Beam Shaping Method Research Articles

Beam shaping using Gaussian beam modes

A beam shaping method is presented where a diffractive optical element (DOE) is designed by optimizing the complex mode coefficient weights of a set of Gaussian beam modes. This method is compared with the more standard unidirectional approach. Differential evolution is used for the optimization in both the unidirectional and Gaussian beam mode optimization methods. For the particular transforms carried out, the Gaussian beam mode set optimization (GBMSO) approach achieved more optimal solutions. The GBMSO approach is extended to design DOEs that control the amplitude distribution of a beam at multiple planes, rather than at just a single plane (i.e., the far field).

Recent Innovations in Carbon-Ion Radiotherapy

In the last few years, hospital-based facilities for carbon-ion radiotherapy are being constructed and proposed in Europe and Asia. During the next few years, several new facilities will be opened for carbon-ion radiotherapy in the world. These facilities in operation or under construction are categorized in two types by the beam shaping method used. One is the passive beam shaping method that is mainly improved and systematized for routine clinical use at HIMAC, Japan. The other method is active beam shaping which is also known as beam scanning adopted at GSI/HIT, Germany. In this paper an overview of some technical aspects for beam shaping is reported. The technique of passive beam shaping is established for stable clinical application and has clinical result of over 4000 patients in HIMAC. In contrast, clinical experience of active beam shaping is about 400 patients, and there is no clinical experience to respiratory moving target. A great advantage of the active beam shaping method is patient-specific collimator-less and compensator-less treatment. This may be an interesting potential for adaptive radiotherapy.

Small-Sized Shaped Beam Base Station Antenna with Superior Intersector Interference Reduction in High Speed Cellular Systems

This paper presents a newly developed small-sized shaped beam base station antenna in order to reduce inter-sector interference for next generation high speed wireless data communication systems. The developed antenna realizes polarization diversity as a single small-sized antenna without decreasing the 3dB main beamwidth compared with the conventional antenna by applying a newly designed beam shaping method. Furthermore, side sub-reflectors are newly installed in the radome to reduce the antenna beam gain in the direction toward the edge region neighboring the other sectors of the horizontal antenna pattern. By adopting this type of reflector, the diameter of the radome can be minimized at 0.65λ, which is slightly longer than that of the conventional antenna. Both a computer simulation and a field measurement test based on an actual cellular network were conducted for the purpose of clarifying the validity of the shaped beam antenna. In the results, the CINR at the service area by the shaped beam antenna was 1dB and 3.5dB better than that of the conventional antenna at the median and 10% of CDF, respectively. The developed antenna will be expected to contribute to the enhancement of the quality of cellular radio systems in the future.

基于倾斜多高斯光束叠加的均匀化照明整形方法

基于倾斜多高斯光束叠加的均匀化照明整形方法

The fabrication of circular cross-section waveguide in two dimensions with a dynamical slit

A waveguide with a circular transverse profile can be obtained by using a slit beam shaping method. Applications about optical circuit chips in glass require a circular cross-section waveguide in two dimensions. Here we reported to realize a fabrication of circular cross-section waveguide in two dimensions by rotating the slit corresponding to the tangent line of the arc of the waveguide. The dependence of cross-section on width of the slit was investigated in experiment. The difference of slit width between geometrical optics prediction and experimental result was explained by considering the focal shift in xy directions due to diffraction effects.

Smallest flattop focus by polarization engineering

Spatial engineering of polarization as a new method of beam shaping is analyzed by using scalar diffraction theory. For the one-dimensional case, it is shown that the smallest flattop far-field distribution can be obtained by adopting a linear polarization that changes direction as a linear function of location in the pupil plane. The resulting light field is functionally equivalent to a cosinusoidal function modulation of the wavefront but maintains high efficiency. This polarization beam shaping technique proves to be highly useful in applications where diffraction effects need to be taken into account. The extension of this technique to two-dimensional beam shaping is also demonstrated.

Polarization beam shaping

Spatial engineering of polarization is proposed as a novel method of beam shaping. It is shown that a flat-top-shaped focus can be obtained in the far field by changing the polarization in the pupil plane in a spatially inhomogeneous manner. Experiments have been carried out to verify the validity of this method in one dimension. By comparison with traditional beam shaping methods, polarization beam shaping yields the smallest flat-top focus while maintaining high efficiency.

