Imprinted diffractive optics for terahertz radiation

Terahertz diffractive optic elements have been fabricated in polypropylene by imprinting with a silicon master. A silicon master is created with eight phase levels for high diffraction efficiency and etched using inductively coupled plasma reactive ion etching. This technique enables the rapid replication of complex optical structures in a high transmission material. Excellent replication of multilevel high efficiency Fresnel lenses is shown. The resulting lenses were tested with a 2 THz quantum cascade laser. The signal strength at the focus was 70 times the base signal strength.     

Nanostructured gradient-index antireflection diffractive optics

We describe the fabrication and characterization of a nanostructured diffractive element with near-zero reflection losses. In this element, subwavelength nanostructures emulating adiabatic index matching are integrated on the surface of a diffractive microstructure to suppress reflected diffraction orders. The fabricated silicon grating exhibits reflected efficiencies that are suppressed by 2 orders of magnitude over broad wavelength bands and wide incident angles. Theoretical models of the fabricated structure based on rigorous coupled-wave analysis and effective medium theory are in agreement with the experimental data. The proposed principles can be applied to improve the performance of any diffractive structures, potentially leading to more efficient Fresnel lenses, holographic elements, and integrated optical systems.     

Laser writing system for fabrication of diffractive optics elements

We report a laser writing system for fabrication of diffractive optical elements with He-Cd laser. The wavelength of the light source is 441.6 nm. The output beam is collimated into parallel light with uniform intensity distribution after passing through the spatial filter with a pinhole of 25μm and the collimating device. A microscopy objective lens with numerical aperture (NA) of 0.65 is used to focus the beam into a small diffraction spot. Any pattern can be written with this system. Experimental results are presented.The written gratings and the phase patterns were verified with a conventional optical microscopy and the Taylor Hobson equipment.     

折衍二元光学用金刚石车刀设计

栏光效应是影响折衍元件衍射效率的一个重要因素,栏光效应与加工刀具有着密切的关系。分析刀具圆弧半径与栏光效应的联系、刀具参数与元件加工后的表面粗糙度的关系以及刀具耐用度等要求,设计了加工折衍二元光学元件的金刚石刀具,给出刀具加工里程数计算公式和车削实验结果。实验结果证明:设计的金刚石刀具能够满足折衍二元光学元件的产业化加工要求,刀具耐用度较强化前提高2倍多。     

Beam-induced damage on diffractive hard X-ray optics

The issue of beam-induced damage on diffractive hard X-ray optics is addressed. For this purpose a systematic study on the radiation damage induced by a high-power X-ray beam is carried out in both ambient and inert atmospheres. Diffraction gratings fabricated by three different techniques are considered: electroplated Au gratings both with and without the polymer mold, and Ir-coated Si gratings. The beam-induced damage is monitored by X-ray diffraction and evaluated using scanning electron microscopy.     

Z-scan sensitivity enhancement using a binary diffractive optics

We report a theoretical study of the sensitivity enhancement of Z-scan technique, using a simple binary diffractive optical element. The latter is a phase aperture made from a transparent plate that has a circular relief introducing a π phase shift in the central region of the incident beam. We demonstrate that the phase aperture acts like a divergence multiplier allowing the Z-scan sensitivity to be increased by a factor of several hundred. PACS 42.25.Fx     

Direct laser writing of diffractive optics in glass

Low-power lasers and a novel thermal expansion process in semiconductor-doped glasses are used to fabricate diffractive optical elements.     

Laser radiation resistance of prospective materials for high-power IR optics

We have conducted comprehensive studies of resistance to radiation from a wide-aperture TEA CO₂ laser. We have classified the types of damage and the conditions for occurrence of damage and we give a qualitative explanation for the characteristic features of fracture of the materials. We have determined the thresholds for laser-induced breakdown of actual IR materials for laser apertures of 0.5–30 cm. We propose a criterion for choosing materials for high-power laser optics. Raduga State Laser Testing Center. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 68–84, October, 1998.     

Double Fourier interferometry with IR single-mode fiber optics

An implementation of double Fourier interferometry with IR single-mode, all-fiber optics is described, in which the optical path difference modulations and beam combinations are performed within waveguides. A laboratory prototype is presented, and the first experimental results that prove the validity of the concept.     

Spin effects in diffractive reactions

Double spin asymmetries in the diffractive \(Q\bar Q\) and J/ψ leptoproduction are discussed. It is shown that the asymmetries for longitudinally polarized lepton and longitudinally or transversely polarized proton can be used to study spin dependent gluon distribution of the proton at small x.     

Electromagnetic optimization of multilevel diffractive elements by use of the wavelet transform

We present an optimization algorithm for the design of multilevel diffractive optical elements in the electromagnetic domain. The method uses the wavelet transform to parameterize the diffractive optical elements according to a set of coefficients that corresponds to a multiresolution basis. Both local and global optimizations can be performed within a single algorithm. A design example consisting of the optimization of a two-dimensional millimeter-wave diffractive lens over a 10% bandwidth is presented.     

