Chunyong Yin

DETERMINING THE RESIDUAL NONLINEARITY OF A HIGH-PRECISION HETERODYNE INTERFEROMETER

The comparison of two methods for determining the residual nonlinearity of the dual-frequency interferometer that has resolution of the order of a nanometer is presented. The first method estimates the maximum residual nonlinearity by determining the visibility of the measurement signal. This method has the advantages of easy operation and high resistance to environmental influence. The other method is high- precision calibration with another interferometer. To verify these two methods, a compact differential dual-frequency interferometer (DDFI) was set up and calibrated with a Fabry-Perot interferometer of China National Institute of Metrology (CNIM). The residual nonlinearity was estimated as 1.4 nm using the first method and 2 nm using the second. These two results fit well in spite of environmental influence.

Sensitivity enhanced roll angle measurement

A novel idea of utilizing a quarter-wave plate (QWP) to enhance the sensitivity of roll angle measurement is verified both theoretically and experimentally. The roll angle measurement is based on optical heterodyne phase detection and its sensitivity is enhanced by setting the polarizing angle, which produces elliptically polarized light. An experimental setup is described and the experimental results presented are considered with the theoretical predications. With this practical configuration, the resolution of roll angle is 0.6 arcsec.

Two dimensional automatic straightness measurements system based on optical activity

In this paper, the principle and diagram of the two-dimensional automatic straightness measurement system are introduced, an automatic readout method is described, and the calibration results are given. This system has been used in an industrial environment.

633-nm tunable external-cavity diode laser with an intracavity glass plate as the fine-tuning device

The application of beatwave Fabry-Perot interferometers (BFPIs) to nonlinearity error calibration is limited by the short tuning range of the slave He-Ne laser. In this paper, a 633-nm tunable externalcavity diode laser (ECL) is proposed as the slave laser of a BFPI. The ECL consists of an antireflection-coated quantum-well laser diode, a collimating lens, and a diffraction grating in Littrow configuration. In addition, an intracavity glass plate is adopted to provide cavity fine tuning, which makes the ECL more convenient, as it is easier to align the light in the cavity. At an optical length of 45 mm, a coarse-tuning range of 4 nm around 633 nm is obtained by rotating the grating. It is also demonstrated that this ECL can operate in a single-mode regime and can be continuously tuned over a frequency range of 1.8 GHz by tilting the intracavity glass plate.

Absolute length measurement using changeable synthetic wavelength chain

There has been much interest in use of a tunable diode laser for absolute distance interferometry. We report on a novel method?using changeable synthetic wavelength chain (CsWC) to measure absolute length?based on a tunable diode laser. During the measurement, the desired synthetic wavelengths are calculated according to the distance to be measured and the measurement uncertainty. Then by tuning the wavelength of the laser, the desired synthetic wavelength chain is created. In addition, a differential measurement setup, which consists of two dual-beam interferometers, is proposed to test the feasibility of the CSWC method. The experiment results demonstrate that the CSWC method can work effectively. Although under present conditions a measurement uncertainty of only 3 x 10-5 is achieved, it is sufficient to design a differential optical probe.

Phasemeter with external trigger applied to PZT-modulated interferometer

The heterodyne interferometric system based on phase measurement plays a significant role in modern metrology fields owing to its convenience of signal processing. In this paper, a phase measurement scheme to determine the fraction of the interference fringe modulated by a PZT in a differential single-frequency interferometer is investigated. To overcome the problem of phase jump and inhomogeneous period of the signal, a differential phase discrimination approach with an external trigger signal is presented. The phase measurement system is carried out using a field-programmable gate array (FPGA) device. It is testified by experiments that, over a frequency range of 300 Hz–10 kHz, the phase measurement system has a stability of ±0.015°; and a maximum error of ±0.07°.

Four-beam two-focus differential laser velocimetry system

A four-beam two-focus differential laser velocimetry system with an acousto-optic modulator, which is suitable for measuring solid deformation or movement at ultralow speed, is presented. The signal-to-noise ratio is good enough for phase discrimination, the frequency response range is 0 to 20 kHz, and the measurable velocity range is 0.001 m/s to 300 mm/s.

Nanometer indicating system based on surface plasmon resonance and its application in an interferometer

A novel method for nanometer indicating based on surface plasmon resonance (SPR) is introduced. A fiber probe with a semispherical end approaching a coated Kretschmann (1971) prism is equivalent to a four-layer prism-metal-air-fiber structure. Theoretical analysis shows that the transmitted intensity coupling into the fiber probe changes as the thickness of the air gap varies. Owing to this property, a noncontact nanometer indicating system can be built. The SpR nanometer indicator can be integrated into a heterodyne interferometer to reduce drift. Askew retroreflector is designed so that the incident angle of its first reflection surface is equal to the resonance angle of SPR to implement the integration SPR indicating experiments show that a maximum deviation of 12 nm and a resolution of 0.1 nm/nV can be achieved. Moreover, the uncertainty of an integrated interferometer whose optical path difference is 300 mm is reduced from 60 to 10 nm when air-conditioning is 0.5 °C/h.

New advance in laser interferometry

Modern technology development requires interferometry of uttermost quality, which is characterized as high measurement speed, large measurement range, low drift and super-high resolution, good accuracy and efficiency. Firstly this paper introduces a frequency stabilized laser with 5MHz beat frequency which is based on the bi-reflection principle, and a high measurement speed dual-frequency laser interferometer whose allowable displacement velocity is over 1m/s using this kind of laser. Secondly it introduces a transverse Zeeman frequency stabilized laser with 300KHz beat frequency and its applications in nanometer measurement, collimation, coaxiality measurement, roll angle measurement and biomembrane measurement. Thirdly a tunable 633nm external-cavity diode laser (ECL) interferometer is presented.

An improved interferometry for laser tracking system

Summary form only given. Laser tracking systems (LTS) include single-beam and multiple-beam tracking system. A multiple-beam tracking system based on the trilateration is treated as with high accuracy. At least four interferometers are needed for 3D measurement and self-calibration, which results in high cost. Here we introduce an improved interferometry, in which three interferometers are linked by only one laser source and one Filed Programmable Gate Array (FPGA) card for numbering.