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We report highest power conductive-cooled Yb:YAG active-mirror amplifier (CcAMA) delivering 1 kW average power in 10 J, 100 Hz.

In this study, the energy transfer mechanism in Cr,Nd,Yb:YAG (yttrium aluminum garnet) materials was investigated. Based on the emission/excitation spectra and the temporal evolutions of the donor and acceptor ions in Cr,Nd:YAG, Nd,Yb:YAG, and Cr,Nd,Yb:YAG materials, the role of the cascaded Cr3+→Nd3+→Yb3+ energy transfer was elucidated in terms of Yb fluorescence enhancement. The quantum yield balance among Cr, Nd, and Yb fluorescences was determined by solving rate equations, which utilized parameters such as the lifetimes of Cr3+, Nd3+, and Yb3+ ions and the energy transfer parameters related to these materials. The quantum yield for Yb fluorescence was determined to be 35–81% at a Yb concentration of 1–7 at%.

Field observations of volcanic debris avalanche (VDA) morphology, sedimentology, and structural features have inspired several hypotheses on their dynamic behaviour. These include plug flow, translational slide, and sliding along multiple shear zones, none of which involve large-scale turbulence during transport. The plug flow model shows normal gradation in the plug, and reverse grading in the laminar boundary layers. During translational sliding, spreading of the mass is accommodated by listric normal faults that flatten into a main sliding plane at the base of or within the avalanche body. Multiple shear zones include progressive fragmentation within the avalanching mass, resulting in pockets of shear and slip. We present case studies for each model and hypotheses for the formation of flowbands on the deposit surface. Processes involved during emplacement include disintegration, dynamic fragmentation, and matrix injection. Near the base, bulldozing and incorporation of substrata change the composition and behaviour of the VDA. In extreme cases, VDAs transform into lahars if sufficient water is available for entrainment. Post-emplacement, lahars can also happen, e.g., through debris dewatering, loading of saturated substrata or in the case of landslide dam failure. VDA also create secondary slides when deflected by topographic barriers or when the margins are oversteepened.

A stable operation of 1.1 J/100 Hz 10 ns laser pulses were achieved from a single cryogenically cooled Yb:YAG rod amplifier with ink-cladding. The efficiency and gain coefficient were 44% and 383, respectively.

High average power lasers with a high pulse energy are of considerable interest in various fields such as high-energy-density physics. Light-absorbing edge cladding is effective in suppressing parasitic oscillations in high-pulse-energy disk lasers; however, the large amount of heat generated from the cladding can affect the laser medium. We develop an improved conduction-cooled active-mirror laser with a double-sided cooled-edge cladding. A stable laser output with a pulse energy of 10 J at a repetition rate of 100 Hz was achieved using six liquid-nitrogen-cooled active-mirrors in the main amplifier. This study shows that aggressive cooling of the edge cladding is highly effective in decreasing the temperature rise and controlling the temperature distribution in the laser medium.

We have developed a conductive-cooled Yb:YAG active-mirror amplifier with an diameter of 50 mm and a liquid-nitrogen circulation system. The high thermal capability that enables 10 J, 50 Hz laser amplification was demonstrated successfully.

Debris avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs) are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion and multi-view stereo (SfM–MVS) photogrammetry, we obtained high-definition digital elevation model (DEM) and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance–size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the debris avalanche, suggesting that the extensional regime of the debris avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding debris underwent a compressional regime, and out into the unconfined terrain where the debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12–15 × 108 m3 gives a mean thickness of 60–75 m, which is much deeper than the reported cases of other DADs. This suggests that the debris avalanche must have flowed further downstream and beyond the current DAD extent. Assessments of the DAD incorporating the topographic constraints can provide further insights into the risk and mitigation of potential disasters in the study area.