Laser diode beam shaping with GRIN lenses using the twisted beam approach and its application in pumping of a solid-state laser

We report a novel beam shaping method for laser diodes based on the concept of twisted Gaussian Schell-model beams using GRIN lenses. This method enables a more symmetric pump as well as a compact setup for pumping of solid-state lasers. In the experiment with a standard 2 W diode, the beam quality factors in the two orthogonal directions were equalized to M x 2 ≈ 24 and M y 2 ≈ 18 , respectively, which pumped an intra-cavity frequency-doubled Nd:YAG laser at 946 nm with an output of 28 mW at 473 nm.

Automatic symmetrical iterative Fourier-transform algorithm for the design of diffractive optical elements for highly precise laser beam shaping

A symmetrical iterative Fourier-transform algorithm (IFTA) using a combination of phase and amplitude freedom for the design of diffractive optical elements for highly precise laser beam shaping is presented. We compare this method with the basic IFTA and the symmetrical IFTA exclusively using phase freedom, and the basic IFTA using both phase and amplitude freedom, by employing these methods for super-Gaussian beam shaping. While the latter three methods fail to produce satisfactory solutions, the first method results in a beam non-uniformity error of 0.44% and a theoretical efficiency of 97.2%. Moreover, the new approach avoids the use of the trial-and-error method for finding the appropriate modified Fourier-domain constraints during the iteration, which can be difficult for some beam-shaping problems.

Symmetric waveguides in poly(methyl methacrylate) fabricated by femtosecond laser pulses

We report on the fabrication of symmetric waveguides in bulk poly(methyl methacrylate) (PMMA) by femtosecond laser pulses. A waveguide with a circular transverse profile can be obtained by using a slit beam shaping method. The refractive index in the core increases by up to 4.6 x 10(-4) and the waveguide works as single-mode waveguide at a wavelength of 632.8 nm. This writing technique is applied to the fabrication of a directional coupler to split a coupled beam with a 1:1 splitting ratio at 632.8 nm.

Statistical approach to beam shaping

A method for beam shaping based on fitting the power moments of the final beam intensity distribution and independent of the optical system particularities is suggested. It is shown how one can analytically calculate any moment of the final phase space distribution using the moments of the initial distribution and the optical system transfer map. Numerical tests carried out for a final focus system have demonstrated the usefulness of the approach developed here.

Laser diode stack beam shaping by reflective two-wedge-angle prism arrays

An innovative beam-shaping method for laser diode stacking is presented by employing a pair of reflective two-wedge-angle prism arrays. Each subprism with two variable wedge angles is designed for deflecting the partial emission from different bars to the dead spaces of the stack, according to the configuration of the real laser diode (LD) stack and the requirement of the system. The formula to determine the parameters of each subprism is deduced by way of geometrical analysis. A beam-shaping system for stack laser diodes with three bars is designed and simulated, and the results show that the stack laser beam is well transformed into a required distribution efficiently. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Slit beam shaping method for femtosecond laser direct-write fabrication of symmetric waveguides in bulk glasses

We report both theoretical and experimental results of a slit beam shaping configuration for fabricating photonic waveguides by use of femtosecond laser pulses. Most importantly we show the method supports focusing objectives with a long depth of field and allows the direct-writing of microstructures with circular cross-sections whilst employing a perpendicular writing scheme. We applied this technique to write low loss (0.39 dB/cm), single mode waveguides in phosphate glass.

Adaptive beam profile control using a simulated annealing algorithm

We present a programmable beam-shaping method based on the combination of a deformable mirror membrane mirror and a simulated annealing algorithm. The algorithm iteratively adjusts the control voltages of 37 independent electrodes to reduce the variance between the chosen shape and the actual beam shape. The experimental results show that the system is capable of adaptively creating, on demand, Gaussian and super-Gaussian beam profiles that closely match the desired target parameters.

Ablation and cutting of planar silicon devices using femtosecond laser pulses

Although lasers are generally able to machine silicon, the major material in many microsystems applications, doing so without influencing the physical properties of the bulk material remains an important challenge. Ultrafast lasers, in particular, with their potential to precisely ablate all kinds of solid materials, are able to perform such processes with high efficiency and accuracy. This article starts with an overview of the general interaction of ultrafast laser radiation with semiconductors, explaining the absorption processes and different fluence regimes for the ablation of silicon. Major parameter influences, especially for cutting processes in thin silicon, are described. By varying pulse energies, beam shaping methods, the beam polarization, and temperatures, the cutting quality and speed can be significantly influenced. One important quality aspect, besides kerf widths and surface roughness, is the amount of back-side chipping when cutting brittle materials. Achievements in speed enhancement using linear focus shapes are presented, with cutting speeds up to five times higher than by conventional spot-focusing. On the other hand, laser processes that cut with a spot focus offer the possibility of free-shape cutting, which is explained using the example of wafers carrying silicon chips with highly increased package densities.

