Warren H. Stevenson

Optical frequency shifting by means of a rotating diffraction grating.

The doppler frequency shift produced in the various diffraction orders of a rotating radial diffraction grating allows such a device to be used as an optical modulator. The theory and performance of such devices is presented.

Miniature fiber‐optic refractometer for measurement of salinity in double‐diffusive thermohaline systems

Information on salinity and temperature distributions is important in the study of thermohaline systems. In order to overcome difficulties associated with existing measurement methods, a miniature fiber‐optic probe has been developed. The probe, which is capable of local quasisteady and fluctuating salinity and temperature measurements, is easily constructed, calibrated, and utilized. Probe measurements compare favorably with results obtained using a slant‐wire shadowgraph technique and clearly show local phenomena in double‐diffusive thermohaline systems.

Influence of Gaussian beam properties on laser Doppler signals

The unique properties of Gaussian beams must be considered when designing and using laser Doppler anemometer systems. This paper presents an analysis of Gaussian beam effects in LDA systems in order to quantify their influence on the Doppler signal. The analytical results, which are verified by experiment, show that both axial and lateral frequency gradients can exist in the probe volume of improperly aligned LDA systems. The effects of lens aberrations and of optical path changes due to the insertion of planar optical elements in the beam are also considered.

Performance characteristics of range sensors utilizing optical triangulation

Many of the performance characteristics of triangulation sensors are obvious, but others are more subtle and do not appear to have been examined in the open literature. The authors examine these characteristics in detail. One aspect was to compare results obtained with a conventional touch trigger probe and a laser triangulation sensor when they are used in a reverse engineering situation. Another aspect involved the investigation of several optical effects which can degrade accuracy. These effects limit the ability of a triangulation sensor to make measurements when sudden changes in surface height occur, on surfaces with significant reflectance variations, and on rough surfaces.<<ETX>>

Oscillatory Flow Measurements with a Directionally Sensitive Laser Velocimeter

The concept, design, and construction of a directionally sensitive laser velocimeter for unsteady flow measurements are presented. Oscillatory flow measurements are compared with theoretical predictions.

Intensity distribution properties of a Gaussian laser beam focus

A generalized method for determining the properties of a Gaussian laser beam focus including waist radius, position, and intensity distribution is presented. Of significance to in situ laser diagnostic methods is a unique analysis of illuminated area as a function of intensity in a plane of the laser beam. The results apply for nontruncating diffraction-limited optical systems and are important in determination of the optical sampling volume of laser instruments for particulate and gaseous species analysis.

A laser velocimeter utilizing laser‐induced fluorescence

Addition of a fluorescent dye to the liquid used for scattering particle production in a laser Doppler velocimeter can result in a number of practical advantages. An investigation of this concept has been carried out using various dyes and solvents to determine its potential and limitations. The term ’’fringe mode fluorescence velocimetry’’ is recommended to describe this technique.

Visual modeling of laser Doppler anemometer signals by moiré fringes

This report describes the employment of moiré patterns to model visually interference phenomena in general and laser Doppler anemometer signals in particular. The modeling includes signals created in dual beam and reference beam anemometers by both single particles and particle pairs. The considerations are extended to visual modeling of multiparticle signals and the decay of signal quality in the presence of many particles. The fringe model of the laser Doppler anemometer is also considered, and moiré patterns are employed to demonstrate the interference fringes in the crossover region of two intersecting laser beams. Gaussian beam properties are taken into account to allow the effects of improperly designed optical systems to be studied. Instructions for using computer generated transparencies to produce the different moiré patterns are provided to allow the reader to study in detail the various interference phenomena described.

CO 2 laser beam shaping with computer generated holograms

In this Letter we wish to report the production of computer generated holographic gratings for use with CO2 lasers. Although these holograms can be reconstructed in the conventional manner, we believe the most interesting configuration is to use the holographic gratings to output couple a CO2 laser; the basic configuration is shown in Fig. 1. The partially reflecting plane mirror of an otherwise standard CO2 laser is replaced with an appropriate reflective phase hologram so the output wavefront can have any desired shape. The first diffracted order of the holographic grating is the output beam; the zero-order reflected beam is returned to the cavity to provide the necessary feedback. The energy associated with the zero order is not lost because the holographic optical element is inside the laser cavity. Since the first diffracted order is the output beam, this configuration does not provide the wavelength selectivity usually associated with the use of reflective gratings in laser cavities; but it does have many other significant advantages and potential applications. For example, the holographic grating could serve to provide a correction for aberrations

Use of laser triangulation probes in coordinate measuring machines for part tolerance inspection and reverse engineering

Laser triangulation range sensors mounted in coordinate measuring machines are finding increasing use for dimensional measurement applications. These applications include confirming that part dimensions are within tolerances and, in some cases, providing the dimensional database needed to reverse engineer products. This paper summarizes the results of recent studies on the performance characteristics of triangulation probes, describes certain effects which are not commonly understood, and presents concepts for improved designs and data analysis.