To assess the geomorphological importance of waterfall recession in volcanic bedrock, we examined recession rates of six waterfalls in the lower reaches of Kaminokawa river basin on the Osumi Peninsula in southern Kyushu. The examination was performed with an empirical equation that uses a dimensionless parameter obtained by dimensional analysis of relevant measured factors, including erosive force, size of waterfall, and bedrock resistance. Welded Ata ignimbrite, formed at approximately 110 ka, may have played an initiating role to maintain such waterfalls because it resists weathering more than other local rocks. Estimated recession rates for the six waterfalls range from 0.2 to 3.0 cm/y, which compare with estimated rates for waterfalls in another region characterised by welded ignimbrite. Comparison of equation-derived recession rates of waterfalls with actual recession distances from confluences supports the idea that an original waterfall will subsequently split into two distinct waterfalls when it recesses past an upstream junction of two channels. Our findings revealed that all six waterfalls likely would have been at almost the same point lower in the watershed in the past, marking the general site of the original waterfall. Moreover, the ancestral original waterfall is highly likely to have started from a point between the caldera rim and present river mouth. There, a knickpoint was likely caused by the river dropping into an inner part of the caldera, possibly just after the eruption of the Ata ignimbrite. The waterfall erodes upstream away from the caldera basin, and this happens to be to the east.

This study demonstrates fast pulse train switching using a coherent polarization beam combiner with a phase difference detection (PDD) algorithm. Based on the highly stable feedback control obtained with the PDD algorithm, stable burst-mode extraction with an arbitrary duty cycle was achieved with a contrast ratio of 800:1 for a third-harmonic light (347 nm) of a 5 MHz pulsed Yb-doped fiber laser. The proposed method can be effectively used for high-speed switching in high-average-power pulsed laser systems.

Development of high-energy and high-repetition rate laser using Yb:YAG is a subject of growing attention to use many scientific and industrial applications. Especially, The Laser Wake Field Acceleration (LWFA) is receiving a lot of attention in the world [1–3]. Laser driven plasma accelerator (LPA) has potential to accelerate electron bunches to high energies in mm-size acceleration length, and still provides high quality bunch characteristics like: high bunch charge, femtosecond duration bunch length, and high pointing stability [4]. However, the accelerated electron charge is no many compare to radio frequency accretion. Therefore, the high repetition rate and high peak power laser is required. We have developed 1 J, 10 Hz cryogenically-cooled active mirror amplifier using Total-reflection active-mirror (TRAM) architecture [5]. At present, we are developing the 100 J, 100 Hz cryogenically-cooled active-mirror amplifier using Yb:YAG. The front end for the laser system is consists of CW distributed feedback laser diode, EO pulse slicer, which generates laser pulse of several ns duration at a pulse energy of few nJ. This pulse amplified up to around 200 mJ in the regenerative amplifier and multi-pass amplifiers using by cryogenically-cooled Yb:YAG. This pulse is amplified energy of 100J through two stage cryogenically-cooled active-mirror amplifier. We are developing the conductive cooled active mirror using the liquid nitrogen circulation. It is possible to 10kW (100J, 100Hz) operation. In order to conductive cooled active mirror, it is necessary to develop a cooling method for suppresses wave front changes in cooling. Therefore, we are developing Key technologies about cooling structure, bonding of amplifier medium and heat sink, wave front compensation. Also, we made the wave front measurement system of cryogenically-cooled active mirror. Figure. 1 (a) show the layout of wave front measurement system for cryogenically-cooled active mirror. The reference laser is fibre coupled CW distributed feedback laser diode at 1030 nm of wavelength. The reference laser is expanded to 50 m diameter by beam expander. The Yb:YAG coated AR and HR coat for 1030 nm. The Yb:YAG bonding at Heat-sink and cooling by cryocooler (Stirling cooler). The refracted laser is reduced to 5 mm diameter by beam reducer and input to the wave front sensor (SID4, PHASICS). Figure.1(b) show the measurement result of wave front shift. The wave front shift is change amount (P-V change) from the reference at room temperature (300K). The wave front shift increases with cooling, it is small value. Also, we measured the Zernike coefficient. It is dominant in low order and easy to compensation.

