Volume structuring of high power LED encapsulates by femtosecond laser direct writing

We report on the micro-fabrication of diffractive optical elements (DOEs) such as 1D, 2D and concentric grating structures inside the volume of thin silicone films by femtosecond laser direct writing. In addition, we show that such structures can also be integrated into silicone films that act as encapsulation layers of high power light-emitting diodes. The latter strategy opens new possibilities to homogenize and to control the light emitted from such devices.     

High-efficiency 1.5 microm thick optical axis grating and its use for laser beam combining

We demonstrate an optical axis grating (OAG) recorded in a nematic liquid crystal that yields a higher than 80% diffraction efficiency and over 800:1 switching contrast between diffraction orders for a laser beam of a red wavelength in a material layer only 1.5 microm thick. The grating was used for combining two laser beams with high efficiency. These observations prove the feasibility of new generation high-efficiency diffractive optical components, which are most promising for infrared and high-power applications owing to their enhanced transparency and reduced thermal effects in thin material layers.     

Highly efficient field emission from nanodiamond films treated by fast reactive ion etching process

A fast reactive ion etching (RIE) treatment method is presented for dramatic enhancement of the field emission performances of nanocrystalline diamond (NCD) films. In this method a moment RIE treatment is able to modify the surface morphologies of NCD films and form a large area of nanoneedle-like arrays on the NCD films, in which the diamond nanoparticles were seeded on the film to serve as an etching mask. These elaborated diamond nanoneedle-like structures showed good uniformity and dense morphology with a controllable aspect ratio and distribution density and thereby significantly increased the electron field emission properties of the NCD films due to the formation of more emitting tips and enhanced field enhancement factor.     

衍射光学二维激光扫描器设计制作研究

提出、设计并采用激光直写和反应离子刻蚀技术制作出一种新型的衍射光学纯相位型二维激光扫描器,并进行了系统参数的实验测试,其扫描角度为２５°×２５°,衍射效率为４１％。     

体Bragg衍射器件在高功率激光中的应用

记录在光热敏微晶玻璃(PTR)中的体Bragg衍射器件具有高衍射效率、可选择的角度和波长选择特性以及高损伤阈值等优点,成为先进激光技术发展中的一种新兴器件。综述了目前各型体Bragg衍射器件在激光技术中的应用,主要包括角选择近场滤波技术、光谱合成技术、外腔半导体稳频技术以及啁啾脉冲压缩与展宽技术。详细地阐述和分析了这些方法的原理、特点、适用范围以及它们的研究现状。     

氢稀释制备的非晶碳膜的绿光和蓝光发射

在电容耦合式PECVD系统中,以CH4和H2为气源,通过控制H2的流量制备了一系列氢化非晶碳膜（a-C:H)样品。利用傅里叶变换红外光谱（FTIR）、光致发光谱（PL）和吸收谱对a-C:H膜的结构及光学性质进行了研究。结果表明：氢稀释可以在一定程度上减少碳的sp^2团簇的形成,增大它的光学带隙,并改变薄的微结构。与此同时,光致发光峰随郑 光学带隙的增大而蓝移;当光学带隙增大2．72eV时,出现了2．4eV（绿光）和2．97eV(蓝光）组成的发光峰。     

Beam steering and deflecting device using step-based micro-blazed grating

The rapidly evolving demands of optical communications and optical switching systems have created a new market for high capacity all-optical beam steering and deflecting techniques. One technology potentially capable of realizing such systems uses the multistep micro-blazed grating optical beam deflectors based on binary and multiple-phase modulation methods. The micro-optical element has been fabricated by introducing very large scale integration (VLSI), stepping photolithography and reactive ion etching (RIE), which can realize beam steering, deflecting, splitting, and switching in free space, and its diffraction properties are determined by the blazed-grating parameters, such as the number of steps, grating depth, grating period, as well as blazed profile. The theoretical analysis and primarily experimental result show that this phase-type element has the advantages of high diffractive efficiency, low cross talk, small feature size, and high reliability due to nonmechanical beam steering without any moving parts. Hence it is ideally suited to applications in optical communication and optical interconnection network.     

