Orthogonal Beams Research Articles

Monte Carlo feasibility study of orthogonal bremsstrahlung beams for improved radiation therapy imaging

The basic characteristics of orthogonal bremsstrahlung beams are studied and the feasibility of improved contrast imaging with such a beam is evaluated. In the context of this work, orthogonal bremsstrahlung beams represent the component of the bremsstrahlung distribution perpendicular to the electron beam impinging on an accelerator target. The BEAMnrc Monte Carlo code was used to study target characteristics, energy spectra and relative fluences of orthogonal beams to optimize target design. The reliability of the simulations was verified by comparing our results with benchmark experiments. Using the results of the Monte Carlo optimization, the targets with various materials and a collimator were designed and built. The primary pencil electron beam from the research port of a Varian Clinac-18 accelerator striking on Al, Pb and C targets was used to create orthogonal beams. For these beams, diagnostic image contrast was tested by placing simple Lucite objects in the path of the beams and comparing image contrast obtained in the orthogonal direction to the one obtained in the forward direction. The simulations for various target materials and various primary electron energies showed that a width of 80% of the continuous-slowing-down approximation range (RCSDA) is sufficient to remove electron contamination in the orthogonal direction. The photon fluence of the orthogonal beam for high Z targets is larger compared to low Z targets, i.e. by a factor of 20 for W compared to Be. For a 6 MeV electron beam, the mean energy for low Z targets is calculated to be 320 keV for Al and 150 keV for Be, and for a high Z target like Pb to be 980 keV. For irradiation times of 1.2 s in an electron mode of the linac, the contrast of diagnostic images created with orthogonal beams from the Al target is superior to that in the forward direction. The image contrast and the beam profile of the bremsstrahlung beams were also studied. Both the Monte Carlo study and experiment showed an improvement of the contrast for lower Z target materials. This study confirms the feasibility, both in terms of intensity and image contrast, of orthogonal bremsstrahlung beams for radiation therapy imaging.

The 2D-S (Stereo) Probe: Design and Preliminary Tests of a New Airborne, High-Speed, High-Resolution Particle Imaging Probe

Abstract The design, laboratory calibrations, and flight tests of a new optical imaging instrument, the two-dimensional stereo (2D-S) probe, are presented. Two orthogonal laser beams cross in the middle of the sample volume. Custom, high-speed, 128-photodiode linear arrays and electronics produce shadowgraph images with true 10-μm pixel resolution at aircraft speeds up to 250 m s−1. An overlap region is defined by the two laser beams, improving the sample volume boundaries and sizing of small (<∼100 μm) particles, compared to conventional optical array probes. The stereo views of particles in the overlap region can also improve determination of three-dimensional properties of some particles. Data collected by three research aircraft are examined and discussed. The 2D-S sees fine details of ice crystals and small water drops coexisting in mixed-phase cloud. Measurements in warm cumuli collected by the NCAR C-130 during the Rain in Cumulus over the Ocean (RICO) project provide a test bed to compare the 2D-S with 2D cloud (2D-C) and 260X probes. The 2D-S sees thousands of cloud drops <∼150 μm when the 2D-C and 260X probes see few or none. The data suggest that particle images and size distributions ranging from 25 to ∼150 μm and collected at airspeeds >100 m s−1 by the 2D-C and 260X probes are probably (erroneously) generated from out-of-focus particles. Development of the 2D-S is in its infancy, and much work needs to be done to quantify its performance and generate software to analyze data.

Optical feedback dependence of anticorrelation polarization dynamics in vertical-cavity surface-emitting lasers

The effects of optical feedback on the magnitude of the anticorrelation of polarization dynamics in vertical-cavity surface-emitting lasers (VCSELs) have been studied experimentally. The correlations are considered in the time domain and in the spectral domain. The correlation in the time domain shows that in the case of the polarization-preserved or orthogonal polarization beam optical feedback into the VCSEL a strong anticorrelation between orthogonal polarizations can arise; however, no strong anticorrelation is observed for parallel polarization optical feedback. Viewed in the frequency domain, the anticorrelation is found to be strong at low frequencies but poor at higher frequencies.

Anisotropy-Induced Effects in the Dynamics of an Ion Confined in a Two-Dimensional Paul Trap

We investigate the role of anisotropy in the dynamics of a single trapped ion interacting with two orthogonal laser beams, considering how it modifies a scheme for the generation of Schrödinger cat states and the so called parity effect in two-dimensional isotropic Paul traps. We find that anisotropy gives rise to a richer class for the generated states and to a larger number of observables sensitive to the parity of the number of excitation of the vibrational motion of the ion.

