Visualization of internal structure and internal stress in visibly opaque objects using full-field phase-shifting terahertz digital holography

We construct a full-field phase-shifting terahertz digital holography (PS-THz-DH) system by use of a THz quantum cascade laser and an uncooled, 2D micro-bolometer array. The PS-THz-DH enables us to separate the necessary diffraction-order image from unnecessary diffraction-order images without the need for spatial Fourier filtering, leading to suppress the decrease of spatial resolution. 3D shape of a visibly opaque object is visualized with a sub-millimeter lateral resolution and a sub-µm axial resolution. Also, the digital focusing of amplitude image enables the visualization of internal structure with the millimeter-order axial selectivity. Furthermore, the internal stress distribution of an externally compressed object is visualized from the phase image. The demonstrated results imply a possibility for non-destructive inspection of visibly opaque non-metal materials.


Fluorescence lifetime estimation by 1 bit photon autocorrelation procedure from time series data recorded using a high speed digitizer


Refractive index sensing with temperature compensation by a multimode-interference fiber-based optical frequency comb sensing cavity

We proposed a refractive index (RI) sensing method with temperature compensation by using an optical frequency comb (OFC) sensing cavity including a multimode-interference (MMI) fiber, namely, the MMI-OFC sensing cavity. The MMI-OFC sensing cavity enables simultaneous measurement of material-dependent RI and sample temperature by decoding from the comb spacing frequency shift and the wavelength shift of the OFC. We realized the simultaneous and continuous measurement of RI-related concentration of a liquid sample and its temperature with precisions of 1.6 × 104 RIU and 0.08 °C. The proposed method would be a useful means for the various applications based on RI sensing.


Dual-comb spectroscopy (DCS) is useful for gas spectroscopy due to the high potential of optical frequency comb (OFC). However, fast Fourier transform (FFT) calculation of a huge amount of temporal data spends significantly longer time than the acquisition time of an interferogram. In this article, we demonstrate frequency-domain DCS by a combination of DCS with lock-in detection, namely LID-DCS. LID-DCS directly extracts an arbitrary OFC mode from a vast number of OFC modes without the need for FFT calculation. Usefulness of LID-DCS is demonstrated in the rapid monitoring of transient signal change and spectroscopy of hydrogen cyanide gas.


Improvement of dynamic range and repeatability in a refractive-index- sensing optical comb by combining saturable-absorber-mirror mode- locking with an intracavity multimode interference fiber sensor

A mode-locked fiber comb equipped with a multimode interference fiber sensor functions as a high-precision refractive-index (RI) sensor benefitting from precise RF measurement. However, its dynamic range and repeatability are hampered by the inherent characteristics of nonlinear- polarization-rotation mode-locking oscillation. In this article, we introduce saturable-absorber-mirror mode-locking for RI sensing with a wide dynamic range and high repeatability. While the RI dynamic range was expanded to 41.4 dB due to high robustness against cavity disturbance, the self-starting capability without the need for polarization control improves the RI sensing repeatability to 1.10 × 108 for each mode-locking activation. The improved dynamic range and repeatability will be useful for enhancing the performance of RI sensing.


1-bit photon cross-correlation-based phase-modulation fluorometer using an OFDM signal-modulated excitation light source


Lens-less fiber coupling of a 1550-nm mode-locked fiber laser light on a low-temperature-grown GaAs photoconductive antenna


Ultrasonic wave sensing using an optical-frequency-comb sensing cavity for photoacoustic imaging

We propose a novel ultrasonic wave sensing method employing an optical-frequency-comb (OFC) cavity, namely, an OFC sensing cavity-based ultrasonic wave sensor. We confirm the fundamental characteristics of the OFC sensing cavity-based ultrasonic wave sensor by using an ultrasonic wave transducer and realize the frequency response of up to 13 MHz with a linear response. We also confirm the potential applicability in photoacoustic imaging employing an 8-ns pulsed laser. Our demonstrations confirm the capability of the concept of the OFC sensing cavity in ultrasonic wave sensing and will also expand the potential of OFC technology.


Scan-Less, Kilo-Pixel, Line-Field Confocal Phase Imaging with Spectrally Encoded Dual-Comb Microscopy

Confocal laser microscopy (CLM) is a powerful tool in life science research and industrial inspection, and its image acquisition rate is boosted by scan-less imaging techniques. However, the optical-intensity-based image contrast in CLM makes it difficult to visualize transparent non-fluorescent objects or reflective objects with nanometer unevenness. In this paper, we introduce an optical frequency comb (OFC) to scan-less CLM to give the optical-phase-based image contrast. One-dimensional (1D) image pixels of a sample are separately encoded onto OFC modes via 1D spectral encoding by using OFC as an optical carrier of amplitude and phase with a vast number of discrete frequency channels. Then, line-field confocal information of amplitude and phase are decoded from a mode-resolved OFC amplitude and phase spectra obtained by dual-comb spectroscopy without the need for mechanical scanning. The proposed confocal phase imaging will further expand the application fields of CLM.

IEEE Journal of Selected Topics in Quantum Electronics


Multicascade-linked synthetic wavelength digital holography using an optical-comb-referenced frequency synthesizer

Digital holography (DH) is a promising method for non-contact surface topography because the reconstructed phase image can visualize the nanometer unevenness in a sample. However, the axial range of this method is limited to the range of the optical wavelength due to the phase wrapping ambiguity. Although the use of two different wavelengths of light and the resulting synthetic wavelength, i.e., synthetic wavelength DH, can expand the axial range up to several hundreds of millimeters, its axial precision does not reach sub-micrometer. In this article, we constructed a tunable external cavity laser diode phase-locked to an optical frequency comb, namely, an optical-comb-referenced frequency synthesizer, enabling us to generate multiple synthetic wavelengths within the range of 32 µm to 1.20 m. A multiple cascade link of the phase images among an optical wavelength ( = 1.520 µm) and 5 different synthetic wavelengths ( = 32.39 µm, 99.98 µm, 400.0 µm, 1003 µm, and 4021 µm) enables the shape measurement of a reflective millimeter-sized stepped surface with the axial resolution of 34 nm. The axial dynamic range, defined as the ratio of the axial range ( = 2.0 mm) to the axial resolution ( = 34 nm), achieves 5.9 × 10, which is larger than that of previous synthetic wavelength DH. Such a wide axial dynamic range capability will further expand the application field of DH for large objects with meter dimensions.


