Laser beam shaping

In this work, an analytical study to detect the ratio of bilirubin in human body by determining the level of it in blood using a 532nm laser light transported through some samples of bilirubin has been presented. A second harmonic generation of Nd:YAG laser with measured maximum output power 52.5 mW was used to determine the concentration of total bilirubin in blood. Initially, the cuvette was filled with a sample of standard bilirubin level and then it is filled by a sample of blood containing unknown levels of bilirubin. The absorption factor was calculated for four samples of adults' blood and five samples of babies' blood, and the scattering factor was neglected for each sample. The unknown concentration of total bilirubin was determined and the transmitted power through these samples of blood was measured. In this work, a good matching was obtained between the results of the concentrations of bilirubin in blood using laser technique and the results of the classical medical procedure of measuring the bilirubin concentrations. Therefore, the jaundice in human was detected. I.

Analyzing of amplitude-phase characteristics of laser beam is topical in experimental physics and in a great number of laser applications, such as, for example, laser material treatment. The task of analyzing the amplitude-phase beam structure may be treated as that of analyzing the modal composition, if this is thought of as both analyzing individual modal powers and intermode phase shifts. In this paper the problem is tackled using a special diffractive optical element (DOE), called MODAN, matched to a group of laser radiation modes and their special combinations. The experimental results reported indicate that such an approach shows promise.

The Fresnel approximation is used in the design of a lens that turns a beam with one intensity distribution into a beam with a different distribution at the focal plane of a Fourier transform lens. In general, this cannot be done exactly, so one must be satisfied with approximate solutions to this problem. It is shown that the difficulty of this problem depends on a parameter b that is a dimensionless measure of how well the geometrical optics approximation holds. An analytical method is given for determining the lens when b is large. The sensitivity of this solution to various imperfections in the system alignment is also analyzed.

Laser beam when expanded shows non-uniform illumination due to the presence of dust particles on mirrors and other optical elements. Due to coherence  interference  among the scattered beam is inevitable, leading to 'pits and valleys' some thing like moon's structure!  So cleaning is needed as a prelude to the experiments to follow. This cleaning itself is an elaborate procedure which is discussed and shown. The shear interferometer patterns are shown with out any theory.

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.

In this paper, we present two optical system design methods for beam circularization, collimation, and expansion of semiconductor laser output beam for possible application in LIDAR systems. Two different optical mirror systems are investigated: an off-axis hyperbolic͞parabolic mirror system and an off-axis parabolic mirror system. Equations specific to these mirror systems are derived and computer package programs such as ZEMAX and MATLAB are used to simulate the optical designs. The beam reshaping results are presented.

We describe the spatial coherence properties of a cold atom electron source in the framework of a quasihomogeneous wavefield. The model is used as the basis for direct measurements of the transverse spatial coherence length of electron bunches extracted from a cold atom electron source. The coherence length is determined from the measured visibility of a propagated electron distribution with a sinusoidal profile of variable spatial frequency. The electron distribution was controlled via the intensity profile of an atomic excitation laser beam patterned with a spatial light modulator. We measure a lower limit to the coherence length at the source of lc=7.8±0.9 nm.

The formulas for the reflection and refraction of a narrow Gaussian beam with general astigmatism at a tilted optical surface are derived by ray-tracing techniques. The propagation direction of the reflected and refracted beams is computed by tracing the central ray of the incident beam, and the characteristic parameters of the respective wavefronts are worked out by applying the formulas developed for the generalized ray tracing. Moreover, the Gaussian form of the reflected and refracted amplitude distributions along the transverse coordinates is determined by requiring the matching of the incident, reflected, and refracted light spots on the optical surface. No limiting assumptions are made regarding the form of the optical interface or the orientation of the incident astigmatic wavefront. In the end, to illustrate a simple application of these formulas, the reflection of a Gaussian beam at a conicoid is considered, and a simple property of the conicoidal mirrors is reported.

Quality control is of utmost importance in the metal industry. It requires online measurement and inspection systems which provide precise feedback to closed-loop controllers in industrial facilities. In rolled products, shape is one of the main quality criteria. In this paper, a low-cost real-time 3-D shape measurement system for long flat (FL)-rolled products based on laser triangulation is proposed. The system provides online measurements of two geometrical features of the shape of rolled products: flatness and width. The proposed system is based on 3-D surface reconstruction of rolled products with which flatness can be measured accurately and continuously across the whole width of the strip. Three-dimensional surface reconstruction provides highly accurate width measurements not only of FL products, as do most other systems, but also of non-FL products. The accuracy of the laser extraction method used to reconstruct the surface of the rolled products is evaluated, as well as the online performance of the system. Index Terms-Feature extraction, flatness measurement, image processing, measurement by laser beam, metal industry, shape measurement, width measurement.

