In this report, lens testing method for small lenses is discussed. Cylindrical or aspherical lenses are included to the scope
of this report in addition to spherical lenses. A shearing interferometer is applied for the measurement. That consists of a
plane parallel plate for inducing lateral shear for the test beam. This method is robust to disturbances because it is a
common path interferometry. Moreover it is not necessary to prepare reference lens. For these reasons it can be said that
this method is practical and is good for using at actual factories.
Phase difference amplification is a technique used to produce a fringe contour map in which the optical path difference between one fringe and the next is a fraction of a wavelength. To ensure high accuracy of the technique, it is usually necessary to generate interference between the high-order diffracted beam and its conjugate beam by means of a holographic recording material that provides sufficiently large nonlinearity to record the original fringe pattern from the test object. This paper shows that not only the nonlinearity of the recording material, but also multiple-beam interference, can be used to produce high-order diffracted beams. A Tolansky-type multiple-beam interferometer has been used in conjunction with an optically addressed liquid-crystal spatial light modulator to set up a system that functions in near real time and provides high accuracy.
Pupil filters can be used to overcome the limits in axial resolution imposed by diffraction in imaging systems. Axial behavior of filters is important for depth resolution in confocal microscopy. Phase filters have the advantage of improved efficiency by virtue of allowing more light to be transmitted, reduced tolerance errors, and in some case increased super resolving performance. In this paper we present a theoretical investigation of phase only filters. In addition, we describe the generation of a phase only filter from an amplitude filter using an optically-addressable liquid crystal spatial light modulator (LCSLM).
This paper reports on the imaging of a phase object using a differentiation filter. The differentiation filter consists of a photographic recording on a film where the amplitude transmittance changes gradually in a continuous manner. The filter is placed in the Fourier plane of a lens, and the differentiation image is taken by a CCD camera. This technique is applicable for objects with wide range of phase variations. A computer was used for image integration and to construct the 3D image. We have presented experimental results for a wedged phase object.
In this paper, we report a variable shearing Michelson interferometer using a converging beam. The beam divider was achieved by sandwiching a partially reflecting film between two identical plane parallel plate. The angle of incidence of the beam divider is adjusted smaller than 22.5 in order to keep the size of the beam divider reasonably small. The variable shear is achieved by rotating the beam divider.
Phase difference amplification is a technique to produce a contour map of an object in which the optical path difference corresponding to one fringe equals a small fraction of the wavelength of light. In this paper we report a method for phase difference amplification using multiple beam interference in conjunction with an optically addressed liquid crystal spatial light modulator. This interferometer operates in near real time and is ten times more sensitive than a conventional interferometer.
We describe an interferometric method for phase difference amplification in near real-time using an optically addressed liquid crystal spatial light modulator (LCSLM). The LCSLM has a rise time of 30ms and a decay time of 40ms, a resolution of 50 lp/mm, and a diffraction efficiency of 30%. The interference fringes obtained by a Michelson interferometer serve as input into the write side of the LCSLM and two beams are used to illuminate the read side. The nonlinearity of the LCSLM recording material produces the high-order diffracted beams. The nth and -nth order diffracted beams interfere with each other and the phase difference amplification is carried out in near real-time. We have demonstrated that it is possble to achieve phase difference amplification by a factor of 6 using phase stepping methods.
Straightness measurement is a very important technique in the field of mechanical engineering. A particular application would be very high accuracy machining on a diamond turning lathe. In this paper a novel optical method for measuring straightness of motion using reflection confocal optics is proposed. The advantage of this method in comparison with the transmission optical systems used by Burch and Williams is that the lateral displacements in the direction of the two axes perpendicular to the optical axis, and the rotation angles around all three axes, can be measured simultaneously. This can be very useful for straightness measurement. Also, reflection optical systems are more compact in length.
Applications of ordinary two-beam shearing interferometry to (1) aberration measurements of an optical system, (2) aberration correction of an optical system, and of Multiple Beam Shearing Interferometry (MBSI), (3) beam collimation, (4) focal length measurements, and (5) a position magnifying sensor, are described. For two-beam shearing interferometry, a holographic shearing interferometer with two separated three-beam holograms, is used. For MBSI, a shear plate with two flat surfaces of glass, wedged at a small angle and coated to obtain high reflectivity, is used. Theoretical and experimental results are presented for both situations.
This paper describes the application of Multiple Beam Shearing Interferometry (MBSI) to beam collimation. To realize MBSI, a plate with two optically flat surfaces, wedged slightly in thickness at an angle of 2.7 arc seconds and coated with silver is used. A high reflecting coating, in our case with 90% reflectance, is necessary to ensure that multiple beams occur resulting in sharp fringes for the transmitted light. Without the high reflecting coating the transmittance level is unsuitable for beam collimation. The small wedge angle is necessary for high accuracy. When a collimated beam is incident on the plate a sharp horizontal fringe line is observed because of the wedge in the plate. When the beam is not collimated the effect of the wedge and shear of the wavefront results in oblique fringe lines. In this paper, theoretical calculations, sensitivity of collimation and experimental results are discussed.
