Laser Meter Research Articles

Analysis of accuracy of measurement by Doppler laser meters

We discuss the accuracy analysis of laser meters based on the Doppler effect and used in the measurement of automobile velocity. Usually, the systematic errors are assessed during calibration and are eliminated by instrumental means. Nevertheless, it is impossible to eliminate random errors. Their analysis is also important for such measurements, and this has been less extensively analyzed in scientific papers. A probabilistic method is used for error analysis assuming that only random errors are present. The accuracy of measurement by Doppler meters depends mostly on parameters of two kinds—laser source stabilization, measuring laser emission frequencies, and the errors in determining the emission speed in the atmosphere. Such analysis shows a value of the random error occurring during the measurement of automobile speed that also can be applied for assessment of other kinds of measurements of moving objects.

Laser-based internal profile measurement system

An automatic laser-based system to measure the internal profiles of various structures has been developed. The system uses a point laser source through a rotating optical device fixed on to a laser measurement meter. A notebook computer with custom software is used to control the laser meter and rotating device to estimate the scanned profile shape and to determine the resulting cross-section area. The information provided by this system is essential to construction industry, including window and door builders; the glass, panel, board, and floor tile manufacturers; carpet venders; and building contractors for cost estimation and production control. As a result, the lead time for delivering the customized windowpanes, woodwork, floor tiles, and ceilings can be reduced. Applications of this system for measuring the shapes of window frames and floor plans are described and demonstrated. The measurement accuracy is evaluated and analyzed. Results have indicated that the measurement accuracy can be achieved within 4% of the measurement distance, for typical window designs and floor patterns required by major widow manufacturers. Recommendations to improve the system are also included.

Detection of the Increment of an Instantaneous Phase in a Long-Base Laser Meter of Small Vibrations

A phase meter for processing signals of a laser meter of small displacements and vibrations at long base distances is described. Vibrations of objects are transformed into small increments of a signal phase at an RF carrier, which are detected by the phase meter and are outputted as signals proportional to microvibrations in the acoustic range. At a given carrier frequency fc = 10.7 MHz, vibrations are detected within a band Δf = 3 kHz. Such vibrations produce phase fluctuations of ≤Δϕ ≈ 10–42π, which correspond to magnitudes of ∼1 nm for a laser wavelength λ ≈ 10 μm.

Optical velocimeters for moving surfaces using gas and semiconductor lasers

A differential arrangement using a laser for the measurement of the velocity of moving surfaces is discussed. Configurations of optical velocimeters with diffraction beam-splitters are shown not to be critical on the wavelength stability of a semiconductor laser. Laser meters measuring the velocity and length of rolled stock have been built on the basis of the devices considered.

Formation of laser meter signals

Formation of laser meter signals

Laser heterodyne method of shift measurement using acousto-optic interaction

Heterodyne methods of optical-field detection using acousto-optic interaction (AOI) have gained use in optical and acoustical holography, optical interferometry and interference microscopy, and ultrasonics. These methods detect the amplitude and phase at each point of the optical field at a given carrier frequency and, in conjunction with scanning, recover the wave fronts scattered by an object. This paper examines another heterodyne method of acoustooptic conversion of light-wave phase shift in which AOI is accomplished at the output of the interference system. The described method allows a differential scheme for conversion of light-wave phase shifts which increases stability and doubles sensitivity. This is a two-channel system and has an electrical reference signal that is formed by acousto-optic conversion in transillumination of the point of the acoustic grating as the measuring signal. The proposed method has provided a basis for designing and putting into serial production laser meters with displacement ranges of up to 10 m and up to 30 m and with discreteness to 0.01 micrometers.