Simple Optical Configuration Research Articles

Noncontact Speckle-Based Velocity Sensor

Laser light illuminating a rough surface generates speckle phenomena in the space around the surface. In this paper, the authors propose a noncontact laser Doppler vibrometer (LDV) sensor, using the speckle phenomena, for the assessment of target velocity and displacement at low vibration frequencies. The sensor is realized using few optical components in a very simple optical configuration. The methodology for the experimental and analytical determination of the sensor sensitivity is reported, and two speckle-processing algorithms have been used to appraise the best cross-correlation function for target velocity measurement. The algorithms are based on binary correlation and fast Fourier transform analysis. Experimental results coming from the comparison of both the proposed techniques are reported. Moreover, results obtained with the proposed speckle sensor have been compared with reference measurement systems. Results show that this noncontact sensor is characterized by a reduced optical complexity and low cost. It appears to be particularly suitable for use in the analysis of low velocity rough surfaces.

Pretilt Angle Measurement Method for Twisted Nematic Cells with Low Cell-Gap

We propose a method to measure the pretilt angle as well as the cell gap in TN cells with low cell-gap with a single wavelength source. We use simple optical configurations with a TN cell between an analyzer and a polarizer. As we rotate the analyzer by 180°, we can find analyzer angles at which the transmittance is minimum or maximum under normal or oblique incidence. By using the measured analyzer angle, we can determine the pretilt angle.

Holographic Data Storage

In the last several years, the research and development of high capacity information storage using holographic technology has been actively carried out by many researchers. This has been driven by several factors. First, the availability and performance of components for drives have changed dramatically. Second, low-cost polymeric storage media which meet many requirements for practical drive systems have been developed. Third, new multiplexing technologies which permit very high density storage with simple optical system configurations have been developed. Holographic data storage technologies could satisfy the requirements of the data warehousing and information processing, as well as of the many applications related with the broadband network to meet the demands of internet traffic. In this paper, we show an outline of holographic data storage technologies. Technology contents relate to a system configuration, recording media and signal processing of two-dimensional digital data. We also discuss the future potential of holographic memory.

Radiative decay engineering 3. Surface plasmon-coupled directional emission

A new method of fluorescence detection that promises to increase sensitivity by 20- to 1000-fold is described. This method will also decrease the contribution of sample autofluorescence to the detected signal. The method depends on the coupling of excited fluorophores with the surface plasmon resonance present in thin metal films, typically silver and gold. The phenomenon of surface plasmon-coupled emission (SPCE) occurs for fluorophores 20–250 nm from the metal surface, allowing detection of fluorophores over substantial distances beyond the metal–sample interface. SPCE depends on interactions of the excited fluorophore with the metal surface. This interaction is independent of the mode of excitation; that is, it does not require evanescent wave or surface-plasmon excitation. In a sense, SPCE is the inverse process of the surface plasmon resonance absorption of thin metal films. Importantly, SPCE occurs over a narrow angular distribution, converting normally isotropic emission into easily collected directional emission. Up to 50% of the emission from unoriented samples can be collected, much larger than typical fluorescence collection efficiencies near 1% or less. SPCE is due only to fluorophores near the metal surface and may be regarded as emission from the induced surface plasmons. Autofluorescence from more distal parts of the sample is decreased due to decreased coupling. SPCE is highly polarized and autofluorescence can be further decreased by collecting only the polarized component or only the light propagating with the appropriate angle. Examples showing how simple optical configurations can be used in diagnostics, sensing, or biotechnology applications are presented. Surface plasmon-coupled emission is likely to find widespread applications throughout the biosciences.

Reduction photolithography using microlens arrays: applications in gray scale photolithography.

This paper describes the application of reduction photolithography, using arrays of microlenses and gray scale masks, to generate arrays of micropatterns having multilevel and curved features in photoresist. This technique can fabricate, in a single exposure, three-dimensional microstructures (e.g., nonspherical microlens arrays) over areas of approximately 2 x 2 cm2. The simple optical configuration consisted of transparency film (having centimeter-sized features) as gray scale photomasks, an overhead projector as the illumination source, and arrays of microlenses as the size-reducing elements. Arrays of 40- and 100-microm lenses achieved a lateral size reduction of approximately 10(3) and generated patterns of well-defined, multilevel structures; these structures may find use in applications such as diffractive optics.

Simultaneous detection of bacteria expressing GFP and DsRed genes with a flow cytometer.

