High-resolution Laser Interferometer Research Articles

Noise characterization in millimeter sized micromanipulation systems

Efficient and dexterous manipulation of very small (micrometer and millimeter sized) objects require the use of high precision micromanipulation systems. The accuracy of the positioning is nevertheless limited by the noise due to vibrations of the end effectors making it difficult to achieve precise micrometer and nanometer displacements to grip small objects. The purpose of this paper is to analyze the sources of noise and to take it into account in dynamic models of micromanipulation systems. Environmental noise is studied considering the following sources of noise: ground motion and acoustic noises. Each source of noise is characterized in different environmental conditions and a separate description of their effects is investigated on micromanipulation systems using millimeter sized cantilevers as end effectors. Then, using the finite difference method (FDM), a dynamic model taking into account studied noises is used. Ground motion is described as a disturbance transmitted by the clamping to the tip of the cantilever and acoustic noises as external uniform and orthogonal waves. For model validation, an experimental setup including cantilevers of different lengths is designed and a high resolution laser interferometer is used for vibration measurements. Results show that the model allows a physical interpretation about the sources of noise and vibrations in millimeter sized micromanipulation systems leading to new perspectives for high positioning accuracy in robotics micromanipulation through active noise control.

High-resolution parallel multipass laser interferometer with an interference fringe spacing of 15 nm

We present a high-resolution laser interferometer based on the parallel multipass configuration with a pair of right-angle prisms to increase the optical fringe subdivision order up to 21. In the experiment, a multipass homodyne Michelson interferometer (MHMI) with the fringe spacing of 15nm was demonstrated, resulting in the displacement measurement with a measurement resolution of 180pm limited by the sampling rate of the employed analog-to-digital converter. We show that the ultimate resolution of the demonstrated MHMI scales with 1/N and it is estimated to be 8.7pm for N=21.

Six-Axis Magnetic Levitation and Motion Control

This paper presents the development of a compact six-axis magnetic levitation stage, including the design and implementation of magnetic actuators, laser interferometer motion sensors, and motion controllers. The designed travel volume of the stage is 2times2times2 mm in translation and 4degtimes4degtimes4deg in rotation. A two-axis linear actuator, based on the magnetic Lorentz force law, was designed, and three two-axis actuators, equivalent to six single -axis actuators, were implemented to achieve six-axis actuation. A high-resolution laser interferometer measurement system was implemented and employed to measure the six-axis motion of the stage, facilitating real-time feedback control. Feedback linearization, based on rigid-body dynamics of the levitated stage, and force distribution were implemented in a computer-controlled architecture so as to establish a decoupled dynamics between the six computed inputs and the resulting six-axis motions. Constant gain controllers were then designed and implemented, according to the concept of loop shaping, for each of the six axes, and high positioning stability, 1.1 nm root mean square (RMS) for x and 0.74 nm RMS for y, has been achieved. Experimental results are presented to illustrate positioning stability, system linearity, dynamic response invariance, nano stepping, multiaxis contouring, and large rotational motion

Development, installation, and performance of the x-ray stepper JSAL 5C

We show the first results from a newly-operation advanced x-ray stepper, and describe an improved type of x-ray mask for use on it. The Mod 5C is the newest x-ray stepper developed by JMAR (JSAL Nanolithography). It is configured for installation at the Center for NanoTechnology (CNTech) on a synchrotron radiation port of the Aladdin storage ring. The alignment system is based on a new IBBI detection system with demonstrated subnanometer resolution. For this system, three microscopes are used for detecting the misalignment between wafer and mask marks with the error signal fed back in the mask positioning stage with the mask locked to the wafer stage through the use of a high-resolution laser interferometer. Both field-by-field and global alignment techniques are possible, and multiple wafer sizes can be used with a NIST format mask held in a kinematic mount, with a gap setting capable of adjustment between 2 and 50microns. A novel beam scanning system was installed to deliver a uniform exposure over a field of 35×35mm2 field. The high power from the storage ring allows exposure times in chemically amplified resists of 5–10s for the CNTech-designed beamline; shorter exposure times could be achieved with a refocusing beamline, and the stepper can be configured for an x-ray point source. To achieve sub-35nm resolution requires very small gaps. A new type of mask had to be developed, on the basis of the mesa mask originally developed at MIT. A very high flatness is required to maintain a parallel mask-wafer exposure environment. Currently, for low cost and easy manufacturing, we employ gold-plated absorber masks with a silicon nitride membrane. From the initial exposures, the resolution achieved is below 50nm with exposure conditions described. The issues of the resolution of the exposure tool are addressed and compared to the outcomes from detailed modeling.

An ultra-precision interference comparator for dimensional measurements usingtwo tunnelling microscopes as probes

A new kind of high resolution, high accuracy comparator for dimensionalmeasurements and its application for the measurement of the thicknessof gauge blocks is presented. This comparator consists of two scanningtunnelling microscopes (STMs) whose tips probe the opposite sides of asample. The STM tips are fixed on two high quality mirrors that are movedby piezoelectric actuators. The positions of the mirrors are measuredby a high resolution laser interferometer, thereby coupling the lengthmeasurements to the unit of length. The detection of the sample’s surface isperformed by the STM probes and utilizes the high dependence of thetunnelling current on the tip-to-sample distance, which follows an exponentialfunction and reaches about 1 nA at a tip-to-sample distance of less than 1nm. This technique allows one to determine the position of the surfacewith a higher degree of accuracy than is possible using mechanical oroptical probes. The determination of a distance consists of two consecutivedisplacement measurements by laser interferometer without and with the samplebetween the two tunnelling tips. The difference of these measurementscorresponds to the object’s length once environmental conditions such astemperature and refractivity are taken into account. In this paper we describethe construction and alignment of the instrument, the optimization ofvarious components and experimental investigations of some parts ofthe measuring process, show first experimental results of the completecomparator obtained on thin gauge blocks and discuss the uncertainty budget.

