Evaluation of a therapeutic carbon beam using a G2000 glass scintillator.

A G2000 glass scintillator (G2000-SC) was used to determine the carbon profile and range of a 290-MeV/n carbon beam used in heavy-ion therapy because it was sensitive enough to detect single-ion hits at hundreds of mega electron Volts. An electron-multiplying charge-coupled device camera was used to detect the ion luminescence generated during the irradiation of G2000-SC with the beam. The resulting image showed that the position of the Bragg peak can be determined. The beam passes through the 112-mm-thick water phantom and stops 5.73 ± 0.03 mm from the incident side to the G2000-SC. Additionally, the location of the Bragg peak was simulated when irradiating G2000-SC with the beam using the Monte Carlo code particle and heavy ion transport system (PHITS). Simulation results show that the incident beam stops at 5.60 mm after entering G2000-SC. The beam stop location obtained from images and the PHITS code is defined at 80% distal fall-off from the Bragg peak position. Consequently, G2000-SC provided effective profile measurements of therapeutic carbon beams.

Coupled-wave analysis of vector holograms. 3. Effects of intrinsic distribution of optical axis in anisotropic media.

We investigated theoretically the interference of two counterpropagating polarized light beams in optically anisotropic media whose optical axis is in the film plane and is gradually rotated around the thickness direction. Results indicated that pure polarization modulation without intensity variation is obtained in the inhomogeneous media when the total angle of the rotation is much smaller than the total retardation. Reflective anisotropic gratings recorded by the polarization modulation were formulated as the perturbation of the dielectric tensor, and diffraction properties were studied using coupled-wave analysis (CWA) and a numerical method. By assuming that the period of the intrinsic distribution is substantially larger than that of the induced one, we demonstrated that CWA estimates the diffraction efficiency and the polarization state of the diffracted light with high accuracy.

Coupled-wave analysis of vector holograms. 2. Reflective gratings formed in photoanisotropic medium with uniaxial birefringence.

The diffraction properties of reflective anisotropic gratings, which can be recorded in photoanisotropic media with uniaxial birefringence by three-dimensional vector holography, were characterized through the use of coupled-wave analysis (CWA). By investigating the perturbation of the dielectric tensor, we demonstrated that the gratings with sinusoidal distribution of the azimuthal angle of the optic axis diffract polarized light in which the ordinary and extraordinary components are converted for incident light. The polarization conversion was consistent with that calculated by a numerical method. In addition, it was shown that CWA enables highly accurate calculation of the diffraction efficiency with wavelength dispersion when the amplitude of the azimuthal angle is small.

All-Optical Wide-Field Selective Imaging of Fluorescent Nanodiamonds in Cells, In Vivo and Ex Vivo.

Fluorescence imaging is a critical tool to understand the spatial distribution of biomacromolecules in cells and in vivo, providing information on molecular dynamics and interactions. Numerous valuable insights into biological systems have been provided by the specific detection of various molecular species. However, molecule-selective detection is often hampered by background fluorescence, such as cell autofluorescence and fluorescence leakage from molecules stained by other dyes. Here we describe a method for all-optical selective imaging of fluorescent nanodiamonds containing nitrogen-vacancy centers (NVCs) for wide-field fluorescence bioimaging. The method is based on the fact that the fluorescence intensity of NVCs strictly depends on the configuration of ground-state electron spins, which can be controlled by changing the pulse recurrence intervals of microsecond excitation laser pulses. Therefore, by using regulated laser pulses, we can oscillate the fluorescence from NVCs in a nanodiamond, while oscillating other optical signals in the opposite phase to NVCs. As a result, we can reconstruct a selective image of a nanodiamond by using a series of oscillated fluorescence images. We demonstrate application of the method to the selective imaging of nanodiamonds in live cells, in microanimals, and on a hippocampal slice culture obtained from a rat. Our approach potentially enables us to achieve high-contrast images of nanodiamond-labeled biomolecules with a signal-to-background ratio improved by up to 100-fold over the standard fluorescence image, thereby providing a more powerful tool for the investigation of molecular dynamics in cells and in vivo.