High-efficiency photon-counting fluorometer with a channel width of 5.0 ps


Refractive-index-sensing optical comb based on photonic radio-frequency conversion with intracavity multi-mode interference fiber sensor

Optical frequency combs (OFCs) have attracted attention as optical frequency rulers due to their tooth-like discrete spectra together with their inherent mode-locking nature and phase-locking control to a frequency standard. Based on this concept, their applications until now have been demonstrated in the fields of optical frequency metrology. However, if the utility of OFCs can be further expanded beyond their application by exploiting new aspects of OFCs, this will lead to new developments in optical metrology and instrumentation. Here, we report a fiber sensing application of OFCs based on a coherent link between the optical and radio frequencies, enabling high-precision refractive index measurement based on frequency measurement in radio-frequency (RF) region. Our technique encodes a refractive index change of a liquid sample into a repetition frequency of OFC by a combination of an intracavity multi-mode-interference fiber sensor and wavelength dispersion of a cavity fiber. Then, the change in refractive index is read out by measuring the repetition frequency in RF region based on a frequency standard. Use of an OFC as a photonic RF converter will lead to the development of new applications in high-precision fiber sensing with the help of functional fiber sensors and precise RF measurement.


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

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.


Application of Scan-less Two-Dimensional Confocal Microscopy Based on a Combination of Confocal Slit With Wavelength/Space Conversion

Confocal laser microscope (CLM) has been widely used in the fields of the non-contact surface topography, biomedical imaging, and other applications, because the confocality gives two-dimensional (2D) optical-sectioning or three-dimensional (3D) imaging capability with the depth selectivity. Combination of line-focused CLM with one-dimensional (1D) spectral encoding CLM enables us to obtain the 2D confocal image without the need for the mechanical scanning. So-called scan-less 2D CLM is a unique imaging modality, however, there are no attempts to apply for practical application. In this paper, we constructed scan-less 2D CLM with the image acquisition time of 0.23 ms, the lateral resolution of 1.2 μm, the depth resolution of 2.4 μm, and apply it for different kinds of application to evaluate its practical potential.


Photon-counting-based diffraction phase microscopy combined with single-pixel imaging

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


Real-Time Amplitude and Phase Imaging of Optically Opaque Objects by Combining Full-Field Off-Axis Terahertz Digital Holography with Angular Spectrum Reconstruction

Terahertz digital holography (THz-DH) has the potential to be used for non-destructive inspection of visibly opaque soft materials due to its good immunity to optical scattering and absorption. Although previous research on full-field off-axis THz-DH has usually been performed using Fresnel diffraction reconstruction, its minimum reconstruction distance occasionally prevents a sample from being placed near a THz imager to increase the signal-to-noise ratio in the hologram. In this article, we apply the angular spectrum method (ASM) for wavefront reconstruction in full-filed off-axis THz-DH because ASM is more accurate at short reconstruction distances. We demonstrate real-time phase imaging of a visibly opaque plastic sample with a phase resolution power of λ/49 at a frame rate of 3.5 Hz in addition to real-time amplitude imaging. We also perform digital focusing of the amplitude image for the same object with a depth selectivity of 447 μm. Furthermore, 3D imaging of visibly opaque silicon objects was achieved with a depth precision of 1.7 μm. The demonstrated results indicate the high potential of the proposed method for in-line or in-process non-destructive inspection of soft materials.

Journal of Infrared, Millimeter and Terahertz Waves


FPGA-based photon-counting phase-modulation fluorometer and a brief comparison with that operated in a pulsed-excitation mode


Numerical simulation of a metal diffraction grating-based SPR sensor with a water immersion lens


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.


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.


High-speed, FPGA-based photon-counting fluorometer with high data-gathering efficiency


Proposal of a new optical system for prism-based surface-plasmon-resonance imaging


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


Optical-rotatory-dispersion measurement approach using the nonlinear behavior of the geometric phase


Scan-Less Full-Field Confocal Microscopy by a Combination of Confocal Slit with Wavelength/Space Conversion

スリット共焦点と波長/空間変換を用いたスキャンレス・フルフィールド共焦点顕微鏡

Journal of the Japan Society for Precision Engineering


Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy.

Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident.


Terahertz frequency-domain spectroscopy of low-pressure acetonitrile gas by a Photomixing terahertz synthesizer referenced to dual optical frequency combs


Phase-controlled Traveling-wave-type Ultrasonic Motor Driven in the Constant-Temperature Mode

位相差制御方式進行波型超音波モータの恒温駆動

We propose a phase-controlled traveling-wave-type ultrasonic motor (USM) driven in the constant temperature mode. By setting the phase difference between two sinusoidal driving signals fed into USM zero, a thermally-equilibrium condition of USM is attained without rotation. We call such an operation mode idling. Because the resonance frequency of the USM depends on the temperature, the rotational speed is decreased with increasing the temperature, which has been made the frequency control of USM somewhat difficult. Unlike the conventional frequency-controlled USM, a phase-controlled one with idling is free from the temperature change and is controllable with ease. We have constructed a feedback loop system for the phase-controlled USM and evaluated its performance in comparison with the conventional frequency-controlled one.


