In order to stably generate pulse lasers, it is necessary to stabilize the polarization of the laser resonator. In this study, a resonator utilizing an optical fiber, which is a flexible waveguide, was employed. Despite the configuration leading to unstable birefringence, stable noise-like pulses were successfully generated. The pulse width is greater than 10 nanosecond. Additionally, successful generation of broadband light using this setup has been achieved, with both temporal and spectral stability being highly reliable.

There is a demand for higher-efficiency neodymium and chromium co-doped yttrium aluminum garnet (Nd/Cr:YAG) ceramics that can be excited by broadband light sources, such as flash lamps. We experimentally investigated the temperature dependence of the gain coefficient of a Nd/Cr:YAG ceramic (Nd: 1.0 at%, Cr: 2.0 at%). The gain coefficient at 1064 nm decreased with increasing temperature when Nd3+ was directly excited at 808 nm. However, when Nd3+ was excited via energy transfer from Cr3+ excited at 610 nm, the gain coefficient increased with increasing temperature. This temperature dependence was theoretically explained by solving the rate equations for Nd/Cr:YAG. Nd/Cr:YAG ceramics pumped with flash lamps may provide good laser performance without loss of gain even at high temperatures.

Stainless-steel type 316L (SS316L) plate was fabricated by selectively laser melting method (SLM) in vacuum. SS316L has excellent properties such as a high corrosion resistance and hardness, but fabricating complicated structures is challenging due to difficulties in processing the material. Although SLM can fabricate complicated shapes because it builds a 3D material layer-by-layer from a powder, some issues have yet to be resolved. One is that spatter is generated by metal powder scattering during laser irradiation. Another one is the denudation zone due to the balling effect. Spatter is considered to be dominated by the recoil pressure of fume caused by melting and evaporation of metal, and it is not possible to suppress the expansion of fume and reduce spattering by changing the atmospheric pressure. In addition, it is considered that the balling effect is dominated by the surface tension of the molten land under atmospheric pressure with a lot of convection. Therefore, in this study, SS316L plate was fabricated by changing the atmospheric pressure in the chamber, and the effect of atmospheric pressure on the spattering and balling effects was clarified. First, SS316L powder was set in a vacuum chamber, depressurized using a vacuum pump, and then irradiated with a single-mode fiber laser. Spatter was captured using a high-speed video camera during laser irradiation of SS316L powder. After that, polishing, edging, and cross-section observation were performed. As a result, it was found that when the atmospheric pressure was lowered, the spatter amount and bead the height decreased, and the denudation zone increased.

© 2019 Elsevier B.V. This work investigates the energy-transfer processes from Cr3+ to Nd3+ in yttrium aluminum garnet (YAG) ceramics by comparing the fluorescence decay of Cr3+ for Nd/Cr:YAG with that of Cr:YAG from 293 to 473 K. The experimentally determined fluorescence decay of Nd3+ excited through Cr3+ is consistent with the theoretical predictions when energy-transfer processes are taken into account by including in the rate equations the dipole-dipole interaction and energy transfer via excitation-energy migration. Furthermore, the results presented herein clarify that the efficiency of energy transfer from Cr3+ to Nd3+ increases slightly with increasing temperature.

We successfully generated a visible Q-switched pulse train at 636 nm in a Pr-doped double-clad structured waterproof fluoride glass fiber with graphene as a saturable absorber (SA) and calculated the slope efficiency as 22.1%. The average radio frequency and the average pulse width of all observed pulses were respectively measured as 633 kHz and 185 ns. We also discussed the required intensity to generate Q-switched operation in graphene using extrapolation and estimated the required intensity of Q-switched oscillation with graphene from kW/cm2 to MW/cm2 depending on wavelength.

© 2018 Laser Institute of America. In laser cladding, in the wavelength range of blue, light absorptivity of copper is much higher than that in the wavelength range of infrared. The authors developed the laser cladding system with the continuous wave blue direct diode laser (blue DDL). The system consists of a number of fiber-coupled blue DDLs with a maximum power of 20 W at a wavelength of 445 nm, a focusing lens, and a powder feeding nozzle. In this study, the authors investigated the fundamental characteristics of the multiple blue DDL system and formed copper film on 304 stainless steel plate using the system.

