International Symposium on Comprehensive understanding of scattering and fluctuated fields and science of clairvoyance

Osamu Matoba, Kobe University, Japan

9:30-10:15 Opening Remarks: Introduction of Grant-in-Aid for Transformative Research Area (A)　“Comprehensive understanding of scattering and fluctuated fields and science of clairvoyance”

Problems such as image quality degradation and limited observation in depth caused by scattering and fluctuations occur on multiple scales, from molecular aggregates at the microscopic level to atmospheric fluctuations at the macroscopic level. We will introduce our activities in the “Comprehensive understanding of scattering and fluctuated fields and science of clairvoyance” project, which aims to establish a comprehensive and systematic approach to overcome scattering and fluctuation problems.

○Naoshi Murakami¹, Kenta Yoneta¹, Mizuki Asano¹, Hiroaki Hayashi¹, Jun Nishikawa²

¹Hokkaido University, Japan, ²National Astronomical Observatory of Japan

10:15-11:00 Technology development of coronagraph and wavefront control for astronomical high-contrast imaging

Astronomical high-contrast imaging plays an important role in direct detection of exoplanets around stars other than the Sun. For the high-contrast imaging, starlight needs to be strongly rejected to mitigate a huge contrast ratio between bright star and faint planet. Key components of the high-contrast imaging are coronagraph and wavefront control system. The coronagraph rejects most of the starlight by modulating phase and/or amplitude of the starlight. However, residual stellar speckles would be observed due to wavefront errors caused by imperfect optical components used in the instrument. The wavefront control system rejects the residual stellar speckles to generate a dark region around a star where one can search for faint exoplanets. We have been developing coronagraphic optical devices based on photonic crystals and wavefront control techniques utilizing a spatial light modulator (SLM). In this talk, recent activities of the coronagraphs and the wavefront control techniques carried out at our laboratory simulators, aimed at searching for an "exoEarth", will be presented.

Kenjiro Kimura, Kobe University, Japan

11:00-11:45 Multi-static scattering field theory and next-generation breast cancer diagnostic imaging technology

In recent years, we succeeded in deriving an analytical solution to the inverse scattering problem which is known as an unsolved problems in applied mathematics, and this analytical solution enables the structures of behind objects to be reconstructed by observing the scattering wave from them [Kenjiro Kimura, Noriaki Kimura, “Inverse Scattering filed theory”, Research Institute for Mathematical Sciences, Kyoto University, Kôkyûroku, No.2186, 2021]. Furthermore, based on this theory, we have firstly developed multi-static ultrawide band radar which has a world’s highest performance among radar technologies [Integral Geometry Science inc. “World's Highest Performance ultrawide band Radar for Nondestructive Inspection of Infrastructure Structures”, i-Construction Grand Award, 2020.] and is applicable for microwave mammography as a next generation breast cancer screening technology to replace X-ray mammography, which is effective even in the case of highly concentrated breasts [K. Kimura, “Development of microwave scattering field tomographic imaging system for next generation breast cancer screening” , The 1st Japan Medical Research and Development Awards, 2017].

Kenji Taira, Delawave, Inc., Japan

11:45-12:30 Intravascular optical coherence tomography for minimally invasive surgery

Optical ranging technology based on time of flight (ToF) has developed over a long period of time. Owing to the continuous improvements, the ToF-based optical ranging has become a popular technology these days, utilized in light detection and ranging (LiDAR) in self-driving cars and ToF cameras in smartphones.

Optical coherence tomography (OCT) is a ToF-based optical ranging technology that uses optical interference effect to provide spatial resolution as high as 1 micron meter. OCT has long been used in medical application, mostly in the field of ophthalmology for diagnosis, but recent years has proven the technology has great advantages in the coronary field as well.

Coronary artery disease (CAD) is one of the most common causes of death globally and 8.9 million of patients die in a year due to CAD. Percutaneous coronary intervention (PCI) is a catheter based minimally invasive procedures for the CAD treatment and has drastically advanced these years. Intravascular OCT is an effective tool to implement the PCI more precisely, providing excellent cross-sectional images of coronary artery with high resolution and information of tissue characteristics.

In this presentation, the clinical use and technology of intravascular OCT will be introduced, and the challenges will also be discussed.

Yoshihisa Takayama, Tokai University, Japan

14:00-14:45 Impact of channel fluctuations on free-space optical communications

The effect of beam propagation path fluctuations on free-space optical communications is presented. The degree of angular variation in the beam propagation direction due to the tilt and distortion of the wavefront caused by the atmosphere is calculated. To carry out the free-space optical communications, the procedures to acquire, track and point the communicating partner are necessary. The impact of the path fluctuations on the characteristics of these procedures are also discussed along with field test measurements showing the wonder of beam propagation and intensity variation. Because of the need to address the adverse effects of a turbulent environment on communication systems, methods for estimating the characteristics of a fluctuating channel and approaches for mitigating the effects on communication terminals are presented.

Keisuke Isobe, RIKEN Center for Advanced Photonics, Japan

14:45-15:30 Adaptive optics for temporal focusing and two-photon patterned illumination

We demonstrate adaptive optics correction in temporal focusing microscopy and fringe- and speckle-free holographic patterned illumination using multifocal time-multiplexed temporal focusing pulses.

Sylvain Gigan, Sorbonne University, France

16:00-16:45　Deep imaging in complex media: wavefront shaping and beyond

Wavefront shaping allows manipulation of light in complex media, for focusing and imaging, at depth where no ballistic light is present anymore. It however conventionally requires coherence, in order to manipulate speckle patterns. Fluorescence remains very challenging, both as a contrast mechanism for deep-imaging, and as a guide-star. I will show how the same concepts allows to tackle fluorescence, and even image extended fluorescent objects. I will present results in functional and structural fluorescence imaging at depth. Interestingly, it doesn’t even always require wavefront shaping.

Enrique Tajahuerce, Universitat Jaume I, Spain

16:45-17:30 Imaging in turbid media with structured light and single-pixel detection

Research on new optical methods for biomedical imaging may be relevant to improve diagnostic techniques. However, when light propagates through biological tissue it undergoes strong scattering and absorption and, therefore, optical imaging techniques suffer from low penetration depth. Great efforts have been made to overcome this limitation by different approaches such as improving the detection of ballistic light, developing new methods for precise wavefront control, or using advanced diffuse imaging techniques.

Single-pixel cameras may help to develop new optical imaging methods more tolerant to scattering. They are based on sampling the scene with a set of microstructured light patterns while a bucket detector, for instance a photodiode, records the light intensity transmitted, reflected or diffused by the object. Images are computed numerically from the photocurrent signal. Unlike a conventional camera-based approach, the single-pixel camera is unaffected by the presence of scattering media between the object to be imaged and the detector. Besides, the simplicity of the sensing device allows working efficiently in conditions where light is scarce. It also makes easier to measure the spatial distribution of multiple optical properties of the light, such as the polarization state or the spectral content, in a simple way. Finally, single-pixel detectors permit to use a broader spectral range compared to conventional cameras, helping to extend imaging techniques to exotic spectral regions.

In this contribution, we review the basic theory of computational imaging techniques using structured light and single-pixel detection. We pay special attention to reconstruction algorithms based on compressive sensing. We describe also recent applications of the technique in multidimensional imaging, providing information about the spatial distribution of different optical parameters with a single optical system. Finally, we show the potential of single-pixel imaging techniques to obtain images through scattering media and to characterize the optical properties of non-homogeneous turbid media.