Kyuki Shibuya

Subpixel-shift cyclic-Hadamard microscopic imaging using a pseudo-inverse-matrix procedure

We propose two subpixel-shift (SPS) imaging methods: a normal SPS (NSPS) and an interleaved SPS (ISPS) method. Both methods use a series of cyclic-Hadamard-mask illuminations and a single channel detector that enhances lateral spatial resolution in proportion to the number of shifts. A sample object (or the illumination mask) is moved in two dimensions in micro-step intervals within the range of an illumination mask unit pixel (or within a range that exceeds it). To reconstruct the original image, we use a pseudo-inverse-matrix procedure that ensures measurement precision in a least-squares sense. Numerical simulation and experimental results obtained using a transmission microscope are shown. Further preliminary results indicate that the SPS method has the potential to enable measurements exceeding the diffraction limit of optics.

Dual-comb spectroscopic ellipsometry

Spectroscopic ellipsometry is a means of investigating optical and dielectric material responses. Conventional spectroscopic ellipsometry is subject to trade-offs between spectral accuracy, resolution, and measurement time. Polarization modulation has afforded poor performance because of its sensitivity to mechanical vibrational noise, thermal instability, and polarization-wavelength dependency. We combine spectroscopic ellipsometry with dual-comb spectroscopy, namely, dual-comb spectroscopic ellipsometry. Dual-comb spectroscopic ellipsometry (DCSE). DCSE directly and simultaneously obtains the ellipsometric parameters of the amplitude ratio and phase difference between s-polarized and p-polarized light signals with ultra-high spectral resolution and no polarization modulation, beyond the conventional limit. Ellipsometric evaluation without polarization modulation also enhances the stability and robustness of the system. In this study, we construct a polarization-modulation-free DCSE system with a spectral resolution of up to 1.2 × 10−5 nm throughout the spectral range of 1514–1595 nm and achieved an accuracy of 38.4 nm and a precision of 3.3 nm in the measurement of thin-film samples.Spectroscopic ellipsometry is an established technique to characterize the optical properties of a material. Here, Minamikawa et al. combine the method with dual-comb spectroscopy, which allows them to obtain ellipsometric parameters including the phase difference between s-polarized and p-polarized light.

Reduction effect of the accumulated number of ghost imaging by circulatory pattern

In this paper, we present experimental results concerning the reduction effect of the accumulated number of computational ghost imaging (CGI) under different light intensities. By using circulatory illumination pattern, the CGI is possible to directly reduce the accumulated number. In addition, for improvement of the spatial resolution of CGI, the illumination pattern scale is reduced illumination to the object by applying microscopic illumination system. Thereby, the propose method can be achieved high spatial resolution imaging that permitted image of microscopic object. Moreover, the proposed method provided image of the biological cell by fluorescence signal detection. As a result, we demonstrated the potential of CGI for applying measurements field of the cell biology.

Single-pixel diffraction-phase microscopic imaging combined with photon counting

We propose a new diffraction phase microscope (DPM), in which a photon counting (PC)-based single-pixel imaging (SPI) technique is introduced for obtaining two-dimensional quantitative phase images (QPIs) of transparent objects. The introduction of the SPI technique is promising for alleviating the sensitivity problem in DPM. This is because a highsensitive single-channel photodetector such as a photomultiplier tube can be used and the spatial multiplex advantage in the signal-to-noise ratio (SNR) can be expected. Furthermore, the employment of the PC technique solves the dynamic range problem inherent to the SPI. As a proof-of-principle experiment, we measured the QPI of a 125-nm thickness ITO layer coated on a silica-glass substrate, demonstrating the superiority of the PC-based SPI-DPM over SPI-DPM in SNR.

Scan-less confocal phase imaging based on dual-comb microscopy

Confocal imaging and phase imaging are powerful tools in life science research and industrial inspection. To coherently link the two techniques with different depth resolutions, we introduce an optical frequency comb (OFC) to microscopy. Two-dimensional (2D) image pixels of a sample were encoded onto OFC modes via 2D spectral encoding, in which OFC acted as an optical carrier with a vast number of discrete frequency channels. Then, a scan-less full-field confocal image with a depth resolution of 62.4 um was decoded from a mode-resolved OFC amplitude spectrum obtained by dual-comb spectroscopy. Furthermore, a phase image with a depth resolution of 13.7 nm was decoded from a mode-resolved OFC phase spectrum under the above confocality. The phase wrapping ambiguity can be removed by the match between the confocal depth resolution and the phase wrapping period. The proposed hybrid microscopy approach will be a powerful tool for a variety of applications.Confocal laser microscopy (CLM) is a powerful tool in life science research and industrial inspection because it offers two-dimensional optical sectioning or three-dimensional imaging capability with micrometer depth selectivity. Furthermore, scan-less imaging modality enables rapid image acquisition and high robustness against surrounding external disturbances in CLM. However, the objects to be measured must be reflective, absorptive, scattering, or fluorescent because the image contrast is given by the optical intensity. If a new image contrast can be provided by the optical phase, scan-less CLM can be further applied for transparent non-fluorescent objects or reflective objects with nanometer unevenness by providing information on refractive index, optical thickness, or geometrical shape. Here, we report scan-less confocal dual-comb microscopy offering a phase image in addition to an amplitude image with depth selectivity by using an optical frequency comb as an optical carrier of amplitude and phase with discrete ultra-multichannels. Our technique encodes confocal amplitude and phase images of a sample onto a series of discrete modes in the optical frequency comb with well-defined amplitude and phase to establish a one-to-one correspondence between image pixels and comb modes. The technique then decodes these images from comb modes with amplitude and phase. We demonstrate confocal phase imaging with milliradian phase resolution under micrometer depth selectivity on the millisecond timescale. As a proof of concept, we demonstrate the quantitative phase imaging of standing culture fixed cells and the surface topography of nanometer-scale step structures. Our technique for confocal phase imaging will find applications in three-dimensional visualization of stacked living cells in culture and nanometer surface topography of semiconductor objects.

