Takeda MITSUO (武田 光夫)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 4000000, indirect: 1200000)
Noting the symmetry between space and time variables in the wave equation, a new realm of statistical optics, called spatial statistical optics, has been created in which the ensemble average is replaced by the spatial average, rather than by the time average in conventional statistical optics.
The following results have been achieved. (1) The conditions on a source and an optical system have been clarified for the statistical field to have wide-sense spatial stationarity. (2) The theory and the method of experiment have been proposed for spatial statistical analysis of vectorial optical fields. (3) The methods for generation of polarization speckle fields with a birefringent scatter plate and their spatial statistical analysis have been proposed. (4) New imaging techniques have been proposed that are based on spatial statistical optics.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 13400000, indirect: 4020000)
A basic principle of a polarization-coherence synthesizer was proposed, and foundation was laid for the technique that can control both polarization and spatial coherence of statistical 3-D vectorial optical fields simultaneously. A novel scheme of coherence holography was devised for controlling the elements of a polarization-coherence matrix of a vectorial optical field. A technique, called Stokes holography, that reconstructs a desired image as a 3-D distribution of generalized Stokes parameters was proposed and experimentally demonstrated.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 14600000, indirect: 4380000)
We studied an unbalanced nulling interferometer(UNI), adaptive optics, and coronagraphs in order to obtain a very high dynamic range optics for direct detection of extra-solar planets. Aλ/600 rms wavefront correction was made virtually when the accuracy of the adaptive optics wasλ/100 rms thanks to the effect of the UNI, and a noise level of the focal image of the coronagraph was suppressed by more than one order of magnitude. An eight-octant phase mask showed a contrast of 2E-8 with a bandwidth of 10%. A four-quadrant phase mask was shown to function as a stable UNI.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 15100000, indirect: 4530000)
太陽系以外の惑星を直接検出する高ダイナミックレンジ光学系として、波面誤差補正によるスペックルノイズ除去と惑星よりきわめて強い恒星の回折光の除去を交互に2回ずつ行う、初段補償光学、非対称ナル干渉計、位相振幅補正補償光学、コロナグラフ、からなる4 段階複合法を研究した。非対称ナル干渉計の波面誤差拡大効果で実質的に補償光学の限界を超えた波面精度を達成し、コロナグラフで広帯域の回折光の除去などを実証した。

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 特定領域研究, Fund Type: -, Overall Grant Amount: - (direct: 9000000, indirect: -)
我々は,太陽系外惑星を直接撮像するため,非対称ナル干渉計(Unbalanced Nulling Interferometer,UNI)および補償光学系(Phase-AmplitudeCorrection,PAC)を用いた超高コントラスト装置(通称,UNI-PAC法)を提案し,検証実験を行った。系外惑星の直接撮像を行うためには,明るい恒星からのスペックルノイズを10^<-10>レベルにまで減らすため,λ/10000rmsもの超高面精度の光学素子や光波面補正が必要とされる。提案する手法は,UNIによる光波面誤差の拡大とPACによる波面補正を行い,更に後置コロナグラフを用いることにより,上記のような高面精度のオプティクスを必要としないという,画期的な手法である。
平成19年度は,UNI部の安定・高性能化を目指した光学系の改修,およびPAC部の構築を行った。具体的には,ナル干渉計の振動抑制のための光学素子マウント製作,傾斜補正鏡の導入,可変形鏡および波面センサ部のマウント製作を行った。その結果,ナル干渉計単体で恒星モデル像のスペックルノイズを,5λ/D以遠で10^<-7>オーダーにまで抑制させることに成功した。また、UNIによる波面誤差拡大の観測に成功し,拡大率がほぼ理論的予測と一致することを確認した。また,後置コロナグラフとして3Dサニャックナル干渉計を導入し,提案する装置全体の検証実験を行った。その結果,3Dサニャックナル干渉計単体と比較して高いコントラストを達成することができた。
更に,後置コロナグラフとして,像面位相マスクコロナグラフの使用も検討した。特に,従来提案されている4分割位相マスクを多分割化(8分割)にすることにより,更に効率的に恒星光除去が行えることを,数値シミュレーションおよび検証実験により明らかにした。

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 14300000, indirect: 2670000)
3次元物体をランダムな光波動場の空間コヒーレンス関数として再生するコヒーレンスホログラフィーの新原理を提案し,実験によりその有効性を実証した.コヒーレンスホログラムを計算機合成することにより,3次元空間コヒーレンス関数を自由に制御・シンセシスする技術を実現した.この新機能を用いた新しい工学的応用として波長分散のない3次元形状計測の可能性を実証した.また,基礎科学面ではコヒーレンス関数に位相特異点をもつコヒーレンス渦場を生成し,コヒーレンス場の運動量や角運動量などコヒーレンス場の力学的性質を解明した.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 14900000, indirect: 1710000)
In our previous report, the optical frequency comb generator consisting of two phase modulators in tandem we used generated the narrow bandwidth of the comb spectrum, only 2 nm, and resulted in the limited resolution up to 300μm. And some noises of many side-lobes appeared around the interferometric peaks due to a rectangular frequency comb spectrum. Furthermore, it took a long time for the data acquisition because the point-to-point scanning was used in a fiber-optic interferometer.
To improve the performance of our previous system, we introduced new functions of a broad band frequency comb and a line-type image sensor to realize a frequency comb-based interferometric microscope. One of the improvements in the proposed system is that a broadband frequency comb spectrum of over 10 nm was obtained by combining a waveguide type-frequency comb generator^<6-8)> consisting of the phase modulator installed in the Fabry-Perot cavity and a subsequent wavelength equalizer^<9)>. The depth resolution is finally improved up to 35 μm, and the side-lobes in the interferometric signals also disappeared. Another important improvement is to realize a high-speed observation of three-dimensional images by the use of a line type-image sensor for capturing a line image in a horizontal direction at a time.
The measurement resolution narrowed finally to 35 μm by introducing the waveguide-type frequency comb generator and the wavelength equalizer. Furthermore, introducing the line image sensor can obtain the simultaneous measurement of the whole horizontal cross sectional image of the interferometric signal. We successfully demonstrated the 3 dimensional surface profilometry of a Japanese 10-yen coin and observation of a cross sectional tomography image of transparent thin films by varying the comb frequency interval without mechanical shift. The dynamic range in the depth direction was about 1.1 mm and the measurement resolution was 35μm. The standard deviation of seven times thickness measurements was 5μm.