Particular features of acousto-optic visualization in scattering media upon detection of nonballistic light

Images of optically inhomogeneous objects immersed into a cell with a scattering liquid through which orthogonal laser and ultrasonic beams pass are obtained upon measuring the scattered light modulated at the ultrasonic frequency. The alternating current from a photodetector recording the optical radiation emerging from the cell was used as a parameter of the acousto-optic visualization. The quality of the visualization is analyzed in relation to the registration conditions and the scattering parameter magnitude, as well as the size and shape of three-dimensional and planar objects. Under the experimental conditions used, the positions of objects immersed into the scattering liquid are detected fairly precisely, with a satisfactory contrast and sharpness of images in the plane perpendicular to the laser beam axis, whereas, along this axis, the object positions are not determined. The experiment was performed under conditions of transition from a regime without scattering to a regime of multiple scattering.

Sci-Fri AM General-04: High Contrast Imaging Using Orthogonal Bremsstrahlung Beams: An Experimental Study of Radiation Quality

Since portal images are created by megavoltage, forward‐directed bremsstrahlung beams, their image quality is inferior to that of images produced by kilovoltage beams. In this study, characteristics of orthogonal bremsstrahlung photons produced by megavoltage electron pencil beams were studied and suitability of their use for improved radiotherapy imaging was evaluated. A 10 MeV electron beam emerging through the research port of a Varian Clinac‐18 linac was made to strike targets of carbon,aluminum and copper. PDD and attenuation measurements of both the forward and orthogonal beams were performed, and experimental results were compared with Monte Carlo‐calculated findings. Images of contrast objects were acquired with Agfa 400 diagnostic films and their contrast levels were analyzed. Photon yield and effective energy are lower for orthogonal beams than for forward beams, and the differences are more pronounced for targets of lower atomic number. The effective energy of a spectrum produced by carbon dropped by a factor of 10 from 1535 keV in the forward direction to 151 keV in the orthogonal direction, while for aluminum the effective energy dropped by 77% to 425 keV, and for copper by 37% to 1107 keV. The imagecontrast of films exposed with orthogonal beams was qualitatively determined to be superior to that obtained using the forward megavoltage beams. Using their relatively low effective energy, orthogonal bremsstrahlung beams produced by megavoltage electrons striking low atomic number targets yield images with a higher contrast than do forward bremsstrahlung beams.

SU‐CC‐ValA‐09: Radiation Quality in High Contrast Imaging with Orthogonal Bremsstrahlung Beams

Purpose: To study the characteristics of orthogonal bremsstrahlung photons produced by megavoltage electron pencil beams and to evaluate the suitability of their use for improved radiation therapy imaging. Method and Materials: A 10 MeV electron beam emerging through the research port of a Varian Clinac‐18 linac was made to strike targets of carbon, aluminum and copper. The quality of resulting forward and orthogonal bremsstrahlung beams was evaluated using PDD and attenuation measurements, and the experimental findings were compared with Monte Carlo‐calculated results using the EGSnrcMP code. Images of contrast objects were acquired with Agfa 400 diagnostic films and their contrast levels were analyzed. Results: Photon yield and mean energy of the forward bremsstrahlung spectra were determined to be essentially independent of the target's atomic number Z. In comparison with forward bremsstrahlung, the yield and effective energy were lower in the orthogonal direction, and this decrease was more pronounced for targets of lower atomic number. The effective energy of a spectrum produced by carbon dropped by a factor of 10 from 1535 keV in the forward direction to 151 keV in the orthogonal direction, while for aluminum it dropped by 77% to 425 keV, and for copper by 37% to 1107 keV. The image contrast of films exposed with orthogonal beams was qualitatively determined to be superior to that obtained using the forward megavoltage beams. Conclusions: Orthogonal bremsstrahlung beams produced by megavoltage electrons have a significantly lower mean energy compared to forward beams. In the orthogonal direction, higher Z targets create higher intensity, while lower Z targets provide a more desirable low energy spectrum. Using their relatively low effective energy, orthogonal bremsstrahlung beams produced by megavoltage electrons striking low atomic number targets yield images with a higher contrast than do forward bremsstrahlung beams.

