Optical Lever Research Articles

Photoinduced bending in bimorph optical fibers

Optomechanical materials directly generate work from light through physical deformation upon illumination. Here, we report an optical fiber-based optomechanical actuator that undergoes bending when illuminated by actinic light. A model for light-induced bending curvature as a function of geometrical and material properties was developed to aid in design. Polymer fibers were fabricated and filled directly during the draw with a molten azobenzene derivative. Upon illumination, photoactivated motion is observed and quantified with an optical lever beam approach.

On the Einstein-de Haas effect in van der Waals microelectromechanical systems

The electric-field–induced gyromagnetic effect in antiferromagnetic 2D films, analogous to the classical Einstein-de Haas effect in ferromagnetic materials, is considered. It is shown that for the micrometer-sized flakes of antiferromagnetic van der Waals materials having a non-diagonal tensor of the magnetoelectric effect, the magnitude of the electrically induced Einstein-de Haas effect is sufficient to be detected with the conventional optical lever approach of an atomic force microscope.

Design and performance simulation of a silica microdisk cavity optical pressure sensor

The opto-mechanical system of optical whispering-gallery mode (WGM) microcavities confines resonant photons in micro-scale resonators for a long time, which can strongly enhance the interaction between light and matter, making it an ideal platform for various sensors. To measure the slim optical pressure in the interaction between the laser and matter, a silica microdisk cavity sensor with metal film is designed in this paper. In this study, the finite element method was employed to investigate the opto-mechanical coupling mechanism in a microdisk cavity. From the aspects of optics and mechanics, the structural parameters of the sensor were optimized and the performance was simulated. The simulation results show that at 1550 nm, the sensor’s optical quality factor (Q) can reach ∼104, the free spectral range is ∼5.3nm, the sensing sensitivity is 5.32mPa/Hz1/2, and the optical force resolution is 6.61×10−12N, which is better than the thin-film interferometry and optical lever method.

A torsion balance as a weak-force testbed for novel optical inertial sensors

Torsion balances (TBs) are versatile instruments known for their ability to measure tiny forces and accelerations with high precision. We are currently commissioning a new TB facility to support the development and testing of novel optical inertial sensor units for future gravity-related space missions. Here, we report on the status of our apparatus and present first sensitivity curves that demonstrate acceleration and torque sensitivities of 5⋅10−11ms−2 and 1⋅10−12NmHz−1 at frequencies around 4mHz , respectively. Capacitive sensors and optical levers measure the dynamics of the system with a displacement sensitivity of down to 9⋅10−10mHz−1 for the former and 2⋅10−11mHz−1 for the latter. Combining the readout of the suspended inertial member (IM) with environmental sensor signals, the system is characterized, and limiting noise sources are identified. We find that, in particular, the coupling of ambient seismic motion is limiting over a broad frequency range and show that due to its high susceptibility to ground motion, our TB is also a promising platform for exploring ground motion sensing in multiple degrees of freedom. Future upgrades will focus on mitigating seismic noise by controlling the torsion fiber suspension point using piezoelectric actuators and the integration of precision interferometric readout of the IM. These improvements will further increase the sensitivity towards the thermal noise limit which constrains the performance to 1⋅10−13ms−2Hz−1 at 4mHz .

Back action evasion in optical lever detection

The optical lever is a centuries old and widely used detection technique employed in applications ranging from consumer products and industrial sensors to precision force microscopes used in scientific research. However, despite the long history, its quantum limits have yet to be explored. In general, any precision optical measurement is accompanied by optical force induced disturbance to the measured object (termed as back action) leading to a standard quantum limit (SQL). Here, we give a simple ray optics description of how such back action can be evaded in optical lever detection. We perform a proof-of-principle experiment demonstrating the mechanism of back action evasion in the classical regime, by developing a lens system that cancels extra tilting of the reflected light off a silicon nitride membrane mechanical resonator caused by laser-pointing-noise-induced optical torques. We achieve a readout noise floor two orders of magnitude lower than the SQL, corresponding to an effective optomechanical cooperativity of 100 without the need for an optical cavity. As the state-of-the-art ultralow dissipation optomechanical systems relevant for quantum sensing are rapidly approaching the level where quantum noise dominates, simple and widely applicable back action evading protocols will be crucial for pushing beyond quantum limits.

