Shojiro Nemoto

University of Tsukuba, Tsukuba, Ibaraki, Japan

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Publications (20)30.65 Total impact

  • Source
    Jixiong Pu, Xiaoyun Liu, Shojiro Nemoto
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    ABSTRACT: We theoretically investigate the three-dimensional intensity distribution of the partially coherent beams focused by a lens. It is shown that the intensity distribution in the neighborhood of the geometrical focus is not only dependent on the intensity distribution of the incident partially coherent beam, but also on its coherence. Based on this, a novel method is presented for achieving a dark focus surrounded by higher intensities. The method is to modulate the spectral degree of coherence of the incident partially coherent beam, and thereby we can change the three-dimensional intensity distribution in the neighborhood of the geometrical focus, and generate an adjustable three-dimensional dark focus.
    Optics Communications 08/2005; · 1.44 Impact Factor
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    Jixiong Pu, Shojiro Nemoto, Xiaoyun Liu
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    ABSTRACT: We demonstrate that when a partially coherent beam with a Gaussian intensity distribution is focused by a lens, the desired partially coherent flat-topped intensity distribution or doughnut-shaped intensity distribution at the geometrical focus can be generated by choice of appropriate form of spectral degree of coherence. We provide a novel approach to beam shaping of a partially coherent beam and offer new schemes for their potential applications such as material processing, optical therapy, and optical tweezers.
    Applied Optics 11/2004; 43(28):5281-6. · 1.69 Impact Factor
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    Jixiong Pu, Chao Cai, Shojiro Nemoto
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    ABSTRACT: We report a phenomenon of spectral anomalies in the interference field of Young's double-slit interference experiment. The potential applications of the spectral anomalies in the information encoding and information transmission in free space are also considered.
    Optics Express 11/2004; 12(21):5131-9. · 3.55 Impact Factor
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    Jixiong Pu, Chao Cai, Shojiro Nemoto
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    ABSTRACT: It is shown that when partially coherent polychromatic light is focused by a filter-lens system with chromatic aberration, a spectral shift exists in the focused field, and a spectral switch that is defined as a sharp transition of the spectral shift also takes place at some positions of the focused field. The influence of the chromatic aberration of the lens, the coherence of the partially coherent light in the filter (a circular aperture), the radius of the aperture, and the spectral width of the partially coherent light in the aperture on the spectral shift and the spectral switch are investigated in detail. The numerical results show that these parameters affect the spectral shift and the spectral switch significantly. Potential applications of the spectral shift and the spectral switch of the partially coherent light are discussed.
    Journal of the Optical Society of America A 07/2004; 21(6):994-9. · 1.67 Impact Factor
  • Jixiong Pu, Chao Cai, Shojiro Nemoto
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    ABSTRACT: The spectral changes of a partially coherent polychromatic light focused by an apertured lens with chromatic aberration are investigated. It is demonstrated that the spectrum in the focused field is different from that in the aperture. Comparing with the spectrum in the aperture, the spectrum in the focused field shifts to lower or higher frequency, which is defined as a spectral shift. The influence of chromatic aberration of the lens, the coherence of the partially coherent light in the aperture, the radius of the aperture, and the spectral width of the spectrum of the aperture on the spectral shift are investigated in detail. The numerical results show that these parameters affect the spectral shift noticeably.
    Chinese Optics Letters 04/2004; 2(4):239-242. · 1.07 Impact Factor
  • Jixiong Pu, Shojiro Nemoto
    Frontiers in Optics; 10/2003
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    Jixiong Pu, Shojiro Nemoto, Baida Lü
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    ABSTRACT: The subject is the spectral characteristics of partially coherent light whose spectral degree of coherence satisfies or violates the scaling law in diffraction by a circular aperture. Three kinds of spectral correlations of the incident light are considered. It is shown that no matter whether the partially coherent light satisfies or violates the scaling law, a spectral switch defined as a rapid transition of spectral shifts is always found in the diffraction field. Different spectral correlations of the incident field in the aperture result in different points at which the spectral switch occurs. With an increment in the correlations, the position at which the spectral switch takes place moves toward the point at which the phase of the center frequency component omega0 becomes singular for illumination by spatially fully coherent light. For light that satisfies the scaling law, the spectral switch is attributed to the diffraction-induced spectral changes; for partially coherent light that violates the scaling law, the spectral switch is attributed to both the diffraction-induced spectral changes and the correlation-induced spectral changes.
    Journal of the Optical Society of America A 10/2003; 20(10):1933-9. · 1.67 Impact Factor
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    Jixiong Pu, Shojiro Nemoto