SU‐FF‐J‐49: Dose Comparsion of MVCB and Orthogonal Pair Portal Images

Purpose: To evaluate the delivered patient doses resulting from MVCB(Mega‐Voltage Cone Beam)and ORTH(orthogonal pairs)portal imaging techniques, and report dose per MU(cGy/MU)and absolute dose(cGy)at isocenter, max dose, and mean doses to the target and critical organs. Method and Material: Both image techniques are based on a Siemens 6 MV LINAC equipped with an A‐Si flat panel and dose calculation done on a Pinnacle 3DRTP system. The ORTH technique was simulated by two orthogonal beams, total 6 MUs and 20cm×20cm field size. The MVCB technique was delivered with a 200° arc beam, total 9 MUs and the same field size. 30 patients representing 6 treatment sites were analyzed. Calculated doses were reported for max dose in patient, dose at the isocenter, and mean doses to target and critical organs. Results: For the cGy/MU analysis, the value at isocenter was similar. The difference of max dose was greater in pelvis and abdomen. The mean dose in normal lung or contralateral breast differed greater than other critical organs. In contrast, the dose difference in the target or critical organs close to isocenter was very small. The absolute dose difference and 2D absolute dose distributions are shown. The high dose area for ORTH technique is located at the proximal corner of rectangular areas intersected by the two beams but anteriorly for MVCB due to the anterior arc, and contributes more dose to anterior organs like normal lung and contralateral breast. Conclusions: From our analysis, high dose region generated by MVCB is shown inside the critical organs, and tends to be larger compared to the ORTH technique. Due to the potential biological effects, the extra dose burden to the critical structures should be monitored carefully. This study provides a quantitative analysis and suggests the number of projections and total MUs are the most important factors for the MVCB technique.

Time-reversal operator target focusing using optimal beam sets

Time-reversal operator (TRO) methods can be used to focus sound on an ocean target using a time-reversal mirror. In order to increase the signal-to-noise ratio, the TRO can be measured by transmitting simultaneously the entire array instead of transmitting source by source. The so-called beam-space. TRO is measured by transmitting a set of orthogonal beams. Acoustic propagation will be simulated in a realistic range and time-dependent ocean environment measured during the TREX04 experiment [Gaumond, J. Acoust. Soc. Am. (in press)]. This paper will compare four different sets of beams: Hadamard, phased planar, spatially phased, and modal. The first two methods require no a priori environmental knowledge, the third requires only waveguide depth, and the final requires a sound-speed profile and geoacoustics measured at the TRM. Results will be discussed in terms of signal gain, complexity to implement, and coherence in an inhomogeneous ocean environment varying in both time and space. [Work supported by the Office of Naval Research.]

Spin transport and manipulation by mobile potential dots in GaAs quantum wells

Mobile quantum dots (denoted as dynamic quantum dots) formed by the interference of orthogonal beams of surface acoustic waves (SAWs) in an undoped GaAs quantum well coherently transport electron spins over distances exceeding 70 μ m . We determine the spin-splitting parameter for a GaAs quantum well to be γ = 17 ± 2 eV Å 3 as well as investigate the effects of the SAW strain field on the spin dynamics.

New advance in confocal microscopy

Step height and line-width are two key parameters in the metrology of micro-electronic masks. A novel common-path heterodyne interferometric confocal measuring system is presented to measure the step height of masks. It combines both the methods of heterodyne interferometry and confocal microscopy. The resolution is 0.01 nm and the measurement range is around 8 µm. The procedure is direct by the integration of the measurement of intensity and phase, hereby faster than a normal scanning microscope. For the line-width measurement of masks, a polarization heterodyne interferometric confocal microscope is proposed, which combines a polarization interferometer with a confocal microscope. An ideal beam spot is obtained and precise focus is realized by using the confocal technique. The phase shifts of the two orthogonal polarization beams differ from each other when they are reflected at the edge of a sample. The experimental results show that the uncertainty of line-width measurement is 21 nm. Both of the systems satisfy the common-path principle, so as to get high ability of resistance to environment disturbances.

