Optical Beam Deflection Research Articles

The collapse and rebound of laser-induced cavitation bubble in viscous fluid

The oscillation property of a laser-induced cavitation bubble in a viscous fluid is investigated by a sensitive fiber-optic sensor based on optical beam deflection. The temporal and spatial evolutions of the bubble wall during the expansion and collapse are traced according to sequential waveforms induced by the bubble oscillation. Both the maximum and minimum bubble radii at each oscillation cycle are determined by experiment. Further, in combination with the theoretical analysis and numerical calculation, the variation of the maximum and minimum radii during oscillation and life-time of the bubble in different viscous fluids is obtained. The experimental results indicate that the liquid viscosity has an obvious influence on the bubble oscillation; larger viscosity makes the bubble contract more slowly, and the corresponding minimum radius and the bubble life-time become larger and longer, while the maximum radius is smaller.

Bioenzymatic detection of troponin C using micro-opto-electro-mechanical systems

Diagnosis and monitoring of critical diseases such as acute myocardial infarction (AMI) require a quantitative analysis of biological molecules. A high-throughput identification of these biological molecules can be generated by using micro-electro-mechanical systems (MEMS) structures like simple cantilever beams, which respond to the intermolecular forces resulting from binding these molecules. Biochemical markers like troponin C are considered the primary markers for myocardial injury and have generated considerable interest. A 26-residue lytic membrane protein of bee venom melittin (ME) is chosen to interact with rabbit skeletal muscle troponin C (TnC) on the surface of the cantilever beams. An optical beam deflection method is employed to identify the enzymatic reaction on the surface of the cantilever due to these proteins. Identification of these proteins is also done using fluorescence spectroscopy (FS) to compliment the optical monitored deflection method. A second set of proteins like horse radish peroxide (HRP) and hydrogen peroxide (H2O2) are applied to atomic force microscopy (AFM) cantilever beams to study their behavior under the enzymatic reactions of proteins. Identification of these proteins is done using Fourier transform infrared spectroscopy (FTIR). An analytical model of the cantilever beam is developed, and its mode shapes are studied by employing orthogonal polynomials in the classic Rayleigh-Ritz method. The surface stress caused by the enzymatic reaction of the proteins that leads to pure bending on the top surface of the cantilever is evaluated. The information provided by the experimental and analytical modeling reported in this work will be useful in the development of a portable biosensor for the detection of AMI.

Impact of a liquid-jet produced by the collapse of laser-induced bubbles against a solid boundary

The mechanical effect induced by the collapse of cavitation bubbles in the neighborhood of a solid boundary is investigated by focusing a Q-switched laser pulse on a metal target in water. By means of a fiber-coupling optical beam deflection technique, the displacement generated by liquid-jet impact at the final stage of the bubble collapse is detected at the epicenter of the rear metal surface. Furthermore, combining a widely used laser-ablation model with the detection principles of this detector, the transient impact-force value loading on the target material can be easily estimated. Besides, according to experimental results and the modified Rayleigh theory, the maximum bubble radius and the liquid-jet pressure are also obtained, which are in good agreement with the results of other studies. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1525–1528, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21706

Temporal position encoding photoacoustics: A technique for surface absorber mapping

A nondestructive photoacoustic method for the evaluation of surface absorber distributions is presented. Ultrasound generated by absorption of a pulsed laser source is detected using optical beam deflection. Temporal encoding of the spatial absorber distribution is achieved using a nonparallel orientation of the probe beam relative to the sample surface. Sound waves launched from individual surface absorbers travel different distances before interacting with the probe beam, thus giving rise to acoustic signatures at different times. With this approach, we resolved eleven identical absorber features in a 3–cm-wide sample. Decreasing the probe beam diameter enhances the temporal and/or spatial resolution. A limiting spatial resolution of 175μm is predicted. The sound wave intensity decays in a roughly inverse square-root manner with increasing distance of travel.

Frequency-modulation atomic force microscopy at high cantilever resonance frequencies using the heterodyne optical beam deflection method

We have developed a frequency-modulation atomic force microscope (FM-AFM) with a wideband cantilever deflection sensor using the heterodyne optical beam deflection method. The method enhances the bandwidth of the deflection measurement up to the maximum frequency for the laser power modulation, which can be as high as gigahertz order. The phase and frequency of the cantilever vibration at 5.24MHz are detected with a deflection noise density of 100fm∕Hz. FM-AFM imaging is performed on a Au(111) surface with a high-frequency cantilever.

