Showing papers on "Interferometry published in 1976"

Differential Gain and Bistability Using a Sodium-Filled Fabry-Perot Interferometer

Abstract: Differential gain and large hysteresis have been seen in the transmission of a Fabry-Perot interferometer containing Na vapor irradiated by light from a cw dye laser. Non-linear dispersion, neglected in earlier work, dominates over nonlinear absorption in Na. The apparatus uses only optical inputs and outputs. Similar apparatus may be useful as an optical amplifier, memory element, clipper, and limiter.

Measurement of the rms roughness, autocovariance function and other statistical properties of optical surfaces using a FECO scanning interferometer.

Abstract: A brief review of techniques for measuring surface roughness and optical figure is given. One of the most promising of these techniques for measuring the roughness of optical surfaces is interferometry employing fringes of equal chromatic order (feco). A feco scanning interferometer is described, which has been used to determine statistics of polished surfaces having roughnesses under 100 A rms. The scanning interferometer resolves square surface elements 2 μm on a side and statistically characterizes the surface in terms of these elements. Height- and slope-distribution functions, rms roughness, rms slope, and modified autocovariance length distributions have been measured for selected optical surfaces. Nearly all surfaces had Gaussian distributions of heights and slopes, but none had Gaussian distributions of autocovariance lengths. Surfaces such as electropolished copper, electroless nickel, and single-point diamond-machined copper were found to have smaller rms slopes than other surfaces of comparable roughness and scattered less than predicted by simple scalar scattering theory.1,2 On the other hand, heavily scratched surfaces such as polished potassium chloride had larger slopes and produced more scattering than expected from simple theory.

Interferometric real‐time display of cw dye laser wavelength with sub‐Doppler accuracy

Abstract: We describe an automatic fringe‐counting interferometer with real‐time wavelength readout for cw laser sources. Sub‐Doppler absolute wavelength accuracy (∼2×10−7) is demonstrated with saturated absorption spectroscopy in neon.

Theory of nonresonant multistable optical devices

Abstract: We show that a Fabry‐Perot interferometer filled with a Kerr medium has a multiple‐valued transmission‐intensity characteristic. ’’On’’ and ’’off’’ field for bistable operation are estimated, and a simple but accurate approximate theory is described.

III. Optical Probing of Surface Waves and Surface Wave Devices

Abstract: [45] C. S. Tsai, Le T. Nguyen. M. A. Alhaider, “Wideband Acoustotwo Tilting Surface Acoustic Waves,” Appl. Phys. Lett. 26, optic Guided-Light Beam Deflector Using Tilting Surface 140-143, February 15,1975. Acoustic Waves,” 1974 Ultrasonics Symposium Proceedings, [47] C. S. Tsai, M. A. Alhaider, Le T. Nguyen and B. Kim, “WideIEEE Cat.. # 74. C H 0 896-1SU. 768-772. band Guided-Wave Acoustooptic Bragg Devices Using Multiple [46] C. S. Tsai, Le T: Nguyen, 8. K.’Yao and M. A. Alhaider, “HighTilting Surface Acoustic Waves,” Talk-36, Conference on Laier performance Acousto-optic Guided-light Beam Device Using Engineering and Applications, Washington, D. C., May 1975

Measurement of nonlinear refractive‐index coefficients using time‐resolved interferometry: Application to optical materials for high‐power neodymium lasers

Abstract: An improved time‐resolved interferometric method for measuring intensity‐dependent changes in the refractive index of optical materials is described. An intense 125‐ps pulse from a 1064‐nm Nd : YAG laser‐glass amplifier system is propagated throguh the sample which is placed in one arm of a modified Michelson interferometer. The nonlinear refractive‐index coefficient is measured from the time‐dependent fringe formed at the output of the interferometer. Values are reported for several low‐index optical glasses (BK‐7, FC‐5, FK‐51), fused silica, a silicate laser glass (ED‐2), a Faraday rotator glass (FR‐5), and a nonlinear crystal (KH2PO4). Possible sources of error in using this approach are discussed.

Study of the frequency distribution of the fluorescent light induced by monochromatic radiation

Abstract: The frequency distribution of the fluorescent light induced by monochromatic dye laser radiation was investigated. To exclude the influence of the Doppler width a strongly collimated atomic beam was used. The spectrum was measured by means of a piezoelectrically tunable spherical Fabry Perot. The interaction region between the laser light and the atomic beam was placed into the center of the interferometer. Thus the observed fluorescence spectrum was considerably more intense than in the case where the interferometer is used separately from the beam. The fluorescence spectrum was observed for different directions of polarization of the incident laser beam. In the case of weak excitation the spectrum consists of a sharp component essentially due to elastically scattered light. At high intensities a structure of three components is observed which is in agreement with theoretical predictions when circularly polarized light is used for excitation.

