Laser Deflection Research Articles

Counterion-dependent microrheological properties ofF-actin solutions across the isotropic-nematic phase transition

We studied microrheological properties of F-actin across the isotropic-nematic phase transition region by video particle tracking (VPT) and by laser deflection particle tracking (LDPT). Both methods track the motion of thermally driven micron-sized beads, and convert the temporal mean square displacement (MSD) to shear moduli. The two methods give consistent results for the elastic modulus G' and less so for the loss modulus G'' . As the nematic order parameter increases with actin concentration, G'|| (measured parallel to the nematic director) and G' perpendicular (perpendicular to the director) grow apart, with G' perpendicular larger than G'||. The moduli scale with actin concentration as G'|| approximately c 0.54+/-0.13 and G' perpendicular approximately c 1.38+/-0.15. Furthermore, G' and G'' dependence on [Mg2+] were measured and compared for 1mg/ml isotropic and 4 mg/ml nematic F-actin solutions, respectively. In the isotropic phase, G' increases with [Mg2+] up to 6mM and then plateaus. In the nematic phase, G' perpendicular is larger than G'||, and both G' perpendicular and G'|| increase with [Mg2+] progressively up to 16 mM , above which F-actin form large bundles. In both isotropic and nematic phases, G'' only weakly depends on [Mg2+] . In conclusion, particle tracking microrheology reveals rich rheological features of F-actin affected by the isotropic-nematic phase transition and by tuning weak electrostatic interactions among the protein filaments.

Mechanics of Single Cells: Rheology, Time Dependence, and Fluctuations

The results of mechanical measurements on single cultured epithelial cells using both magnetic twisting cytometry (MTC) and laser tracking microrheology (LTM) are described. Our unique approach uses laser deflection for high-performance tracking of cell-adhered magnetic beads either in response to an oscillatory magnetic torque (MTC) or due to random Brownian or ATP-dependent forces (LTM). This approach is well suited for accurately determining the rheology of single cells, the study of temporal and cell-to-cell variations in the MTC signal amplitude, and assessing the statistical character of the tracers’ random motion in detail. The temporal variation of the MTC rocking amplitude is surprisingly large and manifests as a frequency-independent multiplicative factor having a 1/ f spectrum in living cells, which disappears upon ATP depletion. In the epithelial cells we study, random bead position fluctuations are Gaussian to the limits of detection both in the Brownian and ATP-dependent cases, unlike earlier studies on other cell types.

Device for characterization of thermal effusivity of liquids using photothermal beam deflection

We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the sample under study. An optical angle sensor is used to measure the laser deflection providing a simple and experimental arrangement. We demonstrate its principle and a simple procedure to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.

Shockwave Acceleration and Attenuation in Glow Discharge Argon Plasma

Experimental investigations of the shockwave propagation in the direction parallel to the electric field in low-pressure longitudinal glow discharge argon plasmas are performed by the simultaneous multipoint laser deflection technique. In the newly developed shock tube at Troy University, Mach 1.5-2.2 shockwaves are produced by a fast capacitor discharge (quarter period tau1/4 = 1.4 mus ). In this paper, the shock propagation measurements are extended to the low pressure limit down to 3.6 torr while confirming the earlier measurements performed at gas pressures 15 torr and above. The shockwaves are launched through a plasma medium inside the shock tube, where the deflections of the laser beams are recorded on a fast oscilloscope. An average shockwave velocity in the plasma is determined from the time history of the laser deflection signals. The shockwave speed and the broadening of the laser deflection signals in the plasma are found to be dependent on the plasma discharge current. Shockwave speeds increase by 18% for the plasma at 3.6 torr over a range of plasma discharge current I = 0-150 mA and by 46% for the plasma at 15 torr over I = 7-150 mA. In addition, shockwave amplitudes are attenuated in the plasma and show linear dependence on the shockwave speed or Mach number.