Our present work develops an all-fiber coherent beam combining (CBC) system to achieve a high energy pulse fiber laser beyond pulse energy limits due to nonlinear effects in rare-earth-doped fibers. Coherent beam combining is a power addition technology that obtains high energy density and high beam quality because it integrates multiple laser beams in a monolight wave. However, the CBC using optical fibers is technically difficult because the optical phases and polarization in optical fibers fluctuate due to disturbances. Therefore, we developed a novel all-fiber CBC system that can precisely control optical path lengths and automatically compensate polarization changes. When the system combined four laser pulses, it achieved a beam-combining efficiency of 96.6% that was about four times as high as a pulse energy before combining. In addition, the system obtained 97.1% beam-combining efficiency of CBC using femtosecond pulses that have very low coherences by minimizing the optical path-length differences between combined two pulses. Moreover, the system successfully regulated the beam-combining-efficiency changes to less than 2.0 percentage points in fullwidth by suppressing optical path-length fluctuations and tracking-control of the optical phases. (C) 2017 Wiley Periodicals, Inc. Electron Comm Jpn, 100(2): 36-42, 2017; Published online in Wiley Online Library (wileyonlinelibrary.com).

複数の青色半導体レーザーを加工点で一点に重畳する青色半導体レーザシステムを用いて、SUS基板上に純銅皮膜を形成した。クラッディング粉末の供給には、加工ヘッドの中心より材料粉末を供給する直噴型の方式を採用した。形成した皮膜の断面観察およびEDS分析を行って、皮膜形成時の中間層を測定した。その結果、中間層はレーザ入熱量に依存して小さくなることを明らかにした。

Our present work is to develop an all-fiber coherent-beam-combining system that achieves a high-energy femtosecond-pulse fiber laser beyond pulse energy limits due to the nonlinear effects in fiber amplifiers. Coherent-beam combining (CBC) using optical fibers is technically difficult because the optical phases and the polarizations in the optical fibers fluctuate due to disturbances. We developed an all-fiber passive CBC system that does not need to control optical phases and polarizations that achieved a beam combining efficiency of 95.9%. The combined output changes of the passive CBC system are the less than 1.0% in full width. (C) 2016 Elsevier B.V. All rights reserved.

© 2016 OSA. Cr3+ fluorescences excited in Cr3+4T1 level for Cr:YAG and Nd/Cr:YAG powders were measured. The energy transfer efficiency from Cr3+ to Nd3+ was increased from 68% to 78% with increasing concentration of Cr3+.

A Pr-doped double-clad structured waterproof fluoride glass fibre (Pr:DC-WPFGF) was successfully drawn, and the laser oscillation was demonstrated. The maximum output power was measured as 251.7 mW at 639.0 nm. The Pr:DC-WPFGF was designed to be single-mode fibre, with 0.08 of numerical aperture and 5.2 mu m of core diameter. The beam-quality factor, M-2, was measured and evaluated to be 1.0.

Material ablation by a focused Extreme ultraviolet (EUV) light is studied by comparing expanding ion properties and plasma parameters with laser ablation. The kinetic energy distributions of expanding ions from EUV and laser ablation showed different spectra implying different geometries of plasma expansion. The calculation results of plasma parameters showed that EUV energy is mostly deposited in high electron density region close to the solid density, while laser energy is deposited in low energy density region. Plasma parameters experimentally obtained from visible spectra did not show noticeable difference between EUV and laser ablation due to the corresponding low cut off density.