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業, Category: 萌芽研究, Fund Type: -, Overall Grant Amount: - (direct: 3500000, indirect: -)
現在までに約260個の太陽系外の惑星(系外惑星と呼ぶ)が発見されているが,そのほとんどは,恒星の測光などの間接的な観測によるものである.現在,系外惑星からの光を直接観測し,特に地球型惑星のスペクトル中に生命の痕跡である酸素の有無を調べることが現代天文学の最大の課題の1つとなっている.
本研究では,コロナグラフとして幾何学的位相変調を用いた3次元サニャックナル干渉計の性能評価実験を行った.緑と赤(532nmと632.8[nm])の2波長のレーザーを同時にナル干渉させ,3次元サニャック干渉計の波長無依存性を検証する実験を行った.像面では,強め合う干渉のピークと弱め合う干渉のピークで,赤色レーザでは8.43×10^<-5>,緑色レーザでは3.15×10^<-5>となり,波長に依存しないナル干渉を確認した。また,瞳面全体での消光比の平均は,赤色レーザで4.88×10^<-4>,緑色レーザで3.42×10^<-4>となり,20%に近い比帯域でアクロマティック性を証明した.これにより,本手法の波長無依存性を実証することができた.
像面,瞳面ともほぼ同様の結果が得られたが,緑色レーザと赤色レーザでの干渉パターンが異なっている.原因としては,系全体のドリフト,ビームスプリッタでの分散などが考えられる.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 10900000, indirect: -)
We studied the quantum reflection of the metastable helium atoms on a flat polished silicon surface. We measured the reflectivity as a function of the normal incident velocity component between 3 and 30 cm/s, and confirm that on a flat surface the reflection of atoms is caused by the attractive van der Waals potential. In our case the atoms are mainly reflected in a region where the retardation effect leads to a potential of the approximate form, U(z)=-C_4/z^4 where z is the distance from the surface. We also studied the reflection and diffraction on surface structures consisting of parallel narrow ridges. The structure consists of wall-like ridges at a distance of L=5μm and with a width at the top of l=100nm. We observed on this structure an increase of the reflectivity by two orders of magnitude, exceeding 10% for normal incident velocities below about 25cm/s. At grazing incidence even fast atoms of 100m/s can be reflected very efficiently at such a surface structure.
In order to quantitatively describe our data, we have developed a theoretical description of the reflection and scattering of atomic waves from our surface structures. As a first approximation we can assume that the van der Waals constant is reduced by a factor l/L, where l is the size at the top of the ridges and L the distance between the ridges. The reflectivity on the ridges structures then follows immediately from the scaling law of the quantum reflection. Deviations appear when the ratio l/L is very small. In the limiting case of l/L→0, i.e. of idealized thin ridges, a new interesting effect can be observed: The atomic wave is reflected due to the Fresnel diffraction at the array of ridges.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 15300000, indirect: -)
A range of techniques, including coherence scanning microscopy, three-dimensional sensing by coherence radar, and scanning white-light interferometry, have been developed for simultaneous measurement of the three-dimensional step height of discontinuous objects and tomographic imaging. These techniques, however, require mechanical scanning with a piezoelectric transducer or a precision translator. Spectral interferometry, on the other hand, potentially offers a powerful means for high-speed absolute threedimensional shape measurement of objects without moving mechanical parts. The practical applicability of such methods, however, remains limited due to the high cost of tunable lasers with sufficiently wide range (e.g., external cavity laser diodes and dye lasers) and the slow speed of data acquisition because of the large number of calculations in the Fourier transform. As an alternative interferometry-based approach, synthesis of the coherence functions has been reported to be suitable for distance measurements. This method involves pseudo-frequency comb generation by frequency modulation of a laser diode. Yet this method is not suitable for surface profilometry because the frequency-comb interval is limited to the order of megahertz.
In this Letter, a novel frequency comb-based interferometry technique for profilometry and tomography is proposed. The optical frequency comb employed by this method can be adjusted simply, allowing interferometry to be performed at frequency intervals of up to gigahertz order. The method is therefore suitable for measurement of absolute distances of several micrometers to several meters without the need for mechanical movement.
Step-height measurement with 9 μm accuracy was successfully performed by sweeping the comb interval frequency. Thickness measurement of a glass plate was also demonstrated. This profilometry method is expected to be useful for both surface profilometry and tomography.