Beam Recombination Research Articles

Controllable beam break-up, spectral broadening and coherent beam recombination using arrays of singular beams

Controllable beam break-up, spectral broadening and coherent beam recombination using arrays of singular beams

Active Optics—Advances of Cycloid-like Variable Curvature Mirrors for the VLTI Array

Elasticity theory and active optics led us to the discovery of three geometrical configurations of variable curvature mirrors (VCMs) that are either cycloid-like or tulip-like thickness distributions. Cycloid-like VCMs are generated by a uniform load—air pressure—applied over the mirror rear surface, and reacts without any bending moment along its circular contour. This particular VCM configuration is of practical interest because it smoothly generates accurate optical curvatures, varying from plane at rest to spherical curvatures up to f/2.9 over 16-mm aperture under 6.5-bar air pressure. Starting from the thin plate theory of elasticity and modeling with NASTRAN finite element analysis, one shows that 3-D optimizations—using a non-linear static flexural option—provide an accurate cycloid-like thickness distribution. VCM elasticity modeling in quenched stainless steel–chromium substrates allows the obtaining of diffraction-limited optical surfaces: Rayleigh’s criterion is achieved over a zoom range from flat to f/3.6 over 13-mm clear aperture up to 6-bar loading. These VCMs were originally developed and built at the Marseille Observatory in 1975 and implemented as a cat’s-eye mirror of IR Fourier-transform interferometers for laboratory recording of fast events in gas molecular spectroscopy. Later, for high-angular resolution astronomy with the ESO VLTI array—an interferometer made of 8 m Unit Telescopes (UTs) and 1.8 m Auxiliary Telescopes (ATs)—such VCMs were inevitable components to provide in a 3″ co-phased field-of-view since 1998. They were implemented (1) as cat’s eye mirrors of the height delay-lines beam recombination lab and (2) as ATs mirror-pair for output pupil conjugation of the movable x–y baseline. From the ESO-AMU approved convention of making 10 VCM spares up to 2024, the present modeling should provide a diffraction-limited extended field-of-view. It is pure coincidence that present results from modeling with an outer collarette are identical to results from analytic theory without collarette.

Generation of highly mutually coherent hard-x-ray pulse pairs with an amplitude-splitting delay line

Beam splitters and delay lines are among the key building blocks of modern-day optical laser technologies. Progress in x-ray free electron laser source development and applications over the past decade is calling for their counter part operating in the Angstrom wavelength regime. Recent efforts in x-ray optics development have demonstrated relatively stable delay lines that most often adopted the division of wavefront approach for the beam splitting and recombination configuration. However, the two recombined beams have yet to achieve sufficient mutual coherence to enable applications such as interferometry, correlation spectroscopy, and nonlinear spectroscopy. We present the first experimental realization of the generation of highly mutually coherent pulse pairs using an amplitude-split delay line design based on transmission grating beam splitters and channel-cut crystal optic delay lines. The performance of the prototype system was analyzed in the context of x-ray coherent scattering and correlation spectroscopy, where we obtained nearly identical high-contrast speckle patterns from both branches. We show in addition the high level of dynamical stability during continuous delay scans, a capability essential for high sensitivity ultra-fast measurements.

Effects of losses on the sensitivity of an actively correlated Mach-Zehnder interferometer

An actively correlated Mach-Zehnder interferometer (ACMZI) renders a number of significant advantages over a conventional Mach-Zehnder interferometer (MZI) with a squeezed vacuum state input such as an active output readout, loss tolerant detection, and multiarms for multiparameter estimation. We theoretically studied the quantum Cram\'er-Rao bound of an ACMZI, where the quantum Fisher information obtained by the phase-averaging method can give the conclusive phase-sensing sensitivity without any external phase reference. We numerically calculate the phase sensitivities with the method of homodyne detection and intensity detection in the presence of losses. Under lossless and very low loss conditions, the ACMZI is operated in a balanced case to beat the standard quantum limit (SQL). As the loss increases, the reduction in sensitivity increases. Fortunately, within a certain range, we can adjust the gain parameters of the beam recombination process to reduce the reduction in sensitivity and realize the sensitivity can continue to beat the SQL in an unbalanced situation. Our scheme provides an optimization method of phase estimation in the presence of losses.