Improved transcription method of graphene saturable absorber mirror (GSAM) is tested to enhance visible pulse fiber laser oscillation properties. When a graphene thin film on a dielectric multi-layered mirror is soaked in nitric acid solution for washing process, the mirror suffers from a deterioration of transmission spectrum, or a detachment of dielectric multilayer from a mirror substrate. New method is the way that a dielectric multi-layered mirror is not washed in nitric acid directly and the transcribed graphene on a silica glass sheet is just put on a dielectric multi-layered mirror with opponent situation. Visible pulse laser oscillation in a Pr-doped double-clad structured waterproof fluoride glass fiber was tested with two types of GSAM whose dielectric multilayered parts are directly (GSAM-I) or not directly (GSAM-II) washed in nitric acid solution. The maximum output average power with GSAM-II was measured to be 9.52 mW at 644 mW GaN-LD excitation, on the other hand, 2.63 mW for GSAM-I and the slope efficiency of GSAM-II one was also improved as four times as GSAM-I one. Therefore, it is considered that the new washing process of transcribed graphene is effective for keeping the mirror properties and enhancement of the laser properties.

Our present work develops an all fiber coherent beam combining system to achieve a high energy pulse fiber laser beyond pulse energy limits due to nonlinear effects in rare-earth-doped fibers. Coherent beam combining is a power addition technology that obtains high energy density and high beam quality because it integrates multiple laser beams in a mono-light wave. However, the coherent beam combining using optical fibers is technically difficult because the optical phases and polarizations in optical fibers fluctuate due to disturbances. Therefore, we developed a novel all fiber coherent beam combining system that can precisely control optical path lengths and automatically compensate polarization changes. When the system combined four laser pulses, it achieved a beam-combining efficiency of 96.6% that was about four times as high as a pulse energy before combining. In addition, the system obtained 97.1% beam-combining efficiency of coherent beam combining using femtosecond pulses that have very low coherences by minimizing the optical path-length differences between combined two pulses. Moreover, the system successfully regulated the beam-combining-efficiency changes to less than 2.0 percentage points in full width by suppressing optical path-length fluctuations and tracking-control of the optical phases.

The gain coefficient of the Nd/Cr:YAG ceramics excited by the absorption line of Cr3+ increased with increasing temperature up to 400 K.

A novel femtosecond mode-locked variable-pulse-width laser system is developed based on coherent coupling technology. The laser system is composed of two fiber ring lasers that share an output coupler. Output longitudinal modes are emitted by the corresponding longitudinal modes of the laser modules. In this study, one longitudinal-mode spacing is changed arbitrarily by tuning the cavity length to control the output longitudinal modes. In the experiment, the laser system generates about 150 fs pulse width. The coupling result, which is the output pulse width, is changed by a length deviation of about 500 mu m. As a result, the laser successful widens the pulse width to 1.5 ps at maximum and the tuning pulse width with 10 fs resolution at minimum. (C) 2014 Optical Society of America

Amplification of 10-ns laser pulses to an energy of 500 mJ at a 10-Hz repetition rate in a cryogenic multi-pass multi-total-reflection-active-mirror (multi-TRAM) amplifier was achieved. By using a multi-TRAM, which is a YAG ceramic composite with three Yb:YAG active layers, a maximum single-pass gain of 12 and a total storage energy of 1.5 J were obtained. (C) 2014 Optical Society of America

A rewriting process was developed for reduced electrical resistance lines on a titanium dioxide (TiO2) film with femtosecond and CW fiber lasers. In this process, lines are written on TiO2 film by femtosecond laser irradiation, where the lines have a lower electrical resistance than the surrounding film. By heating with a CW fiber laser in air, the low electrical resistance lines are erased and their electrical resistances increase. When the erased areas on the TiO2 film are irradiated with the femtosecond laser, the lower electrical resistance lines can be rewritten on the film surface. © 2014 Elsevier B.V. All rights reserved.

Orange laser pulses were successfully generated in a Pr-doped waterproof fluoride glass fibre (Pr:WPFGF) using a graphene thin film as a saturable absorber (SA). Two pulse generation modes were observed: a continuous mode with 0.47 mu s pulse duration with a 2.61 mu s repetition period and a single giant pulse mode with 9.7 ns pulse duration. The peak wavelength was 603 nm. This result shows that a graphene thin film can be effective as an SA in the visible region, and in the future a visible ultra-short pulse laser with a modelocking technique may be demonstrated.

