Publications by authors named "Ichiro Shoji"

11 Publications

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High-power and highly efficient composite laser with an anti-reflection coated layer between a laser crystal and a diamond heat spreader fabricated by room-temperature bonding.

Opt Express 2017 Sep;25(19):22797-22804

We have succeeded in bonding a Nd:YAG crystal and an anti-reflection coated diamond crystal to realize a composite laser which minimizes the Fresnel-reflection loss at the bonded interface for the first time. This newly developed composite laser has realized higher output power at higher pump power than a non-composite Nd:YAG laser while keeping nearly the same slope efficiency.
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http://dx.doi.org/10.1364/OE.25.022797DOI Listing
September 2017

Reflex arc of the teeth clenching-induced pressor response in rats.

J Physiol Sci 2018 Jan 29;68(1):89-100. Epub 2016 Dec 29.

Department of Physiology, National Defense Medical College, Namiki 3-2, Tokorozawa, Saitama, 3598513, Japan.

Although "teeth clenching" induces pressor response, the reflex tracts of the response are unknown. In this study, dantrolene administration inhibited teeth clenching generated by electrical stimulation of the masseter muscles and completely abolished the pressor response. In addition, trigeminal ganglion block or hexamethonium administration completely abolished the pressor response. Local anesthesia of molar regions significantly reduced the pressor response to 27 ± 10%. Gadolinium (mechanoreceptor blocker of group III muscle afferents) entrapment in masticatory muscles also significantly reduced the pressor response to 62 ± 7%. Although atropine methyl nitrate administration did not change the pressor response, a significant dose-dependent augmentation of heart rate was observed. These results indicate that both periodontal membrane and mechanoreceptors in masticatory muscles are the receptors for the pressor response, and that the afferent and efferent pathways of the pressor response pass through the trigeminal afferent nerves and sympathetic nerves, respectively.
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http://dx.doi.org/10.1007/s12576-016-0513-9DOI Listing
January 2018

Thermal characteristics of second harmonic generation by phase matched calorimetry.

Opt Express 2014 Jul;22(15):18268-77

We analyze a solution of the heat equation for second harmonic generation (SHG) with a focused Gaussian beam and simulate the temperature rise in SHG materials as a function of the second harmonic power and the focusing conditions. We also propose a quantitative value of the heat removal performance of SHG devices, referred to as the effective heat capacity Cα in phase matched calorimetry. We demonstrate the inverse relation between Cα and the focusing parameter ξ, and propose the universal quantity of the product of Cα and ξ for characterizing the thermal property of SHG devices. Finally, we discuss the strategy to manage thermal dephasing in SHG using the results from simulations.
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http://dx.doi.org/10.1364/OE.22.018268DOI Listing
July 2014

Phase-matching directions, refined Sellmeier equations, and second-order nonlinear coefficient of the infrared Langatate crystal La₃Ga(5.5)Ta(0.5)O₁₄.

Opt Lett 2014 Jul;39(13):4033-6

We directly measured phase-matching directions of second harmonic, sum, and difference frequency generations in the Langatate La₃Ga(5.5)Ta(0.5)O₁₄ (LGT) uniaxial crystal. The simultaneous fit of the data enabled us to refine the Sellmeier equations of the ordinary and extraordinary principal refractive indices over the entire transparency range of the crystal, and to calculate the phase-matching curves and efficiencies of LGT for infrared optical parametric generation.
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http://dx.doi.org/10.1364/OL.39.004033DOI Listing
July 2014

Ultraviolet vortex generation using periodically bonded β-BaB₂O₄ device.

Opt Express 2014 Jun;22(11):12829-35

This paper describes the first demonstration of ultraviolet (266nm) vortex generation using the combination of a frequency-doubled nanosecond green laser, a spiral phase plate, and a periodically bonded β-BaB2O4 device. For a laser pumping energy of 9.1 mJ, an ultraviolet vortex energy of 1.24 mJ was obtained, corresponding to a conversion efficiency of 13.7%.
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http://dx.doi.org/10.1364/OE.22.012829DOI Listing
June 2014

In vitro experiment for verification of the tandem shunt valve system: a novel method for treating hydrocephalus by flexibly controlling cerebrospinal fluid flow and intracranial pressure.

J Neurosurg Pediatr 2013 Jan 9;11(1):43-7. Epub 2012 Nov 9.

Department of Neurosurgery, Tokyo Women's Medical University, Tokyo, Japan.

Object: The CSF shunt valve is a medical device whose main function is to regulate intracranial pressure and drain excess CSF. The authors have developed a new therapeutic method for treating hydrocephalus, namely the tandem shunt valve system, which has the potential of flexibly controlling the CSF flow rate and intracranial pressure in patients.

Methods: The properties of the tandem system were verified by performing in vitro experiments. An in vitro system with a manometer was built to measure pressure and flow rates of water in open systems using the Codman Hakim Programmable Valve and the Strata adjustable pressure programmable valve. A single valve and 2 single shunt valves connected in series (the tandem shunt valve system) were connected to the manometer to check the final pressure.

Results: Conventional single shunt valve systems require valve pressures to be set higher to slow down the CSF flow rate, which inevitably results in a higher final pressure. On the other hand, the tandem shunt valve system uses the combination of 2 valves to slow the CSF flow rate without increasing the final pressure.