Contactless calibration of microchanneled AFM cantilevers for fluidic force microscopy

AbstractAtomic force microscopy (AFM) is an analytical technique that is increasingly utilized to determine interaction forces on the colloidal and cellular level. Fluidic force microscopy, also called FluidFM, became a vital tool for biomedical applications. FluidFM combines AFM and nanofluidics by means of a microchanneled cantilever that bears an aperture instead of a tip at its end. Thereby, single colloids or cells can be aspirated and immobilized to the cantilever, for example, to determine adhesion forces. To allow for quantitative measurements, the so‐called (inverse) optical lever sensitivity (OLS and InvOLS, respectively) must be determined, which is typically done in a separate set of measurements on a hard, non‐deformable substrate. Here, we present a different approach that is entirely based on hydrodynamic principles and does make use of the internal microfluidic channel of a FluidFM‐cantilever and an external pressure control. Thereby, a contact‐free calibration of the (inverse) optical lever sensitivity (InvOLS) becomes possible in under a minute. A quantitative model based on the thrust equation, which is well‐known in avionics, and finite element simulations, is provided to describe the deflection of the cantilever as a function of the externally applied pressure. A comparison between the classical and the here‐presented hydrodynamic method demonstrates equal accuracy.

Visualizing the motion of a damped torsional oscillator using an optical lever

This study aims to visualize the motion of an underdamped torsional oscillator using an optical lever. This involves employing an optical setup to magnify and measure the angular displacement of the torsional oscillator as it undergoes oscillations and damps over time. By analysing a video recording of an image of a filament formed by a concave mirror attached to the damped torsional oscillator, we observed an exponential decay in the time-averaged amplitude.

In situ thermal noise measurements under nanoindentation of suspended graphene

We demonstrated thermal noise measurement under the nanoindentation of monolayer and bilayer graphene nanodrums. The resonant oscillation of the cantilever excited only by a thermal energy is detectable even in the case of contact with a suspended graphene. The contact resonance fRequency can be obtained in 1 millisecond intervals during the force curve measurement by optimizing the parameters of a real-time spectrum analyzer. The pretension value of the graphene nanodrum is evaluated by the minimum frequency just when the applied force of the cantilever becomes zero. The simultaneous measurement of the force and the resonant frequency with respect to the deformation of the graphene nanodrum enables us to determine the value of InvOLS (inverse optical lever sensitivity) more accurately in each measurement. From the analysis scheme, force curve measurements of the graphene nanodrums with the same diameters show good reproducibility. We also revealed that the effective spring constant of the graphene nanodrums consists of a weak sample-dependent pretension factor and a deformation-dependent factor proportional to the number of graphene layers.

Thermal induced deflection in atomic force microscopy cantilevers: analysis & solution

Atomic force microscopy (AFM) cantilevers are commonly made from two material layers: a reflective coating and structural substrate. Although effective, this can result in thermally induced cantilever deflection due to ambient and local temperature changes. While this has been previously documented, key aspects of this common phenomenon have been overlooked. This work explores the impact of thermally induced cantilever deflection when in- and out-of-contact, including the topographic scan artefacts produced. Scanning thermal microscopy probes were employed to provide direct cantilever temperature measurement from Peltier and microheater sources, whilst permitting cantilever deflection to be simultaneously monitored. Optical lever-based measurements of thermal deflection in the AFM were found to vary by up to 250% depending on the reflected laser spot location on the cantilever. This highlights AFM’s inherent inability to correctly measure and account for thermal induced cantilever deflection in its feedback system. This is particularly problematic when scanning a tip in-contact with the surface, when probe behaviour is closer mechanically to that of a bridge than a cantilever regarding thermal bending. In this case, measurements of cantilever deflection and inferred surface topography contained significant artefacts and varied from negative to positive for different optical lever laser locations on the cantilevers. These topographic errors were measured to be up to 600 nm for a small temperature change of 2 K. However, all cantilevers measured showed a point of consistent, complete thermal deflection insensitivity 55% to 60% along their lengths. Positioning the reflected laser at this location, AFM scans exhibited improvements of up-to 97% in thermal topographic artefacts relative to other laser positions.

Measuring the Adhesion Force and the Spreading Radius between Droplets and a Solid Surface during Short-Time Spreading

When a droplet contacts a solid surface, the liquid spreads over the solid surface to minimize the total surface energy. This phenomenon is widespread in industrial production and nature, so research on droplet spreading is of great significance. Here, the adhesion force and the spreading radius during droplet spreading can be quantified using a highly sensitive photoelectric method. It is possible to study droplet spreading from two dimensions at the microscale. The adhesion force is measured by an optical lever, and the spreading radius is measured by an ultrafast electrical method. The measurement method allows the force resolution and the space-time resolution to reach the nanonewton lever and the nanosecond lever, respectively. We obtain the maximum spreading radius and the maximum adhesion force during short-time spreading through our technique. Moreover, we numerically simulate the droplet spreading process through the lattice Boltzmann solver and confirm the observed results. This study provides a new experimental technique for studying droplet spreading dynamics from multiple perspectives, which can deepen our understanding of droplet spreading and provide guidance for the development of new techniques.