The energy transfer from Cr3+ to Nd3+ for Nd/Cr:YAG (Nd: 1.0%, Cr: 2.0%) materials was investigated by measuring the temperature dependences of fluorescence characteristics. The fluorescence intensity of Nd3+ increased with temperature owing to enhancement of the absorption coefficient of Cr3+. The energy transfer efficiency was constant from 77 to 450 K. The energy transfer time decreased with increasing temperature. (C) 2014 Elsevier EN. All rights reserved

Titanium dioxide (TiO2) has a variety of functions, but cannot be activated by visible-light illumination. It is importance to extend the activity of TiO2 into the visible-light, which comprises the larger portion of the room light. Therefore, the visible-light activated TiO 2 is required. We developed it with the femtosecond laser irradiation. The TiO2 films irradiated with femtosecond laser were darkened without changing topography of the TiO2 film surface. In the visible-light photocataltic function measurements, the TiO2 films were evaluated with the acetaldehyde decomposition test. The concentration of acetaldehyde was decreased to over time. This result indicated that visible-light activated photocatalyst function of TiO2 films were generated by femtosecond laser irradiation. © 2013 Copyright SPIE.

Titanium dioxide (TiO2) has a variety of functions, but cannot be activated by visible-light illumination. It is importance to extend the activity of TiO2 into the visible-light, which comprises the larger portion of the room light. Therefore, the visible-light activated TiO 2 is required. We developed it with the femtosecond laser irradiation. The TiO2 films irradiated with femtosecond laser were darkened without changing topography of the TiO2 film surface. In the visible-light photocataltic function measurements, the TiO2 films were evaluated with the acetaldehyde decomposition test. The concentration of acetaldehyde was decreased to over time. This result indicated that visible-light activated photocatalyst function of TiO2 films were generated by femtosecond laser irradiation.

Titanium dioxide (TiO₂) is functional ceramics and shows the photocatalytic function by ultraviolet light illumination. This photocatalytic function enables decomposition of organic matter such as bacteria, mold and odors. In our previous study, the TiO₂ film was darkened by the femtosecond laser irradiation and electrical resistance of the darkened film was decreased. In this study, we investigated variation of the photocatalytic function of the darkened TiO₂ films. The TiO₂ film was produced by aerosol beam irradiation. The wavelength, the pulse width and the repetition rate of the femtosecond laser were 775 nm, 150 fs and 1 kHz, respectively. The laser spot was scanned on the whole area of the TiO₂ film surface and the laser fluence was changed within the laser fluence regime in which the laser ablation was not caused and topography of the film surface was not varied. The photocatalytic function of the darkened TiO₂ films was evaluated in the acetaldehyde decomposition test. In the test, the films in acetaldehyde were illuminated with the UV and visible light sources, respectively. The acetaldehyde concentration was measured every hour during the illumination. The results of the test shows that the film had photocatalytic function by visible light illumination.

Carbon Fiber-Reinforced Plastic (CFRP) has attractive features like high-durability, high-strength and

We demonstrated a high-power and highly efficient Pr-doped waterproof fluoride glass fiber laser at 522.2nm excited by two-polarization-combined GaN laser diodes and achieved a subwatt output power of 598mW and slope efficiency of 43.0%. This system will enable us to make a vivid laser display, a photocoagulation laser for eye surgery, a color confocal scanning laser microscope, and an effective laser for material processing. Direct visible ultrashort pulse generation is also expected. (C) 2011 Optical Society of America

We have demonstrated a laser oscillation in the highest concentration and the shortest Nd-doped silica fiber, an only 5-cm multimode Nd-doped silica fiber. This fiber-core glass was fabricated by the zeolite method, and the glass contained 1.25 wt.% of Nd(2)O(3), which is 10 times higher than previously reported Nd-doped silica fiber. The laser output power was 10 mW at 1062 nm, and the threshold power and slope efficiency of the laser oscillation was 1.39 W and 2.4%, respectively. (C) 2010 Elsevier B.V. All rights reserved.