Real-time determination of absolute frequency in continuous-wave terahertz radiation with a photocarrier terahertz frequency comb induced by an unstabilized femtosecond laser

Journal of Infrared, Millimeter and Terahertz Waves


マイクロレンズアレイを用いた表面プラズモン共鳴による膜厚分布測定

マイクロレンズアレイを用いた表面プラズモン共鳴による膜厚分布測定


Optical trapping of nanoparticles on a silicon subwavelength grating and their detection by an ellipsometric technique

International Journal of Optomechatronics


Comparison of reconstructed images between ghost imaging and Hadamard-transform imaging


Adaptive sampling dual terahertz comb spectroscopy using dual free-running femtosecond lasers

Terahertz (THz) dual comb spectroscopy (DCS) is a promising method for high-accuracy, high-resolution, broadband THz spectroscopy because the mode-resolved THz comb spectrum includes both broadband THz radiation and narrow-line CW-THz radiation characteristics. In addition, all frequency modes of a THz comb can be phase-locked to a microwave frequency standard, providing excellent traceability. However, the need for stabilization of dual femtosecond lasers has often hindered its wide use. To overcome this limitation, here we have demonstrated adaptive-sampling THz-DCS, allowing the use of free-running femtosecond lasers. To correct the fluctuation of the time and frequency scales caused by the laser timing jitter, an adaptive sampling clock is generated by dual THz-comb-referenced spectrum analysers and is used for a timing clock signal in a data acquisition board. The results not only indicated the successful implementation of THz-DCS with free-running lasers but also showed that this configuration outperforms standard THz-DCS with stabilized lasers due to the slight jitter remained in the stabilized lasers.


Real-time absolute frequency measurement of continuous-wave terahertz radiation based on dual terahertz combs of photocarriers with different frequency spacings

Real-time measurement of the absolute frequency of continuous-wave terahertz (CW-THz) radiation is required for characterization and frequency calibration of practical CW-THz sources. We proposed a method for real-time monitoring of the absolute frequency of CW-THz radiation involving temporally parallel, i.e., simultaneous, measurement of two pairs of beat frequencies and laser repetition frequencies based on dual THz combs of photocarriers (PC-THz combs) with different frequency spacings. To demonstrate the method, THz-comb-referenced spectrum analyzers were constructed with a dual configuration based on dual femtosecond lasers. Regardless of the presence or absence of frequency control in the PC-THz combs, a frequency precision of 1011 was achieved at a measurement rate of 100 Hz. Furthermore, large fluctuation of the CW-THz frequencies, crossing several modes of the PC-THz combs, was correctly monitored in real time. The proposed method will be a powerful tool for the research and development of practical CW-THz sources, and other applications.


Photon-counting 1.0 GHz-phase-modulation fluorometer

We have constructed an improved version of a photon-counting phase-modulation fluorometer (PC-PMF) with a maximum modulation frequency of 1.0 GHz, where a phase domain measurement is conducted with a time-correlated single-photon-counting electronics. While the basic concept of the PC-PMF has been reported previously by one of the authors, little attention has been paid to its significance, other than its weak fluorescence measurement capability. Recently, we have recognized the importance of the PC-PMF and its potential for fluorescence lifetime measurements. One important aspect of the PC-PMF is that it enables us to perform high-speed measurements that exceed the frequency bandwidths of the photomultiplier tubes that are commonly used as fluorescence detectors. We describe the advantages of the PC-PMF and demonstrate its usefulness based on fundamental performance tests. In our new version of the PC-PMF, we have used a laser diode (LD) as an excitation light source rather than the light-emitting diode that was used in the primary version. We have also designed a simple and stable LD driver to modulate the device. Additionally, we have obtained a sinusoidal histogram waveform that has multiple cycles within a time span to be measured, which is indispensable for precise phase measurements. With focus on the fluorescence intensity and the resolution time, we have compared the performance of the PC-PMF with that of a conventional PMF using the analogue light detection method.


Precise measurement of the thickness of a dielectric layer on a metal surface by use of a modified Otto optical configuration


Double-modulation reflection-type terahertz ellipsometer for measuring the thickness of a thin paint coating

We constructed a double-modulation, reflection-type terahertz (THz) ellipsometer for precise measurement of the thickness of a paint film which is coated on a metal surface and which is not transparent to visible or mid-infrared light. The double-modulation technique enabled us to directly obtain two ellipsometric parameters, () and (), as a function of angular frequency, , with a single measurement while reducing flicker noise due to a pump laser. The bias voltage of a photoconductive antenna (PCA) used as a THz pulse emitter was modulated at 100 kHz, and a first lock-in amplifier (LA1) was connected to the output of an electro-optic (EO) signal-sampling unit. In addition, a wire-grid polarizer (WGP) was rotated at 100 Hz to conduct polarization modulation with a frequency of 200 Hz. The output signal from LA1 was fed into a second lock-in amplifier (LA2) that worked in synchronization with the rotating WGP (RWGP). By operating LA2 in a quadrature phase-detection mode, we were able to obtain in-phase and out-of-phase signals simultaneously, from which the two ellipsometric parameters for an isotropic sample could be derived at the same time while cancelling common-mode noise. The lower detection limit of the thickness measurement and the relative standard deviation (RSD) of a black paint film coated on an aluminum substrate were 4.3 µm and 1.4%, respectively. The possibility of determining all elements of the Jones matrix for an anisotropic material is also discussed.


