Quadrant Detector Research Articles

Boost Your Microscope by Exploring New Dimensions

Due to diffraction of light, the conventional fluorescent microscope is a system with a band-limited information spatial channel. Every super-resolved fluorescent microscope circumvents this limitation by avoiding the simultaneous signaling of adjacent (< diffraction limit distance) fluorophores recording them sequentially in time. Notably, the confocal microscope also agrees to this perspective. Thus, the current super-resolved systems encode extra spatial information in the temporal channel.Here we discuss if other channels (dimensions) can be used to further improve the resolution of a fluorescence microscope. In particular, we describe time-gated STED microscopy and image-scanning microscopy (ISM) as examples of exploring extra dimensions, respectively the photon arrival time and the spatial image plane dimensions.Confocal scanning microscopy (CSM) can theoretically surpass the diffraction limit by a factor of √2. Practically, this improvement is sacrificed to obtain a good signal-to-noise ratio (SNR). Image scanning microscopy (ISM) solved this limitation by substituting the single point detector with a 2D array of detector. We showed that ISM can be straightforwardly implemented by using a quadrant detector. This implementation offers resolution close to the CSM theoretical value, improves the SNR by factor of 1.5 with respect to the CSM counterpart, and may be implemented without losing the optical sectioning capability and the system versatility.Time-gated detection increases the spatial resolution of a gated continuous-wave-(CW-) STED microscope, with the drawback of reducing the SNR. Thus, in sub-optimal conditions, such as a low-photons budget regime, the SNR reduction can cancel-out the expected gain in resolution. We developed a method which does not discard photons, but instead sorts all the photons in different time-gates according to their arrival time and recombines them through a multi-image deconvolution. Our results show that the SNR of the restored image improves, thereby improving the effective resolution.

Modelling and simulation of synchro and synchro‐to‐digital converter for electrical motor drives

In this study, modelling and simulation of synchro and synchro-to-digital converter (SDC) are presented. This study is useful to estimate the shaft position and speed of induction motor using SDC through a synchro. The SDC uses scott-T circuit to convert three signals of synchro into two signals format. The position information of synchro shaft is present in peak amplitudes of scott-T outputs. A demodulator circuit is designed to extract the peak amplitude levels. The quadrant in which the shaft angle falls is determined by quadrant detector. On the basis of the peak amplitude levels and quadrant information, the synchro shaft angle is computed. This method provides shaft position and speed in digital form. The reuse of quadrant detector in the evaluation of shaft speed shows the effectiveness of the proposed scheme.

用于四象限探测器光斑位置检测的数据采集传输系统设计

用于四象限探测器光斑位置检测的数据采集传输系统设计

Image scanning microscopy with a quadrant detector.

Confocal scanning microscopy (CSM) is the most widely used modern optical microscopy technique. Theoretically, it allows the diffraction barrier to be surpassed by a factor of 2, but practically this improvement is sacrificed to obtain a good signal-to-noise ratio (SNR). Image scanning microscopy (ISM) solves this limitation but, in the current implementations, the system complexity is increased and the versatility of CSM is reduced. Here we show that ISM can be straightforwardly implemented by substituting the single point detector of a confocal microscope with a quadrant detector of the same size, thus using a small number of detector elements. This implementation offers resolution close to the CSM theoretical value and improves the SNR by a factor of 1.5 with respect to the CSM counterpart without losing the optical sectioning capability and the system versatility.

Improved measurement accuracy of spot position on an InGaAs quadrant detector.

In this paper, a new formula is proposed to improve the accuracy of spot position measurements on an InGaAs quadrant detector (QD). It is obtained by analyzing the relationship between the light spot position and the output signals of the QD and combining the infinite integral method with the Boltzmann method due to their opposite error characteristics. Based on the proposed formula, the measurement accuracy can be improved greatly, which is confirmed by the simulation and experimental results. In addition, it requires fewer parameters compared with the polynomial method when reaching the same accuracy. Thus, the new formula can be practical in applications of spot position measurements.