Strain analysis by one-beam laser speckle interferometry. 2: Multiaperture method.

Abstract: A detailed analysis of using multiple apertures to record laser speckles for strain analysis is presented. It is shown that the basic fringe-forming mechanism is no different from that of single-aperture recording, except that at the Fourier filtering stage the diffracted light energy is concentrated at the spatial frequencies admitted by the apertures. As a result, better isothetic fringes at higher frequencies are obtainable. The concept of moire is not utilized in the analysis. Indeed, it is shown that some of the observed phenomena cannot be explained using the moire concept. Multiaperture arrangements studied include two, three, and four apertures.

Real-time measurement of surface roughness by correlation of speckle patterns

Abstract: In a previous article we have shown that the two speckle patterns produced from the same rough surface illuminated by two coherent plane waves under two different angles of incidence are correlated. The correlation depends on the surface roughness. In this paper a method is described where the rough surface is illuminated simultaneously by the two plane waves. The ensemble-averaged coherence function, that is, the correlation function, of the scattered field is measured by using a two-waves interferometer. This affords a real-time measurement of the surface roughness in the range of large roughness (σ > λ). The theoretical calculations have been performed for a normally distributed surface. The experimental results are in good agreement with theory. We describe the optical arrangement of an instrument based on this principle.

Laser speckle interferometry for plate bending problems.

Abstract: A method is proposed whereby the spatial speckles created in front of a plate with an optically rough surface when illuminated by a coherent laser beam is used to generate slope contour fringes. This is done by photographing the speckles contained in a parallel plane in front of the plate before and after deformation via double exposure. The resulting speckle interferogram is then optically Fourier transformed to yield the fringe pattern of slope contours. It is shown that the method is analogous to the Ligtenberg reflection moire method with a grating of continuously variable pitch and orientation. The method can be applied to plates made of almost any material.

Vibration phase mapping using electronic speckle pattern interferometry.

Abstract: The contours of constant phases across sinusoidally vibrating objects have been mapped using reference wave phase modulation in time-average electronic speckle pattern interferometry.

Modulated submillimeter laser interferometer system for plasma density measurements.

Abstract: A high resolution submillimeter interferometer system for measurement of electron densities in the 1014-cm−3 ≤ ne ≤ 2 × 1015-cm−3 range has been developed for use in high density tokamaks. Phase modulation at ~1 MHz is accomplished by difference frequency mixing of two cavity tuned laser oscillators. The optically pumped CH3OH lasers, which operate on the 118.8-μm line, feature a novel output coupling design that permits good mode quality and low beam divergence. The beat signals are detected using a newly developed Ge:Li photoconductor, and a direct measurement of the phase shift is obtained from the time lag between probe and reference signals. The sensitivity of the resulting phase measurement is independent of the instantaneous phase and unaffected by fluctuations in the amplitude or in the frequency of the modulation.

Digital wavemeter of cw lasers

Abstract: The ratio of an unknown laser wavelength to that of a standard is quickly determined by a two-beam interferometer with a corner-cube reflector moving on an air track. Standard and unknown wavelength beams travel identical paths in opposite directions, so refractive index corrections are minimized. Accuracy is about six parts in 10/sup 8/. Absolute measurements of some iodine hyperfine component wavelengths are reported.

Delay-Lock Tracking of Stochastic Signals

Abstract: The measurement and tracking of the delay between two versions of a stochastic signal by cross-correlation techniques is considered. Such techniques have broad applications, e.g., interferometry, noncontact speed and distance measurement, etc. The paper begins by discussing the functional diagram of the tracking system. From this diagram a mathematically equivalent model of the system is derived and its similarities to the well known baseband model of the phase-locked loop are discussed. Using Fokker-Planck (F-P) techniques the performance of the system, as a function of fundamental system parameters, is computed and graphically illustrated. These results are then compared with experimental results obtained by computer simulation.