First Simultaneous Acceleration of Multiple Charge States of Heavy Ion Beams in a Large-Scale Superconducting Linear Accelerator.

Experimental studies of the simultaneous acceleration of three-charge-state ^{129}Xe^{49+,50+,51+} beam from 17 to 180 MeV/nucleon in a superconducting linear accelerator are presented. The beam parameters for each individual- and multiple-charge-state beam were measured and compared with the particle tracking simulations. Detailed measurements were performed to characterize the multiple-charge-state beam's recombination after a second-order achromat and isopath 180° bending system. As a result of the recombination of three charge states in the six-dimensional phase space, the xenon beam intensity was increased by 2.5-fold compared to the single-charge-state beam. The results presented in the Letter fully validate the possibility to produce and utilize high-quality multiple-charge-state heavy-ion beams in a large-scale superconducting linac to increase the available beam power on an isotope production target.

Impact of real mirror profiles inside a split-and-delay unit on the spatial intensity profile in pump/probe experiments at the European XFEL.

For the High-Energy-Density (HED) beamline at the SASE2 undulator of theEuropean XFEL, a hard X-ray split-and-delay unit (SDU) has been built enabling time-resolved pump/probe experiments with photon energies between 5 keV and 24 keV. The optical layout of the SDU is based on geometrical wavefront splitting and multilayer Bragg mirrors. Maximum delays between Δτ= ±1 ps at 24 keV and Δτ = ±23 ps at 5 keV will be possible. Time-dependent wavefront propagation simulations were performed by means of theSynchrotron Radiation Workshop (SRW) software in order to investigate theimpact of the optical layout, including diffraction on the beam splitter and recombiner edges and the three-dimensional topography of all eight mirrors, on the spatio-temporal properties of the XFEL pulses. The radiation is generated from noise by the code FAST which simulates the self-amplified spontaneous emission (SASE) process. A fast Fourier transformation evaluation of the disturbed interference pattern yields for ideal mirror surfaces a coherence time of τc = 0.23 fs and deduces one of τc = 0.21 fs for the real mirrors, thus with an error of Δτ = 0.02 fs which is smaller than the deviation resulting from shot-to-shot fluctuations of SASE2 pulses. The wavefronts are focused by means of compound refractive lenses in order to achieve fluences of a few hundred mJ mm-2 within a spot width of 20 µm (FWHM) diameter. Coherence effects and optics imperfections increase the peak intensity between 200 and 400% for pulse delays within the coherence time. Additionally, the influence of two off-set mirrors in the HED beamline are discussed. Further, we show the fluence distribution for Δz = ±3 mm around the focal spot along the optical axis. The simulations show that the topographies of the mirrors of the SDU are good enough to support X-ray pump/X-ray probe experiments.

Coherent beam combining of 61 femtosecond fiber amplifiers.

We report on the coherent beam combining of 61 femtosecond fiber chirped-pulse amplifiers in a tiled-aperture configuration along with an interferometric phase measurement technique. Relying on coherent beam recombination in the far field, this technique appears suitable for the combination of a large number of fiber amplifiers. The 61 output beams are stacked in a hexagonal arrangement and collimated through a high fill factor hexagonal micro-lens array. The residual phase error between two fibers is as low as λ/90 RMS, while a combining efficiency of ∼50% is achieved.

Laser interference ablation by ultrashort UV laser pulses via diffractive beam management

Abstract The fabrication of periodic surface patterns on various materials by ultrashort ultraviolet (UV) laser pulses is reviewed. Laser interference ablation using two or more coherent beams leads to deterministic, strictly periodic patterns. The generation of the interfering beams is accomplished by diffractive optical elements like gratings, grating systems or computer-generated holograms. The recombination of the diffracted beams is performed by optical imaging or diffractive beam management. Ultrashort UV pulses are especially suited for generating micron- to submicron-sized deterministic periodic patterns on metals and semiconductors.