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    ABSTRACT: In this paper, we investigate the Fraunhofer diffraction of a class of partially coherent light diffracted by a circular aperture. It is shown that by the illumination of partially coherent light of the special spatial correlation function, the anomalous behaviors of the diffraction patterns are found. We find that the decrease of the spatial coherence of the light in the aperture leads to the drastic changes of the diffraction pattern. Specifically, when the light in the aperture is fully coherent, the diffraction pattern is just an Airy disc. However, as the coherence decreases, the diffraction pattern becomes an annulus, and the radius of the annulus increases with the decrease of the coherence. Flattened annuli can be achieved, when the parameters characterizing the correlation of the partially coherent light are chosen with suitable values. Potential applications of modulating the coherence to achieve desired diffraction patterns are discussed.
    Optics Express 03/2003; 11(4):339-46. · 3.55 Impact Factor
  • Jixiong Pu, Shojiro Nemoto
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    ABSTRACT: We investigate the on-axis intensity of a vector beam focused by a lens with a two-dimensional apodizer. The general formula for describing the on-axis intensity in the diffractive field is derived, indicating that the on-axis intensity is determined not only by the amplitude transmittance of the two-dimensional apodizer, but also by the polarization distribution of the vector beam. This result allows us to modulate on-axis intensity by choosing a suitable apodizer for the particular polarization of the incident vector beam. Simple formulae for estimating the relative focal shift are also derived. Some special examples are illustrated.
    Journal of Optics A Pure and Applied Optics 06/2002; 4(4):463. · 1.92 Impact Factor
  • Jixiong Pu, Shojiro Nemoto
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    ABSTRACT: The off-axis and on-axis spectra in the far zone of an aperture for the case in which a particular class of partially coherent light with a broad spectrum is diffracted by an aperture are studied. It is shown that the spectrum in the far zone is generally different from that at the aperture; i.e., the spectrum is split into two or more peaks. Moreover, the spectrum varies with the diffractive angle. For a fixed diffractive angle, the spectral shift, defined as the difference between the frequencies at which the observed spectrum and the spectrum at the aperture take their maximum, shows a gradual change with the change in the coherence at the aperture. However, as the coherence reaches some critical values, the spectral shift exhibits a rapid transition; i.e., spectral switch occurs. The coherence that causes the spectral switch to take place is different for different diffractive angles. Therefore we propose a new kind of 1 x N spectral switch, where N detectors (output ports) are placed at different diffractive angles in the far zone, and the spectral shifts at different detectors are measured. By adjusting the coherence of the aperture (input port) to the desired values, we obtain a rapid transition of the spectral shift in the desired output ports.
    Journal of the Optical Society of America A 03/2002; 19(2):339-44. · 1.67 Impact Factor
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    Jixiong Pu, Shojiro Nemoto
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    ABSTRACT: The spectral shifts of a partially coherent Gaussian Schell-model beam focused by a lens with chromatic aberration are investigated. It is shown that a moderate chromatic aberration results in the occurrence of red-shift in on-axis focused field, which is unexpected in the case of no chromatic aberration, and that the higher coherence of the beam is, the larger is the magnitude of the spectral shifts. It is also shown that the spectral shifts experience a drastic change from the blue-shift to the red-shift in some region of the focused field. Ó 2002 Elsevier Science B.V. All rights reserved.
    Optics Communications 01/2002; 207(1). · 1.44 Impact Factor
  • Jixiong Pu, Baida Lü, Shojiro Nemoto
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    ABSTRACT: An approximate formula for evaluating the relative focal shift in an annular focusing system illuminated by non-uniformly polarized (NUP) light is derived. It is shown that the relative focal shift is determined by the effective Fresnel number, which is equal to the product of the Fresnel number of the annular focusing system and a parameter characterizing the polarization distribution of the NUP beam across the aperture of the annular focusing system. A three-dimensional intensity distribution of the focused annular NUP beam is presented. It is found that, even if the effective Fresnel numbers for different polarization distributions of the annular NUP beams are identical, i.e. the relative focal shifts are nearly the same, the corresponding threedimensional intensity distributions near the focus are still quite different.
    Journal of Modern Optics 01/2002; 49(9):1501-1513. · 1.16 Impact Factor
  • Jixiong Pu, Shojiro Nemoto
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    ABSTRACT: In this paper a new kind optical switch, which is called spectral switch, is presented. When a particular class of broad-band partially coherent light is diffracted by a circular aperture, the spectrum of the light in the far zone of the diffractive field is different from the spectrum at the aperture, i.e., there exists spectral shift (Delta) (omega) equals (omega) m - (omega) ((omega) m is the frequency at which the spectrum of the diffractive field takes its maximum, and (omega) is the frequency at which the spectrum at the aperture takes its maximum). It is demonstrated that when the spectral coherence of the light at the aperture changes, there will be gradual change in the spectral shift. However when the coherence is equal to a critical value, the spectral shift will exhibit a rapid transition. We call this phenomenon as spectral switch. The scheme for generating 1 X N spectral switch is also discussed.