Silicon micro-levers and a multilayer graphene membrane studied via laser photoacoustic detection

Abstract. Laser photoacoustic spectroscopy (PAS) is a method that utilizes the sensing of the pressure waves that emerge upon the absorption of radiation by absorbing species. The use of the conventional electret microphone as a pressure sensor has already reached its limit, and a new type of microphone – an optical microphone – has been suggested to increase the sensitivity of this method. The movement of a micro-lever or a membrane is sensed via a reflected beam of light, which falls onto a position-sensing detector. The use of one micro-lever as a pressure sensor in the form of a silicon cantilever has already enhanced the sensitivity of laser PAS. Herein, we test two types of home-made sensing elements – four coupled silicon micro-levers and a multilayer graphene membrane – which have the potential to enhance this sensitivity further. Graphene sheets possess outstanding electromechanical properties and demonstrate impressive sensitivity as mass detectors. Their mechanical properties make them suitable for use as micro-/nano-levers or membranes, which could function as extremely sensitive pressure sensors. Graphene sheets were prepared from multilayer graphene through the micromechanical cleavage of basal plane highly ordered pyrolytic graphite. Multilayer graphene sheets (thickness ∼102 nm) were then mounted on an additional glass window in a cuvette for PAS. The movements of the sheets induced by acoustic waves were measured using an He–Ne laser beam reflected from the sheets onto a quadrant detector. A discretely tunable CO2 laser was used as the source of radiation energy for the laser PAS experiments. Sensitivity testing of the investigated sensing elements was performed with the aid of concentration standards and a mixing arrangement in a flow regime. The combination of sensitive microphones and micromechanical/nanomechanical elements with laser techniques offers a method for the study and development of new, reliable and highly sensitive chemical sensing systems. To our knowledge, we have produced the first demonstration of the feasibility of using four coupled silicon micro-levers and graphene membranes in an optical microphone for PAS. Although the sensitivity thus far remains inferior to that of the commercial electret microphone (with an S / N ratio that is 5 times lower), further improvement is expected to be achieved by adjusting the micro-levers and membrane elements, the photoacoustic system and the position detector.

Analysis and alignment of the light path of Gauss beam matched to the fundamental mode ofan optical resonator

In order to reduce the influences of misalignment parameter and mismatch parameter on measurement based on optical resonator, the influence on the coupling efficiency of a source laser is stabilized to a fundamental cavity mode, and two limiting cases are analyzed and derived by using conversion of Gaussian beam, mode coupling theory and coordinate transformation theory, including the expression of coupling efficiency of fundamental cavity mode as two limiting cases emerge simultaneously. Analyses show that for mismatch parameter, only even-indexed Hermite-Gaussians beam is excited; for misalignment parameter, there exists an effect on the proportion of Hermite-Gaussians beam, which should bring about serious measurement error. These optical signals provide the error signals which are minimized. By taking the laser line width into account, we propose two methods for real time alignment of a Gaussian beam for an optical resonator perfectly coupled system: Fabry-Perot electro-optic sensors of a misadjusted system and control loops system depends on detecting emergent light of cavity via multi-dimensional quadrant detector. All of these will provide a theoretical direction for analyzing the measurement error and improving the measurement accuracy.

全捷联激光半主动导引头线性视场研究

Considering the requirement on the wide linear field of the strapdown semi-active laser seeker,the relationship of linear field for four-quadrant detecting( QD) photoelectric system and target distance was analyzed. First,according to the system parameters,the relationship of target distance on different visibility,different target reflectivity and the received power for the laser seeker was calculated. Then by ray tracing method,the power distribution on quadrant detector for different field was found. Finally,the relationship of linear field and the received power was obtained. Linear field increased from zero to the theoretical value of optical design with the target distance decreasing. Experimental results indicate that linear field increases from 0° to± 9° with the received power increasing,which agrees well with the result of theoretic computation. The change law of the linear field should be considered for stapdown semi-active laser system design.

Investigation of atmospheric insect wing-beat frequencies and iridescence features using a multispectral kHz remote detection system

Quantitative investigation of insect activity in their natural habitat is a challenging task for entomologists. It is difficult to address questions such as flight direction, predation strength, and overall activities using the current techniques such as traps and sweep nets. A multispectral kHz remote detection system using sunlight as an illumination source is presented. We explore the possibilities of remote optical classification of insects based on their wing-beat frequencies and iridescence features. It is shown that the wing-beat frequency of the fast insect events can be resolved by implementing high-sampling frequency. The iridescence features generated from the change of color in two channels (visible and near-infrared) during wing-beat cycle are presented. We show that the shape of the wing-beat trajectory is different for different insects. The flight direction of an atmospheric insect is also determined using a silicon quadrant detector. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (Less)

High-resolution STEM imaging with a quadrant detector--conditions for differential phase contrast microscopy in the weak phase object approximation.