In this study, Escherichia coli cells producing red fluorescent protein of Discosoma sp. (drFP583 DsRed) were investigated with flow cytometry by using 488 nm excitation. We also studied whether green fluorescent protein (GFP) and drFP583 could be detected simultaneously from a single bacterial cell. Plasmids pDsRed and pEGFP were used for the production of drFP583 and enhanced GFP, respectively, in E. coli MC1061 cells. To produce enhanced GFP and drFP583 simultaneously, plasmids pG9R and pG19R were constructed. These encode tandem fusions of enhanced GFP and drFP583 to ensure similar production levels for both proteins. Bacteria producing enhanced GFP and drFP583 were found to be brightly green and red fluorescent, respectively. Production of enhanced GFP and drFP583 fusion proteins resulted in bacteria that emitted both green and red fluorescence, which was detected easily by a flow cytometer using single laser excitation. Previously reported tetramerization of drFP583 did not restrict its use as a reporter gene, although it maturated significantly slower than enhanced GFP. The results show that enhanced GFP and drFP583 proteins can be detected simultaneously from single bacteria with a standard flow cytometer with simple optical configuration.

A Method of Reversible Biomolecular Immobilization for the Surface Plasmon Resonance Quantitative Analysis of Interacting Biological Macromolecules

This article presents a new procedure for the immobilization of macromolecules on gold surfaces, with the purpose of studying macromolecular interactions by simple optical configurations rendering surface plasmon resonance. Gold surfaces were covered by a three-layer structure composed of poly-l-lysine irreversibly bound to gold, followed by a second layer of heparin and a third layer of polylysine. The three-layer structure of polylysine–heparin–polylysine remains irreversibly bound to gold, it prevents biomolecules from coming into direct contact with the metal surface, and it allows the irreversible binding of different proteins and polynucleotides. After binding of a macromolecule to the three-layer structure, the interaction with a second macromolecule can be studied, and then the complex formed by the two interacting macromolecules, together with the second heparin layer and the third polylysine layer, can be broken down just by treatment with an alkaline solution having a pH value above the pK value of the amino groups of polylysine. The first polylysine layer remains irreversibly bound to gold, ready to form a new three-layer structure and, therefore, to support a new macromolecular interaction on the same regenerated surface. Polynucleotide interactions, the proteolytic action of chymotrypsin, and the interaction between the component subunits of a heterotetrameric enzyme are described as examples of macromolecular interactions studied by using this system. The method may be especially suitable for developing of low-cost systems aimed to look for surface resonance signals, and it offers the advantage of allowing calculation of parameters related to the size and stoichiometry of the interacting macromolecules, in addition to the kinetic and equilibrium properties of the interaction.

Quantification and evaluation of Joule heating in on-chip capillary electrophoresis.

We present the use of a novel, picoliter volume interferometer to measure, for the first time, the extent of Joule heating in chip-scale capillary electrophoresis (CE). The simple optical configuration for the on-chip interferometric backscatter detector (OCIBD) consists of an unfocused laser, an unaltered silica chip with a half-cylinder channel and a photodetector. Using OCIBD for millidegree-level noninvasive thermometry, temperature changes associated with Joule heating (2.81 degrees C above ambient) in on-chip CE have been observed in 90 microm wide and 40 microm deep separation channels. The temporal response of Joule heating in isotropically etched channels was exponential, with it taking an excess of 2.7 s to reach equilibrium. Buffer viscosity changes have also been derived from empirical on-chip thermometry data, allowing for the determination of diffusion coefficients for solutes when separated in heated buffers. In addition, OCIBD has allowed the reduction in separation efficiency to be estimated in the absence of laminar flow and due to increased molecular diffusion and lower buffer viscosity. A 7% reduction in separation efficiency was determined for a high current drawing buffer such as Tris-boric acid under an applied field of just 400 V/cm. Results indicate that heating effects in on-chip CE have been underestimated and there is a need to readdress the theoretical model.

Fringe projection based on Moiré method for measuring aberration of axially symmetric optics

We present a new approach based on a very simple optical interferometric configuration that can be useful for measuring wave front aberrations in optical components having axial symmetry. The optical configuration requires only two mutually coherent plane wave fronts transmitted through or reflected by the optical component under test. The method can be considered as an interferometric fringe projection method. It can also be interpreted also as a reversal shear interferometer. The finite Moiré beating between the interferograms and the CCD array is used to subtract a linear carrier introduced by defocus and tilt making the presence of third order coma and spherical aberrations more evident. Applications of the technique for measuring aberrations of simple biconvex spherical lens and a plano-spherical laser micro-cavity are reported.

Low-cost device for ratiometric fluorescence measurements

An all-solid-state, low-cost device for fluorescent wavelength-ratiometric detection is described. Ultrabright light-emitting diodes were used as light sources. This allowed electronic modulation of the light, simple optical configuration, and miniaturization of the instrument. Narrow-bandpass interference filters were used for wavelength separation. Detection was accomplished by high-sensitivity, large-surface PIN photodiodes. An integrating double-ramp technique with fixed upper and lower thresholds was employed for conversion of the light intensities into time intervals. The duty ratio of the output signal was a function of the fluorescence intensity ratio. Additionally, the concentration of the fluorophore could be measured. The device could be easily designed as a battery-operated version. It could be used for a variety of ratiometric fluorescence measurements.

