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Dynamic point spread function engineering & next generation microscope

Optical microscope and wavefront control

The optical microscopes that we generally handle is composed of optical elements such as lenses and filters, mechanisms and stages for enclosure, and manually or electrically controlled system for observation. There is a trend toward higher functionality and complexity in recent optical microscopes, such as a confocal microscope that scans the laser bright spot with an electromagnetically driven mirror, an aberration-correcting objective lens with a correction ring that can be rotated manually by devising the lens design, and the invention of stimulated emission depletion microscopy (STED), one of the super-resolution microscopes using a donut shape laser beam. Therefore, we have introduced a spatial light phase modulator (LCOS-SLM) in the microscope optical system to perform wavefront control, so that the direction of the light beam and the light intensity distribution can be freely changed, and the optical microscope can be digitally controlled.

We are focusing on theoretical control and dynamic control by LCOS-SLM of point spread function (PSF), which shows the response characteristics of optical systems to point light sources particularly. To achieve this, both high-precision optical technology, including lens design, and phase control are required. However, we have advanced technology development and applied it to microscopes. We have succeeded in realizing individual or simultaneous multipoints, aberration correction, multifocals, depth of field expansion etc. that were not obtained. In particular, the aberration correction makes it possible to obtain clear images of the deep part of the living body, which has been difficult to observe. Recently, we are studying various PSFs to be applied to mouse brain function measurement, and we are advancing research in collaboration with researchers around the world.

Generation and optical manipulation of higher-order mode light

LCOS-SLM can express arbitrary phase distribution with high accuracy and can generate various special light beams. Taking advantage of this feature, we are researching the generation, measurement, and application of higher-order mode light such as optical vortex using LCOS-SLM. Optical vortices are distributed in a spiral shape around the propagation axis (the figure below: left), so the center of the spiral wavefront (this is called the phase singularity) has zero intensity and a donut-shaped beam pattern. It can be obtained (Figure below: right). Furthermore, there is angular momentum on the orbit of the donut-shaped intensity distribution, and microparticles and molecules of μm to nm size can be rotated by the power of light. Because of these features, it has been attracting attention as a new measurement tool based on the interaction between light and materials and has also been used for optical manipulation and super-resolution microscopic measurements, which have become a hot topic in the Nobel Prize in recent years. We are also working on optical tweezers and have succeeded in realizing optical vortex tweezers that apply high-precision optical vortex generation technology and supply stable torque. We are also researching measurement technology using wavefront sensors to evaluate the generated optical vortex. The optical vortex beam has a phase singularity where the light intensity is zero and the phase cannot be specified. High-order optical vortices have a problem in that it is difficult to identify singular points because the area where the light intensity is almost zero increases. To solve these problems, we proposed a method for detecting singularities with high accuracy and experimentally verified. High-order vortex beams have been reported to have a high ability to penetrate scattering media with conventional Gaussian beams. This measurement technology is expected to be applied to biological measurement in the deep part of the living body with the aim of investigating the distribution and dynamics of phase singularities.

Publications

  1. Yu Takiguchi, Taro Ando, Yoshiyuki Ohtake, Takashi Inoue, Haruyoshi Toyoda, “Effects of dielectric planar interface on tight focusing coherent beam: direct comparison between observations and vectorial calculation of lateral focal patterns”, Journal of the Optical Society of America A 12/2013; 30(12):2605-10
  2. Yu Takiguchi, Hisayoshi Takamoto, Masamitsu Kanada, Takashi Inoue, Naoya Matsumoto, Susumu Terakawa, “Numerical Spherical Aberration Correction Method using Spatial Light Modulator under Deep-Part Fluorescence Observation”, Proceedings of SPIE - The International Society for Optical Engineering 02/2014
  3. Yu Takiguchi, Min-Woong Seo, Keiichiro Kagawa, Hisayoshi Takamoto, Takashi Inoue, Shoji Kawahito and Susumu Terakawa, “Mechanical scanner-less multi-beam confocal microscope with wavefront modulation”, Optical Review 02/2016; 23(2): pp 364–368
  4. Y. Ohtake, T. Ando, N. Fukuchi, N. Matsumoto, H. Ito, T. Hara, "Universal generation of higher-order multiringed Laguerre-Gaussian beams by using a spatial light modulator," Optics Letters, 32, 11, 1411-1413 (2007).
  5. N. Matsumoto, T. Ando, T. Inoue, Y. Ohtaka, N. Fukuchi, T. Hara, "Generation of high-quality higher-order Laguerre-Gaussian beams using liquid-crystal-on-silicon spatial light modulators," Journal Optical Society of America A, 25, 7, 1642-1651 (2008).
  6. T. Ando, Y. Ohtake, N. Matsumoto, T. Inoue, and N. Fukuchi, "Mode purities of Laguerre-Gaussian beams generated via complex-amplitude modulation using phase-only spatial light modulators," Optics Letters, 34, 34-36 (2009).
  7. T. Ando, N. Matsumoto, Y. Ohtaka, Y. Takiguchi, T. Inoue, "Structure of optical singularities in coaxial superpositions of laguerre-Gaussian modes," Journal of the Optical Society of America A, 27, 12, 2602-2612 (2010).
  8. T. Otsu, T. Ando, Y. Takiguchi, Y. Ohtake, H. Toyota, and H. Itoh, “Direct evidence for three-dimensional off-axis trapping with single Laguerre-Gaussian beam,” Scientific Reports 4:4579 (2014), doi:10.1038/srep04579.

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