Conclusions: The authors succeeded in experimentally demonstrating in vitro results of tandem systems and their effectiveness by applying a model to show that the valve with the higher pressure setting determined the final pressure of the entire system and the flow rate became slower than single shunt valve systems.
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http://dx.doi.org/10.3171/2012.10.PEDS12226DOI Listing
January 2013

Thermal performance in high power SHG characterized by phase-matched calorimetry.

Opt Express 2011 Nov;19(23):22588-93

National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan.

We proposed a method to determine device quality in heat removal. Temperature change depending on SH power was analyzed by fitting with a new model to characterize heat removal performance of SHG modules, named as phase-matched calorimetry (PMC). The thermal disposal performance of SHG devices was improved by combination of metal housing and reduced crystal aperture. With a tight aperture, we demonstrated a 19 W single-pass 532-nm SHG at a conversion efficiency of 26.5% in a 10-mm-long PPMgSLT crystal without saturation.
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http://dx.doi.org/10.1364/OE.19.022588DOI Listing
November 2011

Severe hypotension during the decreasing phase of Gz stress in anesthetized rats wearing an anti-G suit.

Aviat Space Environ Med 2011 Nov;82(11):1030-6

Department of Physiology, National Defense Medical College, Tokorozawa, Saitama, Japan.

Introduction: Physiological responses to +Gz stress have been reported in several studies. However, no reports exist on differences in arterial pressure responses between increasing and decreasing G phases. We hypothesized that +Gz stress and/or an anti-G support might disturb the circulation system and cause potential brain hypoperfusion, even if the anti-G support protects against G-induced loss of consciousness.

Methods: Dependency of +Gz magnitude, hemodynamic changes, renal sympathetic nerve activity (RSNA), and aortic blood flow (AoBF) were estimated in anesthetized rats to analyze the effects of +Gz stress and/or an anti-G support on arterial pressure at a level of the brain (APLB). The rats were exposed to +Gz using a centrifuge for small animals while wearing an anti-G suit.

Results: APLB remained at the control level while the anti-G suit was inflated. However, a decrease in APLB was observed twice during increasing and decreasing G phases using the anti-G suit. Hypotension in the decreasing C phase at +5 Gz was significantly deeper than that in the increasing G phase (47.5 +/- 7.7 vs. 29.6 +/- 3.0 mmHg). RSNA responses to Gz loads were greater in the decreasing G than in the increasing G phase (129.7 +/- 8.6 vs. 147.3 +/- 10.4%). Both AoBF and calculated vascular resistance were suppressed more significantly in the decreasing G than in the increasing G phase (38.3 +/- 4.4 vs. 34.4 +/- 3.4 ml x min(-1), 1.44 +/- 0.22 vs. 1.09 +/- 0.14 mmHg x min(-1) x ml(-1)).

Discussion: We conclude that transient excessive decreasing G hypotension may occur during the decreasing G phase, which may be due to anti-G suit functioning.
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http://dx.doi.org/10.3357/asem.2870.2011DOI Listing
November 2011

Thermal-birefringence-induced depolarization in Nd:YAG ceramics.

Opt Lett 2002 Feb;27(4):234-6

The thermal-birefringence effect in Nd(3+) -doped YAG ceramics has been investigated. The amount of depolarization induced by thermal birefringence in Nd:YAG ceramics is nearly the same as that in (111)-cut single crystals at the same Nd(3+) concentration. However, depolarization becomes larger as the Nd(3+) concentration increases, even at the same absorbed pump power.
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http://dx.doi.org/10.1364/ol.27.000234DOI Listing
February 2002

High-energy quasi-phase-matched optical parametric oscillation in a 3-mm-thick periodically poled MgO:LiNbO3 device.

Opt Lett 2004 Nov;29(21):2527-9

Laser Research Center for Molecular Science, Institute for Molecular Science, Myodaiji, Okazaki, Japan.

We have demonstrated high-energy quasi-phase-matched optical parametric oscillation in a 3-mm-thick periodically poled 5-mol. % MgO-doped LiNbO3 device with a 32.1-microm grating period and a 30-mm length. With a large-spot-size pump laser of 2.2-mm diameter, we obtained a total output pulse energy of 22 mJ for both the signal (wavelength 1.82 microm) and the idler (2.56 microm) waves at an input pump energy of 46 mJ.
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http://dx.doi.org/10.1364/ol.29.002527DOI Listing
November 2004

Oscillation spectra and dynamic effects in a highly-doped microchip Nd:YAG ceramic laser.

Opt Express 2004 May;12(10):2293-302

This work reports on a beam quality and dynamic behaviors of a mirror-coated highly-doped YAG (Y(3)Al(5)O(12)) microchip ceramic laser possessing an increased number of grain boundaries. The degradation of beam quality factor in transverse patterns due to spatial inhomogeneity across the beam, multiple split-mode operations, violation of antiphase dynamics and high-speed intensity modulations due to the interference between non-orthogonal transverse modes were observed in a laser-diode end-pumping scheme.
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http://dx.doi.org/10.1364/opex.12.002293DOI Listing
May 2004