Coin-structured tunable beam shaping assembly design for accelerator-based boron neutron capture therapy for tumors at different depths and sizes

In the past decade,boron neutron capture therapy utilizing an accelerator-based neutron source(ABNS)designed primarily for producing epithermal neutrons has been implemented in the treatment of brain tumors and other cancers.The specifications for designing an epithermal beam are primarily based on the IAEA-TECODC-1223 report,issued in 2001 for reactor neutron sources.Based on this report,the latest perspectives and clinical requirements,we designed an ABNS capable of adjusting the average neutron beam energy.The design was based on a 2.8 MeV,20 mA proton beam bombarding a lithium target to produce neutrons that were subsequently moderated and tuned through a tunable beam shaping assembly(BSA)which can modify the thicknesses and materials of the coin-shaped moderators,back reflectors,filters,and collimators.The simulation results demonstrated that epithermal neutron beams for deep seated tumor treatment,which were generated by utilizing magnesium fluoride with lengths ranging between 28 and 36 cm as the moderator,possessed a treatment depth of 5.6 cm although the neutron flux peak shifts from 4.5 to 1.0 keV.When utilizing a thinner moderator,a less accelerated beam power can meet the treatment requirements.However,higher powers reduced the treatment time.In contrast,employing a thick moderator can reduce the skin dose.In scenarios that required relatively low energy neutron beams,the removal of the thermal neutron filter can raise the thermal neutron flux at the beam port.And the depth of the dose rate peak could be adjusted between 0.25 and 2.20 cm by combining magnesium fluoride and polyethylene coins of different thicknesses.Hence,this device has a better adaptability for the treatment of superficial tumors.Overall,the tunable BSA provides greater flexibility for clinical treatment than common BSA designs that can only adjust the port size.

Influence of positioning errors of optical shaping components for single emitter laser diode on beam shaping effects

Beam shaping is required for semiconductor lasers to achieve high optical fiber coupling efficiency in many applications.But the positioning errors on optics may reduce beam shaping effects,and then lead to low optical fiber coupling efficiency.In this work,the positioning errors models for the single emitter laser diode beam shaping system are established.Moreover,the relationships between the errors and the beam shaping effect of each shapers are analysed.Subsequently,the relationship between the errors and the optical fiber coupling efficiency is analysed.The result shows that position errors in the Z axis direction on the fast axis collimator have the greatest influence on the shaping effect,followed by the position errors in the Z axis direction on the converging lens,which should be strictly suppressed in actual operation.Besides,the position errors have a significant influence on the optical fiber coupling efficiency and need to be avoided.

Beam shaping with limited amplitude weight values for satellite active phased array antenna

To gain the tradeoff between lower sidelobe and higher power amplifiers efficiency,a transmitting beam shaping scheme with limited amplitude weight values for satellite active phased array antenna is presented. The scheme is implemented by a dual coding genetic algorithm(GA). Phase and amplitude of array weight vectors for beam shaping are encoded by real coding and finite length binary coding,respectively,which,maintaining accuracy of results,reduces the amplitude dynamic range and improves the efficiency of power amplifiers. The presented algorithm,compared with complex-coded GA,increases the convergence rate due to the search space's decrease. In order to overcome the prematurity and obtain better global optimization or quasi-global optimization,a new dual coding GA based on "species diversity retention" strategy and adaptive crossover and mutation probability are presented.

Laser beam shaping with magnetic fluid-based liquid deformable mirrors

A new controllable laser beam shaping technique is demonstrated, where a magnetic fluid-based liquid deformable mirror is proposed to redistribute the laser phase profile and thus change the propagation property of the beam. The mirror is driven by an inner miniature actuator array along with a large outer actuator. The inner actuator array is used for deforming the magnetic fluid surface, while the outer actuator is used to linearize the fluid surface response and amplify the magnitude of the deflection. In comparison to other laser beam shaping techniques, this technique offers the advantages such as simplicity, low cost, large shape deformation, and high adaptability. Based on a fabricated prototype of the liquid deformable mirror, an experimental AO system was set up to produce a desired conical surface shape that shaped the incident beam into a Bessel beam. The experimental results show the effectiveness of the proposed technique for laser beam shaping.

Design of Diffractive Optical Elements Used for Beam Shaping in the Fresnel Domain

In the Fresnel transform domain, an effective improvement to the conventional iterative algorithm for designing the diffractive optical elements (DOEs) used for spatial beam shaping has been proposed. The algorithm can successfully achieve to design DOEs for beam shaping. Compared with conventional algorithm, this algorithm can provide faster convergence, more powerful ability to overcome local minimum problem and better shaping quality. By computer simulation, the result has shown that the DOEs designed by this algorithm has snch advantages as high uniformity at the main lobe, low profile error and steep edge.