We report, to the best of our knowledge, the highest power conductive-cooled active-mirror amplifier (CcAMA) using Yb:YAG with a pulse energy of 10 J. By using four liquid-nitrogen circulating cooled laser heads, we achieved a repetition rate, pulse energy, and average power of 33.3 Hz, 9.3 J, and 310 W, respectively. The problem of wavefront distortion, which is difficult to solve with a large-aperture active-mirror laser, is suppressed by using reinforcing materials with the same thermal expansion coefficient. We have confirmed that the wavefront distortion is small ( 0.15 λ P-V per head) at 100 Hz operation, which paves the way for 100 Hz operation with the CcAMA concept.

We had developed a unique porous thin films by a special coating method1. In this technique, two dielectric materials A and B having different refractive indices nA and nB ,where nA＞nB are simultaneously deposited in vacuum on a substrate such as fused silica or optical glasses. Then the coated surface is processed in ultra-pure water which preferentially dissolves the material B. These processes result in a porous thin film which has gradient refractive index and has the antireflection (AR) property over broad bandwidth. The porous coating obtained by this method cannot apply depositing a multilayered dielectric thin film. We have developed a novel method. The present technique, a dielectric material D and a plastic P are simultaneously deposited in vacuum on a heated-substrate such as fused silica, ceramic or optical glasses. Then the coated surface forms an adaptively mixed thin film ( AMTF ) with dielectric material and plastic. In this coating process, plastics partially evaporate due to the heated-substrate. The refractive index of the coated AMTF mainly decided by the mixing ratio of the dielectric material and plastic. In our samples the damage threshold was confirmed to be 115 J/cm2 at 10 ns and λ=1064 nm. The band width of AMTF with MgF2 and Teflon (AMTF: MgF2 ) was confirmed to cover from 200 to 8000 nm. This AMTF: MgF2 can be applicable not only to AR thin film, but to a high reflectance mirror and polarizer in various high intensity laser syetems. 1K.Yoshida, H.Yoshida, Y.Kato, and C.Yamanaka, Appl.Phy.Lett.47,911(1985)

Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic depositional landforms including hummocks. Not only sedimentological but also geomorphological analyses of debris avalanche deposits (DAD) are crucial to clarify the size, mechanisms, and processes of the debris avalanche. We investigate the morphology of hummocks newly identified in the DAD at the north-eastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion multi-view stereo photogrammetry (SfM), we obtained high-definition digital elevation model (DEM) and orthorectified image of the DAD surface with hummocks. Detailed geometric features of the hummocks are investigated using the RPAS-derived high-definition DEM. The source volume of the DAD was also estimated by reconstructing the original shape of the mountain body using a lower-resolution satellite-based DEM. For this, topographic cross sections are examined based on the slopes around the scar that are regarded as the remnant topography preserved since the sector collapse. The spatial distribution of hummocks shows an unusual pattern regarding the distance-size relationships, i.e., anomalously concentrated in a certain distance from the source. The hummocks are found to be aligned toward the flow direction of the debris avalanche, suggesting the extensional regime of the debris avalanche. These facts indicate that this debris avalanche did not follow the typical flow type of debris avalanches observed in the other cases. Instead, the topographic constraints by former caldera wall and fault-induced lineaments could have strongly affected the flow course and pattern in this particular case: The pre-existing caldera wall topography could have acted as the topographic barriers for the debris avalanche to force the initial flow to turn northward, and the flow regime to be once compressional followed by extensional at the narrow and steepened outlet valley. Also, the estimated volume of the DAD 12–15 × 108 m3 gives its mean thickness of 60–75 m, which is much deeper than the reported cases of other DADs. This suggests that the debris avalanche could have flown down to the far downstream areas from the presently-observed limit of the DAD extent. Assessments of the DAD including the results of this study can provide further insights into the risk and mitigation of potential disasters in the study area.