Dual-comb single-pixel imaging in both amplitude and phase

Dual comb spectroscopy (DCS) is based on the combination of Fourier transform spectroscopy with an optical frequency comb (OFC), and has a spectral resolution of MHz order over a spectral range of several tens THz. Furthermore, nonmechanical time-delay scanning enables the rapid data acquisition. While DCS imaging is required for hyperspectral imaging, an imaging sensor cannot be used for DCS imaging because of a slow response time compared to the temporal evolution of interferogram signal. Therefore, it is essential to acquire the interferogram signal by use of a single-channel detector while scanning the sample position or the focal point. If DCS imaging can be achieved without the need for such scanning, the application field of the DCS imaging will be largely expanded. One promising method to achieve the scanless imaging is a single-pixel imaging (SPI). SPI enables scan-less imaging by use of optical spatial coding on the sample with a single-channel detector. Also, the spatial averaging effect improves an image quality. In this paper, we present combination of DCS with SPI, namely a DCS-SPI. DCS-SPI provides 12,000 mode-resolved hyperspectral images in both amplitude and phase at a spatial resolution of 46 μm without the need for mechanical scanning. Furthermore, we determined thickness of a chromium layer from a phase image in the near-infrared wavelength region.

Hyperspectral single-pixel imaging with dual optical combs

Dual comb spectroscopy (DCS) is based on the combination of Fourier transform spectroscopy with an optical frequency comb (OFC), and has a spectral resolution below MHz order over a spectral range over several tens THz. Furthermore, non-mechanical time-delay scanning enables the rapid data acquisition. However, in order to expand DCS into spectral imaging, a CCD or a CMOS camera cannot be used because a high-speed, point detector is indispensable to acquire the fast interferogram signal in DCS. Therefore, the first demonstration of DCS imaging was based on the mechanical scanning of the sample position. If DCS imaging can be achieved without the need for mechanical scanning, the application field of the DCS imaging will be largely expanded. One promising method to achieve the scan-less 2D imaging is a single-pixel imaging (SPI), enabling scan-less 2D imaging by use of pattern illumination on the sample and a point detector. Also, the accumulation effect in the random pattern illumination increases a signal-to-noise ratio. In this paper, we present combination of DCS with SPI, namely a scan-less DCS imaging. Spectral imaging of a sample indicated the effectiveness and potential of scan-less DCS imaging.

Scan-less hyperspectral dual-comb single-pixel-imaging in both amplitude and phase

We have developed a hyperspectral imaging scheme that involves a combination of dual-comb spectroscopy and Hadamard-transform-based single-pixel imaging. The scheme enables us to obtain 12,000 hyperspectral images of amplitude and phase at a spatial resolution of 46 µm without mechanical scanning. The spectral resolution given by the data point interval in the frequency domain is 20 MHz and the comb mode interval is 100 MHz over a spectral range of 1.2 THz centered at 191.5 THz. As an initial demonstration of our scheme, we obtained spectroscopic images of a standard test chart through an etalon plate. The thickness of an absorptive chromium-coated layer on a float-glass substrate was determined to be 70 nm from the hyperspectral phase images in the near-infrared wavelength region.

Scan-less dual comb spectroscopic imaging with a single pixel detector

We propose a hyperspectral imaging method based on the combination of dual optical comb spectroscopy with single pixel imaging. We describe the concept of the method and demonstrate a proof-of-principle experiment.

Single-pixel imaging by Hadamard transform and its application for hyperspectral imaging

In this paper, we report on comparisons of single-pixel imagings using Hadamard Transform (HT) and the ghost imaging (GI) in the view point of the visibility under weak light conditions. For comparing the two methods, we have discussed about qualities of images based on experimental results and numerical analysis. To detect images by the TH method, we have illuminated the Hadamard-pattern mask and calculated by orthogonal transform. On the other hand, the GH method can detect images by illuminating random patterns and a correlation measurement. For comparing two methods under weak light intensity, we have controlled illuminated intensities of a DMD projector about 0.1 in signal-to-noise ratio. Though a process speed of the HT image was faster then an image via the GI, the GI method has an advantage of detection under weak light condition. An essential difference between the HT and the GI method is discussed about reconstruction process. Finally, we also show a typical application of the single-pixel imaging such as hyperspectral images by using dual-optical frequency combs. An optical setup consists of two fiber lasers, spatial light modulated for generating patten illumination, and a single pixel detector. We are successful to detect hyperspectrul images in a range from 1545 to 1555 nm at 0.01nm resolution.