Simple System for Generation and Detection of Tunable-Frequency Far Infrared Light

The system described in this paper has a simple optical configuration for guiding far infrared light to a detector, and thus requires neither a Michelson-type diplexer nor a Fabry-Perot-type filter, both of which require fine adjustments. In this system, all the components that generate, guide, and detect far infrared light work at room temperature. It uses a Schottky barrier diode for heterodyne detection rather than a conventional thermal detector, such as a cooled bolometer for direct detection. The system is simpler than the conventional system, yet it maintains high sensitivity to FIR radiation. Experimental results demonstrate the principal behavior of this system. The modulation factor and the tunable-frequency far infrared power is estimated by using an equivalent circuit model with a Schottky barrier diode. The estimated far infrared power is compared with the values reported in other papers. The results of a gas absorption measurement with this system are also discussed.

Integrated cavity output analysis of ultra-weak absorption

It is demonstrated that direct absorption optical measurements with sensitivities of better than 1 part in a million can be made using pulsed light sources and employing a simple cavity optical configuration. A model is presented which demonstrates that the integrated absorption signal provides a quantitative total attenuation measurement if the absorption cavity mirror reflectivities are known. This approach to making absorption measurement provides a sensitivity comparable to that realized using the time-domain cavity ringdown approach with a significant reduction in complexity. The approach is demonstrated using the weak b 1 Σ g(v′=1) – X 3 Σ g(v″=0) forbidden absorption of oxygen near 689 nm.

X-ray absorption beamline at the Mitsubishi compact storage ring.

Beamline #5 (BL#5) at the Mitsubishi compact storage ring (MELCO-SR) is a beamline designed to perform X-ray absorption experiments in the 1-5 keV energy range. MELCO-SR is a racetrack-type storage ring with compact superconducting magnets, which is operated at 600 MeV, mainly for X-ray lithography experiments. As the ring is set in a shield wall of 2 m thickness, a point just outside the shield wall of BL#5 is located at 6.8 m from the source point. A small toroidal mirror, located inside the shield wall at 3.4 m from the source, focuses the beam vertically and horizontally onto the 7.3 m point. This simple optical configuration allows us to bring the source point outside of the shield wall, and to collect about 10 mrad horizontally and maintain small footprints on the monochromator crystal. A new 'Cowan type' monochromator, located at 7.4 m from the source and selected for simplicity of design and for stability, will provide a bright high-resolution and stable X-ray beam for use in the X-ray spectroscopy of electronic materials in MELCO.

Remote semiquantitative two-dimensional flow transport imaging using microendoscopic probes

A flexible microscope is configured, evaluated, and employed in the noninvasive investigation of fluid transport in a tissuelike model or porous, fibrous matrix. A simple optical configuration that employs microendoscopic probes, an objective lens, and a commercial CCD for detection, produces resolution performance in the range of 25 to 40 line pairs/mm (lp/mm). Remote, time-sequenced imaging is shown to be possible using this moderate resolution flexible microscope. The microendoscopes employed are 1 to 3 m in length and range in outer diameter from 1.5 to 2.5 mm; some contain a working lumen for the introduction of a tool or a fluid at the site of investigation. Target lighting is accomplished by an integral fiber bundle built into the endoscope and supplied from an external xenon discharge lamp. This instrumentation is combined with specialized image processing for quantitative, time-sequenced imaging of marker dye transport on a tissuelike model substrate. Quantitative absorbance imaging is accomplished by calibrating response for marker dye standards on the test substrate and correlating camera pixel grayscale values to solute concentration. The quantitative mapping (concentration versus time and position) of fluid transport is used to evaluate convective versus diffusive flow.

Development of electronic shearography for vibration analysis

This paper describes a measuring method of vibration mode shapes by the Electronic Shearography. This method called the speckle interferometer has many merits in practical use, such as low sensitivity to environmental noise, low limit of coherent-length and simple optical configuration. In this study, we developed Michelson-type shearing interferometer provided with a phase stepping mirror and with a bias modulation mirror to quantify the vibration gradient fields. Results of application to a simple cantilever plate show that the vibration amplitude fields obtained are in good agreement with those of the electronic speckle pattern interferometry (ESPI).