A study on motion reduction for suspended platforms used in gravitational wave detectors

We report a reduction in motion for suspended seismic-isolation platforms in a gravitational wave detector prototype facility. We sense the distance between two seismic-isolation platforms with a suspension platform interferometer and the angular motion with two optical levers. Feedback control loops reduce the length changes between two platforms separated by 11.65,textrm{m} to 10,mathrm {pm,Hz}^{-1/2} at 100,textrm{mHz}, and the angular motion of each platform is reduced to 1,mathrm {nrad, Hz}^{-1/2} at 100,textrm{mHz}. As a result, the length fluctuations in a suspended optical resonator on top of the platforms is reduced by three orders of magnitude. This result is of direct relevance to gravitational wave detectors that use similar suspended optics and seismic isolation platforms.

Pancreatic cancer metastasis: Adhesion and stiffness

Pancreatic ductal adenocarcinoma (PDAC) cells undergo a semi-epithelial to mesenchymal transition. They express Cadherin proteins characteristic of both normal (E-cadherin) and cancer (N-cadherin) cells. Cadherins are involved in cell-cell adhesion. Additionally, cells must adjust their mechanical properties to undergo metastasis. We use Atomic Force Microscopy (AFM) to characterise the mechanical properties of PDAC cell lines from the primary tumour sites (PANC1, PL45) and from liver (CFPAC1) and lymph node (Hs766T) metastases. AFM measures forces using the optical lever system. To measure their stiffness, cells were probed using a rectangular cantilever with a three-sided pyramidal tip. The Hertz contact model was used to calculate Apparent Young's modulus (E) from the approach curve. The structural damping model was used to calculate the power-law exponent (α) from force curves with logarithmically oscillating contact part. To probe the adhesive properties of the cells, a single cell was attached to functionalised triangular tipless cantilevers, and then pressed against a confluent layer of cells. When the cell-cantilever is retracted, the contact of the attached cell with the cell layer is broken. The detachment exerts force on the cantilever, and this signal is also recorded by and analysed from the retract curve. PANC1 and PL45 cells are stiffer in a confluent layer as compared to single cells. CFPAC1 cells soften in confluent layers, and have lesser adhesion between them as compared to PANC1. CFPAC1 cells also have reduced cell-cell interaction with endothelial cells (EA.hy926) after inhibiting N-cadherin. Thus, N-cadherin inhibition can increase liver metastatic cell lines’ self-interaction and decrease interaction with endothelial cells. While primary tumour cell lines experience mixed mechanical response to surrounding cells, liver metastasis cells are softer and more viscous.

Correction method for dynamic measurement with an optical lever AFM (Effects of ambient fluid and surface force)

Correction method for dynamic measurement with an optical lever AFM (Effects of ambient fluid and surface force)

Objective measurement technique for mitigating the augmented-reality geometric waveguide double-image problem

In this paper, we propose a method for using angle offset measurements of an augmented-reality (AR) geometric waveguide partially reflective mirrors array (PRMA), to inform the design and manufacture of future iterations. These offsets are the main cause of display defects such as the formation of double-images. Our design provides a method for quantitative measurement to support the solution of the AR geometric waveguide double-image problem. Our study is based on the principle of optical lever amplification, and PRMA high accuracy measurement is achieved. We also provide an analysis that determines the maximum permissible offset limit of the PRMA geometric waveguide module, without affecting the display quality. The technique is validated on virtual models made in SolidWorks that are synchronized with optical components whose parameters are changed in LightTools. This provides a powerful technique for speeding up the design and manufacturing cycle where until now this has been based on subjective innacurate and unreliable human observation. This paper provides the theoretical basis for the development of a rigorous and reliable measurement technique.

Nanosecond pulsed laser induced efficient photophoresis actuating of graphene sponge

Photophoresis actuating shows great potentials in cross-scale light-driven manipulation and fuel-free flight due to efficient conversion of light-to-work. However, photophoresis actuating with rapid light response is rarely reported although it is important in light-driven manipulation. In this work, the pulsed laser induced photophoresis of graphene sponge material (PLPGS) is investigated by a homemade sensitive detection system, and the actuating force is measured quantitatively by an optical lever method. The macroscale graphene sponge material can be driven by a 3–5 ns single laser pulse reproducibly. The actuating force is 1.8 μN when the input laser pulse energy density is 4.0 mJ/cm2, and the PLPGS can be triggered by ultra-low laser pulse energy below 70 μJ/cm2. The PLPGS is proved to be quick-response, repeatable, low-energy, and non-destructive.