Dynamics of laser-induced shock wave by optical probe in air

A new simple optical system based on optical beam deflection combining the holophote corner cube was developed in order to study the dynamics of laser-induced shock waves in air. In this method, we adopt a He–Ne laser beam as the detection beam. The He–Ne laser beam, reflected by corner cube, intersects the propagating shock wave at two successive positions. The measurement of the shock wave velocity benefits from the double peak signals induced by the same acting laser pulse, which is calculated from the time interval between the corresponding oscilloscope signals and the distance of the two He–Ne laser beams. By virtue of this setup, we are also able to determine the pressure of the generated shock waves. It is shown that this method is simple with a fairly good precision and is much easier than the conventional methods used for this task.

Development of a high velocity accessory for atomic force microscopy-based friction measurements

A high velocity accessory for friction force microscopy measurements for velocities up to the mm/s range was developed for a commercial stand-alone atomic force microscope (AFM). The accessory consists of a shear piezo element, which rapidly displaces the sample in the lateral direction, perpendicular to the main axis of the AFM cantilever. Friction forces, which are acquired via conventional optical beam deflection detection, can thus be measured as a function of velocity and load in controlled environment (0–40% relative humidity and 0–40°C). Using the accessory, a broad range of velocities up to several mm/s can be accessed independent of the lateral scan size up to a maximum scan size of 1000nm. The velocity dependence of friction forces and coefficients was measured on organic [poly(methylmethacrylate)], as well as inorganic [oxidized Si(100)] samples to demonstrate the feasibility and underline the importance of high velocity nanotribology using this accessory.

Fabrication of piezoresistive microcantilever using surface micromachining technique for biosensors

A microcantilever-based biosensor with piezoresistor has been fabricated using surface micromachining technique, which is cost effective and simplifies a fabrication procedure. In order to evaluate the characteristics of the cantilever, the cystamine terminated with thiol was covalently immobilized on the gold-coated side of the cantilever and glutaraldehyde that would be bonded with amine group in the cystamine was injected subsequently. This process was characterized by measuring the deflection of the cantilever in real time monitoring. Using a piezoresistive read-out and a well-known optical beam deflection method as well, the measurement of deflection was carried out. The sensitivity of piezoresistive method is good enough compared with that of optical beam deflection method.

Transport of Nanoscale Latex Spheres in a Temperature Gradient

We use a micrometer-scale optical beam deflection technique to measure the thermodiffusion coefficient D(T) at room temperature (approximately 24 degrees C) of dilute aqueous suspensions of charged polystyrene spheres with different surface functionalities. In solutions with large concentrations of monovalent salts, < or approximately = 100 mM, the thermodiffusion coefficients for 26 nm spheres with carboxyl functionality can be varied within the range -0.9 x 10(-7) cm2 s(-1) K(-1) < D(T) < 1.5 x 10(-7) cm2 s(-1) K(-1) by changing the ionic species in solution; in this case, D(T) is the product of the electrophoretic mobility mu(E) and the Seebeck coefficient of the electrolyte, S(e) = (Q(C)* - Q(A)*)/2eT, D(T) = -S(e) mu(E), where and are the single ion heats of transport of the cationic and anionic species, respectively. In low ionic strength solutions of LiCl, < or approximately = 5 mM, and particle concentrations < or approximately = 2 wt %, D(T) is negative, independent of particle concentration and independent of the Debye length; D(T) = -0.73 +/- 0.05 x 10(-7) cm2 s(-1) K(-1).

Development of low noise cantilever deflection sensor for multienvironment frequency-modulation atomic force microscopy

We have developed a low noise cantilever deflection sensor with a deflection noise density of 17fm∕Hz by optimizing the parameters used in optical beam deflection (OBD) method. Using this sensor, we have developed a multienvironment frequency-modulation atomic force microscope (FM-AFM) that can achieve true molecular resolution in various environments such as in moderate vacuum, air, and liquid. The low noise characteristic of the deflection sensor makes it possible to obtain a maximum frequency sensitivity limited by the thermal Brownian motion of the cantilever in every environment. In this paper, the major noise sources in OBD method are discussed in both theoretical and experimental aspects. The excellent noise performance of the deflection sensor is demonstrated in deflection and frequency measurements. True molecular-resolution FM-AFM images of a polydiacetylene single crystal taken in vacuum, air, and water are presented.