Rewriting process of lower electrical resistance lines on a titanium dioxide (TiO2) film was developed. In this process, lower electrical resistance lines were written on a TiO2 film without producing their surface topography changes by femtosecond laser irradiation. By heating with an electrical furnace under air, the electrical resistance of these lines was come back to the higher resistance with no topography changes. This result indicated that the lines could be erased by the heating method under air. When the erasing-treated area was irradiated with a femtosecond laser, the lower electrical resistance lines could be rewritten with no topography changes of the film surface.

We demonstrated a laser oscillation in the shortest Nd-doped silica fiber, an only 4-mm multimode Nd-doped silica fiber. This fiber-core glass was fabricated by the zeolite method, and the glass contained 1.25 wt% of Nd2O3.

Coherent combining is a useful technique that can combine laser beams from two or more fi bers into a

Amount of neutral debris emanated from extreme ultraviolet light source must be minimized to maximize its lifetime. Emanation of neutral atomic debris was experimentally investigated using laser-induced-fluorescence technique for carbon dioxide (CO2, 10.6 mu m in wavelength) and Nd-doped yttrium-aluminum-garnet (Nd:YAG, 1.064 mu m) lasers irradiated tin foils. Total number of neutral atomic debris from CO2 laser-irradiated tin foils was 1/100 times smaller than that from Nd:YAG irradiated ones. Competitiveness of CO2 laser was revealed in terms of debris mitigation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3486170]

Since Ce:YAG materials have wide fluorescence spectra in the visible region, they are considered a

Titanium dioxide (TiO2) films were irradiated with a femtosecond laser beam to alter their electrical resistances. The TiO2 film was produced by aerosol beam deposition. The wavelength, pulse duration, and repetition rate of the femtosecond laser scanned across the sample surface were 800 nm, 100 fs, and 1 kHz, respectively. By attenuating the laser fluence on the TiO2 film, a range was found in which the electrical resistance of the TiO2 film was varied even though the morphology of the film surface was not changed.

24.4 W of laser output has been obtained by sun-pumped, Cr-codoped Nd:yttrium aluminum garnet ceramic. The water-cooled laser rod was pumped with a Fresnel lens focusing the natural sunlight. By using the advantages of the Fresnel lenses, the maximum output for unit area of sunlight was 18.7 W/m(2). Direct concentrated solar illumination was used to pump a 9mm-diameter, 100mm length rod of Cr:Nd:YAG, which was obtained 9%-14% slope efficiency for the laser output. We have analyzed the Cr:YAG laser medium and found it to be an excellent high-power laser candidate for direct solar-pumping schemes which enhances the laser output about 1.8 times more than Nd:YAG.

The beam transport of high-power laser pulses by an optical fiber is an important issue in high-power laser application. For CW lasers, the power of 100's kW can be transmitted by an optical fiber, and 10-MW power could be theoretically possible. However, mirror systems are used for high-power pulse lasers in many fields because the limitation of incident pulse energy in the fiber is not understood well. Our purposes are to make it clear the limitation of incidence and the causes of the limitation, and that develop the techniques and the conditions, which are possible to transmit high-power laser pulses with optical fibers. The limitations of incident energy to large-core multimode optical fibers were estimated experimentally with core size of 600, 800, 1000, and 1200 microns. A Nd:YAG pulse laser system with a 10-ns pulse width at 1064nm was used. The incident energy of the laser pulse was adjusted using a half-wave plate and a polarizer, and focused on the fiber surface with a lens of 3000-mm focal length. The focused beam size was measured with a CCD camera, and adjusted to be 80% of each core size. The transmission efficiency was measured with the input and the output energy, and the damage on the input fiber core was monitored with a microscope for each laser pulse. In the 1000-microns core fiber, the surface damage was happened at 150mJ. Also, the efficiency was decreased with increasing input energy more than 50mJ because stimulated Brillouin scattering was occurred. The dependences of surface damage and stimulated Brillouin scattering on the laser and focusing parameter will be presented.

