本研究では，光学的異方性を有する薄膜試料の顕微分析を可能とするナノプローブの開発を行い，これを用いて10-3 ~ 10-1 の範囲で複屈折を測定することに成功した. 開発したプローブでは集束表面プラズモン（高開口数の顕微鏡対物レンズを用いて集束させた光で励起した表面プラズモン）を利用しており，集束表面プラズモンの空間周波数応答から複屈折の測定を行う．具体的には，試料の複屈折によって，反射光空間周波数分布に生じる楕円状の光吸収パターンの方位と楕円率から，複屈折の大きさと光学軸の方位を求める．このプローブは，従来法に比べ極めて微小な領域における試料の複屈折を測定することができる．はじめに，この手法の妥当性を検証するため，光誘起複屈折を示す薄膜異方性試料の複屈折の大きさと進相軸の方位を，さまざまな条件下で測定した．実験では，アゾ系高分子（PAZO: poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzene-sulfonamide]-1,2- ethanediyl sodium salt]）スピンコート薄膜を作製し，紫外光照射が引き起こすシス型からトランス型への遷移がもたらす複屈折を調べた．その結果，0.01 ~ 0.07の範囲で変化することを測定することができた．また，さまざまな偏向状態の紫外光を照射したときに，反射光の空間周波数分布に生じる楕円状の光吸収パターンの回転から，進相軸の方位の変化を確認することができた. また，大きな複屈折を示す試料の測定におけるプローブの適用性を確認するために，巨大複屈折を示すアゾ系高分子を合成し，これを薄膜化した試料の複屈折を測定し，その結果と従来からの偏光解析手法による測定結果との相関を確認した．さらに，開発したプローブを生体試料の微小複屈折測定に応用する検討を行った．ここでは，ニワトリの表皮や真皮など皮膚のさまざまな部位の複屈折測定を行い，表皮では ~ 0.008 ，真皮では ~ 0.03 の複屈折を示すことを確認した．また，この測定から，皮膚組織がもたらす強い光散乱も無視できることを確認できた．これによって，無標識でさまざまな病理診断が行える潜在性を示すことができ，たとえば，紫外光環境下での繊維芽細胞の複屈折を測定することで，皮膚日射病を診断できると考える．
In this thesis, I have developed a nano-probe for the microscopic characterization of anisotropic samples specially in the form of thin films. The developed probe has been successfully tested to measure birefringence in the range of 10-3 ~ 10-1. The probe was developed with focused surface plasmon (interference of surface plasmons generated by coupling with convergent incident light from a high numerical aperture microscope objective). The birefringence of the sample caused the change in the propagation constant along the principal directions of the sample. Elliptical absorption pattern in the reflected spatial frequency distribution was observed on introduction of anisotropic sample as Kretschmann configuration. The ratio of the propagation constants along the principal directions yields the magnitude of birefringence while the orientation of the elliptical absorption pattern in the reflected spatial distribution denotes the fast axis of the sample. The developed probe is thus able to quantitatively characterize anisotropicity of samples in microscopic region. The detailed characteristics of the anisotropic samples in the form of thin films exhibiting photo-induced birefringence have been analyzed in terms of the magnitude of birefringence and the direction of fast axis. I examined azo-polymer PAZO poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzene-sulfonamide]-1,2-ethanediyl sodium salt] thin films produced by spin coating. The birefringence varies in the range of 0.01 - 0.07 with low density under the influence of ultra-violet radiation due to photo-isomerization (transition from the cis-state to the trans-state). The fast axis of the sample could be rotated with the change in polarization of the ultra-violet light. This could be further correlated with the change in orientation of elliptical absorption pattern at the reflected spatial frequency distribution. Further, to perform high birefringence measurement with the developed probe, I also synthesized gigantic birefringence azo-polymer (exhibiting photo-induced birefringence: Δn ∼ 0.4). I correlated the results with simple in-line polarimetric set-up. Also, I checked the applicability of the developed probe for determining very low birefringence of bio-samples. I analyzed various parts of the chicken skin samples like the epidermal and the dermal layers to observe the birefringence changes. It was found that the dermal layer of the skin showed Δn ∼ 0.03 while that of the epidermis showed Δn ∼ 0.008. Further I confirmed that the effect of scattering on near-field anisotropic characterization is negligible. Thus, this method can be used to characterize highly scattering samples like skin. I believe that the developed probe can find potential application towards disease detection, as most tissues within human body secrete collagen (possessing intrinsic birefringence). The increase of birefringence in such tissues can be used as a label free bio-marker. Potential example include detection of dermatoheliosis from the change in the quantitative birefringence of the fibroblasts in the ultra-violet environment.
Characterization of anisotropic properties by surface plasmon microscopy
A481_summary
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