Position-sensitive Photodiode Research Articles

High-precision magnetic levitation device with electro-optical feedback

We report on a magnetic levitation device with electro-optical feedback which allows for precise stabilization of the vertical position of the levitated piece (LP) within 1 μm. The vertical position of the LP is monitored through the reflection of a laser beam on a mirror placed in the upper part of the LP. The reflected beam goes to a position sensitive photodiode and suitable electronics transforms the fluctuations in the vertical position of the LP to an electrical signal. This signal is fed into a PID controller that drives an electromagnet. The output of the detection stage yields high-precision measurements of the fluctuations in the vertical position of the device and the current fed to the electromagnet provides a precise reading of the vertical force felt by the levitating part. We have also developed a model that explains most of the dynamical behavior observed. We have formulated the dynamical equations of the system and, by means of a linear perturbation technique, we have obtained the stability characteristics which compare well with the experimental response.

Measurement of interfacial shear rheological properties: An apparatus

A new surface shear rheometer was designed on the basis of the principle of a torsion pendulum. The torsion wire transfers the deformation, produced by a stepper motor, via a sharp edge onto the surface. The movement of the edge is registered by a position-sensitive photodiode with an accuracy to ±0.01°. After an impulsive torque is applied by a rapid movement of the torsion head the pendulum performs damped oscillations with a damping factor α and a radian frequency β. This type of apparatus provides information on the surface shear coefficient of viscosity and the surface shear modulus of rigidity in one single experiment. Different instrumental parameters are discussed which influence the range of application and the accuracy of the measurements. Different applications of the set-up to protein solutions (gelatine and human albumin) alone and mixed with a surfactant are discussed. The experimental data demonstrate the high reproducibility and accuracy of the apparatus.

Microfabricated surface plasmon sensing system

Abstract The microfabricated surface plasmon sensor is a hybrid system that integrates optical, mechanical and electronic components. The sensor contains elements that are common to numerous electro-optical systems, creating a miniature optical bench. The microsystem elements include a single-mode optical fiber, a graded index collimating lens, a scanning rotating micro-mirror, a cavity filled with index matching fluid, and a position sensitive photodiode. The elements are both laterally and vertically aligned using multi-substrate bonding and positive component-to-component alignment.

Optical monitoring of the solidification process of polyester and vinyl resins

Ultrasonic waves were generated and detected by laser light in solidifying polyester and vinyl resins, allowing an evaluation of the extent of reaction by a non-contact method. Commercial polyester and vinyl resin samples were prepared following the standard procedure under room conditions. A liquid adjacent to the sample was irradiated by a pulsed Nd:YAG laser beam. The resulting ultrasonic wave was detected in the sample at two distances from the source by the deflection of an HeNe laser probe beam. The displacements of the probe beam were detected by a position-sensitive photodiode. Arrival times of the ultrasonic pulses at various times during the solidification were measured and the corresponding propagation velocities calculated. The method is aimed at monitoring the final part of the solidification, after the gelation has taken place, and will allow the investigation of the influence of various parameters of the course of the reaction and on the final properties of the material.

Surface-plasmon excitation using a polarization-preserving optical fiber and an index-matching fluid optical cell

Existing experimental configurations to excite surface plasmons are reviewed, and a new experimental method for exciting surface plasmons is described. A transverse magnetic polarized wave is guided by a polarization-preserving optical fiber, collimated by a gradient-index lens, and launched into an optical cell filled with index-matching fluid. The wave is reflected off of a rotating mirror and excites a surface plasmon on a dielectric-metal interface by attenuated total reflection. The reflectance and incidence angles are measured simultaneously with a position-sensitive photodiode. The main advantages of this new method, compared with existing methods, are the low equipment costs and the ease with which a variety of surface-plasmon experiments can be performed.

Measurement of mechanical accuracy of isocenter in conventional linear-accelerator-based radiosurgery