    Proc SPIE 10/2001;
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    Jixiong Pu, Huihua Zhang, Shojiro Nemoto
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    ABSTRACT: In this paper, an axicon, which is combined a symmetrically cubic phase plate with a perfect lens, is introduced. Based on stationary phase method and the numerical calculation, the diffraction field behind the axicon is investigated. It is shown that, by using this kind of axicons, we can obtain the uniform-intensity focal segment within the desired range.
    Optical and Quantum Electronics 05/2001; 33(6):653-660. · 1.08 Impact Factor
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    Jixiong Pu, S. Nemoto
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    ABSTRACT: When a particular class of partially coherent light is incident upon a circular aperture, the on-axis spectrum of the light in the far zone is different from the spectrum of the light at the aperture. An explicit expression describing the on-axis spectrum of the light in the far zone is obtained and the numerical calculation is performed. It is shown that by measuring the spectral shifts against some parameter, such as a/L¯(a is the radius of the aperture and L¯ is the effective correlation length of the light at the aperture at the central frequency of the source spectrum); we find that the spectral shifts show a gradual change. However when a/L¯ is equal to particular values, the spectral shifts exhibit a rapid transition, i.e., spectral switches occur. Some parameters, such as the half-width at half-maximum of the source spectrum Γ and the ratio of the central obstruction of the source ε<sub>s</sub> affect the spectral switch positions and the spectral switch performance. The generation of multi-spectral lines in the far zone from a single spectral line is also shown
    IEEE Journal of Quantum Electronics 01/2001; · 2.11 Impact Factor
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    ABSTRACT: The focusing of partially coherent light by a lens with spherical aberration (SA) is studied. The numerical calculation results are given, showing that the axial intensity distribution not only depends on the SA, but also on the coherence of partially coherent light and the Fresnel number of the lens. As the coherence decreases, the influence of the SA on the axial intensity distribution decreases, and the positions of maximum axial intensity shift towards the lens.
    Journal of Modern Optics 03/2000; 47(4):605-612. · 1.16 Impact Factor
  • Jixiong Pu, Huihua Zhang, Shojiro Nemoto
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    ABSTRACT: A lens axicon (a converging lens with spherical aberration) illuminated by a Gaussian beam is studied. It is demonstrated that, when a backward-type lens axicon is illuminated with an appropriate beam radius of the incident Gaussian beam, one can achieve a focal segment with uniform axial intensity, which is similar to that generated by the logarithmic axicon. It is shown that this approach is very simple and efficient. A forward-type lens axicon illuminated by a Gaussian beam is also investigated.
    Optical Engineering 01/2000; 39(3):803-807. · 0.96 Impact Factor
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    ABSTRACT: The design for an annular-aperture uniform-axial-intensity diffractive axicon illuminated by a Gaussian beam is given. The stationary phase method and a numerical calculation are applied to investigate the characteristics of the focal segment produced by this kind of diffractive axicon. It is shown that by Gaussian beam illumination of an appropriate beam radius, the axicon can produce a uniform-axial-intensity focal segment with a much more uniform central-core width than that generated by the axicon utilizing plane wave illumination.
    Journal of Optics A Pure and Applied Optics 10/1999; 1(6):730. · 1.92 Impact Factor
  • Jixiong Pu, Shojiro Nemoto, Huihua Zhang
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    ABSTRACT: In this paper, we theoretically demonstrate that lenses with negative spherical aberration can be used to reshape a Gaussian Schell-model (GSM) beam to uniform profiles. The numerical calculation results show that, when the coherence of the GSM beam is low, we can achieve uniform GSM beams with smooth top. As the coherence increases, some intensity modulation occurs at the top of the uniform GSM beam. This intensity modulation is caused by the interference of highly coherent light.
    Journal of Modern Optics 09/1999; 46(11):1611-1620. · 1.16 Impact Factor
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    Jixiong Pu, Huihua Zhang, Shojiro Nemoto
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    ABSTRACT: Within the Fresnel approximation, we investigate the spectral characteristics in the near zone when a certain class of partially coherent light is incident on a circular aperture. It is shown that, as the distance z between the aperture and the on-axis observation point decreases, the spectral shifts show gradual change. However, when z approaches a critical value, a rapid spectral switch occurs. The evolution from a gradual spectral shift to a rapid spectral switch is illustrated. The effect of the coherence on the spectral switch is also presented.
    Optics Communications 01/1999; · 1.44 Impact Factor

Publication Stats

240 Citations
30.65 Total Impact Points

Institutions

  • 1999–2005
    • University of Tsukuba
      Tsukuba, Ibaraki, Japan
  • 2001–2002
    • National Huaqiao University
      • Department of Electronic Science and Technology
      Zayton, Fujian, China