Imaging apparatus including spatial-spectral interferometer

Abstract: Imaging apparatus for producing the image of a radiating object which exists in a noise-producing background, includes an optical transducer including a focal plane array or radiation detectors. Light collected by a partially filled entrance aperture is relayed to a partially filled focal plane array by relay optics which include one or more variable phase retardation devices. For example, two movable mirrors per dimension driven in push-pull by piezoelectric drives operate as phase shifters. Interference of incident light from separated parts of the entrance pupil at a series of path differences allows the initially distorted image to be dissected into a series of constituent images at several narrow wavelength intervals. The arrangement of the instrument is so chosen that each constituent image carries information about a different region of spatial frequencies. The set of constituent images carries a complete set of spatial frequencies out to a limit much larger than the area of the entrance pupil would ordinarily provide. The detectors in the focal plane are chosen to have a sufficiently wide spectral response to accept all these data. The detectors are arranged at spacings which sample the constituent images adequately for reconstruction. The data collected by the instrument are analyzed by Fourier transformation with respect to imposed path difference by interpolation of detect or samples and by weighting and summing of constituent images.

Laser wavelength comparison by high resolution interferometry.

Abstract: High resolution interferometry has been used to determine the wavelength ratio between two molecularly stabilized He–Ne lasers, one locked to a methane absorption at 339 μm and the other locked to the k peak of 129I2 at 633 nm An optical beat frequency technique gave fractional orders while a microwave sideband method yielded the integer parts Conventional (third derivative) peak seeking servoes stabilized both laser and cavity lengths Reproducibility of the electronic control system and optics was a few parts in 1012, while systematic errors associated with curvature of the cavity mirrors limited the accuracy of the wavelength ratio measurement to 2 parts in 1010 The measured wavelength ratio of the methane stabilized He–Ne laser at 339 μm [P(7) line, ν3 band] to the 129I2 (k peak) stabilized He–Ne laser at 633 nm was 5359 049 260 6 (0000 2 ppm) This ratio agrees with that calculated from the (lower accuracy) results of earlier wavelength measurements made relative to the 86Kr standard Its higher accuracy thus permits a provisional extension of the frequency scale based on the cesium oscillator into the visible spectrum

Digital wavemeter for cw lasers

Abstract: The wavelength of light can be measured by counting the number of fringes as an interferometer mirror is moved through a known distance. The known distance is best obtained by simultaneously counting the number of fringes from a standard wavelength source for the same change of optical path length. The arrangement in Fig. 1 permits rapid and precise comparison of wavelengths by moving a mirror smoothly over long distances. The interferometer is a two-beam, division of amplitude type related to the Michelson and Sagnac interferometers. In it, the standard and unknown beams travel identical paths in opposite directions. They emerge at separate detectors, so that there is no need for a dichroic beam splitter to separate them, and measurements can be made close to the wavelength of the standard if desired. Moreover, the visible spots of light on the mirrors can be brought into coincidence, ensuring that the two pathlengths are nearly identical, and simplifying the alignment of the unknown beam. The effects of vibrations are also minimized by the use of identical paths.

Collimation test by double grating shearing interferometer

Abstract: The double grating shearing interferometry method for determination of the degree of light collimation is described. High accuracy is obtained by performing the observation of fringes in the area of the size twice as big as the one usually assumed in shearing interferometry experiments. The conditions under which such a detection mode is feasible are derived. They represent at the same time a very strong argument proving the highly diffractive (wave optics) character of the classical Ronchi test.

Problem of defocusing in speckle photography, its connection to hologram interferometry, and its solutions

Abstract: The movements, in three-dimensional space, of laser speckles observed from diffusely reflecting objects are described. The description connects these motions to relationships between fringe vectors and fringe localization in hologram interferometry. The results indicate the conditions under which defocusing leads to false measurements with conventional techniques, and methods are suggested that could solve the problem encountered due to defocusing when small displacements are to be measured on highly three-dimensional objects.

High-precision dielectric measurements on liquids and solids at millimeter and submillimeter wavelengths

Abstract: A brief outline is given of the improvements which have been made in the measurement techniques available for the determination of the complex relative permittivity of liquids and low-loss solids in the frequency range v = 100 GHz to 18 THz. These improvements involve very stable interferometric systems with either dielectric beam splitters for the upper frequency end or else free standing wire grid beam splitters for the lower frequency end, novel cell designs, the use of sensitive detectors, and of new computational procedures. The results can be checked by independent spot frequency measurements using HCN and H 2 O lasers coupled to an improved Mach-Zehnder interferometer. The optical properties of the polymeric (polyethylene, TPX, polypropylene, PTFE) and single crystal (quartz, silicon germanium) windows now assume an increased importance and we have determined refractive index n (v) and power absorption coefficient α(v) to much improved precision. With our present technique we can now determine the complex permittivity of very heavily absorbing liquids such as primary alcohols and water as far as 6 THz and beyond in favorable cases as functions of frequency over a wide temperature range.