Influence of Parameters in the Design of a Faceted Structure for Incoherent Beam Shaping

A reflective faceted structure is proposed to reshaping an incoherent light beam into two focalized spots-To obtain the desired irradiance distribution on a detector,custom optimization function is written,and the two dimensional tilt angles of each facet are optimized automatically in a pure non-sequential mode in Zemax OpticStudio 16.The result is also confirmed inside LightTools&2 from Synopsys.For measuring the quality of the optimization result in the case of two spots focalization,four factors including efficiency on the detector,uniformity,the root mean square error and the correlation coefficient are calculated.These four factors are used to evaluate the influence of several parameters on the irradiance distribution.These parameters include the incidence angle,the divergence angle,the facet size,the source type and the resolution of the facet angular positions.Finally,an analysis of those parameters is made and the performance of this type of component is demonstrated.

Terahertz shaping technology based on coherent beam combining

The generation of terahertz(THz) waves by focusing a femtosecond pulsed laser beam at a distance is able to overcome the strong absorption properties of air and has rapidly attracted the attention of industry. However, the poor directionality of the THz wave radiation generated by this method is not conducive to THz wave applications. By controlling the morphology of the ultrafast laser-excited plasma filament and its electron density distribution through coherent beam combining technology, we achieve direct THz beam shaping and are able to obtain THz wave radiation of Gaussian or arbitrary transverse distribution. The novel experimental approach proposed in this paper opens up the research field of direct THz wave shaping using plasma. Moreover, it innovates multi-parameter convergence algorithms and, by doing so, has the potential to find beam patterns with higher energy conversion efficiency and break the energy limit of THz waves emitted by lasers at high power.

Beam shaping in the high-energy kW-class laser system Bivoj at the HiLASE facility

A fully automatic fail-safe beam shaping system based on a liquid crystal on a silicon spatial light modulator has been implemented in the high-energy kilowatt-average-power nanosecond laser system Bivoj.The shaping system corrects for gain nonuniformity and wavefront aberrations of the front-end of the system.The beam intensity profile and the wavefront at the output of the front-end were successfully improved by shaping.The beam homogeneity defined by the beam quality parameters was improved two to three times.The root-mean-square value of the wavefront was improved more than 10 times.Consequently,the shaped beam from the second preamplifier led to improvement of the beam profile at the output of the first main cryo-amplifier.The shaping system is also capable of creating nonordinary beam shapes,imprinting cross-references into the beam,or masking certain parts of the beam.

Laser Beam Shaping and Mode Conversion in Optical Fibers

A new class of all-fiber beam shaping devices has been realized by inverse etching the end face of single mode and multimode fibers to form a concave cone tip. Concave tip fiber can convert a Gaussian beam profile to a flat top beam profile with a uniform intensity distribution. A flat top beam with intensity variation of approx. 5% and flat top diameter to spot diameter ratio of 67% has been achieved. This device can also change the beam shape from a Gaussian to a donut by moving the observation plane. A flat top multimode fiber beam delivery is attractive for applications which require high power and uniform intensity distribution. In single mode fiber, concave tips could be used to reduce the beam spot size diameter, enabling efficient light coupling from a single mode fiber to an integrated optical waveguide.

An adaptive laser beam shaping technique based on a genetic algorithm

A new adaptive beam intensity shaping technique based on the combination of a 19-element piezo-electricity deformable mirror （DM） and a global genetic algorithm is presented. This technique can adaptively adjust the voltages of the 19 actuators on the DM to reduce the difference between the target beam shape and the actual beam shape. Numerical simulations and experimental results show that within the stroke range of the DM, this technique can be well used to create the given beam intensity profiles on the focal plane.

Beam shaping of high power diode laser stack into homogeneous line

In this paper, analysis of beam shaping and homogenization of high power diode laser stack into a line focus with dimension of 10 mm x 0.5 mm was reported. The beam shaping and homogenization was simulated by using ZemaX-ray tracing technique. The results have shown that intensity distribution after beam shaping and homogenization at the work piece is a fiat top for the slow axis with homogeneity over 95% and a Gaussian distribution for the fast axis.

Spatial beam shaping by quartz crystal piano-convex lens

Based on the optical activity of quartz crystal, we proposed a scheme for shaping the spatial intensity distribution of a linearly polarized laser beam by utilizing a quartz crystal piano-convex lens in combination with a polarizer. The intensity profile of the shaped laser beam can be easily switched from one profile to another by controlling the polarization direction of the incident laser beam.

On the Innovation,Design,Construction,and Experiments of OMEGA-Based SSPS Prototype:The Sun-Chasing Project

This study systematically introduces the development of the world’s first full-link and full-system ground demonstration and verification system for the OMEGA space solar power satellite(SSPS).First,the OMEGA 2.0 innovation design was proposed.Second,field-coupling theoretical models of sunlight concentration,photoelectric conversion,and transmitting antennas were established,and a systematic optimization design method was proposed.Third,a beam waveform optimization methodology considering both a high beam collection efficiency and a circular stepped beam shape was proposed.Fourth,a control strategy was developed to control the condenser pointing toward the sun while maintaining the transmitting antenna toward the rectenna.Fifth,a high-efficiency heat radiator design method based on bionics and topology optimization was proposed.Sixth,a method for improving the rectenna array’s reception,rectification,and direct current(DC)power synthesis efficiencies is presented.Seventh,high-precision measurement technology for high-accuracy beam-pointing control was developed.Eighth,a smart mechanical structure was designed and developed.Finally,the developed SSPS ground demonstration and verification system has the capacity for sun tracking,a high concentration ratio,photoelectric conversion,microwave conversion and emission,microwave reception,and rectification,and thus satisfactory results were obtained.

