Dual-beam Setup Research Articles

Dual-beam X-ray nano-holotomography.

Nanotomography with hard X-rays is a widely used technique for high-resolution imaging, providing insights into the structure and composition of various materials. In recent years, tomographic approaches based on simultaneous illuminations of the same sample region from different angles by multiple beams have been developed at micrometre image resolution. Transferring these techniques to the nanoscale is challenging due to the loss in photon flux by focusing the X-ray beam. We present an approach for multi-beam nanotomography using a dual-beam Fresnel zone plate (dFZP) in a near-field holography setup. The dFZP generates two nano-focused beams that overlap in the sample plane, enabling the simultaneous acquisition of two projections from slightly different angles. This first proof-of-principle implementation of the dual-beam setup allows for the efficient removal of ring artifacts and noise using machine-learning approaches. The results open new possibilities for full-field multi-beam nanotomography and pave the way for future advancements in fast holotomography and artifact-reduction techniques.

Single-lens dynamic z-scanning for simultaneous in situ position detection and laser processing focus control

Existing auto-focusing methods in laser processing typically include two independent modules, one for surface detection and another for z-axis adjustment. The latter is mostly implemented by mechanical z stage motion, which is up to three orders of magnitude slower than the lateral processing speed. To alleviate this processing bottleneck, we developed a single-lens approach, using only one high-speed z-scanning optical element, to accomplish both in situ surface detection and focus control quasi-simultaneously in a dual-beam setup. The probing beam scans the surface along the z-axis continuously, and its reflection is detected by a set of confocal optics. Based on the temporal response of the detected signal, we have developed and experimentally demonstrated a dynamic surface detection method at 140–350 kHz, with a controlled detection range, high repeatability, and minimum linearity error of 1.10%. Sequentially, by synchronizing at a corresponding oscillation phase of the z-scanning lens, the fabrication beam is directed to the probed z position for precise focus alignment. Overall, our approach provides instantaneous surface tracking by collecting position information and executing focal control both at 140–350 kHz, which significantly accelerates the axial alignment process and offers great potential for enhancing the speed of advanced manufacturing processes in three-dimensional space.

Covert Millimeter-Wave Communication: Design Strategies and Performance Analysis

In this paper, we investigate covert communication over millimeter-wave (mmWave) frequencies. In particular, a mmWave transmitter, referred to as Alice, attempts to reliably communicate to a receiver, referred to as Bob, while hiding the existence of communication from a warden, referred to as Willie. In this regard, operating over the mmWave bands not only increases the covertness thanks to directional beams, but also increases the transmission data rates given much more available bandwidths and enables ultra-low form factor transceivers due to the lower wavelengths used compared to the conventional radio frequency (RF) counterpart. We first assume that the transmitter Alice employs two independent antenna arrays in which one of the arrays is to form a directive beam for data transmission to Bob. The other antenna array is used by Alice to generate another beam toward Willie as a jamming signal while changing the transmit power independently across the transmission blocks in order to achieve the desired covertness. For this dual-beam setup, we characterize Willie’s detection error rate with the optimal detector and the closed-form of its expected value from Alice’s perspective. We then derive the closed-form expression for the outage probability of the Alice-Bob link, which enables characterizing the optimal covert rate that can be achieved using the proposed setup. We further obtain tractable forms for the ergodic capacity of the Alice-Bob link involving only one-dimensional integrals that can be computed in closed forms for most ranges of the channel parameters. Finally, we highlight how the results can be extended to more practical scenarios, particularly to the cases where perfect information about the location of the passive warden is not available. Our results demonstrate the advantages of covert mmWave communication compared to the RF counterpart. The research in this paper is the first analytical attempt in exploring covert communication using mmWave systems.

Two-pack frequency-selective incoherent holography by using a dual-beam setup

We proposed a new incoherent optical frequency selection method called two-pack frequency-selective (TPFS) incoherent holography, which compresses two on-axis holograms into a single multiplexed on-axis hologram without loss of magnification and resolution. The spectrum we want to reconstruct is intercepted by multiple confounding correlation terms in the spatial frequency domain. The background bias term and conjugate term can be effectively suppressed. This work is the first to attempt a multiplexed reconstruction in the field of incoherent light. Experiment results highlight the potential of the proposed method in several areas, such as compressed holography and extended field of view imaging.