Differential phase contrast is a contrast mechanism that can be utilized in the scanning transmission electron microscope (STEM) to determine the distribution of magnetic or electric fields. In practice, several different detector geometries can be used to obtain differential phase contrast. As recent high resolution differential phase contrast experiments with the STEM are focused on ring quadrant detectors, we evaluate the contrast transfer characteristics of different quadrant detector geometries, namely two ring quadrant detectors with different inner detector angles and a conventional quadrant detector, by calculating the corresponding phase gradient transfer functions. For an ideal microscope and a weak phase object, this can be done analytically. The calculated phase gradient transfer functions indicate that the barely illuminated ring quadrant detector setup used for imaging magnetic fields in the specimen reduces the resolution limit to about 2.5Å for an aberration corrected STEM. Our results show that the resolution can be drastically improved by using a conventional quadrant detector instead.

Optical Trap Stiffness Online Measurement System Based on FPGA

For investigating the mechanical properties of optical tweezers, a data collection/process/control system based on FPGA is designed and developed to measure the optical trap stiffness. A four quadrant detector is used to track the positions of the trapped microsphere, the digital data converted by a high precision ADC is transferred through the USB interface into PC for processing and displaying, and the PC controls an electronically controlled platform to realize zero alignment of the four quadrant detector. Experiments show that this system could be effectively used for on-line optical trap stiffness measurement.

Research Effect of Four-Quadrant Detector Detection Spot in Atmospheric Turbulence

Movement frequency of atmospheric turbulence is varied between a few Hz to hundreds Hz. when laser is transmitted in atmospheric some characteristic will be changed by turbulence modulation. The energy distribution form and shape of spot will be varied with movement frequency of turbulence. When spot is detected by four-quadrant detector output of detector will be effect. In order to test effect of turbulence to detector and ensure output signal can be amplified and processing effectively a kind of spot detection circuit was designed in turbulent environment. Two bands amplification was used in system. The noise suppression was completed in first band and variable gain amplifier was used in second to meet require of light intensity. Testing system was set up which can research characteristic of quadrant detector in turbulence. Experiment of spot detection in field was done. Distance from transmitting to receiving is 800m and 12.5km. Conclusions have been obtained by experimental when Distance is 800m subdivision can be up to 7 in photosensitive surface. At the same time we can see that impact of turbulence on laser transmission is a combination result with modulation of high and low frequency. And ability to spot detection has been invalid in 12.5 kilometers distances because of photosensitive surface occupied by noise from impact of turbulence, which show subdivision of quadrant detector has been broken in long distance.

A novel method to improve detecting sensitivity of quadrant detector

This paper presents a set of formulae for estimating the light spot position projected on a quadrant detector (QD). A novel method of annular segmentation calculus (ASC) is designed to analyze the detecting light spot of QD. The influences of the spot movement mode, spot energy distribution, and dead area to the dynamic range and the detection sensitivity are analyzed. It is shown in simulations that our new formulae have achieved a much better results to increase measurement accuracy. It is also shown that on the condition of the same spot size, the detection sensitivity of Gaussian distribution is prior to uniform distribution. The detection sensitivity of diagonal mode is better than cross mode. The detection sensitivity increases with increase in the size ratio of dead area to spot. The simulating and experimental results show that the measuring range of QD is 400μm, and the resolution is 50μm. The study presented here will be beneficial in developing the nanomechanical displacement detection techniques.

Mid-IR beam direction stabilization scheme for vibrational spectroscopy, including dual-frequency 2DIR

A compact laser beam direction stabilization scheme is developed that provides the angular stability of better than 50 μrad over a wide range of frequencies from 800 to 4000 cm-1. The schematic is fully automated and features a single MCT quadrant detector. The schematic was tested to stabilize directions of the two IR beams used for dual-frequency two-dimensional infrared (2DIR) measurements and showed excellent results: automatic tuning of the beam direction allowed achieving the alignment quality within 10% of the optimal alignment obtained manually. The schematic can be easily implemented to any nonlinear spectroscopic measurements in the mid-IR spectral region.

A computational tool to characterize particle tracking measurements in optical tweezers

Here, we present a computational tool for optical tweezers which calculates the particle tracking signal measured with a quadrant detector and the shot-noise limit to position resolution. The tool is a piece of Matlab code which functions within the freely available Optical Tweezers Toolbox. It allows the measurements performed in most optical tweezer experiments to be theoretically characterized in a fast and easy manner. The code supports particles with arbitrary size, any optical fields and any combination of objective and condenser, and performs a full vector calculation of the relevant fields. Example calculations are presented which show the tracking signals for different particles, and the shot-noise limit to position sensitivity as a function of the effective condenser NA.

