Method and apparatus for testing the deviation of the face of an object from a flat smooth surface using a laser beam having two plane-polarized components, one of a frequency greater than the other to produce a difference frequency with a phase to be used as a reference. The beam also is split into its two components which are directed onto spaced apart points on the face of the object. The object is rotated on an axis coincident with one component as a reference. The other component follows a circular track on the face of the object as the object is rotated. The two components are recombined after reflection to produce a difference frequency having a phase that is shifted in an amount that is proportional to the difference in path length as compared to the reference phase to produce an electrical output signal proportional to the deviation of the height of the surface along the circular track. The output signal is generated by means of a phase detector that includes a first photodetector in the path of the recombined components and a second photodetector in the path of the reference phase. The output signal is dependent on the phase difference of the two photodetector signals. A polarizer, a quarter-wave plate and a half-wave plate are in series in the path of the reference phase. Rotation of the half-wave plate can be used for phase adjustment over a full 360° range for initial calibration of the apparatus.

Laser heterodyne surface profiler

A polarization rotation compensator and an optical isolator using the same are described. The optical isolator comprises a first birefringent wedge plate; a polarization rotation compensator composed of a combination of a half-wave plate whose principal axis is inclined at an angle of θ/2 with respect to the plane of polarization of the incident light and a quarter-wave plate whose principal axis is inclined at an angle of θ with respect to the plane of polarization of the incident light; a Faraday rotator; and a second birefringent wedge plate; wherein the Faraday rotator, quarter wavelength plate, and half-wavelength plate are respectively arranged in the order of propagation of the backward light or of the forward light.

Polarization rotation compensator and optical isolator using the same

In a photomask inspecting method, a photomask is inspected on the basis of the difference between the polarized state of elliptical light produced upon superposition of two linearly polarized light beams having orthogonal polarization directions and passing through two different optical paths and the polarized state of elliptical light produced when two linearly polarized light beams are superposed on each other after a target portion of a photomask is set in the optical path of one of the linearly polarized light beams. A photomask inspecting apparatus is also disclosed.

Photomask inspecting method and apparatus

Elliptical light measuring method

It is shown that an interference-polarizing refractometric detector makes it possible to use microcolumn size-exclusion chromatography (MSEC) columns with inner diameters of 0.2 to 0.5 mm and ensures a detection limit (at a signal to noise ratio of 3) of 8 × 10−8 refractive index units.



Taking into account the above requirements, a micro-gel chromatograph with a refractometric (interference-polarizing) detector was developed. Teflon columns gave reproducibilities (the mean square deviation at the 95% confidence level) of retention times and signal amplitudes of 0.2% and 0.5%, respectively, which ensures reproducibilities of molecular weight determinations within about 2 to 4%. Examples of polymer and protein analyses carried out on this chromatograph are given. It is suggested that a micro-gel chromatograph can be developed for fused-silica capillary columns with inner diameters of 0.2 mm. This would permit analysis of approximately 10 pg of polymer.

Refractometric detector for a microcolumn high-performance size-exclusion and micro gel chromatograph

A method of measuring optical phase differences caused by the presence of optical path differences between two coherent light beams is reported. A polarization technique is used and the phase differences are detected as rotation angles of the plane of polarization. The sensitivity of the method is better than 10 -4 λ and the stability is 3 X 10 -4 λ per minute. These limitations result from thermal fluctuations of the order of 10 -3 °C. A higher sensitivity of about 10 -5 λ, or better, is expected if the effect due to thermal fluctuations can be reduced.

G. Yamamoto

Papers

Measurement of optical phase difference using a polarization technique