Spectropolarimeter on board the Aditya-L1: polarization modulation and demodulation

One of the major science goals of the Visible Emission Line Coronagraph (VELC) payload aboard the Aditya-L1 mission is to map the coronal magnetic field topology and quantitative estimation of longitudinal magnetic field on a routine basis. The infrared channel of VELC is equipped with a polarimeter to carry out full Stokes spectropolarimetric observations in the Fe xiii line at 1074.7 nm. The polarimeter is in a dual-beam setup with a continuously rotating wave plate as the polarization modulator. Detection of circular polarization due to the Zeeman effect and depolarization of linear polarization in the presence of a magnetic field due to the saturated Hanle effect in the Fe xiii line require a high signal-to-noise ratio (SNR). Due to the limited number of photons, long integration times are expected to build the required SNR. In other words, signals from a large number of modulation cycles are to be averaged to achieve the required SNR. This poses several difficulties. One is the increase in data volume and the other is the change in the modulation matrix in successive modulation cycles. The latter effect arises due to a mismatch between the retarder's rotation period and the length of the signal detection time in the case of the VELC spectropolarimeter. It is shown in this paper that by appropriately choosing the number of samples per half rotation, the data volume can be optimized. A potential solution is suggested to account for modulation matrix variation from one cycle to another.

Single-Molecule Studies of Doxorubicin-DNA Interactions using Optical Tweezers

Understanding the binding mechanisms of cancer drugs to DNA at the single molecule level plays a key role to design new and improved cancer drugs for the future. We use counter-propagating laser beams in a dual-beam optical tweezers setup to quantify the binding properties of an anti-cancer drug, Doxorubicin, to DNA. Prior studies that used optical tweezers to study Doxorubicin interactions with DNA at low forces observed intercalation in the micromolar range. The dual-beam setup provides us the capabilities to extend these studies to higher forces. When the DNA was stretched past the over stretching transition in the presence of Doxorubicin, it was observed that melting the DNA felicitated more intercalation in the nanomolar concentration range. We use the lengthening of DNA upon binding to Doxorubicin in conjunction with the McGhee - von Hippel one dimensional lattice binding model to quantify the binding affinity. Our study suggests that during the transcription process when the DNA is under high tensions forming transcription bubbles Doxorubicin can effectively bind in lower concentrations than previously believed.

Investigation of Effect of Filter on the Total Skin Irradiation Using Monte Carlo Simulation

The standard total skin irradiation (TSI) procedure for patients with Mycosis fungoides at our clinic is the Stanford technique where dual overlapping electron beams are directed at patient standing at an extended source to skin distance (SSD) of 300 cm. Patients rotate along the cranial-caudal axis in 6 positions to get full coverage to skin. Recently we developed and implemented a technique of laying down position for frail patients. One key requirement for this technique is the use of customized Cu filter to broaden the beam. The purpose of this study is to investigate the effect of the filter designs on the standard standing technique with a single beam. The filter is placed at the interface mount of the linac. The material studied include Cu, Fe, Au, Zn, and Ag. These materials were chosen based on their availability and stability. The thickness ranges from 0.05 mm to 0.55 mm, depending on the material. The extended SSD ranges from 250 cm to 350 cm. Our recent MC simulation study using the EGSnrc system on the laydown technique with 0.25 mm Cu filter has produced results that agree well with the commissioning measurement. For each material, we varies the thickness and SSD, to study the following quantities: percent depth dose (PDD), profile at dmax, and output at dmax, and compared them with the standard dual beam setup at 300 cm SSD that has been used in the clinic. Higher atomic number material and/or thicker filter has higher scattering power to broaden beam, but also attenuates beam more with lower output. No material can produce acceptable profile flatness (±10% within the central 160 cm region) at the SSD of 250 cm, suitable for a small linac room. At 300 SSD, Au (0.1 mm), Ag (0.25 mm) and Cu (0.45 mm) are acceptable. Zn (0.45 mm) requires SSD of 325 cm to meet the requirement. For all 4 configurations, the dmax is 0.87 - 0.99 cm, similar to dual beam with no filter at 0.97 cm. The R50 is 1.85 – 1.91 cm, compared to 2.06 cm for dual open beams. The output ranges from 0.025 – 0.029, slightly lower than the open beams at 0.040. The Monte Carlo simulation is a very useful tool to investigate the effect of the different filters and provides valuable suggestion in the technique optimizations. The result suggests that the standard standing position TSI technique can be implemented using a single beam instead of dual overlapping beam if the customized filters are used. Actual manufacturing and measurement will be performed to validate these simulation results.

