M2 Mirror Research Articles

Multiple pass laser interferometer

The multiple pass laser interferometer is an instrument made possible because of the extreme temporal coherence of gas lasers. The optical schematic is shown for a system with input and output plane waves which can be used to describe the basic principle and characteristics of this class of interferometers. A laser beam, adjusted for uniphase operation (TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> mode), passes through a collimator which adjusts the beam to the required size. Energy in the beam passes through high reflectance mirror M1. Two telescope systems situated between mirrors M1 and M2, image the two mirrors in coincidence at the object plane (entrance pupils of the telescopes). Beam energy leaves the system through M2 where "read-out" optics image the surface of M1 for viewing.

LUMINANCE DISCRIMINATION OF BRIEF FLASHES UNDER VARIOUS CONDITIONS OF ADAPTATION.

J. Physiol. (1965), 176, pp. 294-310 With 6 text-figures Printed in Great Britain LUMINANCE DISCRIMINATION OF BRIEF FLASHES UNDER VARIOUS CONDITIONS OF ADAPTATION BY T. N. CORNSWEET AND H. M. PINSKER From the Department of Psychology, University of California, Berkeley, U.S.A. (Received 25 May 1964) Weber's law states that the just-noticeable change in luminance is a fixed fraction of the base luminance. The classic studies of luminance discrimination have suggested that Weber's law holds only as a rough approximation over an intermediate range of luminances, and clearly breaks down at both low and high luminances (e.g. Barlow, 1957; Pirenne, 1962). However, most of these studies have been conducted under con- ditions that are somewhat complicated relative to our present under- standing of visual processes. We shall argue that luminance discrimination data to be presented here have been collected under conditions easier to interpret in terms of photochemical and neural processes, as well as signal detection theory. Under these simplified conditions, Weber's law is shown to hold exactly over the entire range of luminances from just above absolute threshold to at least five log units above absolute threshold. METHODS Apparatus. A schematic diagram of the apparatus is shown in Fig. 1. The source was an automobile tail light bulb run from a constant voltage d.c. power supply. Its radiance was constantly monitored by a photocell, and any changes in radiance were compensated for by adjustments in the current through the bulb. Lens L1 formed an image of the filament in the plane of the rotating disk shutter, and lens L2 then collimated the rays. The rays that passed through the beamsplltters BS1 and BS2 formed the main path, and fell upon an opaque stop S2, in which two holes had been placed one above the other. This stop deter- mined the stimulus configuration as it appeared to the observer in Maxwellian view (see inset, Fig. 1). The stimulus disks fell upon an area of the retina containing both rods and cones. Lens L3 was at its focal distance from 82 and from the pupil of the observer's eye, and therefore collimated the rays from the plane of S2 and formed a filament image in the plane of the pupil. This filament image was 2 mm in diameter, and thus changes in the diameter of the observer's pupil did not appreciably change the retinal illuminance. The rays that were reflected from BS1 and from mirrors M1 and M2 formed the side path, and passed through a special stop S, before being recombined with the main path by BS2. SI consisted of two vanes mounted on a shaft that could be rotated silently about a vertical axis (see inset, Fig. 1). The filament image was small enough, and the rays were well enough collimated that each of the vanes completely blocked the light from the side path at one of the holes in stop S9 and did not at all block the light at the other hole. Thus, by rotating S1,

Measurement of standard base line with the Väisälä light-interference comparator

The Vaisala comparator. Dr. Y. Vaisala presented his new method of measuring long distances with light interference 36 years ago [Vaisala, 1923], and the instrument was fully developed by 1929. Measurements of up to 200 meters succeeded with an accuracy of 10−7. The principle of the Vaisala comparator can be seen from Figure 1. White light from the lamp L is made parallel by a collimator lens C. The beam is divided at mirror M2 into two. While one beam passes through the hole of Mirror M2 to the middle point of mirror M8, where it is reflected back through the other hole in mirror M2, the other beam is reflected a certain number of times between the mirrors M1 and M2. The two light beams meet in the focal plane of the observation telescope T. If the paths traveled by the two beams are equal, the diffraction interference lines appear in the image J. If monochromatic light is used the interference can be seen though the difference in length of the paths traveled by the beams is many millimeters, but in white light the lines disappear when the difference is but a few light wavelengths, as a result of the different diffraction of different colors. On the basis of symmetry of the diffraction interference lines the equality of the light paths can be observed to an accuracy of one light wave.

F S型ヒステログラフによるヂュラルミン及びNi-Cr-W鋼の捩り疲勞線圖の測定

F. S. (Fixed Stress) Typed Hysterograph is a torsion fatigue testing machine newly designed by the present writer. It is designed to be measurable the stress-strain diagram of the test piece which is stressed and vibrated by the speed of n=1, 900 rev/min. The mechanism of the hysterograph is very simple as shown in Fig. 1; it composes of the two plane mirrors m1 & m2 inclined both 45° to the axis and to each other. A point light reflected twice by the mirrors, describes on a plate glass the hysteresis loop of the test piece. The change in hysteresis loop of the test piece in the course of fatigue test is able to measure by this hysterograph. The accuracy of this apparatus is as follows: the hysteresis loop begins to appear when the plastic angle of twist θ=1' is introduced in the stress cycle. The mean stress τm=(τ0+τu)/2 is applicable by this machine besides the ordinary vibration ±τ stress. Duralumin, quenched and annealed, and Ni-Cr-W steel were tested. The results are shown in the fatigue diagrams in Figs. 6 and 12. Figs. 7 and 8 show the process of change of the hysteresis loops of duralumin, in which case hysteresis losses increase by fatigue. But Ni-Cr-W steel by this test fatigues and breaks under no hysteresis losses, as shown in Fig. 11. In the Ni-Cr-W steel, the test piece yields some permanent set θset, even in the fatigue limit, when the upperlimit-stress τ0 overcomes the elastic limit, in the case of mean stress applied. Fig. 16 shows the relation of permanent set between fatigue tests and static test. By these tests it is concluded that the θset of fatigue test is about half of the static. The fatigue limit, hysteresis loop and permanent set are measurable by our hysterograph.