This paper investigates the relationship of hummock orientation to the flow dynamics of volcanic debris avalanches. There are opposing views on whether hummocks are systematically aligned along debris avalanche paths, or not. To investigate this geomorphologically fundamental question, I investigated hummock orientation for six Japanese debris avalanches of two simple styles: four “freely spreading” debris avalanches, and two “valley-filling” debris avalanches. Quantitative GIS-based data analysis revealed that hummock orientation along the avalanche flow path alternated between dominantly parallel to and dominantly perpendicular to the flow direction. These changes of alignment reflect dynamic changes of the local stress field within the avalanche, alternating between extensional and compressional in response to changes of the slope of the pre-avalanche ground surface. Changes of hummock alignment from perpendicular to parallel indicate that the local stress regime has changed from compressional to extensional. Conversely, changes of hummock alignment from parallel to perpendicular indicate that the local stress regime has changed from extensional to compressional. Thus, this research demonstrated a clear relationship between hummock orientation and dynamic changes of stress regime within avalanches that are related to changes of the slope of the pre-avalanche ground surface.

Commercial catches of barfin flounder Verasper moseri, an important target flatfish for stock enhancement programs in northern Japan, have recovered remarkably since the large-scale release of seedlings from Hokkaido in 2006. However, their reproductive ecology remains unclear. Our study of 2008–2012 investigated seasonal changes in the maturity of stocked female barfin flounder (n = 4,123) off the Pacific coast from Hokkaido to Tohoku (35.7°–43.4°N). Histological observation of ovaries revealed that fish undergoing vitellogenesis were observed mainly off Hokkaido and partially off northern Tohoku during August–January (40.2°–43.4°N). However, fully matured or spawning fish were not found near those areas. They were observed only in southern Tohoku. Ongoing spawning was observed off southernmost Tohoku (35.8°–37.5°N around 300 m depth) from early February through late April, when commercial landings had decreased drastically off Hokkaido. Spent fish were caught only rarely off southern Tohoku, but were observed frequently off Hokkaido during April–June. These results demonstrate that spawning grounds form at the upper continental slope off southernmost Tohoku during February–April. Relations between maturation traits and seasonal landings strongly suggest that female barfin flounder repeatedly migrate more than 700 km from feeding grounds off Hokkaido to spawning grounds off southern Tohoku.

A morphometric investigation of the longitudinal distribution of hummocks at the southeastern foot of Iriga volcano in the Philippines showed that hummock size decreases away from the volcano. Aerial photographs and GIS analysis revealed that the size–distance relationship can be expressed as the exponential function A = α exp (−β D), where A is the area of a hummock and D is its distance from the source. This relationship is the same as that observed previously for freely spreading debris avalanches in Japan, including two avalanches at Bandai volcano. This size–distance relationship provides information about the physical characteristics of the event: the α value shows a strong correlation with the volume of the collapsed mass of the volcanic edifice, and the β value shows a strong correlation with the coefficient of friction of the debris avalanche. Thus, morphometric analysis of hummocks created by a volcanic avalanche illuminates both the physical properties of the volcanic body and the mobility of the avalanche. For the Iriga debris avalanche, the observed longitudinal hummock distribution is clearly a function of the volume of the collapsed mass and the coefficient of friction of the avalanche. The relationships so defined appear to be a geometric effect related to the areal extent of freely spreading hummocky avalanche deposits, especially their longitudinal dimensions.

Catastrophic collapse of volcanic edifices and the accompanying rockslide-debris avalanches drastically change landforms and cause disasters around volcanoes. Rapid modification of the landforms created by these events makes it difficult to estimate the magnitudes of prehistoric events and evaluate damage. However, the widespread preservation of hummocks along the course of rockslide-debris avalanches is useful for understanding the physical characteristics of these landslides. We analyzed data on hummocks from seven prehistoric events in northern Japan to derive the relationship between hummock size and distance from landslide source, and interpreted the geomorphic significance of the intercept and slope coefficients of the observed functional relationships. Hummock size decreases as an exponential function of distance for volcanic rockslide-debris avalanches, although each event has its own distinct distribution pattern. The intercept coefficient, α, which corresponds to the initial average size of hummocks (blocks) at the origin of the landslide, shows a strong correlation with the volume of the collapsed mass, indicating that the initial size of blocks at the source may be determined by the volume of the collapsed mass. The slope coefficient, β, which describes the rate of decrease in size of hummocks with distance, shows a strong correlation with the coefficient of friction of the rockslide-debris avalanche, indicating that the attrition or size decrease rate of hummocks is controlled by the mobility of the avalanche. These relationships enable us to estimate the volume of the collapsed mass and the travel distance of an avalanche. Because it is sometimes difficult to obtain the evidence directly indicating the volume of collapses and the damage they caused, the findings are significant also for hazard assessment that the size–distance relationships of hummocks can be obtained from fragmentary remnants of a rockslide-debris avalanche to help reveal the characteristics of the events.