Tight focusing of axially symmetric polarized vortex beams

Tight focusing of axially symmetric polarized vortex beams is studied numerically based on vector diffraction theory. The mathematical expressions for the focused fields are derived. Simulation results show that the focused fields and phase distributions at focus are largely influenced by both the polarization order and topological charge of the incident beams. Moreover, focal spots with flat-topped or tightly-focused patterns can be flexibly achieved by carefully choosing the polar- ization order and the topological charge, which confirms the potential of such beams in wide applications, such as optical tweezers, laser printing, lithography, and material processing.

Beam Parameter Product Optimization for High Power SWIR Laser Diode Stack Fiber Coupling

An optimized setup for fiber optic injection of a kilowatt peak power laser diode stack emitting in the SWIR spectral range is proposed. Starting from a fast axis collimated (FAC) and slow axis collimated (SAC) 15 bars, 19 emitters off the shelf laser diode stack, the beam is transformed using spatial beam combining and polarization coupling. Both techniques integrated in a compact design enable to couple the kilowatt level beam into a standard 600 μm core, 0.22 numerical aperture (NA) multimode optical fiber. An application in the field of long range SWIR laser illuminator for gated viewing is presented. A comparison between two illuminators is realized both based on the same laser diode stack but one using beam parameter product (BPP) reduction and one without. It could be demonstrated that BPP reduction is the best way for efficient, narrow divergence and compact semi-conductor based laser illuminators design and realization. The global laser illuminator efficiency could be improved by 75% for the narrowest divergences thanks to this approach.

GA BASED SYNTHESIS OF SATELLITE-BORNE MULTI-BEAM PLANAR ARRAY WITH ARBITRARY GEOMETRY

A planar array antenna with arbitrary geometry synthesis technique based on genetic algorithm is discussed. This approach avoids coding/decoding and directly works with complex numbers to simplify computing program and to speed up computation. This approach uses two crossover operators that can over-come premature convergence and the dependence of convergence on initial population. Simulation results show that this method is capable of synthesizing complex pattern shapes of planar arrays with arbitrary ge-ometry and can realize good sidelobe suppression at the same time.

Propagation of shaped beam through uniaxially anisotropic chiral slab

A general solution is obtained to a canonical problem of the reflection and refraction of an arbitrary shaped beam by using a uniaxially anisotropic chiral slab.The reflected,internal as well as refracted shaped beams are expanded in terms of cylindrical vector wave functions,and the expansion coefficients are determined by using the boundary conditions and method of moments procedure.As two typical examples,the normalized field intensity distributions are evaluated for a fundamental Gaussian beam and Hermite-Gaussian beam,and some propagation properties,especially the negative refraction phenomenon,are discussed briefly.

Wavelength-dependent nonlinear wavefront shaping in 3D nonlinear photonic crystal

A 3D nonlinear photonic crystal containing four parallel segments of periodicχ^((2))grating structure is fabricated employing the femtosecond laser poling of ferroelectric Ca_(0.28)Ba_(0.72)Nb_(2)O_(6) crystal.The second harmonic generation from this foursegment structure is studied with a fundamental Gaussian wave.By tuning the wavelength of the fundamental wave,the second harmonic varies from the Laguerre-Gaussian beam(topological charge l_(c)=1)to the higher-order Hermite-Gaussian beam and Laguerre-Gaussian again(l_(c)=−1).This effect is caused by the wavelength-dependent phase delays introduced by the four-grating structure.Our study contributes to a deeper understanding of nonlinear wave interactions in 3D nonlinear photonic crystals.It also offers new possibilities for special beam generation at new frequencies and their control.

Shaping super-Gaussian beam through digital micro-mirror device

We have set up a novel system for shaping the Gaussian laser beams into super-Gaussian beams.The digital micro-mirror device(DMD)is able to modulate the laser light spatially through binary-amplitude modulation mechanism.With DMD,the irradiance of the laser beam can be redistributed flexibly and various beams with different intensity distribution can be produced.A super-Gaussian beam has been successfully shaped from the Gaussian beam with the use of DMD.This technique will be widely applied in lithography,quantum emulation and holographic optical tweezers which require precise control of beam profile.

Experimental generation and observation of a super-resolution optical tube

We generated a super-resolution optical tube by tightly focusing a binary phase modulated azimuthally polarized laser beam.The binary phase modulation is achieved by a glass substrate with multi-belt concentric ring grooves.We also characterized the 3D beam pro¯le by using a crossshaped knife-edge fabricated on a silicon photo-detector.The size of the super-resolution dark spot in the tube is 0.32
,which remains unchanged for
4
within the tube.This optical tube may¯nd applications in super-resolution microscopy,optical trapping and particle acceleration.