Enhancement of the Sensitivity of a Diffraction Grating-Based Surface-Plasmon-Resonance Sensor Uitilizing the 1st- and the -2nd-Order Diffracted Lights


Prediction of the Thickness of a Thin Paint Film by Applying a Modified Partial-Least-Squares-1 Method to Data Obtained in Terahertz Reflectometry

Journal of Infrared, Millimeter and Terahertz Waves


Method using optical polarization for achieving low-voltage-driven ferroelectric memory devices


Photothermal Imaging for Single Nanoparticle Using Single Element Interferometer


Time-Between-Photons Method for Measuring Fluorescence Lifetimes


All polarization properties of PLZT ferroelectric ceramics observed in two dimensional distributions under applied voltage by the Mueller matrix


Phase-Modulation Fluorometer Using a Phase-Modulated Excitation Light Source


Optically driven method for magnetically levitating diamagnetic material using photothermal effect


A nanosecond gate-mode-driven silicon avalanche photodiode and its application to measuring fluorescence lifetimes of Ce-doped YAG ceramics


Thin Film Thickness Measurement by Surface Plasmon Resonance Using a Modified Otto's Configuration Combined with Ellipsometry

International Journal of Automation Technology (IJAT)


Comparison of Pulsed-Excitation and Phase-Modulation Methods for Estimating Fluorescence Lifetime Values Using a Convolved-Autoregressive Model and a High-Gain Photomultiplier Tube


Ellipsometric measurement technique for a modified Otto configuration used for observing surface-plasmon resonance

In order to carry out precise measurements of the thickness of a dielectric layer deposited on a metal surface, we have introduced an ellipsometric measurement technique (EMT) to the modified Otto's configuration (MOC) that is used for observing surface plasmon resonance (SPR). For that purpose, we have measured the thickness of the Au layer by the EMT at four different locations on an elliptic fringe pattern obtained from the MOC basing on a four-layer structure model: prism (BK7)-air-Ausubstrate (BK7). Then, we have measured that of a TiO(2) layer deposited on the Au layer by the EMT basing on a five-layer structure model: prism (BK7)-air-TiO(2)-Au-substrate (BK7). We have found experimentally that the combination of EMT and MOC is effective for measuring the thickness of the dielectric layer on the metal.


Autoregressive-Model-based Fluorescence-Lifetime Measurements by Phase-Modulation Fluorometry Using a Pulsed-Excitation Light Source and a High-Gain Photomultiplier Tube

We propose a novel method for measuring fluorescence lifetimes by use of a pulsed-excitation light source and an ordinary or a high-gain photomultiplier tube (PMT) with a high-load resistor. In order to obtain the values of fluorescence lifetimes, we adopt a normal data-processing procedure used in phase-modulation fluorometry. We apply an autoregressive (AR)-model-based data-analysis technique to fluorescence- and reference-response time-series data obtained from the PMT in order to derive plural values of phase differences at a repetition frequency of the pulsed-excitation light source and its harmonic ones. The connection of the high-load resistor enhances sensitivity in signal detection in a certain condition. Introduction of the AR-model-based data-analysis technique improves precision in estimating the values of fluorescence lifetimes. Depending on the value of the load resistor and that of the repetition frequency, plural values of fluorescence lifetimes are obtained at one time by utilizing the phase information of harmonic frequencies. Because the proposed measurement system is simple to construct, it might be effective when we need to know approximate values of fluorescence lifetimes readily, such as in the field of biochemistry for a screening purpose.


A Proposal of a Pseudo-Lock-in Light-Detection Scheme by Sinusoidal Modulation of Bias Voltages Applied to Two Dynodes in a Photomultiplier Tube


Measurements of Complex Refractive Indexes of Metals at Several Wavelengths by Frustrated Total Internal Reflection Due to Surface Plasmon Resonance

By employing a modified Otto's configuration for measuring surface plasmon resonance that has been proposed by Bliokh and his coworkers [Appl. Phys. Lett.89, 021908 (2006)APPLAB0003-695110.1063/1.2220540] we have obtained complex refractive indices of metals at several wavelengths. We demonstrate that the configuration has high potential for obtaining dispersion relations of metal conductors in bulk samples as well as in thin films from the visible to the near-infrared wavelength region. Furthermore, we show that the configuration enables us to obtain the complex refractive indices of metals or a thickness or refractive index of a dielectric layer on the metal at different points simultaneously. We have constructed a measurement system and carried out basic experiments. The experimental results agreed well with numerically simulated values or published ones.


A Deconvolution Procedure for Determination of a Fluorescence Decay Waveform Applicable to a Band-Limited Measurement System That Has a Time Delay


Improvement of minimum paint film thickness for THz paint meters by multiple regression analysis

We propose a numerical parameter fitting method to determine the time delay between two temporally overlapped echo pulses in terahertz (THz) tomography measurements. The method is based on multiple-regression analysis with the least-squares method and is applied to decrease the minimum paint film thickness for THz paint meters. Applying multiple-regression analysis to paint thickness measurements is five times more sensitive with regard to the minimum thickness than numerical Fourier deconvolution. We apply the proposed method to determine the optical thickness, geometrical thickness, and group refractive index of dry paint film and wet paint film. The proposed method is useful for decreasing the minimum thickness for a THz paint meter and other THz tomography measurements.


Analysis of Data Obtained from a Frequency-Multiplexed Phase-Modulation Fluorometer Using an Autoregressive Model

In order to derive plural values of fluorescence lifetimes simultaneously from a multi-component sample, we formulate a mathematical method for analyzing data obtained from a frequency-multiplexed phase-modulation fluorometer (FM-PMF) using an autoregressive (AR) model. Various parameter settings necessary for performing accurate data analysis based on the AR model are studied through numerical simulations. Measurement results of fluorescence lifetimes of real samples, 10 ppm quinine sulfate in 0.1 N H(2)SO(4), 10 ppm rhodamine 6G in ethanol, and their mixture with a volume ratio of 1:1, demonstrate that the proposed method works quite well.


