ABSTRACT
This paper presents a fiber-based chromatic dispersion probe for the simultaneous measurement of dual-axis absolute and relative displacement with nanometric resolutions. The proposed chromatic dispersion probe is based on optical dispersion. In the probe, the employed light beam is split into two sub-beams, and then the two sub-beams are made to pass through two optical paths with different optical settings where two identical single-mode fiber detectors are located at different defocused positions of the respective dispersive lenses. In this way, two spectral signals can be obtained to indicate the absolute displacement of each of the dual-axes. A signal processing algorithm is proposed to generate a normalized output wavelength that indicates the relative displacement of the dual-axis. With the proposed chromatic dispersion probe, the absolute and relative displacement measurements of the dual-axis can be realized simultaneously. Theoretical and experimental investigations reveal that the developed chromatic dispersion probe realizes an absolute measurement range and a measurement resolution of approximately 180 µm and 50 nm, respectively, for each axis. Moreover, a relative displacement measurement range and a measurement resolution of about 240 µm and 100 nm, respectively, are achieved for the dual-axis.
ABSTRACT
We studied a multi-metallic microscale 3D printing based on the meniscus-confined electrodeposition (MCED). The composition of Cu/Pt alloys can be controlled by applying different bias voltages to the CuSO4/H2PtCl4 mixed solution in MCED. We find that a double-barrel system had higher Cu/Pt alloy purity (maximum 100% Cu or maximum 80% Pt) than a single-barrel system. A Λ-shaped microstructure was printed to verify the capability to multi-metal microstructures in a single printing process.
ABSTRACT
In this paper, a fiber-based chromatic dispersion probe for simultaneous measurement of X-axis and Z-axis displacements with nanometric resolutions by using the full width at half maxima (FWHM) of the detected spectral signal has been proposed and demonstrated. For X-axis, FWHM is employed for indicating the X-axis displacement based on the fact that the FWHM remains almost constant with the varying Z-axis displacement of the fiber detector and shows a linear relationship with the X-axis displacement within a specific Z-axis displacement range. For the Z-axis, the linear relationship between the centroid wavelength λ of the detected spectral signal and the Z-axis displacement is employed for indicating the Z-axis displacement based on the fact that the sensitivity (slope of the λ-Z curve) is also linear with X-axis displacement within a certain X-axis displacement range. Theoretical and experimental investigations have verified the feasibility of the proposed chromatic dispersion probe, which yields X- and Z-axis measurement ranges of 2.3 µm and 15 µm and X- and Z-axis measurement resolutions of better than 25 nm and 50 nm, respectively. Experiments were further performed to evaluate the basic performance of the prototype probe and the maximum measurement errors were less than 10 nm and 60 nm for X- and Z-axis displacements, respectively.
ABSTRACT
In this paper a new concept of a liquid-surface-based three-axis inclination sensor for evaluation of angular error motion of a precision linear slide, which is often used in the field of precision engineering such as ultra-precision machine tools, coordinate measuring machines (CMMs) and so on, is proposed. In the liquid-surface-based three-axis inclination sensor, a reference float mounting a line scale grating having periodic line grating structures is made to float over a liquid surface, while its three-axis angular motion is measured by using an optical sensor head based on the three-axis laser autocollimation capable of measuring three-axis angular motion of the scale grating. As the first step of research, in this paper, theoretical analysis on the angular motion of the reference float about each axis has been carried out based on simplified kinematic models to evaluate the possibility of realizing the proposed concept of a three-axis inclination sensor. In addition, based on the theoretical analyses results, a prototype three-axis inclination sensor has been designed and developed. Through some basic experiments with the prototype, the possibility of simultaneous three-axis inclination measurement by the proposed concept has been verified.
ABSTRACT
A new method, in which the wavefronts of the zero-order and the positive and negative first-order diffracted beams from a planar scale grating in Littrow setup are analyzed by a Fizeau interferometer, is proposed to evaluate the Z-directional out-of-flatness as well as the X- and Y-directional pitch deviations of the planar scale grating over a large area. Meanwhile, the surface profile of the reference optical flat in the Fizeau interferometer can also be determined in a much simpler and more efficient approach than the commonly used liquid-flat reference and three-flat test calibration methods. Simulations are presented to verify the feasibility of the proposed method.
ABSTRACT
Polarization control is of vital importance in two-axis Lloyd's mirror interference lithography to achieve the preferred interference fringes. In this work, we first establish a three-dimensional polarization ray-tracing model to trace the evolution of polarization states of incident beams through the corner-cube-like interferometer unit of an orthogonal two-axis Lloyd's mirror interferometer. With the established model, we then derive the optimal combination of initial polarization directions of the incident beams according to the orthogonality of polarization states and the contrast of interference fringes. The comparison between the simulated and experimental interference fringes obtained under different combinations of initial polarization states of incident beams verify the feasibility of the established model and the achieved optimal polarization modulation.