Microtribological investigations of stick/slip phenomena using a novel oscillatory friction and adhesion tester

A novel friction and adhesion tester bridging the gap between macro- and nanotribology is introduced. A friction and/or adhesion induced deflection of a spring is detected using a high-resolution laser interferometer. Unlike force microscopes, where a sharp tip interacts with the surface, this approach allows two plane substrates to be brought into contact. In this way, the exact tribological analysis of microtechnological devices is possible. Since the tester can be operated in air as well as under high vacuum conditions, the environment can be controlled over a wide range. Using this tester, micro-stick/slip phenomena have been investigated as a function of sliding velocity, surface morphology, normal force and contact area. All experiments presented in this paper were carried out on air.

High-resolution analysis of the complex wave spectrum in a cylindrical shell containing a viscoelastic medium. Part II. Experimental results versus theory

The complex frequency spectrum of axisymmetric wave modes in a circular cylindrical shell containing various viscoelastic media is measured. A new measurement technique has been developed for this purpose by combining a high-resolution laser interferometer with modern spectrum estimation methods. To decompose the complex wave-number dependence, a complex spectrum estimation method has been implemented. Up to 40 dispersion curves of traveling, axisymmetric modes are decomposed simultaneously in a frequency range between 1 kHz and 2 MHz. The guided structural waves are excited by piezoelectric transducers. Linear elasticity can be considered as an extreme case of viscoelasticity (long relaxation times compared with the deformation periods). To ascertain the validity of the theory, dispersion curves are calculated for a shell containing a viscoelastic material behaving like the elastic shell and are compared with the measured curves of an isotropic aluminium rod. The phenomenon of “backward wave propagation,” in which the group velocity and the phase velocity of one mode have opposite signs, is clearly measured. Excellent agreement between experimental and theoretical results, which are also presented in a corresponding paper [J. Vollmann and J. Dual, J. Acoust. Soc. Am. 102, 896–908 (1997)], is found over a wide parameter range, including the case of a linear elastic rod.

The influence of thermal and surface treatments on the anelastic creep of Al-Zn and Al-Cu alloys

In many industrial applications, like high precision force measurements or nanopositioning, the elastic and dimensional stabilities of materials are required at a nanometric scale. Therefore, some aspects of room temperature creep of commercial Al-Zn and Al-Cu alloys have been studied. The anelastic creep was measured at room temperature by means of a high resolution laser interferometer. The irreversible component of the deformation was quantified by measuring the viscoelastic after-effect. The anelastic relaxation of Al-Zn has been studied as a function of annealing time and temperature. The results are correlated with the size and the density of precipitates and the extension of the precipitate free zone. The influence of a surface treatment (sandblasting, electropolishing, Cu-galvanizing, chroming, Zn-plating) on anclastic relaxation has also been considered and explained in terms of the anelastic and elastic properties of both the surface layer and the bulk.

Some aspects of anelastic and microplastic creep of pure Al and two Al-alloys

Anelastic creep of pure Al, commercial Al-Cu and a binary Al-Cu alloy has been measured at room temperature by means of a high resolution laser interferometer. The irreversible component of the deformation was also quantified from measurements of the anelastic creep recovery. The dependence of the deformation-time curves on thermal treatment and cold work is analyzed. The mechanisms responsible for the room temperature anelastic creep are discussed. Materials loaded below their elastic limit can present either a pure anelastic behavior (commercial Al-Cu) or additional viscoelastic creep (pure Al, high purity Al-Cu). For commercial Al-Cu, the presence of an irreversible deformation appears to be mainly related to the state of the surface. A viscoelastic after effect has been measured for this alloy after a Cu-electroplating treatment. As a typical result for room temperature creep, the irreversible deformation depends logarithmically on load time

The dynamic mechanical behavior of polymethyl methacrylate

In order to investigate the short time response of solid polymers, a high resolution laser interferometer has been employed to observe the detailed structure of stress waves produced by the impact of polymeric plates. From the observed stress waves the loading and unloading stress-strain paths followed by the material can be determined. For the polymer, polymethyl methacrylate, over the stress range from 0–60 kbar such observations have disclosed a stress-strain behavior which exhibits large strain nonlinearities and significant rate-dependence. For stress levels below ≈7 kbar and above ≈40 kbar, rate-effects are of secondary importance and the observed wave profiles may be modeled using a nonlinear elastic description of the material behavior. However, at about 7 kbar, a transition is observed in the dynamic stress-strain behavior which is characterized by greater stress relaxation and significant hysteresis upon unloading. This transition, which we attribute to a yield phenomenon, requires a rate-dependent description of the material behavior to be used in the stress range of approximately 7–40 kbar.

High-resolution laser interferometer for measurement of electron density in transient plasma

A laser interferometer of the Mach-Zehnder type based on the use of a single-mode frequency-stabilised He-Ne gas laser, 6329 A in wavelength and with 100 μV output, has been used to measure accurately electron densities in the range 1014–1015cm−3 in a transient mercury-vapour plasma. An ‘amplitude’ (intensity) modulation system is employed in order to obtain a wide dynamic range. The interferometer system is mounted on a massive movable table in order to obtain the spatial distribution of electron density by means of sequential discharges. The experimental results show clearly that there are definite time delays between the peak of current in the discharge and the maximum value of the (average) electron density. The results are in good agreement with the values of electron densities obtained by the extrapolation from microwave measurements.