Extrapolation of Band-Limited Frequency Data Using an Iterative Hilbert-Transform Method and Its Application for Fourier-Transform Phase-Modulation Fluorometry


Simulation of Absorption-Based Surface-Plasmon Resonance Sensor by Means of Ellipsometry

Through numerical simulations, we point out that introduction of an ellipsometric measurement technique to an absorption-based surface-plasmon resonance (SPR) sensor enhances precision and sensitivity in measuring the imaginary part k of the complex refractive index of the sample. By measuring a pair of ellipsometric Delta-Psi parameters, instead of the conventional energy reflectance R(p) of p-polarized light in the Kretschmann optical arrangement, we can detect a small change of k that is proportional to that of the concentration of the sample, especially when k < 1. While one has difficulty in determining the value of k uniquely by the standard technique, when the thickness of Au under the prism is thin (20-30 nm), the ellipsometric technique (ET) overcomes the problem. Furthermore, the value of k and the thickness d(s) of the absorptive sample that is adsorbed on Au can be determined precisely. The ET based on the common-path polarization interferometer is robust against external disturbance such as mechanical vibration and intensity fluctuation of a light source. Although only the p-polarized light is responsible for the SPR phenomenon, we show that the introduction of the ET is significant for quantitative analysis.


レーザー誘起ナノ秒蛍光寿命マッピングによる歯の形成と老化の可視化

レーザー誘起ナノ秒蛍光寿命マッピングによる歯の形成と老化の可視化

The auto-fluorescence characteristics of human teeth change with age. AGEs (advanced glycation endproducts), which are a crosslink of collagen, are considered to be involved in the mechanisms that cause the fluorescence characteristics to change. Although fluorescence intensity is a well-examined index of aging, it has inherent limitations. In contrast, fluorescence lifetime is useful for the evaluation because it can be reviewed quantitatively. Therefore, we mapped the distribution of fluorescence lifetime of teeth in relation to the formation and aging of teeth. The fluorescence decay profile of teeth was measured by time-correlated single photon counting, and lifetime was calculated from the fitting curve of the decay profile in a two-component exponential function. As a result, the distribution of fluorescent lifetime in dentin corresponded to tooth development; fluorescent lifetime of the crown dentin was shorter than that of the root dentin. Furthermore, the fluorescence lifetime decreased as human age increased. Because these changes in fluorescent lifetime are attributed to the accumulation of AGEs, whose fluorescence lifetime is short, our mapping of fluorescent life visualizes the formation and aging of teeth.

Transactions of the Japanese Society for Medical and Biological Engineering


Construction of a Pseudo-Lock-in Light Detection System Using a Gain-Enhanced Gated Silicon Avalanche Photodiode

アバランシェフォトダイードをゲート動作をさせることによって，通常よりもゲインがエンハンスされた擬似ロックイン光検出システムが構築できることを示した．


Construction of a Fourier-Transform Phase-Modulation Fluorometer

筆者が初めて提案したフーリエ変換型位相変調蛍光寿命計の構築と評価を行った．

筆者が初めて提案したフーリエ変換型位相変調蛍光寿命計の構築と評価を行った．


ゲート動作アバランシェフォトダイオードを用いた高感度反射型パルスオキシメータ

ゲート動作アバランシェフォトダイオードを用いた高感度反射型パルスオキシメータ

We propose a reflection-type pulse oximeter that employs two pairs of a light-emitting diode (LED) and a gated avalanche photodiode (APD). One LED radiates a red line with an emission wavelength of 635 nm and the other a near-infrared line with 945 nm. These are driven with a pulse current at frequency f (=10 kHz). Superposition of a transistor-transistor-logic (TTL) gate pulse on a direct-current (dc) bias, which is set so as not to exceed the breakdown voltage of each APD, makes the APD work in a gain-enhanced operation mode. Each APD is gated at frequency 2f (=20 kHz), and the signal output is fed into a laboratory-made lock-in amplifier that works synchronously with the pulse modulation signal of each LED at frequency f (=10 kHz). A combination of the gated APD and lock-in like signal detection scheme is useful for the reflection-type pulse oximeter owing to the capability of detecting a weak signal against a large background light.


Phase-Modulation Fluorometer Using a Dynode-Voltage Burst-Modulated Photomultiplier-Tube

光電子増倍管のダイノード電圧をバースト状に正弦波変調するという新規な位相変調蛍光寿命計の考案·試作·評価を行った．


キセノンランプの直接電流変調

キセノンランプの直接電流変調

通常は直流点灯させるのが常識のキセノンランプを正弦波振幅変調させる手法を考案·試作し，周波数特性を調べた．このような光源とロックイン光検出手法を併用すれば，小型，安価の汎用分光計測システムが構築できることを示した．

Journal of the Spectroscopical Society of Japan


Pseudo-Lock-in Light Detection Method for a Sinusoidally-Gain-Modulated Photomultiplier Tube

光電子増倍管のダイノード電圧を正弦波変調させ，出力部にそれと同期して動作する簡易ロックイン方式のアンプを接続して微弱光を検出するf-2f方式能動型光検出器を考案·試作した．評価実験の結果，当初の目的が達成できていることを確認した．


Simple Photomultiplier-Tube Internal-Gating Method for Use in Subnanosecond Time-Resolved Spectroscopy

光電子増倍管の2つのダイノードに幅の狭いゲートパルスを同時に印加するだけで，そのパルス幅から該当ダイノード間の電子走行時間を引き算した値の分解時間が達成可能な，光電子増倍管内部ゲート法を考案した．評価実験の結果，0.3 nsの分解時間が達成されていることが確認できた．これはこの種のゲート手法の中では最高の値である．