ABSTRACT
A mode-locked laser autocollimator, in which a group of first-order diffracted beams from a grating reflector are detected by an autocollimation unit, has an expanded angle measurement range compared with a conventional autocollimator using a single-wavelength laser source. In this paper, a new optical frequency domain angle measurement method is proposed to increase the visibility of output signal of the mode-locked femtosecond laser autocollimator, which is limited by the overlap of the focused diffracted light spots. The output visibility of a prototype femtosecond laser autocollimator has been increased by the proposed method to approximately 100% over a large range of 21600 arc-seconds.
ABSTRACT
This paper presents a detailed analysis on the influence of misalignment errors of optical components in an orthogonal two-axis Lloyd's mirror interferometer, which can fabricate two-dimensional grating structures in a single exposure. In an ideal condition, defect-free two-dimensional grating structures can be fabricated by the interferometer. However, in a real case, visible stripes caused by misalignment errors of the optical components in the interferometer always appear on the fabricated grating structures. In this paper, theoretical analysis and experiments are carried out to analyze the influences of the misalignment errors of the optical components in the orthogonal two-axis Lloyd's mirror interferometer.
ABSTRACT
A mode-locked laser is employed as the light source of a laser autocollimator, instead of the conventionally employed single-wavelength laser, for an expanded range of tilt angle measurement. A group of the spatially separated diffracted beams from a diffraction grating are focused by a collimator objective to form an array of light spots on the focal plane of the collimator objective where a light position-sensing photodiode is located for detecting the linear displacement of the light spot array corresponding to the tilt angle of the reflector. A prototype mode-locked femtosecond laser autocollimator is designed and constructed for achieving a measurement range of 11000 arc-seconds.
ABSTRACT
An ultra-sensitive angle sensor employing single-cell photodiodes, which allows tighter focusing leading to a higher angular resolution better than 0.001 arc-second, has been designed based on laser autocollimation. Aiming to investigate the influences of spherical aberrations in the optical system on the sensor sensitivity, an optical model has been established based on wave optics. Computer simulation has been carried out by using the model, and its feasibility has been verified in experiments. In addition, a prototype optical angle sensor has been designed in a compact size of 100 mm × 150 mm, and its measurement resolution has been verified in experiments.
ABSTRACT
A compact but practical scanning tunneling microscope (STM) with high aspect ratio and high depth capability has been specially developed. Long range scanning mechanism with tilt-adjustment stage is adopted for the purpose of adjusting the probe-sample relative angle to compensate the non-parallel effects. A periodical trench microstructure with a pitch of 10 µm has been successfully imaged with a long scanning range up to 2.0 mm. More innovatively, a deep trench with depth and step height of 23.0 µm has also been successfully measured, and slope angle of the sidewall can approximately achieve 67°. The probe can continuously climb the high step and exploring the trench bottom without tip crashing. The new STM could perform long range measurement for the deep trench and high step surfaces without image distortion. It enables accurate measurement and quality control of periodical trench microstructures.
ABSTRACT
A prototype STM system with high aspect ratio measurement capability is developed to fulfill accurate profile measurement of a high step microstructure with 90° steep sidewall. Distinguished from the traditional STM, the new system consists of a long range piezoelectric (PZT) actuator with full stroke of 60 µm as Z-direction servo scanner, a specially customized high aspect ratio STM probe with effective tip length of 300 µm, and an X-Y motorized driven stage for planar scanning. A tilt stage is used to adjust the probe-sample relative angle to compensate the evitable non-parallel effects. Based on the new STM system, sample-tilt-scanning methodology is proposed for eliminating the scanning blind region between the probe and the microstructure. A high step microstructure with height of 23 µm, 90° steep sidewall and width of 50µm has been successfully measured. The slope angle of the sidewall has been achieved to be 85° and the step height at the rising edge and the trench depth at the falling edge are both measured to be 22.96 µm. The whole measuring process only spent less than 10 min. It provides an effective and nondestructive solution for the measurement of high step or deep trench microstructures. In addition, this work also opens the way for further study on sidewall roughness and the tip-sample interaction at the edge of the sidewall, which are highly valuable for fabrication and quality control of high step microstructures.
ABSTRACT
Using custom made experimental apparatus, the art of electrochemical etching was systematically studied for fabricating micro/nano tungsten probes with controllable tip profiles of exponential, conical, multidiameter, and calabashlike shapes. The characteristic parameters of probe including length, aspect ratio, and tip apex radius could also be well defined. By combining of static and dynamic etching, the conical-shape probe with length up to several millimeters, controllable tip apex radius, and cone angle could be fabricated. In addition, by continuously lifting the tungsten wire up during the electrochemical etching with different speeds and distances, the multidiameter shape probe could be fabricated. Finally by controlling the anodic flow, the multiple "neck-in" could be realized creating a calabashlike probe. The aspect ratio of probes depends on (i) the effective contact time between the surrounding electrolyte and the wire, (ii) the neck-in position of immersed tungsten wire. Under the optimized etching parameters, tungsten probes with a controllable aspect ratio from 20:1 to 450:1, apex radius less than 20 nm, and cone angle smaller than 3° could be achieved. The technique is well suited for the tungsten probe fabrication with a stabilized stylus contour, ultra-sharp apex radius, and high production reproducibility. The art for preparing microprobes will facilitate the application of such microprobes in diverse fields such as dip-pen nanolithography, scanning probe microscopy, micromachining, and biological cellular studies.