Thermal Lens Spectroscopy for Quantitative Determination of a Cu(II) Complex With an 8-Aminoquinoline Derivative in Tap Water and Mining Wastewater Samples Using a Dual Beam Technique

This article describes the quantitative determination of Cu(II) using thermal lens spectrometry. The chromogenic reaction involving Cu(II) and 5-(4-sulphophenylazo)-8-aminoquinoline in alkaline solution was studied in different experimental conditions such as pH, ligand concentration, methanol volume, and presence of interfering ions. A collinear dual beam set-up has been used for direct quantitation in water samples without a pre-concentration step. The optimized conditions provided a linear calibration in the concentration range from 3.0 to 15.0 × 10−7 mol L−1. The detection and quantitation limits were 6.13 × 10−8 and 2.04 × 10−7 mol L−1, respectively. Resultantly, an application to Cu(II) determination in tap water (recovery 99.8–103.3%) and mining (synthetic) wastewater (95.3–98.0%) shows relative SDs ≤ 3.1%. The method is presented as a new alternative for the direct Cu(II) determination in real samples.

Quality improvement of the surface of laser micro welds by using a dual beam setup

Laser micro welding on functional surfaces, for example, in medical engineering applications or in food industries, is gaining more and more importance. The ongoing development of high-brilliance laser beam sources allows processing of parts in the micron range with a minimum of energy input. Nonetheless, the welding process reduces the surface quality of the processed part. Every weld defect or irregularity in the molten pool has a direct impact on the surface roughness and therefore on the quality of the weld, which can cause increased expenditure for post-processing cleaning or damages on sensitive objects. By using a spatial power modulation – a linear feed with superposed circular motion – the molten pool dynamic can be influenced to achieve a more stable process, leading to a decreased surface roughness. Furthermore, an additional laser source can heat up and extend the end of the molten pool on the surface to decrease the dynamics of the molten pool even more. To achieve this, the second laser source is focused with a larger spot diameter to avoid a second keyhole generation and to create a longer molten pool with a shallower solidification front and a more stable fluid dynamic. As a further parameter, the output power of the continuously-emitting laser beam source can be modulated with a varied frequency and amplitude. This paper presents recent results on the influence of the spatial and temporal power modulation method in connection with a second laser source on the surface roughness during laser micro welding via laser measuring of the weld surface.

Polarization-multiplexed, dual-beam swept source optical coherence tomography angiography.

A polarization-multiplexed, dual-beam setup is proposed to expand the field of view (FOV) for a swept source optical coherence tomography angiography (OCTA) system. This method used a Wollaston prism to split sample path light into 2 orthogonal-polarized beams. This allowed 2 beams to shine on the cornea at an angle separation of ~14°, which led to a separation of ~4.2 mm on the retina. A 3-mm glass plate was inserted into one of the beam paths to set a constant path length difference between the 2 polarized beams so the interferogram from the 2 beams are coded at different frequency bands. The resulting OCTA images from the 2 beams were coded with a depth separation of ~2 mm. A total of 5 × 5 mm2 angiograms from the 2 beams were obtained simultaneously in 4 seconds. The 2 angiograms then were montaged to get a wider FOV of ~5 × 9.2 mm2 .

Optical assessment of the cardiac rhythm of contracting cardiomyocytes in vitro and a pulsating heart in vivo for pharmacological screening.

Our quest in the pathogenesis and therapies targeting human heart diseases requires assessment of the contractile dynamics of cardiac models of varied complexity, such as isolated cardiomyocytes and the heart of a model animal. It is hence beneficial to have an integral means that can interrogate both cardiomyocytes in vitro and a heart in vivo. Herein we report an application of dual-beam optical reflectometry to determine noninvasively the rhythm of two representative cardiac models-chick embryonic cardiomyocytes and the heart of zebrafish. We probed self-beating cardiomyocytes and revealed the temporally varying contractile frequency with a short-time Fourier transform. Our unique dual-beam setup uniquely records the atrial and ventricular pulsations of zebrafish simultaneously. To minimize the cross talk between signals associated with atrial and ventricular chambers, we particularly modulated the two probe beams at distinct frequencies and extracted the signals specific to individual cardiac chambers with phase-sensitive detection. With this setup, we determined the atrio-ventricular interval, a parameter that is manifested by the electrical conduction from the atrium to the ventricle. To demonstrate pharmacological applications, we characterized zebrafish treated with various cardioactive and cardiotoxic drugs, and identified abnormal cardiac rhythms and atrioventricular (AV) blocks of varied degree. In light of its potential capability to assess cardiac models both in vitro and in vivo and to screen drugs with cardioactivity or toxicity, we expect this approach to have broad applications ranging from cardiopharmacology to developmental biology.