High-precision and long-range measurement of micro-gear starting torque.

The ability to measure micro-starting torque is pivotal for micromechanical equipment, which has wide usage in mechanical manufacturing, electrical, electronic, and other industries. However, the measurement range of existing methods is about N⋅m or mN⋅m. There is not much research on the measurement of micro-torque starting in the µN⋅m. In this paper, a novel micro-gear starting torque measurement system, to the best of our knowledge, is proposed based on an optical lever with a long range from 1 to 10µN⋅m. The system device consists of the optical lever, cantilever, and position sensitive device. A micro-gear was used to assess the performance of the proposed method. The standard deviation of the measured starting torque is 1.2µN⋅m. The external factors that can contribute to the uncertainty of the measurement system, such as force measurement, arm of force, and repeatability, have been analyzed and quantified. The relative combined uncertainty is estimated at 3.0%, approximately.

On AFM Measurements of the Interaction Force Vector by Means of Interferometry, Optical Lever, and the Piezoresistive Method

On AFM Measurements of the Interaction Force Vector by Means of Interferometry, Optical Lever, and the Piezoresistive Method

Development of a High-Resolution Touch Trigger Probe Based on an Optical Lever for Measuring Micro Components

The characterization of a high-precision component with its dimensions has become a key problem in ensuring the performance of system parts. A touch trigger probe plays an important role in experimentally measuring these properties. In this study, a new high-resolution touch trigger probe based on a modified optical lever method is proposed. Only one optical sensor is adopted. The sensing principle of the developed probe in 3D is investigated through the probe’s sensitivity models. An optimizing design of the elastic suspension is demonstrated. Experiments on probe performance are conducted by measuring a step height and a gauge block. Experimental results indicate that the probe achieves a resolution of up to 1 nm in 3D and a measurement standard deviation of 18.3 nm. The probe has a permissible range of ± <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{m}$ </tex-math></inline-formula> in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}/{y}$ </tex-math></inline-formula> -axis and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{m}$ </tex-math></inline-formula> in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -axis. The drift of the probe is 5.2 nm within 30 min. The comprehensive uncertainty of the probing system is 18.45 nm. The developed probe can be used in micro/nano coordinate measuring machines.

High precision six-degree-of-freedom interferometer for test mass readout

High precision six-degree-of-freedom sensing plays an important role in future gravitational space missions. In gravitational or geodesy missions, measurements of all six degrees of freedom of freely floating test mass are required for reducing the cross-coupling noise, which is frequently an important limiting factor in the performance. Interferometry and capacitive sensing have been successfully combined in LISA pathfinder to achieve six degrees of freedom measurements. In this paper, we report a six-degree-of-freedom interferometer system based on multiplex differential wavefront sensing and longitudinal pathlength sensing. Compared to conventional capacitive sensing or optical levers, it has a higher measurement accuracy. The results of our table-top experiment show motion in all six degrees of freedom of a cubic test mass are simultaneously measured with a translational and tilt sensitivity of 100 pm/Hz1/2 and 10 nrad Hz−1/2 above 1 Hz, respectively. The translational dynamic range is greater than ±10 mm with nonlinear residuals less than 6 μm, and the tilt dynamic range is approximately ±500 μrad with nonlinear residuals less than 60 μrad. The coupling errors between multiple degrees of freedom are dominated by tilt-to-translation and tilt-to-tilt coupling, which are roughly 2–4 μm and 15–25 μrad, respectively, within a range of [−500 μrad, +500 μrad].

Environment-Robust Polarization-Based Phase-Shift Dynamic Demodulation Method for Optical Fiber Acoustic Sensor

In this paper, an environment-robust polarization-based phase-shift dynamic demodulation method for optical fiber acoustic sensor is proposed. Through optical lever effect of polarization low-coherence interference and amplitude scaling differential cross multiplication (AS-DCM) algorithm, acoustic-source induced interference phase of the acoustic sensor can be demodulated in real-time with high precision. The maximum relative phase demodulation error was only 0.694% when the cavity length had an offset ∼4 μm. The maximum cavity length demodulation error was keeping less than 3.988 nm under the optical power reduced ten times, which demonstrated an ultra-stable demodulation for the largest permitted optical power attenuation range, to our best knowledge. The proposed method has a capability of tolerating large optical power attenuation and large cavity length random offset, providing an environment-robust way for optical fiber acoustic sensor working in extreme environments.