Novel butler matrix using CPW multilayer technology

In this paper, a novel 4 times 4 two-layer Butler matrix based on a broad-band two-layer slot-coupled directional coupler is presented and implemented at 5.8 GHz using coplanar waveguide technology. With the slot-coupled directional coupler, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices, which leads to significant size reduction and loss minimization. To examine the performance of the proposed matrix, experimental prototypes of the multilayer directional coupler and the Butler matrix were fabricated and measured. Furthermore, a four-antenna array was also designed and fabricated at 5.8 GHz and then connected to the matrix to form a beamforming antenna system. As a result, four orthogonal beams at -45deg, -15deg, 15deg, and 45deg are produced. Measured results on the entire system agree well with the theoretical predictions, validating the proposed design

Polarization holography: orthogonal plane-polarized beam configuration with circular vectorial photoinduced anisotropy

This paper presents a complete model for the complex underlying mechanisms of vectorial holography using orthogonal S- and P-polarized beams. This configuration is of great interest, being the only one allowing creation of purely-vectorial holographic gratings. We model both the interference process and the material's photoinduced vectorial anisotropy using simple matrix formalism. We demonstrate further that combined linear and circular vectorial anisotropy makes the grating polarization-selective in diffraction allowing non-destructive polarization-measurement on the incident beam. This strict material condition explains the very few experimental successes previously reported. Appropriate material selection might open the path to complete non-destructive polarimetric solutions, polarization-discrimination or routing applications. The presented model can be easily extended further to other polarization configurations.

Evaluation of Three-Beam and Four-Beam Profiler Wind Measurement Techniques Using a Five-Beam Wind Profiler and Collocated Meteorological Tower

Abstract In this paper a five-beam wind profiler and a collocated meteorological tower are used to estimate the accuracy of four-beam and three-beam wind profiler techniques in measuring horizontal components of the wind. In the traditional three-beam technique, the horizontal components of wind are derived from two orthogonal oblique beams and the vertical beam. In the less used four-beam method, the horizontal winds are found from the radial velocities measured with two orthogonal sets of opposing coplanar beams. In this paper the observations derived from the two wind profiler techniques are compared with the tower measurements using data averaged over 30 min. Results show that, while the winds measured using both methods are in overall agreement with the tower measurements, some of the horizontal components of the three-beam-derived winds are clearly spurious when compared with the tower-measured winds or the winds derived from the four oblique beams. These outliers are partially responsible for a larger 30-min, three-beam standard deviation of the profiler/tower wind speed differences (2.2 m s−1), as opposed to that from the four-beam method (1.2 m s−1). It was also found that many of these outliers were associated with periods of transition between clear air and rain, suggesting that the three-beam technique is more sensitive to small-scale variability in the vertical Doppler velocity because of its reliance on the point measurement from the vertical beam, while the four-beam method is surprisingly robust. Even after the removal of the rain data, the standard deviation of the wind speed error from the three-beam method (1.5 m s−1) is still much larger than that from the four-beam method. Taken together, these results suggest that the spatial variability of the vertical airflow in nonrainy periods or hydrometeor fall velocities in rainy periods makes the vertical beam velocities significantly less representative over the area across the three beams, and decreases the precision of the three-beam method. It is concluded that profilers utilizing the four-beam wind profiler technique have better reliability than wind profilers that rely on the three-beam wind profiler technique.

Orthogonal switched beams for downlink diversity transmission

A downlink transmission scheme in a switched-beam antenna system for providing diversity and beamforming simultaneously based on the space-time block coding technique is proposed. The scheme involves selecting multiple beams based on the uplink reception of the switched-beam antenna system, and determining multiple orthogonal beams from the selected beams. With the orthogonal transmit beams, the proposed switched-beam antenna system outperforms conventional switched-beam systems and approaches the optimal performance achievable by a much complex adaptive antenna system.

Design of Extended Depth-of-Focus Laser Beams Using Orthogonal Beam Expansions

Laser beams with extended depth of focus have many practical applications, such as scanning printed bar codes. Previous work has concentrated on synthesizing such beams by approximating the nondiffracting Bessel beam solution to the wave equation. In this paper, we introduce an alternate novel synthesis method that is based on maintaining a minimum MTF value (contrast) over the largest possible distance. To achieve this, the coefficients of an orthogonal beam expansion are sequentially optimized to this criterion. One of the main advantages of this method is that it can be easily generalized to noncircularly symmetrical beams by the appropriate choice of the beam expansion basis functions. This approach is found to be very useful for applications that involve scanning of the laser beam.