Experimental Investigation of Shear Capacity of Precast Reinforced Concrete Box Culverts

This study presents an experimental program to investigate the shear capacity of precast reinforced concrete box culverts. Each culvert was subjected to monotonically increasing load through a 254 mm×508 mm (10 in.×20 in.) load plate in order to simulate the HS20 truckload per AASHTO 2005. Instrumentation included strain gauges, high-resolution laser deflection sensor, and automated data acquisition. Four tests were conducted on 1.22 m×1.22 m×1.22 m (4 ft×4 ft×4 ft) box culverts. The location of the load plate was varied to identify the position, which introduces the maximum shear stresses. Laser sensor data and dial gauge readings were recorded to measure the deflection profile of the box culvert. Strain gauges were placed on the steel reinforcement to measure axial strain at locations of maximum positive and negative bending moments. The test results include reporting the loads at which each crack initiated and propagated. The displacement profile of the top slab from the laser instrumentation output al...

Raman intensity enhancement in silicon-on-insulator substrates by laser deflection at atomic force microscopy tips and particles

It is shown that Raman intensities of bulk and film in silicon-on-insulator substrates strongly depend on the incident angle of the exciting laser. In a backscattering geometry with perpendicular laser incidence, deflection at particles or atomic force microscopy tips can thereby lead to a selective enhancement of the film signal, which can be misinterpreted as surface/tip enhanced Raman scattering. The authors report strong enhancement effects by scattering at dielectric particles on silicon-on-insulator and silicon substrates as well as smaller effects for deflection at tips. In evaluating field enhancements on such substrates, this must be considered.

Shock velocity in weakly ionized nitrogen, air, and argon

The goal of this research was to determine the principal mechanism(s) for the shock velocity increase in weakly ionized gases. This paper reports experimental data on the propagation of spark-generated shock waves (1<Mach<3) into weakly ionized nitrogen, air, and argon glow discharges (1<p<20Torr). In order to distinguish between effects due solely to the presence of electrons and effects due to heating of the background gas via elastic collisions with electrons, the weakly ionized discharge was pulsed on/off. Laser deflection methods determined the shock velocity, and the electron number density was collected using a microwave hairpin resonator. In the afterglow of nitrogen, air, and argon discharges, the shock velocity first decreased, not at the characteristic time for electrons to diffuse to the walls, but rather at the characteristic time for the centerline gas temperature to equilibrate with the wall temperature. These data support the conclusion that the principal mechanism for the increase in shock velocity in weakly ionized gases is thermal heating of the neutral gas species via elastic collisions with electrons.

Measurement of Shock Waves Using an Acousto-Optic Laser Deflector

Laser interference fringe patterns and shadowgraphs were obtained with a minimum exposure time of 200 ns using an acousto-optic laser deflector. Experimental results showed that this method has sufficient spatial and temporal resolution to image the wavefront of shock waves generated by laser-induced breakdown in air. The shock waves propagated at a speed of over 103 m/s immediately after breakdown, and at a nearly constant speed of about 510 m/s for 3-9 μs after breakdown. The width of the wavefront of the shock wave was measured to be 0.17 mm, and the neutral density variation at the wavefront was estimated to be 9×1024 m-3.

Advances in CTIX Accelerator Study

Several new experiments have been conducted on the UC Davis repetitive-pulsed spheromak-like compact toroid (SCT) accelerator (CTIX). (1) SCT density and kinetic energy density has been increased by gas puffing in the acceleration section. With gas puffing, SCT electrical to kinetic energy conversion efficiency has been increased to >20%. (2) SCT interaction with targets has been recorded with a fast visible imaging system, combined with target-region helium gas puffing for increased brightness. Images of both coherent waves and turbulent flow patterns were observed in the target region after the interaction. (3) A laser deflection density diagnostic has been improved to obtain better reliability and resolution. Operated with high-density gas-puffed SCTs, the second-generation diagnostic has successfully measured axial as well as radial deflection. The measured line averaged densities are in good agreement with a conventional quadrature laser interferometer.

Transmission Fabry–Pérot interference thermometry for thermal characterization of microelectronic devices

The suitability of the thermometry based on transmission Fabry–Pérot interferences in semiconductor devices and ICs under working conditions is experimentally shown. Usually, they work at short time scales producing internal temperature increments, which are crucial for understanding their failure mechanisms. Thanks to this technique, the temperature profile in semiconductor devices and ICs is extracted with a very good depth resolution (below 35 µm). By means of versatile apparatus, transmission Fabry–Pérot and internal infrared laser deflection temperature measurements are simultaneously performed on a specific thermal test chip device. Concretely, the temperature evolution at various depths of the thermal test chip during the device heating and cooling processes is obtained. Experimental results are compared with the analytical model which thermally describes the thermal test chip behaviour during the heating process, achieving a very good agreement.

