Neisei Hayashi

High-repetition-rate target injection and precise steering of multiple laser beams are essential for realizing laser-driven inertial fusion energy (IFE) reactors. EX-Fusion Inc. has established a facility to demonstrate these capabilities for the Fast Ignition scheme named the EX-Fusion Continuous Operation Laser Reactor (XF-COLR). Laser beam tracking and illumination of a free-falling stainless steel ball with a diameter of 1 mm were carried out at 10 Hz using multiple nanosecond and femtosecond lasers. The system with real-time correction of beam positions continuously operated for up to 12 h under ambient conditions and for 2.5–3 min under vacuum. Tracking performance, evaluated as standard deviations for 1500 shots under vacuum conditions, reached 121–139 μ m in the horizontal direction and 63–121 μ m in the vertical direction. The expected uncertainty at the engagement point propagated from the sensors was approximately 157 μ m. To the best of our knowledge, this is the first demonstration of dynamic tracking of an injected target using multiple laser beams steered by mirrors at 10 Hz, providing a reference for the development of future IFE reactors.

The measurement range of the MicroLiDAR was enhanced with multi-reference paths. The multi-reference paths were composed of four paths with polarization maintaining optical fibers, each with different lengths. 50-mm-long measurement range was demonstrated with an oscilloscope with 15-GHz bandwidth. Reducing the time of calculation of the distance, we induced the dual entry method and demonstrated it. The stable distance measurement was demonstrated up to 50 mm.

The shape of an instance hole (keyhole) created via a high-power laser was measured using a low-coherence interferometer with a 10-MHz repetition rate, a 10-um absolute spatial resolution and a 5-mm measurement range.

The shape of an instance hole (keyhole) created via a high-power laser was measured using a low-coherence interferometer with the following parameters: repetition rate, 10 MHz; center wavelength, 1550 nm; absolute spatial resolution, 10 µm; and measurement range, 5 mm. The keyhole was created on a 3-mm-thick stainless-steel plate using a high-power laser with 8-kW peak power and 1070-nm center wavelength. The cross-sectional area of the keyhole was measured to be 0.42 mm × 0.78 mm (width × depth) using the interferometer, and its side dimension was 0.46 mm × 0.78 mm (width × depth).

Forward Brillouin scattering (FBS) has been regarded as a key tool for distributed sensing of strain, temperature, acoustic impedance, etc. To date, FBS-based distributed sensing has been experimentally reported only by time-domain techniques. In this paper, we demonstrate correlation-domain distributed temperature sensing using cascaded FBS seeded by backward stimulated Brillouin scattering (SBS). By localizing the backward SBS using synthesized optical coherence function, cascaded FBS can also be localized. In the proof-of-concept experiment, we detect a 104 m long heated section in a 397 m long highly nonlinear fiber.

We investigate, for the first time, the temperature and strain dependencies of the spectral dips of the multimodal interference patterns in hetero-core-fiber structures at telecom wavelength. With increasing temperature and strain, the spectral dips shifted to shorter wavelengths with dependence coefficients of –3.5 nm °C ⁻¹ and –0.62 pm/ μ ε, respectively. Their absolute values were ∼60 times larger and ∼30 times smaller than the temperature and strain sensitivities of a standard single-mode-multimode-single-mode sensor, respectively. This result implies that the hetero-core-fiber structures can be potentially used to develop highly sensitive temperature sensors with reduced strain sensitivity.

We develop a new noise suppression technique to perform distributed strain and temperature sensing based on a higher-speed configuration of Brillouin optical correlation-domain reflectometry even when a polymer optical fiber (POF) is used as a sensing fiber. We acquire the spectral difference between with and without reference light, leading to selective observation of the beat signal of Brillouin-scattered light and reference light, which is effective for distributed sensing. After experimentally showing the usefulness of this technique, we demonstrate POF-based distributed temperature sensing and dynamic strain sensing.

Power-based refractive index (RI) sensing is demonstrated by exploiting an ultrasonically pressed plastic optical fiber (POF). We can be easily and cost-efficiently fabricate this structure, within a short while ( ~1 s), without using external heat sources or chemical materials. We have only to simply press the horn connected to an ultrasonic transducer against part of the POF. The RI dependence of the transmitted power exhibits linear trends in the RI ranges from ~1.32 to ~1.36 (coefficient: −62 dB/RIU (RI unit)) and ~1.40 to ~1.44 (coefficient: −257 dB/RIU)). We also study the temperature dependence of the transmitted power. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.