P. Hariharan

Triangular Path Macro-Interferometer

A triangular path shearing interferometer is described which can be used for the examination of large transparent objects. It has the advantage that it can be conveniently adapted to an existing schlieren system, affording the possibility of quantitative measurements. The additional optical elements required are only of comparatively small aperture and are therefore quite inexpensive.

Double-Passed Two-Beam Interferometers

When the rays emerging from a conventional two-beam interferometer are reflected back through the instrument, fringes similar in appearance and behavior to three-beam fringes are obtained. Extremely accurate measurements are possible with the help of these fringes, using a photometric setting criterion. The mode of formation of these fringes, as well as the theoretical intensity distribution in them under various conditions, are discussed.

Double-Passed Fabry-Perot Interferometer

Increased contrast and resolution can be obtained with the Fabry-Perot interferometer by reflecting the transmitted beams back through the instrument. An arrangement for this purpose is described in which the double-passed interference pattern is isolated by means of a simple polarizing system.

New Gauge Interferometer

An interferometer for the absolute measurement of the length of end standards is described in which the optical path difference introduced between the interfering beams is only half the length of the gauge. This permits the direct measurement of gauge blocks up to 1 meter long with the isotope sources currently available. Other advantages of the instrument are its relatively compact layout and simplicity of operation.

Fringes of Equal Inclination in the Double-Passed Michelson Interferometer

The formation of fringes of equal inclination in the double-passed Michelson interferometer is discussed and a theoretical expression is obtained for the intensity distribution in the interference pattern. It is shown that the intensity distribution in these fringes undergoes a periodic modulation as the path difference in the interferometer is varied. Accurate measurements are possible with these fringes using a photometric setting criterion.

The Double-Passed Fizeau Interferometer

When the transmitted beams from a Fizeau interferometer are reflected back through the instrument, a new system of fringes is observed in which the intensity distribution undergoes a periodic modulation as the separation of the plates is changed. Accurate measurements are possible with the help of these fringes, using a photometric setting criterion. The mode of formation of these fringes, as well as the theoretical intensity distribution in them under various conditions, is discussed.

Double-Passed Two-Beam Interferometers. II. Effects of Specimen Absorption and Finite Path Difference

Expressions are obtained in this paper for the irradiance distribution in the fringe systems in double-passed Jamin and Twyman-Green interferometers with an absorbing specimen in one of the paths. Expressions are also obtained in the latter case for the effects of the spectral coherence of the source, the degree of collimation of the incident beam, and the wedge angle of the virtual air film in which interference takes place, on the irradiance distribution in the fringe pattern obtained with an appreciable optical path difference. The theoretical loss in setting accuracy in the various cases, as well as the corrections to be applied to obtain the true optical path difference are evaluated.

Double-Passed Fizeau Interferometer. II. Fringe Systems Formed by the Reflected Beams

The theoretical intensity distribution in the fringes formed when the reflected beams from a Fizeau interferometer are reflected back through the instrument is obtained. It is shown that, under certain conditions, the intensity distribution in these fringes exhibits a periodic modulation as the separation of the plates is changed, so that they can also be used for very accurate measurements.

Simple Logarithmic Ratio-Recording Spectrophotometer Attachment

A double-beam system is described which uses a single photomultiplier tube operated in a logarithmic difference circuit to give direct readings of log transmittance. The circuit compensates for changes in the incident energy as well as variations in the spectral sensitivity of the photocathode, over a very wide range.The attachment can be used to convert any good monochromator into a recording spectrophotometer, and permits measurements of spectral densities as high as 3 with an accuracy better than 0.02 density unit.