The validity of the paraxial approximation for laser beams in free space is studied via an integral criterion based on the propagation invariants of Helmholtz and paraxial wave equations. This approach allows one to determine the paraxial limit for beams with nondefined spot size and for beams described by more parameters in addition to typical longitudinal wavelength and transverse waist. As examples, the paraxiality of higher-order Hermite, Laguerre, and Bessel-Gaussian beams was completely determined. This method could be extended to nonlinear optics and Bose condensates.

We demonstrate that hollow Gaussian beams can be obtained from Fourier transform of the differentials of a Gaussian beam, and thus they can be generated by spatial filtering in the Fourier domain with spatial filters that consist of binomial combinations of even-order Hermite polynomials. A typical 4f optical system and a Michelson interferometer type system are proposed to implement the proposed scheme. Numerical results have proved the validity and effectiveness of this method. Furthermore, other polynomial Gaussian beams can also be generated by using this scheme. This approach is simple and may find significant applications in generating the dark hollow beams for nanophotonic technology.

The formulas for the reflection and refraction of a narrow Gaussian beam with general astigmatism at a tilted optical surface are derived by ray-tracing techniques. The propagation direction of the reflected and refracted beams is computed by tracing the central ray of the incident beam, and the characteristic parameters of the respective wavefronts are worked out by applying the formulas developed for the generalized ray tracing. Moreover, the Gaussian form of the reflected and refracted amplitude distributions along the transverse coordinates is determined by requiring the matching of the incident, reflected, and refracted light spots on the optical surface. No limiting assumptions are made regarding the form of the optical interface or the orientation of the incident astigmatic wavefront. In the end, to illustrate a simple application of these formulas, the reflection of a Gaussian beam at a conicoid is considered, and a simple property of the conicoidal mirrors is reported.

This paper reports on a novel construction of a deformable mirror for laser beam shaping. The deformable mirror is actuated by screen-printed thick film piezoceramic unimorphs based on lead zirconate titanate (PZT). Different actuator layouts are realized and will be presented. We use Low Temperature Cofired Ceramics (LTCC) as a substrate material with a metallization as reflective surface. LTCC offers easy integration of holding structures. The reflective mirror surface is electroplated copper. After deposition, the copper layer is diamond machined to achieve excellent optical surface quality <10 nm (rms). We build deformable mirrors with 1, 13 and 19 actuators and a total stroke of more than 20 µm and characterize them with a wave front sensor.

We present two optical system designs using aspherical lenses for beam circularization, collimation, and expansion of semiconductor lasers for possible application in lidar systems. Two different optical lens systems are investigated; namely, two aspherical lens and single aspherical lens systems. Software package programs of ZEMAX and MATLAB to simulate the optical designs are used. The beam reshaping results are presented for one specific laser beam output.

The integration of a time-variable array of pinholes can be used to perform high-resolution imaging with high energy efficiency, and significantly extend the field of view when combined with an imaging lens. Lenses are used for imaging in a wide range of applications, but in many cases this leads to drawbacks. For example, in smart phone cameras the use of imaging lenses limits the flatness of the device, and in medical devices, such as micro-endoscopes, the field of view (FOV) is limited. In many applications, such as tera-hertz (THz) imaging—used for security purposes—or gamma-ray imaging, which is used in single-photon emission computed tomography (SPECT), conventional imaging lenses cannot be used. Instead, existing THz detectors require space scanning and bulky hemispherical lenses or mirrors, 1 whereas gamma-ray imaging requires an array of collimators to allow only forward-propagating rays to pass. We have found that the integration of a time-variable array of pinholes can be used to carry out high-resolution imaging. This array provides high energy efficiency if it is used to replace an imaging lens, 2 and it can significantly extend the FOV 3 if it is integrated into the aperture plane of an imaging lens. Avoiding the use of imaging lenses enables much flatter and cheaper imaging optics to be used in the visible and near-IR regions, and also in other spectral regions in which the use of conventional lenses is not feasible. Whether the array is used to replace a lens, or is integrated into a lens, its operating principle involves time-variable encoding of the aperture plane, followed by decoding to recover the resolution and FOV of the enhanced image. We have demonstrated experimental results for both the above-mentioned uses of the array. 4 We achieved lens-free imaging by combining a variable-aperture wheel, as shown in Figure 1, with a CCD sensor. Figure 1. Left: Variable-aperture wheel for use in combination with a CCD sensor to acquire images. Right: Experimental setup using the screen of a smartphone to display the imaged object. After capturing a set of images and performing inverse filtering, we obtained a high-resolution, high-intensity image. We then used the lens-free system for gamma-ray medical imaging using a GE Discovery NM/CT 670 SPECT gamma camera with a blue plate as a sample object: see Figure 2(d). 5 The time-variable arrays of pinholes were made of lead with tungsten inserts. We compared the results of experiments carried out using three systems: a single pinhole with a hole insert diameter of 4.45mm, and single and multiple pinhole arrays with hole insert diameters of 2mm. Using a multiple pinhole array, the experimentally measured sensitivity was improved by a factor of 2.33. In this test, we used a 1D design of the array. Using the same design in 2D, the improvement in sensitivity reached a factor of 5.67. The ratio of the gamma-radiation activity of the 2mm system to that of the 4.45mm system was 4.95, which corresponded to the ratio of the respective pinhole areas. Figure 2(a–c) shows the experimental results obtained with an image accumulation time of 18s. We also integrated a digital micromirror device (DMD) into the imaging lens of a near-IR camera. The DMD provides the same transmission function as the time-variable set of pinholes, by determining whether energy reaches the detector according