High‐speed imaging of laser intensity distribution using an acousto‐optic deflector

AbstractAn acousto‐optic laser deflector was used to image the intensity distribution of a continuous wave laser of microsecond order. Undeflected light was blocked while the deflected light was directed to a CCD camera, which allowed imaging of the incident laser intensity distribution of microsecond order. Experiments using a test pattern showed that there was no distortion in the deflected image. The resolution limit, estimated from diffractive effects, was about 0.2 mrad. Using this method of high‐speed imaging, density variations accompanying laser‐induced breakdown in air were visualized by shadowgraphy and interferometry. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 55–61, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20386

Atomic Force Microscopy in Dynamic Mode with Displacement Current Detection in Double Cantilever Devices

A cantilever array for dynamic mode atomic force microscopy (AFM) is presented, the vertical displacement of which is analyzed by the detection of displacement currents in the electrodes. Each cantilever in the array consists of an actuation part that allows an independent vertical movement, and a sensor part. The lateral distance between the tips of the different cantilevers is fixed to 10 µm. When operated as an actuator, a voltage is applied between the silicon membrane and the underlaying electrode. Due to the resulting coulomb forces, the vertical position of the tip is controllable. The reaction time in this mode is shorter than the response time of a piezostack. The sensor part, on the other hand, allows the device to work in dynamic mode without a laser deflection system. The vertical resolution achieved is below 1 nm. The dependence of force distance curves on the excitation amplitude is shown.

Calibrating laser beam deflection systems for use in atomic force microscopes and cantilever sensors

Most atomic force microscopes and cantilever-based sensors use an optical laser beam detection system to monitor cantilever deflections. We have developed a working model that accurately describes the way in which a position sensitive photodetector interprets the deflection of a cantilever in these instruments. This model exactly predicts the numerical relationship between the measured photodetector signal and the actual cantilever deflection. In addition, the model is used to optimize the geometry of such laser deflection systems, which greatly simplifies the use of any cantilever-based instrument that uses a laser beam detection system.

Shock-wave-induced enhancement of optical emission in nitrogen afterglow plasma

This paper reports measurements of optical emission enhancement at the shock front of Mach 1.5 to Mach 3.5 shockwaves propagating in the afterglow of a 0.75 Torr nitrogen glow discharge. Electrically-generated shocks pass through the afterglow and create noticeable enhancements of the B 3Pig-A 3Sigma+u and C 3Piu-B 3Pig transitions of nitrogen. Under our discharge conditions, the electron Debye length was approximately the same magnitude as the shock thickness; this allows the possibility of a space-charge region extending beyond the neutral shockwave discontinuity. Previous researchers have measured enhancement in the B 3Pig-A 3Sigma+u optical emission at the shock front, but only in the active discharge. Fibers connected to photomultipler tubes measure the optical emission from the discharge. Laser deflection measures the shock velocity. The data reveals that the emission enhancement increases with Mach number, and also indicates that the emission enhancement decreases exponentially with time in the afterglow. Since the discharge voltage has already been shut off, the energy needed to create the emission enhancement cannot come from the power supply. We conclude that under our discharge conditions there is an increase in the already non-equilibrium energy of the electrons at the shock front via a shockwave-induced strong double layer.

Wear of dentine in vitro by toothpaste abrasives and detergents alone and combined

To measure in vitro the abrasion of dentine by toothpaste detergents and abrasives alone and combined. Detergents used were tego betain, sodium lauryl sulphate (SLS), adinol and pluronic diluted to 1% w/v. Abrasives were three artificial silicas, tixosil 73 and 123 and Zeodent 113, and calcium carbonate used at 2.5% w/v. Flat human dentine specimens were brushed with aqueous detergent solutions or abrasive slurries, detergent abrasive slurries and water for 20,000 brush strokes. Dentine loss was measured by non-contacting profilometry at 10,000 and 20,000 strokes. Silica particle size distribution was measured by laser deflection. Loss of dentine occurred with all detergents, abrasives and detergent abrasion combinations, but was not linear with number of brush strokes. Water appeared to remove the smear layer only, but all detergents exceeded the predicted smear layer thickness. The silica abrasives differed in abrasion properties despite similar particle size distribution. Different detergents modulated the abrasives actions in mainly positive or mainly negative directions. Detergents appear able to attack the dentine surface to produce wear. Abrasives vary considerably in wear produced under similar conditions. Detergents modulate the effect of abrasives in a way that may reflect the rheological properties of the mixture.