Off-axis collimation of diode laser beams by means of single-element holographic diffractive optics

Principles of single-element holographic diffractive optics for collimation of diode laser beams with a large divergence, an elliptic cross-section, and astigmatism are presented. Holographic off-axis transformation enables collimation of the beam in two variants: one with a perpendicular input beam and an oblique output beam, and the other with the beams arranged vice-versa. Diffraction due to an elliptic aperture is analyzed. Inspection of experimental samples demonstrates an agreement with theory in the case of diffraction limited focal pattern and shows increase of astigmatism with the departure from diffraction only limitation.     

Absorptive effects in the diffractive dissociation of nucleons

Absorptive effects are found to be important in diffraction dissociation. For pp→(nπ⁺)p and np→(pπ^?)p, at small excitation mass, a significant dip structure is created in the production momentum transfer distribution $\text{d}\text{σ}\text{d}\text{t}\text{d}\text{M}\text{near}\text{t = ?0.3 (}\text{GeV}\text{c}\text{)}{}^2$, in agreement with data from Fermilab and the CERN-ISR. The mass-slope correlation, seen in the data, is also reproduced. Most other distributions are affected much less by absorption.     

IR synchrotron diagnostics. Part 1: Wide-band long-focus optics

An optical channel for extracting, transporting, and applying (to a detector) IR synchrotron radiation covering a wide wavelength range is developed. The design and study of optical systems with long-focus entrance objective and mirror lenses, as well as with a field condenser lens, are reported. Practical use of IR optics combined with integrated and position-sensitive detectors in accelerator experiments with synchrotron radiation is described.     

Transverse spin effects in diffractive hadron leptoproduction

We consider double spin asymmetries for longitudinally polarized leptons and transversely polarized protons in diffractive vector meson and production at high energies within the two-gluon model. The connection of the two-gluon approach with skewed gluon distributions is discussed. The asymmetry predicted for meson production is quite small. The asymmetry for production contains two independent terms which are large and can be used to obtain information on the polarized skewed gluon distributions in the proton. Received: 19 February 2002 / Revised version: 19 March 2002 / Published online: 22 May 2002     

轻量化超宽温度折/衍混合红外热像仪光学系统设计

设计一个用于红外热像仪的轻量化超宽温中波折/衍混合红外热像仪光学系统。光学系统参数:工作波段为3.7 m～4.8 m,相对孔径为1/2,焦距为120 mm,全视场角为5.18,满足100 %冷光栏效率。采用三片式结构,使用硅和锗两种常用的红外材料,以及一个非球面和一个衍射面,系统实现了轻量化和超宽温度下工作。系统在-60℃～160℃温度范围内成像质量接近衍射极限,可供像元尺寸为30 m、像元数256256的凝视型中波红外探测器使用,可探测到2.3 km远的坦克目标。     

Use of steel substrates in diffractive optics: Near field of high surface quality steel tape gratings

Steel tape is used in optical applications due to its mechanical properties. However, roughness of steel surfaces affects to wave propagation. The effect can be observed using diffraction gratings with low periods. In such a case, self-images of the grating appear at certain periodic distances from the grating (Talbot planes). When standard steel is used, the contrast of Talbot self-images strongly decreases with the distance from the grating. In this work, we prove that controlling the surface quality of steel, it is possible to improve its optical behavior and, as a consequence, high quality surface steel represents a good choice for diffractive optics when the use of chrome-on-glass masks is not indicated. As an example, we have manufactured a diffraction grating over a high quality steel surface by means of an ablation process with a nanosecond pulsed laser. The contrast of the self-images for these gratings decreases very slowly with the distance, in comparison with the self-images obtained with standard steel tape gratings.     

Radiative effects in processes of diffractive vector meson electroproduction

The electromagnetic radiative correction to the cross section of the vector meson electroproduction is calculated. Explicit covariant formulae for the observed cross section are obtained. The dependence of the radiative correction on the experimental resolution and on the inelasticity cut is discussed. The FORTRAN code DIFFRAD, based on both exact (ultrarelativistic) and approximate sets of the formulae for the radiative correction to the cross section, is presented. Detailed numerical analysis for kinematical conditions of the recent experiments on the diffractive electroproduction of vector mesons is given. Received: 23 August 1998 / Published online: 15 April 1999     

Modelling of magnetic effects in near-field optics

Green's dyadic technique represents a powerful tool for calculations in electrodynamics, especially in modelling optical properties of nanoscopic objects. The method does not only provide field distributions, but also maps of susceptibilities and densities of states. Whereas the formalism is well established for dielectrics and electric fields, I present here a straight forward extension to tensors of both electric and magnetic type as well as mixed ones and furthermore to the situation where objects with dielectric and magnetic permeabilities are present together. As examples, characteristic field patterns are compared for elementary dielectric and magnetic perturbations. Green's tensors calculated for a coral structure reveal that mixed susceptibilities can exhibit other symmetries than pure electric or magnetic ones. Maps of all tensor components can thus give essential clues to the interpretation of near-field images. Received 15 December 2002 Published online 20 June 2003 RID="a" ID="a"Files “maths.ps” and “tensors.ps” are only available in electronic form at http://www.edpsciences.org RID="b" ID="b"e-mail: Ursula.Schroeter@uni-konstanz.de