We present two optical system designs using aspherical lenses for beam circularization, collimation, and expansion of semiconductor lasers for possible application in lidar systems. Two different optical lens systems are investigated; namely, two aspherical lens and single aspherical lens systems. Software package programs of ZEMAX and MATLAB to simulate the optical designs are used. The beam reshaping results are presented for one specific laser beam output.

Single-mode diode lasers are well-established light sources for a huge number of applications but suffer from astigmatism, beam ellipticity and large manufacturing tolerances of beam parameters. To compensate for these shortcomings, various approaches like anamorphic prism pairs and cylindrical telescopes for circularization as well as variable beam expanders based on zoomed telescopes for precise adjustment of output beam parameters have been employed in the past. The presented new approach for both beam circularization and expansion is based on the use of microlens arrays with chirped focal length: Selection of lenslets of crossed cylindrical microlens arrays as part of an anamorphic telescope enables circularization, astigmatism correction and divergence tolerance compensation of diode lasers simultaneously. Another promising application of chirped spherical lens array telescopes is stepwise variable beam expansion for circular laser beams of fiber or solid-state lasers. In this article we describe design and manufacturing of beam shaping systems with chirped microlens arrays fabricated by polymer-on-glass replication of reflow lenses. A miniaturized diode laser module with beam circularization and astigmatism correction assembled on a structured ceramics motherboard and a modulated RGB laser-source for photofinishing applications equipped with both cylindrical and spherical chirped lens arrays demonstrate the feasibility of the proposed system design approach.

Laser-produced plasmas (LPP) are laboratory-scale, table-top and high-brightness sources of partially coherent radiation that can be tuned between the extreme ultraviolet and the hard X-rays. A few LPP emission wavelengths find important applications in bio-photonics. As an example, LPP emitting in the so called “water window” (spectral range λ= 4.4 nm – 2.3 nm) allowed the world first X-ray scanning microscopy and contact microscopy, the latter being able to perform in vivo molecules imaging with 50-nm spatial resolution.

A new (to our knowledge) technique for the generation of a propagation-invariant elliptic hollow beam is reported. It avoids the use of the radial Mathieu function and hence is mathematically simpler. Bessel functions with their arguments having elliptic locus are used to generate the mask, which is then recorded using holographic technique. To generate such an elliptic beam, both the angular Mathieu function, i.e., elliptic vortex term, and the expression for the circular vortex are used separately. The resultant mask is illuminated with a plane beam, and the proper filtering of its Fourier transform generates the expected elliptic beam. Results with both vortex terms are satisfactory. It has been observed that even for higher ellipticity the vortices do not separate.

Based on angular spectrum engineering, we report the generation of optical lattices whose two-dimensional transverse nondiffracting pattern can be reduced to a quasi-one-dimensional intensity structure formed by either a single or multiple parallel channels. Remarkably, many features for each channel such as its maximum intensity, modulation, width, or separation among channels, can be controlled and modified in order to meet the requirements of particular applications. In particular, we demonstrate that these lattices can provide useful schemes for soliton routing and steering. We demonstrate the existence domain of ground-state solitons for the single quasi-onedimensional lattice, and we show that these nondiffracting beams allow "push and pull" dynamics among the neighbor solitons propagated along the nondiffracting channels generated.

We demonstrate a simple all-fiber device that can transform a Gaussian-shaped laser beam into a uniform intensity beam. The device is based on the interaction of a core mode and a cladding mode partially coupled out by a long-period grating. It has achieved good beam uniformity, and reduced beam divergence while introducing negligible insertion loss. The measured beam uniformity and divergence angle matches well with simulated results. The device can be applied to applications that require a uniform surface and volume irradiation such as laser medical treatment and laser material processing.

