The invention is a system and method of measuring the shape of a surface. The corneal topographer specifically shown comprises a rigid reference member having a reference surface of a predetermined shape applied to the surface of the eye. The shape of the reference surface is correlated with the measured information to determine the shape of the corneal surface. Several specific designs are shown that use optical, acoustic, acousto-optic or capacitive techniques to determine a distance between the reference surface and the corneal surface over a multiplicity of data points sufficient in number and spacing to represent the local topography of the surface of the eye.

Method and system for topographic measurement by measuring the distance between a rigid reference member and a surface of an eye

An acousto-optic modulator for use with a multichannel laser beam system, for instance, is of conventional structure except that two different RF (radio frequency) signals (f1, f2) drive the modulator. These signals each produce at least one output beam (30b, 30c) as diffracted by the modulator body (34). These two beams (30b, 30c) are angularly and spatially separated. One of the sets of beams (30b) is incident upon a beam stop (40), and therefore is not used for writing. Only the other set of beams (30c), driven by the other of the frequencies, performs the actual writing. The optical stop (40) in addition to blocking one of the sets of diffracted beams (30b) also blocks the transmission of the zero order (undiffracted) beam (30a). The sum of the load power of the signals at the two frequencies (f1, f2) is kept approximately constant, thereby maintaining a constant thermal condition within the modulator.

Thermally balanced acousto-optic modulator

Digital control of frequency and/or amplitude modulation techniques of an intracavity and/or extracavity AOM ( 60 ) facilitate substantially full extinction of a laser beam ( 90 ) to prevent unwanted laser energy from impinging a workpiece ( 80 ); facilitate laser pulse amplitude stability through closed-loop control of pulse-to-pulse laser energy; facilitate beam-positioning control including, but not limited to, closed-loop control for applications such as alignment error correction, beam walk rectification, or tertiary positioning; and facilitate employment of more than one transducer on an AOM ( 60 ) to perform any of the above-listed applications.

AOM modulation techniques for facilitating pulse-to-pulse energy stability in laser systems

The quality demands for steel plate and strip products are increasing, and flatness and dimensional measurements performed on these products must fulfill quality standards, and above all the needs of the clients. Many quality assurance methods exist with regard to flatness and dimensional measurements in the steel industry. Manual gauging methods are often still used, but they are costly in terms of time and labour. Automated noncontact optical measurement systems are becoming more common due to their benefits over traditional methods. In this thesis a projection moire topography is applied for automatic measurement of the flatness of large steel plates and a fully automated system applicable to varying surface properties of large steel plates is implemented in a hostile industrial environment. The specifications, design and performance of the system are presented. The measurement area of the system is 3.5 metres x 1.0 metre (width x length), and it achieves a specified depth resolution of 0.3 mm. The system operates in real time on the production line at a speed of 1 m/s. Experiences gained with the system and the different requirements applying to another measurement site then led to the invention of a novel multipurpose flatness measurement system, the design, laboratory prototype and performance of which are also described in this thesis. The usability and competitiveness of the novel system have been increased by adding 2D dimensional measurements such as edges, widths, lengths etc., and even surface quality inspection, to the same unit. The depth resolution of the laboratory system is better than 0.6 mm.

On-line flatness measurement of large steel plates using moiré topography

Digital control of frequency and/or amplitude modulation techniques of an intracavity and/or extracavity AOM (60) facilitate substantially full extinction of a laser beam (90) to prevent unwanted laser energy from impinging a workpiece (80); facilitate laser pulse amplitude stability through closed-loop control of pulse-to-pulse laser energy; facilitate beam-positioning control including, but not limited to, closed-loop control for applications such as alignment error correction, beam walk rectification, or tertiary positioning; and facilitate employment of more than one transducer on an AOM (60) to perform any of the above-listed applications.

AOM modulation techniques for improving laser system performance

A Q-switch modulator for a high power laser having a randomly polarized output beam and large divergence angle employs a cascaded arrangement of longitudinal mode acousto-optic modulators, each of which has a Raman Nath or near Raman Nath interaction length. The modulators are optically cascaded such that the distance the randomly polarized laser beam travels through the modulators is effectively confined to the sum of the non coherent interaction lengths thereof. Due to the substantial power level of the laser output, there is heating of the bulk material, which usually results in a shift in the Bragg angle. This has minimal if any effect on the shorter interaction length of the Q-switch modulator of the invention. Also, heating of the bulk material is countered by the incorporation of cooling fluid channels in a heat sink support block coupled in thermal communication with the bulk material. The heat sink support structure is configured to be effectively mechanically floating with respect to a support housing for the Q-switch.