First on-sky demonstration of an integrated-photonic nulling interferometer: the GLINT instrument

ABSTRACT The characterization of exoplanets is critical to understanding planet diversity and formation, their atmospheric composition, and the potential for life. This endeavour is greatly enhanced when light from the planet can be spatially separated from that of the host star. One potential method is nulling interferometry, where the contaminating starlight is removed via destructive interference. The GLINT instrument is a photonic nulling interferometer with novel capabilities that has now been demonstrated in on-sky testing. The instrument fragments the telescope pupil into sub-apertures that are injected into waveguides within a single-mode photonic chip. Here, all requisite beam splitting, routing, and recombination are performed using integrated photonic components. We describe the design, construction, and laboratory testing of our GLINT pathfinder instrument. We then demonstrate the efficacy of this method on sky at the Subaru Telescope, achieving a null-depth precision on sky of ∼10−4 and successfully determining the angular diameter of stars (via their null-depth measurements) to milliarcsecond accuracy. A statistical method for analysing such data is described, along with an outline of the next steps required to deploy this technique for cutting-edge science.

Super-sensitive measurement of angular rotation displacement based on the hybrid interferometers.

We theoretically study the angular rotation displacement based on the hybrid interferometers, which contain a beam splitter (BS) and an optical parameter amplication (OPA) for beam splitting and recombination. Two schemes with different orders of an OPA and a BS are discussed and both of them can realize the super resolving and sensitive angular rotation displacement. The sensitivity of angular rotation displacement can surpass the shot noise limit 12l N with the orbital angular momentum input beams. The squeezing strength of an OPA and the reflectivity of the BS play a decisive role on the resolutions and sensitivities while the losses play a negative effect on the sensitivity.

43 Reference dosimetry for high dose rate pulsed scanned proton beams

Introduction The newly installed ProteusONE (IBA PT, LLN, Belgium) relies on a super-conducting synchro-cyclotron which delivers a pulsed scanned proton beams from 100 MeV to 226 MeV with a dose rate between 2.65 μGy/pulse and 230 μGy/pulse respectively. Its beam structure of 1 kHz frequency and high dose rate per pulse makes it particular considering recombination effect in plane parallel ionization chambers. Methods The aim of this work is firstly to characterize the beam monitor ionization chambers response in a pulsed scanned proton beam with a high dose rate per pulse, and secondly to find a proper protocol for reference dosimetry with a plane parallel ionization chamber in this kind of proton beams. Following the TRS398 protocol [1] , temperature and pressure (kT,P), polarity effect (kpol), beam quality factor (kQ,Q0) and recombination effect (ks) correction factors were computed and applied to the considered ionization chamber. In particular, for a scanned pulsed proton beam the recombination effect in the ionization chamber is not negligible. Therefore, the recombination factor has been theoretically evaluated with Boag’s formulae [2] and measured in water for a plane parallel ionization chamber through saturation curves. The quality beam kQ,Q0 factor evaluation was based on Monte-Carlo Goma’s results [3] for PBS proton beams. The assumptions made for a high dose rate per pulse pulsed scanned proton beam based on TRS 398 for 3 energies were validated against water calorimetry [4] measurements for 3 energies. Results The recombination factor study shows that plane parallel ionization chamber should be used with −500 V voltage to limit the effect of recombination. In the same set-up conditions, water calorimetry and ionometry give less than 2% difference for the 3 mono-energetic beams. Conclusions The presented reference dosimetry protocol is validated for clinical high dose rate per pulse pulsed scanned proton beams.