A very-long-baseline interferometer system for geodetic applications

Abstract: A very-long-baseline interferometer system was designed and built for geodetic applications. Each interferometer terminal records a 360-kHz spectral band of noise from a compact extragalactic radio source. The center frequency of the spectral band can be selected to sample sequentially bands covering a much wider frequency range to obtain subnanosecond accuracy in group-delay measurements. A tunnel-diode pulse generator is used to calibrate the delays in the receiver. The necessary sets of algorithms and computer programs have been developed to analyze the data and have allowed the system to be employed to make accurate determinations of vector baselines, radio-source positions, polar motion, and universal time.

Simple stabilization scheme for maintenance of mirror alignment in a scanning February-Perot interferometer

Abstract: A circuit is described which varies the relative alignment of the mirrors of a repetitively scanned plane Fabry-Perot interferometer until the transmitted light intensity of the strongest spectral component is maximized. Using this scheme an interferometer can be completely stabilized against all drifts arising due to thermal and mechanical instabilities.

Spherical-wave theory of the zero-absorption LLL X-ray or neutron interferometer

Abstract: Amplitude and intensity distributions within the outgoing beams of the triple-Laue-case (LLL) interferometer have been calculated for the case of zero absorption, which in practice is predominantly encountered with thermal neutrons. The type-1 wavefield with antinodes on the atomic sites, which with X-rays is quite frequently anomalously attenuated in the lattice, is here fully taken into account together with the type-2 wavefield of anomalous low absorption. After the combined diffraction by beam splitter, mirror, and analyser crystal of the interferometer for an incident plane wave has been solved, the solution for an incident spherical wave is developed by Fourier expansion, by a similar method to that first given by Kato [Acta Cryst. (1961), 14, 526–532] for just one diffracting crystal plate. In order to optimize the interferometer geometry spatial intensity profiles as functions of the geometric dimensions of the interferometer and of the phase shift between the interfering beams are calculated. The influence of deviations from the ideal geometry is investigated. Deviations of the order of the extinction length can result in a drastic reduction of interference contrast. Very good energy-converging and contrast properties are found if tM = 2tS= 2tA where tM, tS, tA are the thicknesses of mirror, beam splitter, and analyser respectively. The calculated intensity profiles are in agreement with preliminary experimental profiles obtained recently with a silicon interferometer at the HFR in Grenoble.

Displacement measurements in the interior of 3-D bodies using scattered-light speckle patterns

Abstract: Two new techniques making use of the scattered-light speckle pattern have been developed which yield the displacements on an arbitrary interior plane of a 3-D body. When a sheet of coherent light passes through a transparent 3-D body, a small fraction is scattered. This scattered light produces a speckle pattern in an imaging system. By recording two superimposed images of this speckle pattern, one before and one after body deformation, the displacements on the interior illuminated plane can be found. The technique of scattered-light photography uses a single illuminating beam and is sensitive to displacements greater than one speckle diameter, approximately 3 μm. Scattered-light speckle interferometry uses two illuminating beams and is sensitive to displacements greater than one half the wavelength of light being used, approximately 0.2 μm. With both techniques, the double-exposed speckle photograph is optically processed to yield displacement information. With both techniques, the maximum displacement measurable is limited by correlation requirements between the two speckle patterns. Experimental results are presented demonstrating the two new techniques.

Measurements of the atmospheric attenuation of the spectral components of astronomical images

Abstract: Measurements are presented of the long and short exposure visibility of fringes produced by stellar wave fronts, distorted by atmospheric turbulence. A variable shear rotation interferometer is used. Parameters relevant to image degradation are deduced.

Light-scattering heterodyne interferometer for vibration measurements in auditory organs

Abstract: An interferometric optical heterodyne technique has been developed especially for vibrational amplitude and phase measurements on auditory organs of live animals. Laser light diffusely scattered from the vibrating structure is used for the measurement. Continuous calibration and feedback compensation systems were developed to cope with the problems of drift in interferometer alignment and small background movements. Vibrational amplitudes from below 0.1 A to above 400 A have been detected on the posterior tympanic membranes of live crickets.Subject Classification: [43]65.20; [43]40.60; [43]35.65.