Exposure-induced high-pass filtering of a volume by means of an absorption hologram recording technique

High-pass filtering effects have long been noted during recording of Fourier-type holograms on a saturable medium [Collier et al., Optical Holography (Academic, New York, 1971), p. 405]. The origin of the filtering effect lies in recording an absorption hologram such that the diffraction efficiency of strong spatial frequencies is significantly reduced by the saturable nature of the film. A simple optical configuration is used to take advantage of this effect in order to reduce the depth-of-focus noise associated with particle holography. The origin of the noise is clutter produced by a field of out-of-focus particles in which the particle under scrutiny exists [Reynolds et al., The New Physical Optics Notebook: Tutorials in Fourier Optics(Society of Photo-Optical Instrumentation Engineers, Belling-ham, Washington, 1989), p. 2054. A theoretical basis for the filtering is presented. Experimental results are shown.

Capillary-Scale Refractive Index Detection by Interferometric Backscatter

We describe a novel approach for measuring fluid bulk properties such as refractive index (RI) and temperature changes in tubes of capillary dimensions based on a simple optical configuration which uses an unfocused He-Ne laser, a cylindrical tube, and a photodetector. Side illumination of a fused silica capillary produces a fan radiation in a 360° plane normal to the central axis of the capillary that is spatially well defined in the lateral direction. It is shown that, upon viewing a high-contrast interference pattern contained in the beam profile on a flat imaging plane in a direct backscattering configuration, the physical characteristics of the capillary and the bulk properties of the fluid contained within the tube can be determined. Position changes in the maxima and minima in the intensity-modulated profile (interference fringes) are directly related to the refractive index of the fluid in the tube. Measurement of the fringe shift by a slit-photodetector assembly facilitates the determination of dn/n at the level of 1.8 x 10 -7 , while temperature changes can be measured using the fringe centroid position at a level of 5.8 x 10 -5 °C (DL = 3σ). Each determination can be made within a probe volume of 2.6 nL. Also, awide range of tube diameters can be employed (75-775 μm i.d.) with no modification to the optical train or measurable degradation in system performance. We report results for an optical ray trace model for predicting fringe pattern energy distributions, optimization of the optical configuration, and general system performance predictions. Comparison of our four-beam interference model with experimental results illustrates the utility of the model.

Polarimetry in Capillary Dimensions

Microinterferometeric backscatter is employed to detect optically active molecules in capillary tubes. The capillary polarimetric detector (CPD) is based on the interaction between a polarized laser beam and a capillary tube. The simple optical configuration employs a He−Ne laser, a glass polarizing plate, a fused silica tube, and a CCD-based laser beam analyzer. Side illumination of the capillary produces a 360° fan of scattered light that contains two sets of high-contrast interference fringes. These light and dark spots are viewed on a flat plane in the direct backscatter configuration. It is shown that the modulation depth for the high-frequency component is sensitive to the polarization plane for the illumination source and facilitates the quantitative determination of optical activity for a fluid contained in a capillary. A 90° rotation of exciting plane-polarized light results in a depth of modulation change of ∼80% when unmodified capillaries ranging from 75 to 530 μm i.d. are employed. Signal interrogation in the CPD is based on quantifying the relative intensities (depth of modulation) of adjacent high-frequency interference fringes. Mandelic acid, [α]23 of −153°, is used as the optically active molecule and can be detected at a 2σ detection limit of 1.49 × 10-3 M within a probe volume of about 30 nL. This limit of detection corresponds to 44 pmol or 6.7 ng of mandelic acid. The folded optical arrangement is simple and can be miniaturized with low-cost components. Initial investigations suggest that the CPD can be employed for detection in capillary electrophoresis or for studying the onset and level of solute aggregation.

Efficient low-energy near-infrared KTiOPO_4 optical parametric converter

We report a widely tunable near-infrared holosteric KTiOPO(4) optical parametric converter featuring a low pump energy threshold and high conversion efficiency. The converter uses two 10-mm-long crystals in a simple optical parametric oscillator amplif ier configuration and is tunable from 750 to 1040 nm for the signal. The pump energy threshold at 920 nm is 0.44 mJ for the 532-nm 8-ns 50-Hz input. The system produces as much as 0.45 mJ of energy at 920 nm with an external pump-to-signal energy conversion efficiency of 27% for pump inputs from just two times the threshold value. The internal pump-to-signal and idler energy conversion efficiency is estimated to be 58%. The low pump energy requirement of this system makes it compatible with small laser-diode-pumped solid-state lasers.

Fiber-optic high-temperature sensor based on the fluorescence lifetime of alexandrite

A fiber-optic sensor for continuous temperature measurement from room temperature to ≳700 °C is presented. The device is based upon the excitation of the synthetic crystal alexandrite with light from a diode laser operating at 670 nm and the measurement of its fluorescence lifetime. A simple low cost optical configuration is described together with the introduction of a new effective signal processing scheme for fluorescence lifetime measurement, and a high sensitivity and repeatability are observed, at best ±1 °C.