Surface potential and charging of polymer films submitted to defocused electron beam irradiation

The surface potentials and dynamic charging properties of polymers subjected to electron irradiation in scanning electron microscopy are investigated by using a novel method applied in parallel with simulation and experimental methods. We perform our simulation through a parallel computing method with various microscopic parameters. The results show that under the given microscopic parameters, the charging time concomitantly decreases as the film thickness, electron mobility, trap cross and recombination rate increase. The surface potential decreases as electron energy, beam current density, capture cross section, sample thickness and electron-hole recombination rate increase and as electron mobility decreases. Charging time increases with increasing beam density, sample thickness, recombination rate and change in capture cross-section, and decreases with increasing electron mobility. The primary-electron energy exhibits an inflection point at 35 keV. This study offers an intuitive analytical and measurement method for understanding microscopic charge characteristics in electron-based surface microscopy.

Non-Gaussian precision metrology via driving through quantum phase transitions

We propose a scheme to realize high-precision quantum interferometry with entangled non-Gaussian states by driving the system through quantum phase transitions. The beam splitting, in which an initial non-degenerate groundstate evolves into a highly entangled state, is achieved by adiabatically driving the system from a non-degenerate regime to a degenerate one. Inversely, the beam recombination, in which the output state after interrogation becomes gradually disentangled, is accomplished by adiabatically driving the system from the degenerate regime to the non-degenerate one. The phase shift, which is accumulated in the interrogation process, can then be easily inferred via population measurement. We apply our scheme to Bose condensed atoms and trapped ions, and find that Heisenberg-limited precision scalings can be approached. Our proposed scheme does not require single-particle resolved detection and is within the reach of current experiment techniques.

47. Commissioning of new prototype ProteusOne© PBS proton therapy system

Introduction We report the commissioning and monitor unit calibration process of new prototype S2C2TM proton therapy system with pulsed PBS high dose rate proton beam. Methods The S2C2TM has a frequency of 1 kHz and delivers a pulsed proton beam of dose rate between 2.65 μGy/pulse and 230 μGy/pulse for the lowest (96 MeV) and highest (226 MeV) energies respectively. The facility is equipped with a compact gantry which rotates from −35° to 188° and delivers PBS proton beams of field sizes up to 20 × 24 cm 2 . The nozzle monitor ionization chambers (IC) were designed to be able to measure high dose rate per pulse delivered charges. A prototype 14 cm plane parallel IC and a multi-layer IC were used to measure integrated depth dose curves. Spot profiles and field size and penumbra were acquired with a 2D-scintillator detector while 2D-fields uniformity and symmetry were measured with a prototype 2D-array IC. Absolute dose/monitor unit calibration was based on dose measurements in single-layer fields of size 10 × 10 cm 2 . Plane parallel ionization chamber was used with −500 V voltage to limit the effect of recombination. Following the TRS398 protocol [1] , temperature and pressure (kT,P), polarity effect (kpol), beam quality factor (kQ,Q0) and recombination effect (ks) correction factors were computed and applied to the considered ionization chamber. The TRS398 pulsed beams model [2] and 3 additional Boag’s models [3] were investigated to compute the fraction of free electron for the recombination effect correction, while the kQ,Q0 factor evaluation was based on Monte-Carlo Goma’s results [4] for PBS proton beams. Results S2C2TM high dose rate per pulse beam causes mainly recombination effects in IC based detectors, and prototype detectors and nozzle IC were developed in order to take into account these beam characteristics. Measurements performed with these detectors show lateral and longitudinal dose uniformity better than 2.5% for clinically significant field sizes, ranges, modulations and air–gaps. For Absolute dose the measurements were achieved in single-layer fields with plane parallel IC. The standard deviations between the ks values obtained with the 4 methods are not larger than 0.02% and 0.3% for the lowest and the highest energies respectively. ks value of 1.009 was selected for all the energies. In order to verify our measurement method absolute dose was also made with water calorimeter: measured dosimetry data agreed within 2% for the lowest and the highest energies. Conclusion The new prototype S2C2TM PBS proton therapy system was successfully commissioned and released for clinical use.