Optimized detection of normal vibration modes of atomic force microscope cantilevers with the optical beam deflection method

Recently, higher-order normal vibration modes of atomic force microscope cantilevers were utilized for functional imaging applications. Here, we present a detailed theoretical investigation of the sensitivities with which these modes are detected using the optical beam deflection method. The detection sensitivities depend strongly on the size and position of the focused optical spot. Optimization of the sensitivities is performed for the individual (transverse) normal modes. For the case that multiple normal modes need to be detected simultaneously, a universal sensitivity function is constructed. This function generates accurate values for the detection sensitivity as a function of spot diameter and mode number. Finally, different optimization strategies for the simultaneous detection of multiple normal modes are presented.

Calculation of thermal noise in an atomic force microscope with a finite optical spotsize

We present a method to calculate the thermal noise in an atomic force microscope (AFM)that employs the optical beam deflection (‘optical lever’) detection technique with a finitefocused optical spot size. This method is based on optical diffraction theory and extendsthe formulation by Butt and Jaschke (1995 Nanotechnology 6 1), who assumed a spot ofinfinitesimal size. We consider multiple flexural vibration modes of the cantilever and showthat the measured thermal noise strongly depends on the spot size. In general, largerfocused spots result in less measured thermal noise, while this dependence is morepronounced for a cantilever with a pinned tip than for a cantilever with a free tip. Weanalyse the amount of thermal noise that appears in contact mode and force spectroscopymeasurements, and discuss how to reduce it by selecting beneficial experimental conditions.

Piezoresistive Scanning Proximity Probes for Nanoscience (Piezoresistive Raster-Kraftsonden für die Nanowissenschaften)

Abstract This article is devoted to the realization of piezoresistive sensors used in scanning probe microscopy. It is expected that in the near future major technological breakthroughs in scanning proximal probe nanotools will allow for key scientific impact on analysis and synthesis of nanostructures. All the piezoresistive cantilever sensors described here are based on advanced silicon micromachining and standard CMOS processing. Moreover, using a newly optimized piezoresistive detection scheme process comprising a Wheatstone bridge, we have designed and fabricated piezoresistive cantilevers for atomic force microscopy, which improve surface topography resolution by an order of magnitude to 0.1 nm. The elegance of this concept is that by using an almost identical detection principle and differently functionalized tips or cantilever surfaces, we can detect subtle sample interactions (mechanical, electrical, thermal, and chemical) with a significantly more compact system than with optical beam deflection techniques. For noncontact scanning force microscopy, we integrate a thermally driven bimorph actuator with the piezoresistive cantilever and make use of direct-oscillation in a higher flexural mode. The cantilever then operates in the phase-shift atomic force microscopy (AFM) detection technique.

Dynamic force microscopy at high cantilever resonance frequencies using heterodyne optical beam deflection method

We have developed a dynamic force microscope (DFM) with a wideband cantilever deflection sensor using heterodyne optical beam deflection (HOBD) method. The bandwidth of HOBD method is limited only by the maximum frequency for laser power modulation, which can be as high as gigahertz order. This technique allows us to use high cantilever resonance frequencies for improving the sensitivity and time response of DFM. In this letter, basic principle and experimental setup of HOBD method are described. Deflection measurement of a cantilever vibration at about 7MHz is demonstrated. Using this cantilever, DFM imaging with a relatively fast scanning speed is performed.

Optical sequential readout of microcantilever arrays for biological detection

A technique for the readout of the nanomechanical response of multiple microcantilevers is presented. This combines the optical beam deflection technique and the scanning of a laser beam illuminating the cantilevers of an array sequentially. The individual motion of each microcantilever is obtained by correlating the total photocurrent collected in a photodetector array, the position of the laser beam and the coordinates of the laser spot centroid on the photodetector. The technique provides sub-angstrom resolution in the cantilever deflection and it allows the readout of tens of cantilevers per second. This is applied for the quasi-simultaneous detection of single-stranded DNA with an array of five microcantilevers. Moreover, this technique also allows the measurement of the resonant frequency of individual microcantilevers into an array. This can be applied for multiple detection of several pathogen targets.