In situ Quality Assessment of a Novel Underwater pCO2 Sensor Based on Membrane Equilibration and NDIR Spectrometry

Abstract This paper presents a detailed quality assessment of a novel underwater sensor for the measurement of CO2 partial pressure (pCO2) based on surface water field deployments carried out between 2008 and 2011. The commercially available sensor, which is based on membrane equilibration and nondispersive IR (NDIR) spectrometry is small and can be integrated into mobile platforms. It is calibrated in water against a proven flow-through pCO2 instrument within a custom-built calibration setup. The aspect of highest concern with respect to achievable data quality of the sensor is the compensation for signal drift inevitably connected to absorption measurements. Three means are used to correct for drift effects: (i) a filter correlation or dual-beam setup, (ii) regular zero gas measurements realized automatically within the sensor, and (iii) a zero-based transformation of two sensor calibrations flanking the time of sensor deployment. Three sensors were tested against an underway pCO2 system during two major research cruises, providing an in situ temperature range from 7.4° to 30.1°C and pCO2 values between 289 and 445 μatm. The average difference between sensor and reference pCO2 was found to be −0.6 ±3.0 μatm with an RMSE of 3.7 μatm.

Three-dimensional intracellular optical coherence phase imaging

Quantitative phase imaging has many applications for label-free studies of the nanoscale structure and dynamics of cells and tissues. It has been demonstrated that optical coherence phase microscopy (OCPM) can provide quantitative phase information with very high sensitivity. The excellent phase stability of OCPM is obtained by use of a reflection from the microscope cover glass as a local reference field. For detailed intracellular studies a large numerical aperture (N.A.) objective is needed in order to obtain the required resolution. Unfortunately, this also means that the depth of field becomes too small to obtain sufficient power from the cover glass when the beam is focused into the sample. To address this issue, we designed a setup with a dual-beam sample arm. One beam with a large diameter (filling the 1.2 N.A. water immersion objective) enabled high-resolution imaging. A second beam with a small diameter (underfilling the same objective) had a larger depth of field and could detect the cover glass used as a local phase reference. The phase stability of the setup was quantified by monitoring the front and back of a cover glass. The standard deviation of the phase difference was 0.021 rad, corresponding to an optical path displacement of 0.9 nm. The lateral and axial dimensions of the confocal point spread function were 0.42 and 0.84 μm, respectively. This makes our dual-beam setup ideal for three-dimensional intracellular phase imaging.

Positional Imprinting of Optical Traps Corrects for Mechanical Drift in High-Resolution Instruments

The performance of high-resolution optical traps typically depends on the passive mechanical stability of several critical optical components. Passive stability demands stringent requirements for the laboratory environment to limit instrumental drift arising from vibrations, acoustics, and temperature variations. To follow the real-time position of biological motors taking base pair steps along DNA, angstrom resolution is needed. Limiting the positional drift of an optical trap to one angstrom requires that a collimated beam be held angularly stable to 40 nanoradians. To minimize instrumental drift, our lab uses a dual-beam setup wherein two traps are used to perform measurements in solution, isolated from the microscope stage. Consequently, angular drift from optical elements interacting with both beams is correlated and therefore cancelled. Even in this dual-beam configuration, however, four optical elements can introduce relative angular drift between the beams, resulting in uncorrelated motions that are indistinguishable from single molecule activity. We have identified this necessary portion of all dual-beam instruments as the primary source of relative positional drift between the traps. Unfortunately, even stringent environmental controls are expected to be insufficient to prevent nanoradian-level motions of these optical components. We therefore seek instead to measure and correct for drift that inevitably occurs. Here, we present a new advance in trap design that enables us to correct for the relative positional instability of dual optical traps in real-time using a novel positional imprinting technique. We show that our new optical trap design is capable of virtually eliminating mechanical drift, consistently yielding noise characteristics under high-noise conditions that are comparable to the quietest conditions we can achieve in our laboratory. This technology will potentially reduce the engineering controls necessary for high-resolution optical trapping, making the technique available to research labs lacking specialized facilities.

Experimental techniques in two-photon spectroscopy

A historical outline of two-photon spectroscopy traces the different motivations for this kind of nonlinear optical experiment. Different selection rules as compared to linear optical effects (one-photon absorption), the possibility of spectroscopy in omega -K space and Doppler-free absorption in gases open up a wide field of useful applications of this technique. A rough estimate of the expected magnitude of the two-photon absorption constant clearly indicates the sort of experimental equipment necessary. Detailed descriptions of a single-beam and a dual-beam set-up follow. Finally a short description of an indirect method, namely the detection of two-photon absorption by subsequent luminescence, and some remarks on future developments are presented.