用低功率532nm激光及新的引发剂全息聚合制作周期性微结构

研制了一种包含新的光引发剂的三元光聚合物。实验证明,利用该材料可在较低功率(数十毫瓦)532nm连续激光下实现一维,二维及三维周期性微结构的单光子全息聚合。介绍了该材料的制备方法及其光谱吸收特性,给出了所得结构的衍射图。该方法成本低廉,对全息法制备光子晶体的研

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Fabrication of Microstructures by

Holographic Photopolymerization with a

Low-power cw Laser of 532 nm and a New

Photoinitiator1

X.Q.Yu*1, X. L. Yang2, Y. Z. Wu1, Y. R. Wang2, L. Z. Cai*2,

Z. S. Shao1, X. F. Meng2, Y. M. Sun2, M.H. Jiang1

1State Key Laboratory of Crystal Materials, Shandong University, PRC 250100

2Department of Optics, Shandong University, PRC 250100

*yuxq@http://doc.guandang.net, *lzcai@http://doc.guandang.net

Abstract

A new ternary photopolymer system consisting of a new photoinitiator, an oligomer

and a binder has been developed. Experiments show that one-, two- and

three-dimensional microstructures can be holographically fabricated by single-photon

photopolymerization with this material and a low-power (tens mW ) continuous-wave

(cw) laser at 532 nm successfully. The preparation of this material is explained and its

absorption spectra are tested. The optical setup and the experimental results including

the diffraction patterns verifying the formation of periodic structures are given.

Compared to other methods with the use of high-power lasers, this approach is much

more accessible to most laboratories and researchers and then may promote the use of

holographic fabrication techniques of photonic crystals.

Keywords:Photonic Crystals, Holographic Interference, Microstructure Fabrication, Photopolymerization, Photoinitiator.

1 Introduction

Recently much attention has been paid to the three-dimensional (3D) periodic microstructures, the photonic crystals (PHCs) [1,2], which can create a photonic band gap, a region of the frequency spectra where propagating modes are forbidden in all directions [3]. Due to the periodicity matching the wavelength of electromagnetic waves, the frequency-momentum dispersion relationship for photos is modified in such PHCs, providing a possibility to manipulate and control light [4]. The potential use of PHCs include, just name a few, the photonic crystal fiber [5], zero-threshold lasers [6], cavity _______________

1

NSFC/RGC (50218001), National Key Lab Foundation, PhD Training Foundation and Foundation for University Key Teacher by the of Education Ministry, China, and the China Postdoctoral Foundation. Supported by the National Natural Science Foundation of China (50173015 and 60177002), foundation

研制了一种包含新的光引发剂的三元光聚合物。实验证明,利用该材料可在较低功率(数十毫瓦)532nm连续激光下实现一维,二维及三维周期性微结构的单光子全息聚合。介绍了该材料的制备方法及其光谱吸收特性,给出了所得结构的衍射图。该方法成本低廉,对全息法制备光子晶体的研

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resonators [7] and so on. Naturally, the fabrication techniques of the microstructures have also been developed rapidly, for example, the ion-beam [8], the wafer-fusion and laser beam assisted alignment method [9], the air spheres in titania [10], the porous carbon structure [11], and the array of air bubbles in polymer films [12].

In addition to these techniques mentioned above, some researchers have utilized the photopolymerization to make the microstructures. This technique has some particular advantages such as convenience, flexibility, economy and automation. In 1999, Cumpston et al [13] employed two-photon initiated photopolymerization (TPIP) to form a 3D microstucture. After this various microstructures formed by TPIP have been reported and their band gaps have been investigated [14-17]. According to these reports, TPIP can allow a deeper penetration in volume due to the use of a near-IR laser as a radiation source. But the TPIP can only occur near the vicinity of focal point of a beam under tight-focus conditions owing to the quadratic intensity dependence of the two-photon process. Consequently the microstructures by TPIP are generally fabricated by a time-consuming point-by-point scanning. On the other hand, it will be more convenient to use the single-photon holographic photopolymerization to make microstructures. In 2000, a microstructure was fabricated by using the holographic technique of ns pulse of 355nm [18]. However the 355 nm is too short to allow a deeper penetration. Most recently Wang et al [19] attempted the holographic preparation of microstructures using a continuous-wave (cw) laser at 514 nm.

Because the cw laser at 532 nm is handier than one at 514 nm, it will be beneficial to realize the holographic fabrication of 3D microstructures by means of a cw laser at 532 nm. Sutherland et al [20] formed a photonic crystal by holographic polymerization-induced phase separation of liquid crystal from a monomer-liquid crystal mixture with a higher power cw laser of 532 nm from a frequency-doubled diode-pumped Nd:YVO4 laser. In this work, we report the successful use of a low-power (tens mW) cw laser at 532 nm in making a series of periodic misconstructions by single-photon holographic photopolymerization with our new synthesized photopolymer recording material including a special photoinitiator. We will first explain the preparation of this material and its property of spectral absorption, and then give the optical setup of holographic fabrication and the experimental results. The diffraction patterns of the resultant structures are also provided to verify the formation of periodic microstructures.

2 Material preparation and the spectral absorption of resultant

photopolymer

To realize the holographic fabrication at 532 nm an appropriate photoinitiator must be synthesized first. The synthetic path is shown in Fig. 1. A 1.7g of eosin (0.00246 mol) is refluxed and di …… 此处隐藏：16025字，全部文档内容请下载后查看。喜欢就下载吧 ……