed in a temperature-controlled chamber to reduce thermal convection and conduction at the specimen. A method for precisely measuring temperature and longitudinal velocity in the water couplant has been developed, and a measurement procedure for precisely measuring the LSAW velocities has been completed, achieving greater relative accuracy to better than /spl plusmn/0.002% at any single chosen point and /spl plusmn/0.004% for two-dimensional measurements over a scanning area of a 200-mm diameter silicon single-crystal substrate. The system was developed to address various problems arising in science and industry associated with the development of materials and device fabrication processes.

Development of the line-focus-beam ultrasonic material characterization system

Acoustic characterization of doped silica glasses with a GeO2, P2O5, F, TiO2, Al2O3, or B2O3 dopant having different concentrations is presented. Quantitative measurements were performed with a 225-MHz line-focus-beam scanning acoustic microscope. The acoustic velocity variation due to different dopant concentrations is given. It has been found that the Al2O3 dopant increases, but the other dopants decrease, the acoustic velocity as compared with that of the pure fused silica. We have also found that the fractional change in acoustic velocity is greater than that in refractive index for a given dopant concentration.

Acoustic Characterization of Silica Glasses

Absolute accuracy of the line-focus-beam (LFB) acoustic microscopy system is investigated for measurements of the leaky surface acoustic wave (LSAW) velocity and attenuation, and a method of system calibration is proposed. In order to discuss the accuracy, it is necessary to introduce a standard specimen whose bulk acoustic properties, (e.g., the independent elastic constants and density) are measured with high accuracy. Single crystal substrates of gadolinium gallium garnet (GGG) are taken as standard specimens. The LSAW propagation characteristics are measured and compared with the calculated results using the measured bulk acoustic properties. Calibration is demonstrated for the system using two LFB acoustic lens devices with a cylindrical concave surface of 1-mm radius in the frequency range 100 to 300 MHz.

A method for calibrating the line-focus-beam acoustic microscopy system

Langasite-type single crystal Ca3NbGa3Si2O14 (CNGS) was grown by the Czochralski technique. Dielectric, elastic and piezoelectric constants of CNGS were measured by the resonance-antiresonance method. At room temperature, dielectric constants e11T/e0 and e33T/e0 were 17.8 and 27.9, respectively. Electromechanical coupling coefficients k12, k25 and k26 were also determined as 10.9, 17.3 and 11.9%, respectively. The measurements were carried out in a temperature range from -30 to 80°C. Temperature coefficients of the dielectric, elastic and piezoelectric constants were obtained. The line-focus-beam and plane-wave ultrasonic material characterization system was employed for measuring bulk acoustic velocities, and longitudinal and transverse wave velocities of 7408.4 m/s and 3136.2 m/s, respectively, in the c-direction uncoupled with piezoelectricity at 23°C were obtained. This was in good agreement with the results determined by the resonance-antiresonance method. The density of CNGS was 4125 kg/m3. All the parameters of the CNGS crystal for bulk and surface acoustic wave applications were determined in this research.

Jun-ichi Kushibiki

Papers

Accurate measurements of the acoustical physical constants of LiNbO/sub 3/ and LiTaO/sub 3/ single crystals

Development of the line-focus-beam ultrasonic material characterization system

Acoustic Characterization of Silica Glasses

A method for calibrating the line-focus-beam acoustic microscopy system

Piezoelectric Properties of Ca3NbGa3Si2O14 Single Crystal