Structural and optical properties of Fe-doped hydrogenated amorphous carbon films prepared from trans-2-butene by plasma enhanced metal organic chemical vapor deposition

Fe-doped hydrogenated amorphous carbon (a-C:H:Fe) films were deposited from a gas mixture of trans-2-butene/ferrocene/H₂ by plasma enhanced metal organic chemical vapor deposition. X-ray photoelectron spectroscopy, Fourier transform infrared spectra and Raman spectra were used to characterize the composition and the bonding structure of the a-C:H:Fe and a-C:H films. Optical properties were investigated by the UV–visible spectroscopy and the photoluminescence (PL) spectra. The Fe-doped films contain more aromatic structures and C=C bonds than the undoped films. The sp ² carbon content and sp ² clustering of the films increase, and aromatic-like rings’ structures become richer after Fe-doping. The Tauc optical gap of the a-C:H:Fe films become narrower by 0.3 eV relative to the value of the a-C:H films. The PL peak shifts from 2.35 eV of the a-C:H films to 1.95 eV of the a-C:H:Fe films, and the PL intensity of the a-C:H:Fe films is greatly enhanced. A deep level emission peak around 2.04 eV of the a-C:H:Fe films is observed.     

有限口径非周期亚波长衍射聚焦偏转器的严格矢量优化

有限口径非周期亚波长衍射光学器件的亚波长结构特性使得传统标量衍射理论失效,必须借助严格电磁理论进行器件的设计。提出一种循环平面波谱算法(IterativePlaneWaveSpectrumAlgorithm,IPWSA)作为器件优化算法,利用二维时域有限差分方法作为严格电磁计算模式,根据Farn方法对器件面型进行亚波长处理,设计出有限口径非周期具有亚波长结构的衍射聚焦偏转器件,偏转角为24.8°,该器件可与激光器集成构成微型集成光学系统,也可以用在红外量子阱系统中。详细分析了算法原理,设计实例验证了算法的优化效果。     

Laser in micro and nanoprocessing of diamond materials

Basic processing operations will be presented. These include diamond polishing and shaping, production of conductive pathways, micro‐ and nanostructures on the diamond surface, such as diffractive optical elements. The possibility to laser produce conductive and hollow structures in the diamond bulk, including curved elements, will be demonstrated. Finally, the techniques of laser assisted diamond CVD, that allow production of smooth or selective‐area grown films will be presented     

Infrared radiation transmission through GaAs/AlGaAs quantum well infrared photodetector

This paper discusses experimental and theoretical studies of the efficiency of optical coupling in GaAs/AlGaAs multiple-quantum-well-infrared photodetectors (QWIPs) via optical diffraction grating. Optical responsivity has been studied to compare the effectiveness of different grating structures fabricated by chemical wet and reactive ion etching (RIE) methods. By the unique measurement of infrared radiation transmission spectrum of the QWIP system, we have clearly demonstrated the optical interference effect in the GaAs/ AlGaAs active MQW layer and the potential utilization of the interference effect in designing and optimizing QWIP systems has been discussed. An optical grating processed by the RIE technique is advantageous due to its accurate control over the feature size of optical apertures.     

Diffractive optics: Design, realization, and applications

This paper presents methods for designing and recording optimal computer-generated diffractive optical elements. The design method is based on an analytic ray-tracing procedure for minimizing aberrations. The recording involves computer-generated masks and multiple lithographic processes in order to form reflective and transmissive multilevel, surface relief-phase, diffractive elements. As a result, the elements can have high diffraction efficiencies over a broad range of incidence angles. Even generalized diffractive elements that operate with highly uniform diffraction efficiency and polychromatic radiation can be designed and recorded by optimizing the shape and height of the relief gratings. To illustrate the effectiveness of the diffractive optical elements, they have been incorporated into a number of applications, involving visible as well as infra-red radiation. Some that deal with coordinate transformation, beam shaping, and polarization control are briefly reviewed.     

Optical image encryption based on coherent diffractive imaging using multiple wavelengths

Coherent diffractive imaging is an optical technique in which the information of an object is encoded in the diffraction intensity using a single-path wave propagation strategy. In recent years, coherent diffractive imaging has attracted much attention in many fields due to its marked advantages, such as robustness to vibration and the suitability for various wavelengths. In this paper, we propose to apply coherent diffractive imaging using multiple wavelengths for optical image encryption. A light wavelength is tuned during the encryption, and a series of diffraction intensity maps (i.e., ciphertexts) is sequentially recorded in the Fresnel domain. During image decryption, an iterative retrieval algorithm is further developed, and cryptosystem security and robustness of the proposed method are also analyzed. Numerical simulation results are presented to demonstrate feasibility and effectiveness of the proposed method.     