Controlled spatial shaping of nondiffracting patterns and arrays

It is verified that the condition of nondiffracting propagation of an optical beam provides the degrees of freedom that are applicable to the controlled shaping of the beam's transverse intensity profile. The proposed method of beam shaping permits experimental realization of nondiffracting patterns and arrays with a predetermined spatial shape.

A millimeter-wave cassegrain antenna using shaped beam waveguide feed

As a way to increase the efficiency of the focused beam-fed Cassegrain antenna with a large aperture for use at millimeter-wave frequencies, a method is proposed for shaping the surface of two focusing reflectors in the focused beam waveguide feed. The reflector surface shaping method is presented. Since the reflector is used at millimeter-wave frequencies, it is necessary to take into account the effect of the aberration caused by the deformation of the reflector surface on the radiation characteristics. Both the sub- and main reflectors have quadratic surfaces. The aberration in the main reflector due to self weight deformation can be corrected with the deformation of the subreflector in the homologic design. Hence, in order to validate the present beam shaping method, it is necessary to evaluate the effects of the aberration caused by the alignment error of each focusing reflector on the radiation characteristics. In this paper, a method of shaping the two focusing reflectors is applied to the new 10-m antennas for the millimeter-wave interferometer of Nobeyama National Observatory (model No. 6). The alignment errors in the parallel shift in three axis directions and the rotating motion about the axes are assumed, and the aberration and the gain degradation are quantitatively investigated when each focusing reflector is deformed. It is shown that the grain degradation is small in the range of realizable alignment errors and that the method of shaping the surfaces of two focusing reflectors is effective as a reflector shaping method for a millimeter-wave large-aperture antenna. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(4): 39–47, 2001

Wave-front design algorithm for shaping a quasi-far-field pattern

To design a fully continuous wave-front distribution suitable for focused beam shaping by a deformable mirror, we modify the phase-retrieval algorithm by employing a uniformly distributed phase as a starting phase screen and spatial filtering for the near-field phase retrieved during the iteration process. A special phase unwrapping algorithm is not required to obtain a continuous phase distribution from the retrieved phase since the boundary of the 2pi-phase-jumped region in the designed phase distribution is perfectly closed. From the computational result producing a uniform square beam transformation from a circular defocused beam, this algorithm has provided a fully continuous wave-front distribution with a lower spatial frequency for a deformable mirror. The transformed square beam has a normalized intensity nonuniformity of varsigma(rms) = 0.14 with respect to a desired flat-topped square beam pattern. This beam-shaping method also provides a high energy-concentration rate of more than 98%.

Analytical beam shaping with application to laser-diode arrays

In contrast to numerical methods for beam shaping, analytical beam shaping consists of two steps: first, finding a purely geometrical distortion between the input plane and the output plane redistributing the intensity of the incoming wave front; and, second, computing a phase-only element realizing this coordinate transform. For the latter the method of stationary phase may be applied. The known classes of possible analytical wave transformation are extended to comprise separable and isotropic super-Gaussian-to-super-Gaussian conversion as well as transformation of Gaussian arrays to super-Gaussian distributions, and vice versa. The resulting optical phase elements contain no spiral phase dislocation and may thus be realized as refractive or diffractive elements. In addition, the outgoing wave front does not contain spiral phase dislocations.

Use of a dynamic rangeshifter for modifying the depth‐dose distributions of negative pions

In order to use negative pions for the treatment of large deep-seated tumors in radiotherapy, it is necessary to produce depth-dose distributions tailored to specific shapes. We present here a method of beam shaping which utilizes a fluid-filled piston having a programmable, computer-controlled, time-dependent thickness. The fluid alters the residual range of the pions such that predetermined depth-dose distributions can be obtained. Changing from one distribution to another can be accomplished simply and rapidly without access to the treatment room. Depth-dose distributions which are flat over a range in depth up to 10 cm have been produced. Distributions tailored to produce flat "effective dose" versus depth have also been obtained.