Pin Cushion Plasmonic Device for Polarization Beam Splitting, Focusing, and Beam Position Estimation

Great hopes rest on surface plasmon polaritons' (SPPs) potential to bring new functionalities and applications into various branches of optics. In this paper, we demonstrate a pin cushion structure capable of coupling light from free space into SPPs, split them based on the polarization content of the illuminating beam of light, and focus them into small spots. We also show that for a circularly or randomly polarized light, four focal spots will be generated at the center of each quarter circle comprising the pin cushion device. Furthermore, following the relation between the relative intensity of the obtained four focal spots and the relative position of the illuminating beam with respect to the structure, we propose and demonstrate the potential use of our structure as a miniaturized plasmonic version of the well-known four quadrant detector. Additional potential applications may vary from multichannel microscopy and multioptical traps to real time beam tracking systems.

A high average power beam dump for an electron accelerator

The electron beam dump for Cornell University's Energy Recovery Linac (ERL) prototype injector was designed and manufactured to absorb 600kW of electron beam power at beam energies between 5 and 15MeV. It is constructed from an aluminum alloy using a cylindrical/conical geometry, with water cooling channels between an inner vacuum chamber and an outer jacket. The electron beam is defocused and its centroid is rastered around the axis of the dump to dilute the power density. A flexible joint connects the inner body and the outer jacket to minimize thermal stress. A quadrant detector at the entrance to the dump monitors the electron beam position and rastering. Electron scattering calculations, thermal and thermomechanical stress analysis, and radiation calculations are presented.

Comparison between a Camera and a Four Quadrant Detector, in the Measurement of Red Blood Cell Deformability

The ability of red blood cells (RBC) to deform under vascular conditions is essential for circulation. RBC deformability, measured at different shear rates and osmolalities, provides a useful way to evaluate RBC function and is used to diagnose several hereditary blood disorders. In clinical practice, ektacytometry has been used as a routine automated technique for measuring RBC deformability under shear stress at known osmolalities. RBC suspension is exposed to laser light and the resulting diffraction pattern is recorded. The mean deformability of the cells is characterized by the diffraction pattern. Our study is the first to compare the correspondence between two methods that measure diffraction simultaneously, on the same apparatus. Additionally, while others conducted studies under varying shear we used varying osmolalities. A laser beam splitter produced two identical diffraction patterns, evaluated by synchronous data acquisition and analysis: One pattern was acquired by a digital camera and analyzed by image processing software. The other was analyzed using photodiode measurement at four fixed points and a microcontroller interface. Data analysis resulted in two deformability vs. osmolality curves. Comparing these curves shows excellent overlap in shape with a clear difference in amplitude. Since routine Manuscript received Jan 15, 2013; revised March 1, 2013. patient curves are always compared to a normal control curve, the amplitue difference is not significant. Our results indicate that either method may be used for clinically-usable interpretation of RBC deformability, but also that additional studies are required in order to compare repeatability for both methods, and to demonstrate that the two curves overlap for a variety of pathologies.

An Improved Fast Intelligent Tracking Algorithm with the Gain Adjustable

Realize the goal quick and accurate location when the detection signal is weaker, puts forward a Fast Intelligent Tracking algorithm(FITA) with the Gain Adjustable. Wiht the goal image move in four quadrant detector, it’s size, location and output signal related to a linear probe interval. In this interval, a liner relation can be get between the spot position and the corresponding output signal. The target quick location algorithm is realized with this relation. On the other hand, the sum signal of the four quadrant detector is sampled in real-time, this sum is related to the sensor’s signal strength, then the change rate of the signal strength can be get, using adaptive learning ways to get the change trend of signal strength, and realized dynamic adjustment of the signal gain, in order to improve the signal resolution ratio when signal is weak, the tracking accuracy can be improved with this way. The experimental data show that FITA algorithm can rapidly locate position in the linear interval and accurately track through the dynamic change signal gain for the weaker signal. The track error can be improved to 1.9%.

Position measurement of non-integer OAM beams with structurally invariant propagation

We present a design to generate structurally propagation invariant light beams carrying non-integer orbital angular momentum (OAM) using Hermite-Laguerre-Gaussian (HLG) modes. Different from previous techniques, the symmetry axes of our beams are fixed when varying the OAM; this simplifies the calibration technique for beam positional measurement using a quadrant detector. We have also demonstrated analytically and experimentally that both the OAM value and the HLG mode orientation play an important role in the quadrant detector response. The assumption that a quadrant detector is most sensitive at the beam center does not always hold for anisotropic beam profiles, such as HLG beams.