We report the absorption characteristics of ceramics for amplified-spontaneous-emission-absorbing cladding and their temperature dependence. We measured YAG ceramics doped with Cr4+, Co3+, Co2+, and Sm3+. Our results indicate that Cr4+- and Co3+-doped YAG ceramics are suitable for 1-μm lasers and that Co3+ have higher temperature robustness than Cr4+.

The Japanese Islands are tectonically active and humid. Thus, erosion and deposition are the primary processes controlling geomorphic development. Catastrophic sector collapses at volcanoes should be considered significant in this context. This study examines the geomorphological role of volcanic sector collapses in Japan, introducing 58 cases with their respective occurrence ages and volumes (≥ 1×108 m3). We find that the frequency of sector collapses becomes exponentially higher as the collapse magnitude decreases. The total volume of the dissected volcanic edifice caused by catastrophic collapses amounts to ca. 6.4 km3 (640×108 m3) during the last 500 years. This value can be translated into an annual denudation rate of 0.53 mm/y per unit area of the Quaternary volcanoes (ca. 24000 km2), which is comparable to the contemporary denudation rate of non-volcanic mountains in Japan. Therefore, although volcanic sector collapses occur intermittently, we have to consider them as sediment sources that are indispensable to an understanding of geomorphology in Japan.

Many hummocky terrains are found preserved along the courses of debris avalanches. This research investigates the functional relation between the size (plane area) and the run-out distance of hummocks on debris avalanche depositional surfaces in Japan. The geomorphic meanings of coefficients of the function expressing this size-distance relation are discussed, along with the geomorphological role of catastrophic volcanic sector collapses. The sizes of hummocks decrease with distance and can be expressed by an exponential function of distance for individual debris avalanches, although their distribution patterns vary from one debris avalanche to the next. Concerning the function expressing the size-distance relation, slope coefficients, implying the rate of decrease of the sizes of hummocks with distance, show a correlation with the equivalent coefficients of friction. This indicates that the downsizing rate of hummocks is controlled by the mobility of debris avalanches. Intercept coefficients, which mathematically indicate the initial average size of hummocks at a distance of 0 km, show a high correlation with the volumes of collapsed masses. The initial average sizes of hummocks at the source area are potentially determined by the volume of collapsed mass of the volcanic body. During the last 500 years in Japan, catastrophic collapses at volcanoes have accounted for an annual denudation rate of ca. 0.5 mm/y per unit area of Quaternary volcanoes, which is comparable to the contemporary denudation rate of non-volcanic mountains in Japan. Furthermore, accompanying debris avalanches cause severe disasters in and around the volcanoes. In such situations, the size-distance relation of hummocks, even for part of a debris avalanche, would contribute to revealing the magnitude and damage of debris avalanches.

火山麓に分布する流れ山は，大規模山体崩壊が過去に発生した証拠として，また，岩屑なだれのメカニズムを推察するうえで，重要な研究対象とされてきた．本研究では，流れ山地形がなお崩壊や岩屑なだれに関して地形学的に重要な情報を提供してくれるものと捉え，岩屑なだれの流下方向における流れ山の分布様式を検討し，流れ山地形に新たな地形学的意義を与えることを試みた．研究対象は，日本における4つの岩屑なだれが形成した流れ山であり，これら岩屑なだれは山麓に拡散した典型例とみなされる．空中写真判読により抽出した流れ山の数は，尻別火山の172，有珠火山の262，岩木火山の200，那須火山の643であり，GISを用いて流れ山の形態データを取得した．いずれの事例も，流れ山地形は山麓の下部斜面から平地にかけて緩やかな斜面として存在する．そして，流れ山のサイズは下流方向に減少する傾向が認められる．この減少傾向は，流れ山のサイズと給源からの距離との回帰分析によれば，指数関数で近似しうる．まず，回帰関数は，距離ゼロ（給源）における流れ山のサイズが崩壊の体積に規定されていることを示している．すなわち，崩壊の規模に応じて，崩壊部に発生する初期段階での割れ目の大きさが決まるらしい．他方，流れ山のサイズの減少割合は，等価摩擦係数の逆数で示されるような岩屑なだれの流動性に規定されていると考えられる．換言すれば，流動性の小さい岩屑なだれでは流れ山が急速に縮小するのに対し，大きい岩屑なだれでは緩やかである．以上の検討により，流れ山のサイズと給源からの距離との関係は，火山体ならびに岩屑なだれの流動特性を反映していることが明らかとなった．