A highly sensitive atomic force microscope for linear measurements of molecular forces in liquids

We describe a highly improved atomic force microscope for quantitative nanomechanical measurements in liquids. The main feature of this microscope is a modified fiber interferometer mounted on a five axis inertial slider which provides a deflection sensitivity that is significantly better than conventional laser deflection based systems. The measured low noise floor of 572.0fm∕Hz provides excellent cantilever amplitude resolution. This allows us to operate the instrument far below resonance at extremely small cantilever amplitudes of less than 1 Å. Thus linear measurements of nanomechanical properties of liquid systems can be performed. In particular, we present measurements of solvation forces in confined octamethylcyclotetrasiloxane and water with amplitudes smaller than the size of the respective molecules. In general, the development of the instrument is important in the context of quantitative nanomechanical measurements in liquid environments.

An experimental study of the flame propagation and combustion characteristics of LPG fuel

This work investigates the flame propagation and combustion characteristics of LPG (Liquefied Petroleum Gas) fuel. To clarify the combustion process of the heavy duty LPG engine, the flame propagation and combustion characteristics were investigated using a CVCC (constant volume combustion chamber) and a port injection type heavy duty LPLi (Liquefied Petroleum Liquid injection) engine system. Both the laser deflection method and the high-speed Schlieren photography method were employed to measure the flame propagation speed of LPG fuel. In addition, the single cylinder heavy duty LPLi engine was manufactured to analyze the combustion characteristics of the LPG. The experimental results indicated that the laser deflection method showed the measuring accuracy of this method to be less than 5% when compared with the result of the high-speed camera. According to the CVCC and heavy duty LPLi engine experimental results, the flame propagation reached a maximum speed at the stoichiometric equivalence ratio, regardless of operating conditions, and the effect of the equivalence ratio on both flame propagation and combustion characteristics was greater than that of ambient conditions. In addition, we found that the coefficient of variation of combustion duration increased when the equivalence ratio decreased. Furthermore, the combustion stability worsened as the equivalence ratio moved into the lean region.

音響光学レーザ偏向器を用いた高速現象の可視化

An acousto-optic laser deflector was used for visualization of high-speed phenomena, such as shock waves and density perturbations accompanying an impulse discharge, or shock waves generated by laser-induced breakdown in air. Using a continuous wave laser as the light source, shadowgraphs of shock waves and density perturbations were obtained at shutter speeds down to 1µs. Results showed that shock waves propagated at a speed of 417 m/s in the case of an impulse discharge, and 485 m/s in the case of laser-induced breakdown. Prebreakdown phenomena such as leaders progressing from the high-voltage electrode were also visualized. Compared to conventional high-speed imaging techniques, this method is useful when using a laser light source, since the acousto-optic crystal can accommodate high-intensity laser light. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 9–15, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20279

Visualization of high-speed phenomena using an acousto-optic laser deflector

An acousto-optic laser deflector was used for visualization of high-speed phenomena, such as shock waves and density perturbations accompanying an impulse discharge, or shock waves generated by laser-induced breakdown in air. Using a continuous wave laser as the light source, shadowgraphs of shock waves and density perturbations were obtained at shutter speeds down to 1µs. Results showed that shock waves propagated at a speed of 417 m/s in the case of an impulse discharge, and 485 m/s in the case of laser-induced breakdown. Prebreakdown phenomena such as leaders progressing from the high-voltage electrode were also visualized. Compared to conventional high-speed imaging techniques, this method is useful when using a laser light source, since the acousto-optic crystal can accommodate high-intensity laser light. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 9–15, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20279

音響光学偏向器を用いたレーザ光強度分布の高速度撮影

An acousto-optic laser deflector was used to image the intensity distribution of a continuous wave laser in the order of μs. Undeflected light was blocked while the deflected light was directed to a CCD camera, which allowed imaging of the incident laser intensity distribution in the order of μs. Experiments using a test pattern showed that there was no distortion in the deflected image. The resolution limit, estimated from diffractive effects, was about 0.2 mrad. Using this method of high-speed imaging, density variations accompanying laser-induced breakdown in air were visualized by shadowgraphy and interferometry.