Dacheng Li

High-accuracy long distance alignment using single-mode optical fiber and phase plate

Abstract A long distance alignment technique is developed using the combination of a single-mode optical fiber and a phase plate. The characteristics of the diffraction pattern of a Gaussian beam passing through a π step phase plate are analyzed theoretically. The feasibility of the method is validated in theory and with computer-simulation, and the factors affecting the alignment precision are discussed. The reliability of the alignment technique is demonstrated when it is used in the measurement of the straightness of a 12 m -track, in which measured results using the new technique coincide very well with those using an HP5528 dual frequency laser interferometer.

Practical common-path heterodyne surface profiling interferometer with automatic focusing

Abstract In modern semiconductor and optics industries, there is a strong demand for a highly sensitive and non-contact surface profilometer. This paper describes a practical heterodyne surface profiling interferometer for on-line non-contact measurement which has been developed recently. The essential feature of the profilometer is a newly designed common-path configuration to minimize the effects caused by vibration, air turbulence and other environmental variations. A single-mode frequency-stabilized laser diode ( 780 nm ) serves as the light source to make the whole system compact (total volume 250L×200W×100H mm ). A powerful signal processing scheme is also developed, which includes three parts: automatic voltage control, phase measurement with wide range and automatic focusing control. All these make the repeatability and stability of the profiling interferometer greatly improved. The system has vertical resolution of 0.39 nm and lateral resolution of 0.73 μm . During approximately an hour, the stability is within 1.95 nm (3σ) .

CCD probe: application of linear array CCD in large-dimension measurement

A research on using linear array CCD detecting technique in measuring form and position errors of large scale dimension is described in this paper. The basic idea of this kind of measurement is that using a stable aligned laser beam incident on a 1D asymmetrical phase plate to form a black line as the reference of the beam, form and position datum lines and planes can be established through a scanner. A linear array CCD is used to measure deviation between the datum and the quantity be measured directly and absolutely. In the paper, we also discuss the reading error of the CCD probe caused by various factors in detail and introduce the CCD probe and its signal processing circuit. Some of experiment results and its application are shown.

Noncontact measuring profile of magnetic disk with optical methods

The paper discusses some optical methods of measuring the profile of disk non-contacting. Grazing incident interferometer, Color schieren, and Moire deflectometer. Especially in the paper a new measuring method and instrument is introduced which is a pointwise instrument with an optical probe. It can measure a global and local profile of a disk in tangential and radial direction at the same time, without sacrificing the measurement accuracy. The resolution of the probe is 0.3 nm, the instrument accuracy better than 0.04 micrometers , the dynamic range larger than 5 mm.

Fabrication and characterization of near-field optical fiber nanoprobes with high resolution and high transmission efficiency

As one of the key components in scanning near-field optical microscopes (SNOM), optical fiber probes can be fabricated by use of either laser-heated pulling or chemical etching. For high-resolution near-field imaging, the near-field optical signal is rapidly attenuated as the aperture of probes decreases. It is thus important to fabricate probes optimized for aperture size and optical transmission. We present a two step fabrication method of 50 - 70% reproducibility to obtain probes with high optical transmission efficiency as well as small tip diameters. First, optic fiber probes with the transitional taper in hyperbolic or parabolic shape are produced by use of the simple home-made device for heating- pulling. Then, a rapid chemical etching with 40% buffered hydrofluoric acid is used to sharpen the tip while keeping the taper shape and the conic angle unchanged. The method renders us to achieve probes with tip diameters in the range of 20 nm - 200 nm and the tape angle near the tip apex in the range of 20 degree(s) - 60 degree(s). Particularly, the length of the non- propagating evanescent wave modes region decreases greatly to tens of micrometers or even less. In order to test the achieved probes, we give the photon tunneling decay curve and scanning near-field optical image of holographic grating by use of PSTM mode and collection-mode SNOM, respectively. In addition, an approach curve of shear force with hyperbolic probe is shown to verify its applicability to sample-tip distance regulation on basis of the principle of shear-force.

Application of laser diode fiber alignment in measuring large-scale perpendicularity and parallelism

In this paper, a system for measuring perpendicularity and parallelism derivation using a laser diode fiber aligned beam and CCD detector is described. A stable aligned laser diode beam is used to form datum planes by rotating scanner equipped with pentagonal prism. Using a linear array CCD detector as the sensing probe, the system can detect the deviation of height related to the datum plane directly and absolutely. The experiment result is shown in the paper.

Surface profiling method for large aspheres: diffraction image-forming approach

Investigation of surface profiling method for large aspheres becomes more and more important and imperative with the great development of the synchrotron radiaiton facility (SRF), since the latter puts greater demands on surface quality, shape and figure parameters of the optical elements used in itself. MEanwhile, things became more difficult because of the unique characteristics of the optics used in SRF. As a result, novel surface measurement methods and systems have to be developed to cope with such problems.

Practical heterodyne surface profiling interferometer with automatic focusing

In modern semiconductor and optics industries, there is a strong demand for a highly sensitive and non-contact surface profilometer. This paper describes an optical heterodyne surface profiling interferometer for on-line non-contact measurement with automatic focusing which has been developed recently. The essential feature of the profilometer is a newly designed common-path configuration to minimizes the effects caused by vibration, air turbulence and other environmental variations. A single-mode frequency-stabilized laser diode (780 nm) serves as the light source to make the whole system compact (total volume 250L x 200W x 100Dmm). A powerful signal processing scheme is also developed, which includes three parts: automatic voltage control, phase measurement and automatic focusing control. All these make the repeatability and stability of the profiling interferometer greatly improved. The system has vertical resolution of 0.39 nm and lateral resolution of 0.73 micrometer. During approximate an hour, the stability is within 1.95 nm (3σ).

Novel nonoptical method of tip-sample distance regulation based on shear force in scanning near-field optical microscopy

In this paper a novel method for tip-sample distance regulation based on shear-force is presented. A semicircular piezo-electric ceramic plate is used as the excitation as well as detection element, the electrode of which is divided into three segments. The first segment is excited by a generator and the second one is used to fix the fiber tip. The induced voltage on the third segment is used to detect the tip-sample distance. The approach curves show that it is very sensitive and the tip-sample distance can be regulated below 5 nm. Experimental results indicate that when the sample is covered with liquid the approach curve is different from that in the air. In addition, during experiments we found that at some resonant frequency the approach curve is different from the conventional shape. The phenomenon, if proved reliable, can be used to realize automatic and rapid tip-sample approach as well as small-scale distance regulation.

Experimental research on vibration characteristics of four-segment scanning PZT tube using a laser vibrometer

A four-segment scanning PZT tube is characterized using a laser vibration measurement system. Several periods of quasi-decay mechanical oscillation are observed in the experiments when the scanning tube is driven by series of step signals. The oscillation frequency is much lower than the lowest resonant frequency calculated base on the reported formula. The mechanism of the oscillation is analyzed. The possible reasons include mechanical inertial or damping, driving power supply impedance properties and the base vibration are discussed. The low resonant frequency of the scanning tube may be the result of its own complicated boundary conditions based on the experimental result of amplitude and frequency properties although there is a considerable difference between theoretical and experimental results. Some possible approaches to reduce or eliminate oscillation are proposed.