We have demonstrated an efficient high energy 2 μm laser generation with a 36 mm long large aperture 5 mol% MgO-doped periodically poled LiNbO3 (PPMgLN) nonlinear optical crystal. A high power Q-switched Nd:YAG laser (1.064 μm) was used to pump the quasi-phase matched (QPM) optical parametric oscillator (OPO). A total output energy of 186 mJ with 58% slope efficiency was obtained in two separate beams at 2 μm.

We have proposed the cryogenic TGG ceramics based Faraday rotator for High peak and high average power laser. As the first demonstration of Faraday effect in a TGG ceramics, its Verdet constant at 1053 nm is evaluated to be 36.4 rad/Tm at room temperature which is same as that of the single crystal. In addition, the temperature dependence of Verdet constant is obtained experimentally. At liquid helium temperature, it is 87 times greater than that at room temperature. The measured thermal conductivity was corresponding to TGG single crystal.

A rapid, large-scale sediment transport event due to a catastrophic landslide plays an important role in changing drainage basin topography. However, volumetric evaluation of such events that occurred before the Holocene has been limited. This study quantitatively examines the volume of sediments derived from the Late Pleistocene (24 ka) sector collapse of Asama volcano, central Japan. A sequence of sediments supplied from the sector collapse was identified based on geological and geomorphological field surveys and literature search. The total volume of the sediments was estimated from borehole columns to be 4.9–5.4 km3. Reconstruction of the morphology of the volcanic edifice before and after the collapse provided an estimated volume of the lost sector of 4.0 km3. The greater estimated volume of the sediments released by the collapse is attributed to the entrainment of fluvial material during the flow of volcanic debris and to dilation of the original volcanic material.

Experimental results are reported on the compensation of thermal lensing caused by the radial thermal gradient in an optically pumped Nd:YAG laser. Poly(methyl methacrylate) (PMMA) with a higher negative dn/dT, a high damage threshold and low absorbance is very useful for compensating thermal effects in the amplifier. The results revealed that the use of PMMA resulted in the complete reduction of the thermal lens effect by an order of magnitude.

The northern Ayasegawa fault is a part of the Fukaya fault system, which is the longest active fault in the Kanto district. The paleoseismology of the northern Ayasegawa fault was revealed by a combination of arrayed boring and ground penetrating radar (GPR) survey. The northern Ayasegawa fault produced a fold scarp with the NW-SE direction running along the boundary between the Oomiya 2 (O2) surface and fluvial lowland. The O2 was formed in Marine Isotope Stage 5a, and was slightly deformed with a wide warping zone. Sixteen sediment cores arrayed across the warping zone contain a series of tephra layers such as Hk-TP (ca. 60-65 ka), KMP, AT (26-29 ka), As-BP group (20-25 ka), and As-YP (15-16.5 ka). These key beds except Hk-TP were deposited and deformed parallel to each other, suggesting that no faulting events occurred between KMP and As-VP fall. The timing of the last faulting event is after the As-YP fall, and is probably younger than 10 ka based on an interpretation of GPR profiles and 14C ages. KMP should be deposited horizontally because it intervened in the peaty silt layer, which accumulated conformably on lacustrine deposits overlapping the fold scarp. Thus, the KMP horizon roughly indicates the vertical offset produced by the events occurred after the As YP fall. The events were probably singular, and the last one formed a vertical offset of more than 4 m. The older event occurred at around 70 ka between Hk-TP fall and O2 formation. Vertical deformation of the O2 was at least 7 m, indicating the possibility that the vertical offset caused by the penultimate event is at least 3 m. The vertical slip per event might reach 5 m, and the average vertical slip rate is nearly 0.1 mm/yr because the warping zone detected by the arrayed boring above is within the flexure zone shown by the P-wave seismic profile. The northern Ayasegawa fault is considered to be a single behavioral segment because of its longer recurrence interval and lower slip rate of 0.1 mm/yr in comparison with those of the other part of the Fukaya fault system.