Non-Abelian Gauge Potentials for Ultracold Atoms with Degenerate Dark States

We show that the adiabatic motion of ultracold, multilevel atoms in spatially varying laser fields can give rise to effective non-Abelian gauge fields if degenerate adiabatic eigenstates of the atom-laser interaction exist. A pair of such degenerate dark states emerges, e.g., if laser fields couple three internal states of an atom to a fourth common one under pairwise two-photon-resonance conditions. For this so-called tripod scheme we derive general conditions for truly non-Abelian gauge potentials and discuss special examples. In particular we show that using orthogonal laser beams with orbital angular momentum an effective magnetic field can be generated that has a monopole component.

SU-FF-T-312: Feasbility Study of Orthogonal Bremsstrahlung Beams for Improved Radiation Therapy Imaging

Purpose: To study the feasibility of using orthogonal bremsstrahlung beams for imaging in radiation therapy. The orthogonal bremsstrahlung is produced in linac targets in directions perpendicular to the incident electron beam. Method and Materials: BEAMnrc MC modeling was used to design different targets and to obtain energy spectra and relative intensities of orthogonal beams as well as forward-directed beams. The reliability of the simulations was checked by comparing results with benchmark experiments. Two different targets and a collimator were designed and built. The primary electron beam from the research port of a Varian Clinac-18 accelerator impinging on Al and Pb targets was used to create orthogonal beams. For these beams diagnostic image contrast was tested by placing simple Lucite objects in the path of the beams and comparing image contrast obtained in orthogonal to forward direction. Results: The simulations showed that a thickness of 80% of CSDA range is sufficient to completely remove electron contamination in the orthogonal direction. The intensity of the orthogonal beam for high-Z targets is larger compared to low-Z targets by a factor 20 for W compared to Be. For a 6 MeV electron beam, the average energy for low-Z targets is lower (330 keV for Al, 170 keV for Be) compared to high-Z targets (900 keV for Pb) and lower compared to the forward beam (0.56 MeV, 0.8 MeV and 1.4 MeV for Be, Al and Pb, respectively). For irradiation times of 1.2 s in electron mode the contrast of diagnostic images created with orthogonal beams from the Al target is superior to that in the forward direction. Conclusion: Because of the lower average energy of orthogonal beams, image contrast obtained with these beams is superior. This study confirms feasibility, both in terms of intensity and image contrast, of orthogonal bremsstrahlung beams in radiation therapy.

Measurements of temperature scaling laws in an optically dense magneto-optical trap

We have studied the temperature scaling laws for the conditions under which a cloud of trapped ^85Rb atoms in the sigma+/sigma- configuration makes the transition from the temperature-limited regime to the multiple-scattering regime. Our experimental technique for measuring temperature relies on measuring the ballistic expansion of the cloud after turning off the confining forces and imaging the cloud size as a function of time with two CCD cameras. In the transition regime, the temperature T is shown to depend on the number of atoms N and the peak density n as (T-T_0) proportional N^1/3 and as (T-T_0) proportional n^2/3, in a manner consistent with theoretical predictions. Here T_0 is defined as the equilibrium temperature of a low-density optical molasses. In the multiple-scattering regime we find that T proportional Omega^2/(delta Gamma), where Omega and delta are the Rabi frequency and the detuning of the trapping laser, respectively, and Gamma is the natural linewidth of the cycling transition. We have also measured the ratio of temperatures along the axial and radial directions of the magnetic field gradient coils and find that the temperature is isotropic only if the intensities of the three orthogonal trapping beams are equal, and that the ratio is generally independent of trapping laser intensity and magnetic field gradient. Finally we demonstrate a measurement of the gravitational acceleration precise to approximately 0.1% by tracking the center of the cloud during ballistic expansion.

Quantification of the intensity enhancements for the double-pulse laser-induced breakdown spectroscopy in the orthogonal beam geometry

Simple- and double-pulse laser-induced breakdown spectroscopy was studied on aluminum samples at atmospheric pressure in air. The double-pulse experiments were carried out in the orthogonal beam geometry in two different ways: the reheating scheme and the pre-ablation spark dual-pulse scheme. An ablation laser emitting at 532 nm was combined with a second laser operating at 1064 nm according to the orthogonal geometry. For both schemes, the influence of the delay between the two laser pulses was investigated. In particular, different optima of interpulse delays were determined, underlying the differences of physical mechanisms involved in both processes. The estimation of the plasma temperatures provided explanations on the signal increases for both schemes. Whatever the configuration developed in the orthogonal geometry, a correlation between the increases in emission lines intensities and their excitation energy levels was established in the double-pulse approach. Besides, the effect of laser energy for both pulses was studied so as to make comparisons of the different configurations at the same total laser energy.