Optical Deflection Technique for Investigation of Laser-Induced Oscillating Bubble on Metal Surface

The oscillation of a laser-generated single cavitation bubble on a metal surface is investigated by a fiber-optic diagnostic technique based on an optical beam deflection (OBD). The sequence of waveforms induced by the bubble pulsation is obtained with respect to detection distance. The maximum and minimum bubble radii for each oscillation cycle are determined from the experimental results. Furthermore, by tracking the arrival time of a bubble wall during its expanding and collapsing stages, the temporal development of a cavitation bubble on the metal surface is obtained.

High Aspect Ratio Micromirrors With Large Static Rotation and Piston Actuation

Monolithic high aspect ratio silicon micromirror devices were demonstrated with fully isolated vertical comb drives micromachined from the back side and front side of a 50-/spl mu/m silicon-on-insulator device layer. The devices are suspended by torsional support beams and exhibit bidirectional single-axis rotation, as well as independent up- and down-pistoning actuation. The comb drives are fabricated with initial comb-finger preengagement of up to 10 /spl mu/m for constant force actuation and have accurately self-aligned comb-fingers. Device 1 with a 30-/spl mu/m-thick support beam measured static optical beam deflection from -20/spl deg/ to 19/spl deg/ and bidirectional pistoning motion from -7.5 to 8.25 /spl mu/m. Device 2 utilizes a highly compliant 10-/spl mu/m-thick support beam and measured static optical beam deflection from -14/spl deg/ to 16/spl deg/ and downward pistoning motion to -12.5 /spl mu/m, all at <70 V.

High-resolution optical angle sensors: approaching the diffraction limit to the sensitivity.

We carry out a detailed analysis of angle-sensitive devices based on the critical-angle effect. We consider their use in measuring small angular deflections of a laser beam. We establish the diffraction limit to the sensitivity for optical-angle sensors based on reflection and transmission of a laser beam. We find that this limit is identical to that of the triangulation scheme when using a position-sensitive detector or the autocollimation scheme. We analyze the main proposals to date of optical-angle sensors based on the critical-angle effect, focusing on their maximum sensitivity and their polarization dependence in practical conditions. We propose and analyze theoretically a novel and simple angle-sensitive device for sensing optical-beam deflections with very low polarization dependence and a maximum sensitivity close to the diffraction limit when used with typical laser beams. We discuss the basic principles for designing this type of device, provide numerical results, and point out a convenient fabrication procedure.

Shock-wave propagation and cavitation bubble oscillation by Nd:YAG laser ablation of a metal in water.

A highly sensitive fiber-optic sensor based on optical beam deflection is applied for investigating the propagation of a laser-induced plasma shock wave, the oscillation of a cavitation bubble diameter, and the development of a bubble-collapse-induced shock wave when a Nd:YAG laser pulse is focused upon an aluminum surface in water. By the sequence of experimental waveforms detected at different distances, the attenuation properties of the plasma shock wave and of the bubble-collapse-induced shock wave are obtained. Besides, based on characteristic signals, both the maximum and the minimum bubble radii at each oscillation cycle are determined, as are the corresponding oscillating periods.

Self-Hold and Precisely Controllable Optical Cross-Connect Switches Using Ultrasonic Micro Motors

In this paper, we propose new optical cross-connect switches using ultrasonic micro motors, whose features are self-hold, precise control, and low electric power consumption. Two methods are examined for optical beam deflection. One method is moving the lens and the other is rotating the mirror by using ultrasonic micro motors. The light from the optical fiber is collimated using a self-focusing (SELFOC) lens and is deflected by moving the lens, with an ultrasonic linear motor, perpendicularly to the fiber axis. The light is then coupled to another fiber. Another proposed method is to use reflection mirrors. This structure is composed of a magnetized material attached to a micro mirror and a permanent magnet mounted on a shaft of an ultrasonic rotation motor. The reflected beam is deflected by rotating the mirror. In both methods, precise beam deflection is demonstrated, and optical switching characteristics are confirmed.