We have demonstrated a polarization-maintaining (PM) Yb mode-lock highly stable fiber laser with high beam quality. The characteristics of side-hole type PM Yb-doped fiber (YDF) were examined. The splicing connection between PM-YDF and PANDA fiber was optimized. We optimized the laser oscillation output and improved the efficiency of the fiber length in the Fabry-Perot cavity. We demonstrated an all PM single-mode fiber ring cavity. Mode-locking was produced by inserting a semiconductor saturable absorption mirror (SESAM). A PM photonic crystal fiber (PCF) was used for dispersion compensation in the cavity. Stable mode-lock operation with 500-ps pulses at 7.2 MHz was observed. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 90(5): 27–32, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20326

A liquid-cooled ceramic Nd:YAG split-disk laser amplifier has been designed for a high-average-power laser system. The maximum average output power of 17.1 W (1.71 J at 10 Hz) and the beam size of far-field pattern with 1.5 times diffraction limit was obtained. The combination of liquid cooling for disk laser material and wavefront compensation with a phase conjugation mirror was demonstrated. The wavefront degradation by liquid cooling was observed and measured with Michelson interferometer and far-field patterns.

Laser oscillation with the input/output characteristics of bulk-type Nd-doped silica glass with a high thermal shock parameter was demonstrated for the first time. The thermal shock parameter was estimated to be 12.0 W/cm, which is 1.5 times larger than that of Nd:YAG crystal (7.9 W/cm). The maximum output energy of 154 mJ was obtained with an output mirror of 20% transmittance. Although the output energy was 154 mJ, if without loss, output energy increases up to 1.69 J, eleven times larger than the present state. These results mean that Nd-doped silica glass can work as a high-average or a high-peak-power-laser.

A prototype split-disk amplifier consisted of four Nd:YAG ceramics and single crystals was demonstrated with a 3.7 cm square clear aperture. A single-pass small-signal gain of 2.0 and a total stored energy of 11.1 J in the eight YAG disks were obtained. The maximum output energy of 10.4 J with the YAG disk amplifier was achieved in a single-shot operation. A near-field pattern of 31 mm × 31 mm square with super Gaussian shape was measured.

We have demonstrated the short pulse generation of Nd:YAG laser at the fundamental wavelength by using stimulated Brillouin scattering (SBS) in liquid FC-75 at the energy of 1.5 J with a compact single set-up consists of generator and amplifier. Minimum pulse width obtained without attenuator and with attenuator are 770 ps and 600 ps respectively. SBS Conversion efficiencies are 90% without attenuator and 55% with attenuator. The brightness of the compressed pulse was about twelve fold higher than that of incident pulse.

The dependence of the bulk damage threshold of nonlinear crystals, such as KDP, KTP, LBO, BBO, CLBO, LiNbO3, and LiTaO3 on laser irradiation direction and their polarization under a single-shot operation have been investigated. We found that the intrinsic bulk-damage threshold for nonlinear crystals was mainly caused by dielectric breakdown from self-focusing with nonlinear refractive index. LBO single crystals have the highest value studied among nonlinear crystals. For KDP, BBO, and CLBO crystals, the damage threshold when an incident laser was propagated along the axis is approximately twofold that in the {100} or {010} plane at a 1.064 µm wavelength. The damage crack pattern is also suggested to be in the mechanically weak direction due to inner pressure caused a laser-induced plasma in the crystal as a result of the laser breakdown due to electron avalanche breakdown.