Linglin Zhu

Simultaneous measurement of retardance and fast axis angle of a quarter-wave plate using one photoelastic modulator

A method for simultaneous measurement of the retardance and the fast axis angle of quarter-wave plate using one photoelastic modulator is presented. A laser beam passes through a polarizer, a photoelastic modulator, the quarter-wave plate to be measured, and an analyzer to be detected. Before and after the quarter-wave plate is rotated 45° at any initial fast axis direction, two detection signals are obtained to resolve simultaneously the retardance and the fast axis angle. In experiments, a quarter-wave plate was measured with fast axis angles from -89° to 90°. The average and the standard deviation of the retardances at different fast axis directions are respectively 89.50° and 0.17°. The maximum measurement deviation of the fast axis angle is 0.5°. The usefulness of the method is verified.

Lateral shearing interferometer with variable shearing for measurement of a small beam

A lateral shearing interferometer with variable shearing for measurement of a small beam is proposed. The interferometer is composed of a polarization beam splitter, a thick birefringent plate, a quarter-wave plate, a mirror, and an image sensor. The shearing amount can be tiny by using the thick birefringent plate as the shear generator. The shearing amount of the interferometer can be continuously adjusted by rotating the thick birefringent plate, and 2D interferograms can be obtained by rotating the thick birefringent plate along the mutually perpendicular directions. The optical path difference is compensated with a double lateral shearing by using a quarter-wave plate and a mirror. The interferometer is verified by simulation and experiment; the experiment result is well coincident with the simulation result. The usefulness of the interferometer is verified.

Real-time measurement of retardation and fast axis azimuth for wave plates

Real-time measurement of retardation and fast axis azimuth of wave plates is proposed. The light emitted from the laser passes through a circular polarizer and the sample successively. Then the beam is diffracted to three sub-beams by a grating. One sub-beam passes through a standard quarter-wave plate and then is split and analyzed by a Wollaston prism. The other two sub-beams are all directly split and analyzed by Wollaston prisms. Six intensities are simultaneously detected to calculate the retardation and the fast axis azimuth. Experiments show that for the quarter-wave plate the average and standard deviation of the retardation are 89.78° and 0.14°, respectively, and the maximum deviation of the fast axis azimuth is 0.6°; for the eighth-wave plate, the average and standard deviation of the retardation are 45.15° and 0.15°, respectively, and the maximum deviation of the fast axis azimuth is 0.53.

Polarization phase shifting lateral shearing interferometer

A polarization phase shifting lateral shearing interferometer based on a polarization beam splitting plate(PBSP) is proposed. The front surface of the PBSP is coated with polarization beam splitting film and its back surface is coated with total reflection film. The beam to be tested is split by the PBSP with an incidence angle of 45° and divided into two mutually perpendicular linearly polarization beams. Phase shifting can be introduced to the interferometer when the PBSP is combined with a polarzation temporal or spatial phase shifter. A polarizaiton temporal phase shifting lateral shearing interferometer system is built up both with the ASAP software and the experiments. The usefulness of the interferometer is verified.

Resolution analysis method of retardance measurement instrument

The wave plate is an indispensable optical element for transforming polarization state in various optical fields. In the retarder’s applications, precise measurement of the retardance is necessary. However, there is no common and effective way to analyze resolution of the retardance measuring instrument. For ensuring the retardance measurement accuracy, an analysis method involving a wedge wave plate with a tiny angle between two planes is proposed to characterize the resolution. The retardance of the wedge wave plate varies linearly and slightly due to its linear and diminutive variation of thickness. The diminutive variation of retardance versus displacement can be measured when the instrument has enough resolution. And the instrument demonstrates higher resolution when it can measure smaller retardance variation. In the experiment, a wedge wave plate is mounted on a two dimensions stage and its one surface is normal to the detecting light of the instrument. And then the retardance is measured along one certain direction and the results are fitted linearly. The method can be used to evaluate the resolution differences of retardance measurement instruments. The gained resolution of both two instruments is superior to 0.1nm. Through several experiments, it can be demonstrated that the proposed analysis method has the advantages of easy operation, high efficiency and simple configuration.

Simple phase shifting lateral shearing interferometer based on a thick birefringent plate

A simple phase shifting lateral shearing interferometer based on a thick birefringent plate is proposed. The interferometer is composed of a thick birefringent plate and a polarizer. The thick birefringent plate works as the shear generator as well as the phase shifter. The optical path difference and shearing amount between the two sub-beams emerging from the thick birefringent plate change depending on the incident angle. For incident angles in a certain range, the shearing amount stays almost constant while the optical path difference varies linearly. Thus phase shifting can be obtained by rotating the thick birefringent plate. It is a very simple structure for the testing of a small beam, and equidistant phase shifting can be obtained by equal incident angle variation. The validity of the interferometer is verified by both simulation and experiment.

Design and simulation of illuminator with micro scanning slit array for NA 0.75 lithography system

An illuminator with a micro scanning slit array for NA 0.75 lithography system has been proposed in this paper. In this illuminator, the beam is shaped by a diffractive optical element (DOE), a zoom and axicon lenses. The beam is homogenized by a micro intergrator rod array. The micro scanning slit array is used to substitute for the traditional internal rema. A micro lens array and a condenser image the micro scanning slit array onto the mask. This illuminator needs no illumination lens group and reduces the effect of the vibration introduced by the internal rema. The illuminator is designed and simulated. The result shows that the illuminating field on the mask has good uniformity and trapezoidal distribution along the scanning direction. The feasibility of the illuminator is verified.

Real-time Measurement of Full Field Retardation near Quarter Wavelength

A real-time method to measure full field retardation near quarter wavelength is proposed. The circularly polarized beam passes through a sample with a large aperture. The measuring beam then goes through a quarter-wave plate and is then split by a Wollaston prism. An image with two sub-images is then detected by a high-speed image sensor. The full field retardation near quarter wavelength can be obtained in real time by processing the image. The measured retardation is independent of the fast axis angle of the sample and the fluctuation of the initial intensity. In experiments, a wedge waveplate is measured with different fast axis angle and initial intensity, and the full field retardations are acquired. The maximum and standard deviation of the full field retardation is 1.5° and 0.4°. The validity of the method is verified.

Simultaneous phase-shifting Fizeau interferometer based on birefringent thin film and Dammann grating

A simultaneous phase-shifting Fizeau interferometer based on birefringent thin film and Dammann grating is presented. The circularly polarized laser is reflected by the reference plate to form the reference beam and transmitted from the reference plate with the birefringent thin film to form the test beam. The test beam is reflected by the test surface and transmitted from the reference plate again. Its rotation direction is reversed. The orthogonally circularly polarized reference and test beams are obtained. A Dammann grating and an analyzer array are used to achieve simultaneous phase shift. This interferometer can reduce the effect of residual birefringence to increases the measurement accuracy. It is strictly common-path simultaneous phase-shifting Fizeau interferometer with simple structure and easy operation. In experiments, a wedge plate was measured and its simultaneous phase-shifting interferograms were obtained. With these results, the feasibility of the interferometer is verified.