Adiabatic Mach–Zehnder interferometer in a dipolar spin-1 condensate

We propose and analyze a realizable scheme for performing a Heisenberg-limited Mach–Zehnder interferometry with a dipolar spin-1 condensate. Based upon adiabatic processes of sweeping the transverse magnetic field, we demonstrate a perfect phase transition, which accomplishes the beam splitter, phase shifter and recombiner as for a Mach–Zehnder interferometer. The attractive dipolar interaction ensures the existence of a path-entangled state which enhances the phase measurement precision to the Heisenberg limit. We also study the spin squeezing of the state generated in the beam splitter and show that the spin squeezing exhibits an extremum near the critical point of phase transition.

Active SU(1,1) atom interferometry

Active interferometers use amplifying elements for beam splitting and recombination. We experimentally implement such a device by using spin exchange in a Bose–Einstein condensate. The two interferometry modes are initially empty spin states that get spontaneously populated in the process of parametric amplification. This nonlinear mechanism scatters atoms into both modes in a pairwise fashion and generates a non-classical state. Finally, a matched second period of spin exchange is performed that nonlinearly amplifies the output signal and maps the phase onto readily detectable first moments. Depending on the accumulated phase this nonlinear readout can reverse the initial dynamics and deamplify the entangled state back to empty spin states. This sequence is described in the framework of SU(1,1) mode transformations and compared to the SU(2) angular momentum description of passive interferometers.

Vector Addition of Light’s Velocity Versus the Hafele-Keating Time Dilation Test

The equivalence between the constancy of light in all inertial, nongravitated frames and time dilation is derived in this paper. Length contraction is not part of this equivalence and is eliminated by Occam’s razor. The null result of the Mickelson-Morley experiment requires a different explanation for the same intensity of the recombination of split light beams as originally transmitted, especially in the perpendicular component. Vector addition of velocities applies to light’s behavior in both parallel and perpendicular components of the moving Mickelson-Morley and Kennedy-Thorndike experiments. If the one-way speed of light is not a universal constant in all directions for moving inertial frames, then the time dilation formula is incorrect. One must question any time dilation experiments, particularly the claims in the Hafele-Keating report, which contains several inaccuracies and data manipulation. Another time dilation experiment with better atomic clock and rigorous testing is warranted.

Phase sensitivity at the Heisenberg limit in an SU(1,1) interferometer via parity detection

We theoretically investigate the phase sensitivity with parity detection on an SU(1,1) interferometer with a coherent state combined with a squeezed vacuum state. This interferometer is formed with two parametric amplifiers for beam splitting and recombination instead of beam splitters. We show that the sensitivity of estimation phase approaches Heisenberg limit and give the corresponding optimal condition. Moreover, we derive the quantum Cram\'er-Rao bound of the SU(1,1) interferometer.

Demonstration on range imaging of 256 × 256 pixels and 30 frames per second using short wavelength infrared pulsed time-of-flight laser sensor with linear array receiver

We demonstrated the range imaging with high resolution of 256×256 pixels and high frame rate of 30 frames per second (fps) using a short wavelength infrared pulsed time-of-flight laser sensor, which is suitable for long range imaging. We additionally demonstrated the long range imaging of more than 1 km and wide field of view imaging of 12 deg× 4 deg, 768×256 pixels, and 10 fps. For these demonstrations, we developed the linear array devices of the aluminum indium arsenide avalanche photodiode array and silicon germanium bipolar complementary metal oxide semiconductor read-out integrated circuit array. We also deployed the flattop beam illumination optics with the beam division and recombination method and realized efficient line shape illumination.

Dispersion in closed, off-axis orbit bumps

In this paper we present a proof to show that there exists no system of linear or nonlinear optics which can simultaneously close multiple local orbit bumps and dispersion through a single beam transport region. The second combiner ring in the CLIC drive beam recombination system, CR2, is used as an example of where such conditions are necessary. We determine the properties of a lattice which is capable of closing the local orbit bumps and dispersion and show that all resulting solutions are either unphysical or trivial.