Diffusionless oxidation and structure modification of thin Cr films by the action of ultrashort laser pulses

Results of impact on Cr thin metal films by ultrashort laser pulses are investigated in the paper. For the first time thermochemical action of such pulses is shown and confirmed by analytical approaches (micro-Raman spectroscopy, CAES and others) and selective chemical etching both. It is impossible to ascribe this effect to well-known mechanism of heterogeneous diffusion at the irradiation specified conditions. Possible reasons of Cr thin films diffusionless oxidation and structure modification are observed. Discovered phenomena open up new opportunities for developing of optical thermochemical data recording on Cr thin films, which are widely used in microelectronics as photomasks and in the process of diffractive optical elements manufacturing.     

利用二维杨-顾算法设计非对称结构衍射光学元件

杨 顾算法是一种设计衍射光学元件的相位恢复方法。在大多数文献中,主要用它来设计一维衍射光学元件和具有旋转对称结构的二维衍射光学元件,故在此称之为一维杨 顾算法。二维杨 顾算法可用来设计任意结构的二维衍射光学元件。在基于非幺正变换光学系统中,用振幅 相位恢复理论建立了二维杨 顾算法的数学模型,给出了迭代算法。利用自编的仿真程序包设计了一个具有非对称结构的衍射相位元件。     

Dependence of solar cell performance on Si:H nanostructure

Nanocrystalline Si:H (nc-Si:H) films were prepared to fabricate solar cells, of which the output properties were investigated. Nanocrystals are indicated in the films by electron microscopy. Raman experimental data of phosphorus doped nc-Si:H films were well simulated by Fano effect (FE) profiles due to Fano interference between discrete optical phonons and a continuum of electronic excitations in the nanocrystals. Raman measurement signals of the phosphorus doped and intrinsic nc-Si:H layers can be fitted well by a strain-calibrated phonon confinement effect (S-PCE) model owing to incorporated effects of phonon confinement and tensile strain. For the Raman signals from intrinsic films, the fit according to the S-PCE model is better than that based on FE. The output properties of P–I–N type nc-Si:H solar cells, depending on the material structures, including the mean size of the nanocrystals, crystalline volume fraction and disorder, were analyzed.     

Transfer of continuous-relief diffractive structures into diamond by use of inductively coupled plasma dry etching

The transfer of continuous-relief diffractive structures from resist into diamond by use of direct-write electron-beam lithography followed by dry etching in an inductively coupled plasma is demonstrated. The gases used for the diamond etching are O(2) and Ar. The chemical-vapor-deposited diamond substrate is of optical quality. Our results show that the transfer process generates fairly smooth etched structures. Blazed gratings with periods of 45mum and Fresnel lenses have been manufactured. The blazed gratings have been optically evaluated with a femtosecond laser operating at 400 nm. The diffraction efficiency was 68% in the first order, with a theoretical value of 100%. We intend to investigate the transfer process further and then to fabricate diffractive and refractive elements for use with Nd:YAG high-power lasers.     

Controlled diffractive optical elements containing a vanadium dioxide film

The principles of constructing optical devices on the basis of diffractive structures with a vanadium dioxide film for the control of radiation in the mid-IR range are analyzed. Methods are described for the practical implementation of such devices at λ=10.6 μm, and their response characteristics are calculated. It is shown that a contrast of 1:10⁷ can be attained in diffractive optical elements, and the actuation time of the elements when switched on by an intense laser beam can be shortened to tens of nanoseconds. Zh. Tekh. Fiz. 69, 91–96 (November 1999)     

The efficiency of relief-phase diffractive elements at a small number of Fresnel zones

A technique and investigation results are presented on the effect of the number of Fresnel zones on the diffraction efficiency and quality of the wave front formed by a diffractive optical element. Equations are presented for the microstructure reliefs of diffractive optical elements making (regardless of the number of Fresnel zones) the wavefront shape coinciding with the calculated one and ensuring 100% diffraction efficiency at a single wavelength and, in the case of two-layer structures, almost 100% diffraction efficiency in a wide spectral range.     

Fast fabrication of super-hydrophobic surfaces on polypropylene by replication of short-pulse laser structured molds

A new two-step method, facilitating the rapid generation of super-hydrophobic surface structures via parallel laser processing followed by a replica generation by injection molding is reported. A self-made fused silica-based diffractive optical element (DOE) is applied to distribute the laser energy into a 25×25 dot matrix. This DOE is used as a transmission mask for surface ablation of metal molds, applying short-pulse UV laser pulses. In a subsequent process step, replicas of the processed stamp are produced by variothermal injection molding, enabling the mass production of the surface pattern on plastics parts. The resulting topography facilitates a super-hydrophobic behavior of the fabricated components.