Correction of the Intensity-Dependent Phase Delay in a Silicon Avalanche Photodiode by Controlling Its Reverse Bias Voltage

アバランシェフォトダイオードの応答時間に入射光強度依存性があることを指摘し，その原因を考察するとともに，逆バイアス電圧を適切に制御することにより，応答速度の入射光強度依存性を補正できることを実験的に示した．


二次元DCMP法によるGPS用十字形状アレーアンテナの指向性パターンの形成

二次元DCMP法によるGPS用十字形状アレーアンテナの指向性パターンの形成

二次元アレーアンテナにDCMP (Directionally Constrained Minimization Power) 法を適用するアルゴリズムを構築し，GPS受信のマルチパス問題に対応できる可能性があることを実証した．さらに，アンテナ素子間の干渉の低減などを考慮して，十字形状のアレーアンテナの提案とシミュレーションを行った．

高速信号処理応用技術学会誌(電子技術)

高速信号処理応用技術学会誌(電子技術)


Proposal for Fourier-Transform Phase-Modulation Fluorometer

従来，位相変調蛍光寿命法では蛍光減衰波形の取得は原理的に不可能であったが，励起光の変調波長をある周波数範囲で高速掃引させることにより，これを可能にする手法を考案した．この手法をフーリエ変換型位相変調蛍光寿命測定法と命名し，実際にプロトタイプを製作してその有効性を確認した．


Externally Controlled Nanosecond Xe Discharge Lamp Equipped with a Synchronous High-Voltage Power Supply Using an Automobile Ignition Coil

自動車用イグニションコイルを用いて高電圧パルスを発生させ，それを整流·充電することで直流高電圧を得る方式のデジタル制御高圧電源を考案した．そして，それをナノ秒パルス点灯Xeランプの電源として使用し，さらに高電圧半導体スイッチを用いて外部制御方式のナノ秒白色光源を実現した．


Combination of a Gated Photomultiplier Tube and a Phase Sensitive Detector for Use in an Intensive Pulsed Background Light Situation

高強度のバックグラウンド光に重畳した信号光を検出する目的で，光検出器である光電子増倍管に内部ゲート動作をさせ，出力部にゲート動作と同期して動作する位相敏感検波回路を配置した微弱光検出方式を考案した．実際に試作を行い，当初の目的性能を得た．


Application of the Multiple Signal Classification (MUSIC) method for One-Pulse Burst-Echo Doppler Sonar Data

高分解能スペクトル推定法であるMUSIC法をドップラーソナーから得られるワンパルスバースト状信号に適用した．その結果，そのような短時間パルスの信号から，従来の手法では不可能な低速度の船速推定が可能であることを初めて示した．


極微弱光に対応可能なフォトンカウンティングタイプの位相変調型蛍光寿命計を始めて考案し，提案を行った．そして，実際に装置を設計·製作し，当初の予想通りの性能を得られることを確認した．さらに，発癌性物質として知られているベンゾピレンの蛍光寿命測定を行った．


マイクロチップを用いた蛍光検出型NO2モニタリング装置

マイクロチップを用いた蛍光検出型NO2モニタリング装置

大気環境センサとして，石英マイクロチップ上に蛍光検出型のNO2モニタリング装置を設計·製作し，その評価を行った．光源は紫外LEDとし，NO2モニタのための蛍光試薬を開発した．

The Transactions of The Institute of Electrical Engineers of Japan


Elimination of the Uninformative Calibration Sample Subset in the Modified UVE-PLS Method

UVE-PLS法において，多変量解析用のデータとしての情報を殆ど有さない伽リブレーション用データセットを除去するアルゴリズムを考案し，その評価を行った．


Phase-Modulation Fluorometer Using an Ultraviolet Light-Emitting Diode

紫外LEDを変調光源として用い，デジタルオシロスコープを信号記録装置として用いた位相変調型蛍光寿命測定システムを考案·構築し，基礎性能評価を行った．非常に簡便かつ安価なシステムであるが，ナノ秒オーダーの蛍光寿命が精度良く測定できることを示した．


An Externally Controlled, Nanosecond-Pulsed, Xe Lamp Using a High Voltage Semiconductor Switch

TTL制御可能な高電圧半導体スイッチを用いて，外部制御方式のナノ秒白色Xe光源を実現した．従来手法を使用するとすれば，サイラトロンのような真空管を使用する以外方法がなく，提案案手法によってXeランプのナノ秒パルス点灯の外部制御が非常に簡便に行えるようになった．


自走放電型ナノ秒Xeパルス白色光源の空間過渡発光特性

自走放電型ナノ秒Xeパルス白色光源の空間過渡発光特性

直流モードで使用されるキセノンランプを高速ナノ秒パルス点灯させたときの電極間の放電挙動が，万能投影機を用いて視覚化できるようにした．さらにこのシステムを用いて，放電の空間分解過渡発光特性を調べた．その結果，位置によって放電の時間的挙動が異なることを見出した．すなわち，空間的なマスクを用いれば，さらに短パルス光源が実現できることを示した．


Reduction in Time Jitter for Free-Running, Nanosecond-Pulsed, Xe Lamp by Supplementary Illumination with Blue Light-Emitting Diode

通常，直流モードで使用されるキセノンランプを高速ナノ秒パルス点灯させる手法を考案したが，その際にキセノンランプの電極に青色LED光を照射すると，発光のジッターが低減される現象を見出した．このジッターの定量的な計測手法を考案し，照射光の波長依存性を調べた結果，電極表面での光電効果に起因していることをつきとめた．


Application of the Modified UVE-PLS Method for a Mid-Infrared Absorption Spectral Data Set of Water-Ethanol Mixtures

