Subnanometric Precision Research Articles

NANOCRINOLOGY.

We conceptualize and define nanocrinology as the science that studies the nanometric and subnanometric precision that operates in diagnostic and therapeutic endocrinology. It includes advanced generation assays, which can detect low concentrations of hormones, and modern drug delivery systems that allow more efficient delivery of endocrinotropic agents. Nanocrinology is a rapidly growing field of endocrinology, and we call for greater research and adoption of this science.

MicroMegascope based dynamic surface force apparatus

Surface force apparatus (SFA) allows accurate resolving of the interfacial properties of fluids confined between extended surfaces. The accuracy of the SFA makes it an ubiquitous tool for the nanoscale mechanical characterization of soft matter systems. The SFA traditionally measures force–distance profiles through interferometry with subnanometric distance precision. However, these techniques often require a dedicated and technically demanding experimental setup, and there remains a need for versatile and simple force–distance measurement tools. Here we present a MicroMegascope based dynamic SFA capable of accurate measurement of the dynamic force profile of a liquid confined between a millimetric sphere and a planar substrate. Normal and shear mechanical impedance is measured within the classical frequency modulation framework. We measure rheological and frictional properties from micrometric to molecular confinement. We also highlight the resolution of small interfacial features such as ionic liquid layering. This apparatus shows promise as a versatile force–distance measurement device for exotic surfaces or extreme environments.

Experimental validation of joint phase and amplitude wave-front sensing with coronagraphic phase diversity for high-contrast imaging

Context. The next generation of space-borne instruments dedicated to the direct detection of exoplanets requires unprecedented levels of wavefront control precision. Coronagraphic wavefront sensing techniques for these instruments must measure both the phase and amplitude of the optical aberrations using the scientific camera as a wavefront sensor. Aims. In this paper, we develop an extension of coronagraphic phase diversity to the estimation of the complex electric field, that is, the joint estimation of phase and amplitude. Methods. We introduced the formalism for complex coronagraphic phase diversity. We have demonstrated experimentally on the Très Haute Dynamique testbed at the Observatoire de Paris that it is possible to reconstruct phase and amplitude aberrations with a subnanometric precision using coronagraphic phase diversity. Finally, we have performed the first comparison between the complex wavefront estimated using coronagraphic phase diversity (which relies on time-modulation of the speckle pattern) and the one reconstructed by the self-coherent camera (which relies on the spatial modulation of the speckle pattern). Results. We demonstrate that coronagraphic phase diversity retrieves complex wavefront with subnanometric precision with a good agreement with the reconstruction performed using the self-coherent camera. Conclusions. This result paves the way to coronagraphic phase diversity as a coronagraphic wave-front sensor candidate for very high contrast space missions.

An analytic expression for coronagraphic imaging through turbulence. Application to on-sky coronagraphic phase diversity

Abstract The ultimate performance of coronagraphic high-contrast exoplanet imaging systems such as SPHERE or GPI is limited by quasi-static aberrations. These aberrations produce speckles that can be mistaken for planets in the image. In order to design instruments, correct quasi-static aberrations or analyse data, the expression of the point spread function of a coronagraphic instrument in the presence of residual turbulence is most useful. Here, we derive an analytic expression for this point spread function that is an extension to coronagraphic imaging of Roddier's expression for imaging through turbulence. We give a physical interpretation of its structure, we validate it by numerical simulations and we show that it is computationally efficient. Finally, we incorporate this imaging model into a coronagraphic phase diversity method (COFFEE) and validate by simulations that it allows wave-front reconstruction in the presence of residual turbulence. The preliminary results, which give a sub-nanometric precision in the case of a SPHERE-like system, strongly suggest that quasi-static aberrations could be calibrated during observations by this method.