Five Varian linear accelerators were studied to determine whether their mechanical isocentric accuracies were sufficient for radiosurgery and, if not, if the observed errors were sufficiently consistent and predictable to be correctable by some form of secondary collimator steering device to maintain isocentric alignment. A 0.3 mW 670 nm diode laser was mounted in the secondary collimator insert of a radiosurgery extended collimator assembly. A cylindrical lens was used to create a laser fan beam that passed through isocenter and could be oriented parallel or perpendicular to the plane of rotation. A position sensitive photo-diode having an electrical output that varied with the portion of its surface illuminated was mounted at isocenter in a rotational mount. This mount tracked the accelerator gantry such that the surface of the photo-diode remained perpendicular to the laser beam during gantry rotation. An X/Y recorder was connected to the gantry-angle potentiometer of the accelerator and to the photo-diode and plotted the positional variation from isocenter with gantry rotation. The root-mean-square error for the five machines was +/- 0.06 to +/- 0.08 mm in the plane of rotation and +/- 0.17 to +/- 0.35 mm out of (perpendicular to) the plane of rotation. The in-plane-of-rotation errors tended to be maximal near the diagonal gantry angles and the out-of-plane-of-rotation errors were maximal in the over and under vertical positions. Both types of errors were predictable but only the out-of-plane-of-rotation errors were considered large enough to warrant consideration of correction (although the need is debatable). On all the tested machines, the out-of-plane-of-rotation error curve was a relatively smooth bell-shaped function that would be readily amenable to correction. The diode laser/photo-detector system used should prove useful in accurately defining isocenter and facilitating the precise adjustment of the laser isocenter lights.

(PS) 2: a new semiconductor device for positron-sensitive picosecond detection of single optical photons

A position-sensitive photodiode of new concept is introduced. The device is operated biased above the breakdown voltage in the so-called Geiger mode. The absorption of a single photon results in a mA-range avalanche pulse. The time and position (one coordinate) information of the photon arrival are carried by the avalanche current leading edge. The physics of the device operation is discussed: constraints in the device design are derived. Experimental measurements on silicon test structures with a position-sensitive area of 70 by 14 μm 2 are presented. Spatial resolution better than 10 μm FWHM (full width at half maximum), limited by the spot size of the light beam, and temporal resolution better than 100 ps FWHM are demonstrated.

High-resolution vibration measurements using a posiltion-sensitive photosensor

An integrated two-dimensional position-sensitive photosensor is used for contactless measurements of vibration amplitudes down to the sub-micron region. The sensor includes a position-sensitive silicon photodiode with high linearity over the full sensitive area and analog electronics integrated by thick-film hybrid technology for signal amplification and conditioning. Using hybrid integration of the transducer element with the following electronics we get a position-sensitive transducer, which is easy to handle under industrial conditions and gives output signals (response of the light-spot motion) that are easy to transmit over large distances. Vibration measurements have been carried out on a calibrated vibration exciter to test the sensor and on industrial equipment. The evidence of vibration amplitudes up to 0.01 μm shows that the position-sensitive hybrid circuit has the same sensitivity as the inductive displacement transducer but a better linearity in the lower frequency range from 0–100 Hz. The device is capable of performing two-dimensional sensing of the light beam from the vibrating part and does not need additional calibration, e.g., in the case of object drift during the measuring process.

The Improvement of Position‐Sensitive Photodiode Performance by Phosphorus Ion Implantation Gettering Technique

The improvement of position‐sensitive photodiode (PSPD) performance by phosphorus ion implantation gettering technique has been studied. The dark current of junction‐type and nonlinearity of resistor‐type large area PSPDs are significantly reduced, These improvements are attributed to the reduction, in the device active region, of impurities and crystal structural defects which are gettered to the back side of the wafer. The most effectively gettered impurity atom is copper, which is identified by inductively coupled plasma atomic emission spectrometer (ICPAES).

Diffraction-grating interferometer for very cold neutrons: Questions of adjustment

Questions of the adjustment of a diffraction grating neutron interferometer are considered. An aberration analysis of wavefronts propagating in this interferometer is carried out. It allows us to evaluate the requirements concerning the parallelism of the grating planes and the equality of the interferometer arms. A method for the mutual parallel alignment of the grating strips by a position-sensitive photodiode is suggested.

Sensor for the detection of the incident point of an electron beam

A novel sensor to detect the position of incidence of an electron beam on a target has been introduced where the X-rays starting from the point of incidence are detected by a position sensitive photodiode which is connected to an analyzing circuit. As part of an automatic control system the sensor allows the accurate guidance of the electron beam in vaporization and melting plants. To meet the high requirements in sensitivity, dynamics and position resolution, a special electronic circuit arrangement was developed to generate a signal that depends only on the position and not on the intensity of the incident radiation. The relative position resolution achieved with the described system is 1:1000. The admissible maximum frequency for the deflection of the electron beam is 20 Hz-2 kHz, dependent on the radiant intensity. The tensor can be used with all electron beam sources for acceleration voltages of at least 6 kV and a beam power exceeding 1 kW.