High loss modulation acousto-optic q-switch for high power multimode laser

Video technology is applied to the problem of moire metrology. In the past, moire metrology seemed a promising yet limited method in the measurement and comparison of surface shape. The use of video technology has widened the area of application of moire metrology by reducing the complexity of the optical set up and providing real time information on surface shape and deformation. A continuously variable grating projector and analog video circuitry are used to generate real time additive (bright line) and transmissive (dark line) moire patterns. These patterns are used to compare a test object against a “perfect” reference object. This is done in both real time and through the use of computer image processing. Depth resolutions on the order of 0.3 mm are obtained on a cone 25.4 mm high and 50.8 mm wide. The projection system allows easy expansion to large objects. Because of the use of video technology moire metrology can now be more readily applied to robotic vision and factory assembly line quality control over a wide range of scales.

Video Applications to Moiré Metrology

A polarization-independent polychromatic light modulator applies one or more pairs of predetermined RF drive frequencies to an acousto-optic transducer of an acousto-optic modulator body upon which a single beam of randomly polarized or unpolarized polychromatic input light is incident. No precursor polarization separation elements are employed. For each optical wavelength to be extracted from the incident beam, two RF drive frequencies are employed. The acoustic waves launched into the acousto-optic medium by the application of the two frequencies of a given RF drive frequency pair produce respective +1 and -1 order output beam components of the selected output wavelength (as well as a zeroth order beam for that wavelength). Because the +1 and -1 order beams depart the modulator body along spatially diverse paths, they are intercepted by a set of recombination optics, which blocks the zero order beam component and recombines the desired +1 and -1 order beams into a single composite beam containing a selected wavelength. Where the output beam is to contain a mixture of multiple wavelengths for producing a composite color output light beam, as in the case of a modulated laser projector entertainment system, multiple pairs of RF drive frequencies are applied to the acousto-optic modulator.

Acousto-optic modulator for selective extraction of one or more wavelengths from randomly polarized polychromatic light beam

A dual solenoid-based linear motion actuator has a single input for supplying both electrical power and positioning signals for a pair of solenoid coils. A binary control signal alternates between first and second voltage levels, one of which is used for powering the dual solenoid actuator and its control electronics, and also for controllably displacing a movable element to a first of a pair of spaced apart positions terminated by electrically conductive stops. The moveable element is electrically coupled to the second voltage level so that contact with either of the stops will apply the second electrical voltage level to control logic circuitry. The actuator's input terminal is coupled to an electrical energy storage circuit, such as a battery and/or capacitor in parallel with the battery, that serves as the power supply for the actuator, extracting and storing power necessary for operating the control circuitry and energizing the solenoid coils.

Double solenoid linear motion actuator

A moire profilometry method has been developed that is capable of inspecting objects whose size is limited only by the available laser power. The moire contours are generated in real time by projecting variable spacing gratings upon the target and filtering the image either optically, in the video signal, or in the computer. The system is designed to compare the surface shape of a test object with a previously stored image of a perfect object, and to display the surface errors superimposed on a video image of the test object. A unique feature of the system is the continuously variable depth resolution which makes it usable either for human or robot adjustment of the test object or for automated pass/fail inspection.A moire profilometry method has been developed that is capable of inspecting objects whose size is limited only by the available laser power. The moire contours are generated in real time by projecting variable spacing gratings upon the target and filtering the image either optically, in the video signal, or in the computer. The system is designed to compare the surface shape of a test object with a previously stored image of a perfect object, and to display the surface errors superimposed on a video image of the test object. A unique feature of the system is the continuously variable depth resolution which makes it usable either for human or robot adjustment of the test object or for automated pass/fail inspection.

Robert V. Belfatto

Papers

High loss modulation acousto-optic q-switch for high power multimode laser

Video Applications to Moiré Metrology

Acousto-optic modulator for selective extraction of one or more wavelengths from randomly polarized polychromatic light beam

Double solenoid linear motion actuator

3-D Inspection of Large Objects by Moire Profilometry