Study of Laser Feedback Phase Under Self-Mixing Leading to Improved Phase Unwrapping for Vibration Sensing

In this paper, the inherent error as well as the robustness of a previously published displacement retrieval technique called the phase unwrapping method (PUM) is analyzed. This analysis, based on a detailed study of laser feedback phase behavior, results in a new algorithm that removes the PUM inherent error while maintaining its robustness. The said algorithm has been successfully tested on simulated and experimental self-mixing (SM) interferometric signals. Simulations in weak and moderate feedback regimes demonstrate that the said algorithm can reach a subnanometric precision compared with approximately 25 nm for PUM. For experimental SM signals affected by noise, the measured rms displacement error and the maximum absolute error are 14 and 37 nm, respectively, for the proposed algorithm and 34 and 123 nm for the PUM, which indicates a threefold displacement precision improvement over the PUM. Finally, it is explained that the precision can be further improved by a reduction of the noise level of experimental SM signals.

Subnanometric stabilization of plasmon-enhanced optical microscopy

We have demonstrated subnanometric stabilization of tip-enhanced optical microscopy under ambient condition. Time-dependent thermal drift of a plasmonic metallic tip was optically sensed at subnanometer scale, and was compensated in real-time. In addition, mechanically induced displacement of the tip, which usually occurs when the amount of tip-applied force varies, was also compensated in situ. The stabilization of tip-enhanced optical microscopy enables us to perform long-time and robust measurement without any degradation of optical signal, resulting in true nanometric optical imaging with high reproducibility and high precision. The technique presented is applicable for AFM-based nanoindentation with subnanometric precision.

Sub-nanometric precision displacement sensing using low mass and rough surfaces as movable targets

A novel speckle interferometric method has been developed to measure lengths and displacements over a distance of 100 μm with a resolution less than 1 nm using rough surfaces as movable targets instead of using conventional cube corners or mirrors. The speckle method is able to use Michelson and new configurations to combine the two scattered beams or fields from rough movable and stationary reference targets. The targets can be attached and can be produced directly onto movable actuator type of mechanisms. The phase information is extracted from the randomly modulated signals by employing an apertured disc system or an alternative optical fibre arrangement. This method exploits the concept of using narrow angle scatterers for economical use of laser light, enhanced reliability and modulation criteria. A prototype low-mass interferometric displacement sensor has been constructed to provide a compact and a flexible system. Apart from the measurement of changes in displacements in force and pressure measuring devices, it can also be used for the assessment of small range scanning probes, stylus profilers and in medical field the measurement of elastic properties of ear drums, etc. The sub-nanometre resolution and displacement values are repeatable to within ±1 nm can be demonstrated over distances of up to 2 mm by employing appropriate actuators and translation devices. The performance has been confirmed by comparison work against a conventional interferometric transducer.

Thin-Film Electrostatic Actuators on Flexible Plastic Substrates

ABSTRACTThin-film silicon micromachined bridge actuators are fabricated at temperatures below 110°C on flexible polyethylene terephthalate plastic substrates. The micromechanical structures are electrostatically actuated both at the resonance frequency and at below-resonance frequencies, and the resulting deflection is optically monitored. Deflections up to 100 nm are measured below the resonance frequency with subnanometric precision. Resonance frequencies in the MHz range are observed in vacuum with quality factors of the order of 100. The movement is studied as a function of the geometrical dimensions of the actuators, of the actuation voltage and of the measurement pressure. The experimental data are analyzed using an electromechanical model. The performance of hydrogenated amorphous silicon based resonators on PET substrates is compared to that of similar microstructures on glass substrates.

Phase-modulation scatterometry.

Phase-modulation scatterometry is a metrology technique for determining, by means of a phase modulator as a key device, the parameters of gratings. The main source of error to be dealt with are the fluctuations of the phase-modulation amplitude. The grating zeroth-order reflectance modulated by the phase modulator is converted into a signal by the photodetector. The measurables are the direct term and the first two harmonics of the signal. For experimental data fitting, we used the ratio of the harmonics over the direct term because it significantly improves the accuracy. A sensitivity analysis was performed for two samples, one real and one theoretical, to find the measurement configuration that insures optimum determination precision for the grating parameters. For the real sample, comparison of the theoretical predictions for sensitivity with the actual values showed a good agreement. For both samples the sensitivity analysis indicated subnanometric precision for the critical dimension (grating linewidth).