Hybrid integrated sensor for position measurement

The design, fabrication and performance of an integrated two-dimensional position-sensitive photodetector are presented. The optoelectronic device used as the sensitive element in the circuit is a full-area position-sensitive photodiode (PPD) with high linearity over the full sensitive area. The PPD is integrated with the analogue electronics in a hybrid circuit using thick film technology. The analogue electronics include the signal amplification and the signal conditioning to form the output signals proportional to the light beam centre position at the sensor surface and an output signal proportional to the light beam intensity. Using hybrid integration, a new position-sensitive transducer is developed, giving output signals which can transmit above large distances without problems and drive directly actuators in any control system.

Elasmobranch eye motor dynamics characterised using pseudorandom stimulus.

A pseudorandom binary sequence electrical pulse rate stimulus was delivered to the abducens nerve of an elasmobranch preparation. Ipsilateral eye movements were recorded using a position-sensitive photodiode to measure the position of a reflective patch attached to the fish's eye. Eye position data was cross-correlated with the stimulus pattern, and exponential decay curves were fitted to the cross-correlograms to estimate the time constant of a linear first order low-pass filter model. The cross-correlograms were transformed into the frequency domain using a Digital Fourier Transform, and Bode plots of eye dynamics were plotted. Eye motor plant dynamics in the elasmobranch Cephaloscyllium isabella can be accurately characterised by a linear first order low-pass filter model with a corner frequency of 0.73 +/- 0.10 Hz. Non-minimum phase lag reaches 90 degrees at about 4 Hz, indicating a time delay of some 50-60 ms. Integration of the canal signal is not required for producing compensatory eye movements above the characteristic frequency of the eye motor plant. However, the canal signal may be integrated to ensure that the vestibulo-ocular reflex is compensatory at lower frequencies. Substantial phase compensation or prediction is required for effective control of the vestibulo-ocular reflex.

New soft x-ray emission spectrograph

We have built a new soft x-ray emission spectrograph covering the photon energy range 20–800 eV. It incorporates toroidal holographic grazing incidence diffraction gratings and a position-sensitive photodiode array as a detector. The detector electronics are remote from the array which is under vacuum at nitrogen temperature, and features a double-correlated sampling scheme. The sample is excited with a Pierce-type electron gun using a quadrupole focusing lens. The performance of the instrument is described.

PHOTOTHERMAL DISPLACEMENT SPECTROSCOPY OF SURFACES AND THIN FILMS

We have developed a new technique, photothermal displacement spectroscopy, for studying the optical and thermal properties of surfaces. Photothermal displacement spectroscopy is based on optical detection of the thermal expansion of a sample as it is heated by absorption of electromagnetic radiation. Details of the experimental configuration are shown. An optical absorption spectrum is generated as an intensity modulated, tunable light beam (pump beam) is focussed onto the sample, and, depending on the optical cross section, some fraction of the radiation is absorbed. As the excited electrons decay nonradiatively, the sample is heated. The illuminated surface is then displaced as the sample expands. A probe beam reflected from the surface is deflected by the slope of the surface displacement. This deflection is measured by a position sensitive photodiode whose output is then amplified by a phase sensitive lock-in amplifier referenced to the pump beam modulation. Thermal information can be obtained by measuring the shape and phase of the photothermal displacement relative to the illumination as a function of the modulation frequency.

Novel technique for dynamic surface tension and viscosity measurements at liquid–gas interfaces

A novel means of generating and detecting surface waves at liquid-gas interfaces has been successfully developed. Electrocapillarity is used to generate the waves which are detected via specular reflection of a laser beam from the fluid surface to a position sensitive photodiode. Such a scheme is compact, sensitive, and does not mechanically touch the fluid surface. A preliminary study of highly damped waves on the magnetically oriented liquid crystal MBBA is reported.

Use of a system comprising an He–Ne laser and a position-sensitive photodiode in recording of angular displacements

A method was developed for measuring the instantaneous value of the azimuthal (angular) displacement of an impact of vibration bench under laboratory conditions. The main parts of the apparatus were an He–Ne laser (λ = 0.63 μ) and a detector with an FD-19KK silicon position-sensitive photodiode. The error in the determination of the angle of rotation under dynamic conditions depended on the nature of the laser and was 2–5''. The range of angles that could be measured was 0–10'. The pass band of the apparatus was 0–5 MHz.

Use of a position-sensitive photodiode to record the angle of arrival of optical radiation

Use of a position-sensitive photodiode to record the angle of arrival of optical radiation

A simple sensitive recording differential refractometer for column chromatography

Light passes through a hollow prism containing the sample liquid and is then focussed on a position-sensitive photodiode. Movement of the image due to a change in the refractive index of the sample produces an electrical signal which is recorded directly on a potentiometer recorder.