多変量解析手法の一つであるPLS法において，情報を有さない変数を除去するというUninformative Variable Elimination法を，スペクトルデータに適用することを前提として，推定精度を向上させるという観点で改良した．実際に中赤外の水·エタノール混合物スペクトルデータセットに適用して良好な結果が得られることを報告した．


Time-Resolved High-Performance Liquid Chromatography Fluorescence Detector Using a Nanosecond Pulsed Light Source for Detecting Lanthanide-Chelated Compounds

We have constructed a time-resolved fluorescence detection (TRFD) system for the analysis of amino compounds with high-performance liquid chromatography (HPLC) using lanthanide ion chelates. In order to carry out time-resolved measurements, we have employed a nanosecond pulsed xenon-arc lamp as an excitation light source. Amino compounds derivatized by isothiocyanobenzyl-EDTA (IEDTA) with the lanthanide chelate are mixed with an enhancer solution in a post-column manner and detected by TRFD. Taking advantage of a property of the long fluorescence lifetime of the lanthanide chelates, high selectivity against background fluorescence was achieved. In order to demonstrate the usefulness of TRFD, fundamental performance tests were carried out. Details of the system are also described.

通常，直流モードで使用されるキセノンランプを高速ナノ秒パルス点灯させる手法を考案·製作し，高速液体グラフィー用時間分解蛍光検出器としてシステムを構築した．そして，ユーロピウムキレート化合物を用いたタンパク，アミノ酸類の分析を行い，高感度，高選択性な分析が可能であることを実際に示した．


Simulation of a Zero-Dispersion Filter Monochromator for Image-Spectroscopic Measurements

ダブルモノクロメータの水平方向と垂直方向の合成主点位置が一致するな位置に入射スリットと撮像素子を配置した全く新しいタイプのイメージング分光器のシミュレーションを行いその有効性を報告した．


Proposal for High-Resolution, Wide-Bandwidth, High-Optical-Throughput Spectroscopic System Using a Fabry-Perot Interferometer

ファブリペロー干渉計と通常のフーリエ分光器，またはマルチチャネルフーリエ分光器，またはマルチチャネル検出器を装着した分散型回折格子分光器をタンデム接続した全く新しいタイプの，高分解能，広帯域，高オプティカルスループットの分光システムの提案とシミュレーションを行った．


Electropherograms in Cappilary Zone Electrophoresis Plotted as a Function of the Quantity of Electric Charge

キャピラリー電気泳動のデータであるエレクトロフェログラムの横軸を，従来のリテンションタイムの代わりに電荷量でプロットし，分離ピークの積分値を計算できるようにした．この提案によって，定性定量分析の精度が向上することを実証した．


多変量解析 - 近赤外分光法による塗料用樹脂の水酸基価と酸価の同時定量

多変量解析 - 近赤外分光法による塗料用樹脂の水酸基価と酸価の同時定量

ポリエステル系ポリマー塗料樹脂の水酸基価と酸価の同時定量を目的として，近赤外透過スペクトル測定と多変量解析を行った．近赤外透過スペクトル測定においては，拡散透過の理論式を用いる際に，試料表面での反射ロスの補正を行った後，吸収係数を波数の関数として取り扱って試料内部で散乱補正が必要であることを示した．


Proposal for Aberration-Corrected Imaging Spectrograph

ダブルモノクロメータの水平方向と垂直方向の合成主点位置が一致するような条件を見出し，そこにそれぞれ入射スリットと撮像素子を配置することにより，非点収差やコマ収差が除去された新しいタイプの収差補正分光器が構成できることを初めて提案し，さらに光線追跡手法によって確認した．


Construction of Time-Resolved Fluorescence Detector for Amino Compounds after High Performance Liquid Chromatography Using Europium Chelate

サブミリ秒という長い寿命，高い量子効率，大きなストークスシフトを有する遅延蛍光性物質ユーロピウムキレート化合物の特性に着目して，タンパク，アミノ酸類の高感度，高選択性分析を目的とした高速液体グラフィー用時間分解蛍光検出器を考案し，実際に試作，評価を行った．


Temperature Dependence of the Mid-Infrared OH Spectral Band in Liquid Water

水は簡単な分子構造をしているにもかかわらず，その液体構造は複雑であり特異な物理化学的性質を示す．これは水素結合の温度依存性に起因しているとの観点から，赤外全反射分光法を用いてOH伸縮振動バンドの温度依存性の詳細な測定と解析を行った．


赤外フーリエ分光法における光導電型MCT検出器の非線形性補正

赤外フーリエ分光法における光導電型MCT検出器の非線形性補正

赤外フーリエ分光法における光導電型MCT検出器は，入射光量が大きくなると非線形応答を示し，スペクトル中に擬似ピークが現れる．入射光量を制限するとSN比の低下をもたらす．この問題を，検出器の周波数特性を考慮した数学的な非線形最適化問題として取り扱うことにより解決できることを始めて示した．


反射スペクトルからのK-K変換による光学定数の算出誤差

反射スペクトルからのK-K変換による光学定数の算出誤差

反射スペクトルからクラマース·クローニッヒ変換によって試料固有の光学定数スペクトルを取得する場合に，外部反射，内部反射，全反射といった光学的測定配置と入射光の偏光状態が最終結果に及ぼす影響について詳細なシミュレーションを行った．これまでこのような検討はあまりなされていなかったが，実用に際して有益な知見が得られた．


既に報告した「行列の特異値分解を用いたノイズ除去アルゴリズム」を，一般的な連続スペクトルにも適用できるように拡張し，その有効性を示した．


スペクトルデータのPLS法における前処理について

スペクトルデータのPLS法における前処理について

Partial Least Squares 法を用いてスペクトルデータ多変量解析を行うための，前処理手法について詳細な検討を行った．その結果，各種パラメータ設定に関して有効な指針が得られた．