Coupled-wave analysis of vector holograms: effects of modulation depth of anisotropic phase retardation.

The diffraction properties of thick vector holograms were analyzed with the use of a simple coupled-wave theory. Two eigenpolarizations in the holograms were determined based on the dielectric perturbation, and diffraction efficiencies for the polarizations were calculated by applying the Kogelnik method. The results were compared with those simulated by the finite-difference time-domain method. As a result, it was demonstrated that the diffraction efficiencies calculated by the two methods are in good agreement for any incident polarization when the modulation depth of the anisotropic phase retardation is substantially smaller than the mean retardation. In addition, we confirmed that coupled-wave analysis provides reasonable accuracy for relatively large modulation in the case of Bragg incidence with eigenpolarization.

Optimization of Wide-Field ODMR Measurements Using Fluorescent Nanodiamonds to Improve Temperature Determination Accuracy.

Fluorescent nanodiamonds containing nitrogen-vacancy centers have attracted attention as nanoprobes for temperature measurements in microenvironments, potentially enabling the measurement of intracellular temperature distributions and temporal changes. However, to date, the time resolution and accuracy of the temperature determinations using fluorescent nanodiamonds have been insufficient for wide-field fluorescence imaging. Here, we describe a method for highly accurate wide-field temperature imaging using fluorescent nanodiamonds for optically detected magnetic resonance (ODMR) measurements. We performed a Monte Carlo simulation to determine the optimal frequency sweep range for ODMR temperature determination. We then applied this sweep range to fluorescent nanodiamonds. As a result, the temperature determination accuracies were improved by a factor ~1.5. Our result paves the way for the contribution of quantum sensors to cell biology for understanding, for example, differentiation in multicellular systems.

Triple nitrogen-vacancy centre fabrication by C5N4Hn ion implantation.

Quantum information processing requires quantum registers based on coherently interacting quantum bits. The dipolar couplings between nitrogen vacancy (NV) centres with nanometre separation makes them a potential platform for room-temperature quantum registers. The fabrication of quantum registers that consist of NV centre arrays has not advanced beyond NV pairs for several years. Further scaling up of coupled NV centres by using nitrogen implantation through nanoholes has been hampered because the shortening of the separation distance is limited by the nanohole size and ion straggling. Here, we demonstrate the implantation of C5N4Hn from an adenine ion source to achieve further scaling. Because the C5N4Hn ion may be regarded as an ideal point source, the separation distance is solely determined by straggling. We successfully demonstrate the fabrication of strongly coupled triple NV centres. Our method may be extended to fabricate small quantum registers that can perform quantum information processing at room temperature.

Rugate filters fabricated by a radio frequency magnetron sputtering system by use of an optical in situ monitoring technique.

We propose, for the first time to our knowledge, a new feedback fabrication technique for rugate filters with sinusoidal refractive index distribution. The technique uses an in situ optical monitoring system, in contrast to conventional techniques for rugate filters that are based on time control, which is generally unsuitable for accurate fabrication of a continuous index distribution. We employed a-SiOx:H thin film as the material for the rugate filters because its refractive index can be successively controlled. Using the proposed technique and material, we fabricated near-infrared rugate minus filters having multiple and continuous refractive index distributions. The experimental and calculated spectra were well correlated as a result of applying the proposed feedback fabrication technique.

a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical filters.

We examined the optical properties of a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical bandpass filters (BPFs). Because of the high refractive-index contrast between a-Si:H and SiO2, the total number of layers of an a-Si:H/SiO2 multilayer can be relatively small. We obtained an a-Si:H refractive index of 3.6 at lambda = 1550 nm and its extinction coefficient k < 1 x 10(-4) and confirmed by Fourier-transform infrared spectroscopy that such small k is influenced by the Si-H bonding in the film. We fabricated a-Si:H/SiO2 BPFs by using in situ optical monitoring. Thermal tuning of a-Si:H/SiO2 BPF upon a silica substrate was also performed, and a thermal tunability coefficient of 0.07 nm/degree C was obtained.