Scalar and resonance domain diffractive optical elements are proposed for use within high power laser systems. Resonance domain elements are described for beam deflection and polarization selection. Scalar domain elements for harmonic separation filtering and beam shaping in the near- and far- fields are also described. Experimental results are presented for far-field beam shaping and harmonic separation filtering elements.
A new method for measuring the straightness of travel of a moving table is described. The method uses two conjugate beams diffracted from a holographic grating that is mounted on the moving table. The intensity of two-beam interference is measured and the transverse displacement of the table is calculated from the change in intensity. The system is theoretically capable of measuring the transverse displacement to nanometer-order accuracy. Experimentally, a transverse displacement measurement with an accuracy of 0.12 μm was obtained over a staged travel of 100 mm.
A novel optical signal processor has been developed for analyzing laser Doppler velocimeter output signals. Optical Fourier transform techniques are used to determine the spectrum of the laser Doppler signals, with a liquid crystal spatial light modulator used as the input device to the optical system. The optical Fourier transform is one dimensional, performed by an anamorphic lens system that performs a Fourier transform in the horizontal direction of the input plane while imaging in the vertical direction. The system is therefore capable of simultaneously analyzing multiple laser Doppler input signals. The capabilities of the system are demonstrated using both synthetic computer-generated input signals and "real" input data obtained from a laser Doppler velocimeter.
A high-resolution laser Doppler velocimeter with small measurement volume is described. This instrument uses a novel frequency shifter incorporating a moving glass prism that gives stable frequency shifts up to 7 kHz and determines the velocity measurement range, which is 0.1 to 7 mm/s. The instrument has been used to measure blood flow velocities in microvessels and results are presented that demonstrate the capabilities of the system.
A simple optoelectronic system for high-speed determination of binary phase-only filters for use in an optical correlator is described. Filters determined using the system were implemented using a liquid crystal spatial light modulator in the Fourier plane of an optical correlator. Results demonstrating the operation of the system are presented.
Fringe counting techniques are often used in modern laser interferometers for measuring displacement. These interferometers are essentially integrating devices, where the displacement is derived from an accumulated fringe count; that is, they measure travel rather than static displacement. If the interferometer optical paths are interrupted during a measurement cycle, the reference for the instrument is lost and accuracy suffers. In this paper, we describe a holographic technique whereby displacement is measured by analyzing a fringe pattern localized at infinity which is equivalent to Haidinger or Brewster fringes in conventional interferometry. The phase distribution of the fringe pattern is measured to high accuracy using phase-stepping interferometry, and then analyzed by computer. Using this technique, we were able to measure in plane displacements with an accuracy of about 0.2 micrometers , while the accuracy for out of plane displacements was about 2 micrometers .
A theoretical analysis of a joint transform correlator that uses a phase-only spatial light modulator to input joint transform plane intensity data into the second Fourier transform system is presented. It is shown that this correlator produces signals that differ from, but are related to, the mathematical correlation between the test and reference input images. An undesirable characteristic of the correlator is that the form of the output signals depends on both the intensity-to-phase transfer characteristic of the phase modulator and the intensities of the input images. However, apodization of the joint transform intensity distribution by the reciprocal of the intensity distribution of the reference image Fourier transform can overcome this problem, and results in a correlator with narrow matching output peaks and high discrimination, in which the autocorrelation peak can be eliminated. Theoretical results are demonstrated by computer simulation.
New methods to determine the central position of rotation of a rotating object using laser Doppler velocimetry (LDV) are described. The principle is based on the fact that the tangential velocity of the rotating object is proportional to the distance from the center of rotation and that it can be measured by LDV with a microscope optical system. To realize this principle, three methods (angular and tangential velocity method, multiple-point method, and two-point method) are proposed. In the third method, a holographic optical element was used to play the role of multiple beamsplitter and a lens to obtain a rigid and simple optical system. From experimental results, it has been indicated that the position of the center of rotation is determined with an accuracy of 1 to 2 μm by these methods.
An optical method for the precise measurement of the angular errors of a table
moving along a slideway is described. The system is arranged so that angular errors
of the table give rise to sideways shifts of a random wavefront generated by a
ground glass screen. The shifted wavefront is made to interfere with a
reconstruction of the original unshifted wavefront produced by a hologram, and the
angular errors determined from the interference fringes which appear. This technique
has several advantages over usual autocollimator methods.
**Fuji Photo Optical Co. Limited Ooiniya-shi Saitama-ken Japan A new type of shearing interferometer has been developed in which sharp multiple beam interference fringes which directly represent the lateral aberration of the lens under test are produced holographically. 1 .
An interferometer for the precise measurement of rough surface deformation is described. The interferometer uses a liquid crystal phase only SLM controlled by computer in place of the usual hologram. The panel acts as a kinoform which phase modulates light scattered from the test object. Digital phase shifting techniques are used to measure both the initial phase distribution of light from the object and the phase of the interference fringes which appear when it is stressed. Surface deformations may be measured with a resolution of about 1/30 wavelength. 1 .
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