Curve Resolution of Highly-Overlapping Lorentzian Peaks Based on the Autoregressive Model

スペクトル波形にフーリエ変換を施し，自己回帰モデルを適用することにより，高度にオーバーラップしたローレンツ型スペクトル波形を分離するアルゴリズムの提案と検証を行った．

Journal of the Spectroscopical Society of Japan


Enhancement of the Sensitivity and Resolution by Flow Counter-Balanced Capillary Electrophoresis

キャピラリー電気泳動において，電気浸透流と反対方向にサイフォン法によって圧力を印加した．電気浸透流を低速になるように制御できるため，検出器からの出力信号の積分強度が稼げ，検出感度が向上する．一方，分離分解能は殆ど影響がないことを実験的に確認した．


マルチチャンネル検出器からのスペクトルデータのデコンボリューション

マルチチャンネル検出器からのスペクトルデータのデコンボリューション

マルチチャンネル検出器によって取得されるスペクトルデータを対象とした分解能向上のためのデコンボリューションの問題提起を初めて行った．さらに，具体的なアルゴリズムの考案と検証結果を報告した．


New Method to Eliminate the Background Noise form a Line Spectrum

行列の特異値分解の手法を用いて，輝線スペクトルに重畳しているバックグラウンドノイズを数値的に除去する全く新しい手法の提案を行った．実際のスペクトルデータに適用してその有用性を示した．


多点インターフェログラムデータへのMEMとLOMEP法の適用

多点インターフェログラムデータへのMEMとLOMEP法の適用

フーリエ分光において，MEM法とLOMEP (Line Shape Optimized Maximum Entropy Linear Prediction) 法の多点インターフェログラムデータへの適用について比較検討した．その際，多点インターフェログラムデータをデジタルフィルターにかけ，ヘテロダイン検波の手法を導入すれば，計算時間を大幅に短縮した高分解バンドスペクトルの推定が可能であることを示した．


フーリエセルフデコンボリューション法に関する研究

フーリエセルフデコンボリューション法に関する研究

フーリエセルフフーリエセルフデコンボリューション法を行うためにFIRO (Finite Impulse Response Operator)法が提案されていたが，この従来のFIRO法に対して計算時間の短縮を目的とした近似FIROフィルターの提案を行い，各種パラメータの詳細検討と応用を行った．


計測制御用の統合ソフトウェアであるMacintosh/LabVIEWの有用性に一早く着目し，分光データ収集システムの構築が可能であることを示した．


Simple Method to Measure the Coherence Time of a Mode-Locked Laser

モードロックトピコ秒レーザのコヒーレンスタイムの簡便な計測手法を考案し，実際に測定システムを設計·製作してその有用性を確認した．空間的に作成した干渉縞を撮像素子で検出し，その可視度を算出するというのが基本原理である．


デュアルフォトダイオードアレー検出器を用いた偏光CARSシステム

デュアルフォトダイオードアレー検出器を用いた偏光CARSシステム

コヒーレントアンチストークスラマン散乱分光において問題となる非共鳴バックグラウンドを，偏光光検出手法を導入して抑制し，さらにデュアルフォトダイオードアレー検出器を用いて，リアルタイムでバックグラウンド補正されたスペクトルが取得可能なマルチプレックスCARSシステムを考案·設計·製作·評価を行った．


マルチチャンネルバーニアクロノトロンの分解時間の向上

マルチチャンネルバーニアクロノトロンの分解時間の向上

マルチチャネルバーニアクロノトロン方式の蛍光寿命測定装置において，測定時間を増加させずに分解時間の向上する手法を考案し，実際に装置を設計·製作して動作確認を行った．


A Nanosecond Photon-Counting Fluorimetric System Using a Modified Multichannel Vernier Chronotron

ナノ秒オーダーの微弱な蛍光減衰波形を高い効率で取得するために，光子列同時検出法を初めて提案し，マルチチャネルバーニアクロノトロン方式の蛍光寿命測定装置の考案·設計·製作·評価について報告した．


高周波再励起パルス動作ホローカソードランプの過渡発光特性

高周波再励起パルス動作ホローカソードランプの過渡発光特性

通常，原子吸光用光源として用いられるホローカソードランプを高速大電流パルス動作させ，さらにバースト状高周波を重畳させて発光輝度の増大を図った．共鳴線とイオン線の過渡発光特性の差異を見出し，最終的にそれを利用した原子蛍光分析が可能であることを示した．


高速光子計数回路評価用疑似フォトンパルス発生器の試作

高速光子計数回路評価用疑似フォトンパルス発生器の試作

光子計数型高速時間分解測光システムの，製作·評価に不可欠なナノ秒ダブルパルスパルサーおよび微弱蛍光減衰波形エミュレーターの考案·設計·製作と評価を行い，その有用性を報告した．


Hyperspectral single-pixel imaging with dual optical combs

Progress in Biomedical Optics and Imaging - Proceedings of SPIE


Comparison of the Reproducibility in Migration Times between a Constant-Current and a Constant-Voltage Mode of Operation in Capillary Zone Electrophoresis

キャピラリー電気泳動には，定電圧モードと定電流モードの二種類の動作モードが存在している．しかし，定電圧モードで使用するのが一般的であった．本論文ではこの点に関して考察を行い，定電流モードでの分析が定量精度向上の観点では望ましいことを実験的に示した．


Indirect Time-Resolved Fluorescence Detection of Both Non-Fluorescent and Fluorescent Compounds Separeted by High Performance Liquid Chromatography

遅延蛍光性のユーロピウムキレートをバッファ溶液とした間接時間分解蛍光測定による高速液体クロマトグラフィーの提案を行い，非蛍光性試料の検出が可能であることを初めて示した．