Optical surface structuring shows great interest for antireflective or scattering properties. Generally, fabricated surface structures are periodical but random surfaces that offer new degrees of freedom and possibilities by the control of their statistical properties. We propose an experimental method to create random rough surfaces on silicon by laser processing followed by etching. A photoresist is spin coated onto a silicon substrate and then exposed to the scattering of a modified laser beam. The beam modification is performed by using a micromirror matrix allowing laser beam shaping. An example of tuning is presented. An image composed of two white circles with a black background is displayed and the theoretical shape of the correlation is calculated. Experimental surfaces are elaborated and the correlation function calculated from height mapping. We finally compared the experimental and theoretical correlation functions.

A general analytical formula has been found to describe the evolution of the pulse width of the femtosecond pulses in a Gaussian beam after passing an angular disperser without the assumption of well collimation. This formula is experimentally verified by measuring the pulse width with an autocorrelator based on twophoton absorption. It is found that the effect of the spectral lateral walk-off and group delay dispersion on the pulse-width evolution, and its dependence on the distance traveled, are substantially different when the beam has not been well collimated than from when it has been collimated. These differences result from the decaying nature of the angular dispersion of the Gaussian beam sent across a distance.

A systematic three-dimensional focus engineering method based on the dipole-array radiation pattern is proposed. High numerical aperture focusing of generalized cylindrical vector beam is interpreted as the reversing of the radiation from electrically small dipole arrays. Required pupil plane illumination can be found for the desired focal field with specific characteristics. Magnetic-dipole array radiation is utilized to create ultra-long (~8λ) diffraction limited three-dimensional optical tube with maximal uniformity. Combined with a recently reported optical needle field generation with the help of electric dipole array radiation, ultra-long (~8λ) three-dimensional flattop focus that has top hat profiles in both transversal and longitudinal directions can be realized with the help of radiations pattern from co-located magnetic and electric dipole arrays.

We consider the effect of laser beam shaping on proton acceleration in the interaction of a tightly focused pulse with ultrathin double-layer solid targets in the regime of directed Coulomb explosion. In this regime, the heavy ions of the front layer are forced by the laser to expand predominantly in the direction of the pulse propagation, forming a moving longitudinal charge separation electric field, thus increasing the effectiveness of acceleration of second-layer protons. The utilization of beam shaping, namely, the use of flat-top beams, leads to more efficient proton acceleration due to the increase of the longitudinal field.

We demonstrate that hollow Gaussian beams can be obtained from Fourier transform of the differentials of a Gaussian beam, and thus they can be generated by spatial filtering in the Fourier domain with spatial filters that consist of binomial combinations of even-order Hermite polynomials. A typical 4f optical system and a Michelson interferometer type system are proposed to implement the proposed scheme. Numerical results have proved the validity and effectiveness of this method. Furthermore, other polynomial Gaussian beams can also be generated by using this scheme. This approach is simple and may find significant applications in generating the dark hollow beams for nanophotonic technology.

We demonstrate laser beam shaping by utilizing the linear electro-optic effect in patterned ferroelectric domains in lithium tantalate. The phase function essential for the conversion of a 633 nm wavelength laser light from a Gaussian to a flat-top intensity profile was computed using the Gerchberg-Saxton algorithm. The corresponding ferroelectric domain pattern required to induce the equivalent phase function was fabricated on a lithium tantalate crystal, and the performance compared with design specifications.

We present a theoretical and experimental investigation of a very simple binary Diffractive Optical element referred as a phase slit. The latter is made up of two transparent plates of glass in which a phase step has been patterned using ion beam etching. The two phase steps are set parallel and are able to slide each on the other so that one can adjust continuously the width of the phase shifting zone that suffers an incident Gaussian beam. It is shown that the phase slit is able to make a 1-D transformation of a Gaussian beam either into a uniform profile or a hollow profile having a central depression whose depth can be continuously adjusted just by changing the width of the slit.

We demonstrate a simple and compact laser source that directly produces a Bessel–Gauss beam. The laser resonator consists of a diode-end-pumped Nd:YAG crystal, a planar mirror, and a diffractive mirror designed to phase-conjugate only the lowest-order Bessel–Gauss beam.

We present a variant of the method of Fox and Li [Bell Syst. Tech. J. 40, 453 (1961); Proc. IEEE 51, 80 (1963)] dedicated to intracavity laser beam shaping for resonators containing an arbitrary number of amplitude and phase diffractive optics. Contrary to Fox and Li, the starting point is the desired field. The latter is injected into the usual sequence of lenses representing just a single round trip, and the optimization process iterates until the input and the output fields match as much as possible. We illustrate this technique by deriving a simple model for generating single cylindrical TEM p0 modes, thanks to a π-phase plate placed inside a plano-concave cavity. The experimental validation attests an excellent agreement with numerical predictions.