The authors achieved 11%-14% slope efficiency of solar-pumped laser by Cr-codoped Nd:yttrium aluminum garnet ceramic and Fresnel lens focusing from natural sunlight. The laser output of 24.4 W was achieved with 1.3 m(2) Fresnel lens. The maximum output for unit area of sunlight was 18.7 W/m(2), which is 2.8 times larger than previous results with mirror collector. The utilization of Cr3+ ion enabled efficient absorption and energy transfer to Nd3+ ion of solar spectrum. The fluorescence yield at 1064 nm for various pumping wavelengths was measured both for Crcodoped and nondoped laser media, and 1.8 times enhancement of laser output from sunlight is predicted. (c) 2007 American Institute of Physics.

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.

本研究では,高安定かつ高ビーム品質動作が可能な偏波保持(PM)型Ybモードロックファイバレーザの開発を行った.まずサイドホール型のPM-Yb添加ファイバ(YDF)の特性について調べ,PM-YDFとPANDAファイバ(通常用いられるPMファイバ)との融着条件(放電パワー,放電時間)の最適化を行った後,ファブリペロー型共振器を構成した。ファイバ長をパラメータとしてレーザ発振出力の最適化を行い,高効率化を図った.その後,PM-YDFを用いて全PM型シングルモードファイバリング共振器を構成した.半導体可飽和吸収ミラー(SESAM)を挿入することでセルフモードロック動作を行い,正常分散の補償のためにPM型フォトニック結晶ファイバ(PCF)を共振器内に使用した.その結果,パルス幅500psで繰返し7.2MHzの安定なモードロック動作が確認された.

Self-starting pulse generation from a ytterbium-doped fiber (YDF) ring laser is presented. The laser consisted of an allpolarization-maintaining (PM) fiber system, specifically a single-mode PM-YDF with a side hole. Environmentally stable pulses and a wide tuning range of 60 nm were obtained with a polarization extinction ratio > 20 dB. The YDF oscillator described in this study is compact, reliably self-starting, and has excellent long-term stability in light of its robustness to thermal and mechanical disturbances.

A self-starting pulse laser with an erbium-doped fiber cooled at liquid-nitrogen temperature was demonstrated. The self-starting-pulse fiber-ring laser can produce an approximately 1 ns pulse train without the need for devices for polarization control and compensation of birefiringence.

A self-starting pulse laser with an erbium-doped fiber cooled at liquid-nitrogen temperature was demonstrated. The self-starting-pulse fiber-ring laser can produce an approximately 1 ns pulse train without the need for devices for polarization control and compensation of birefringence. Copyright © 2006 The Institute of Electronics, Information and Communication Engineers.

Laser propulsion has very unique advantage of producing exhausting gas (ions) of very high velocity. Specific impulse from laser plasma could easily exceed 10,000 seconds that reduce the current propellant consumption rate on space born thrusters significantly. For efficient propellant usage, it is desirable that the exhaust plasma has rather narrow velocity distribution of fast ions. In order to accomplish the requirements, thermal conduction and neutral particle losses at and vicinity of the laser heated region have to be eliminated. A concept of spot size limited propellant shape has been proposed and tested in terms of the effects of the loss reduction. Ion and neutral particle measurements from laser plasmas produced on the above mentioned carbon targets are used to characterize the performance of the propellant. © 2005 American Institute of Physics.

A simple pulse-fiber-ring laser system with the Yb-doped fiber was demonstrated. The fiber laser can produce 1 ns pulse with the devices neither polarization control nor compensation of birefringence.

It is reported on micro-machining using as a laser source, a high peak power fiber pulse laser, MITSU-BISHI CABLE'S LP155R that consists of a two stage erbium doped fiber amplifier (EDFA) designed spe-cialty for pulse amplification. The output of the fiber laser is a transversal single mode and its wavelength is 1.55mum. The peak power and the pulse width of FWHM in our catalogued products are 10 kW and 2ns; re-spectively. A laser source having preliminary specification of 2kW and 80ps is also used. The high peak power and short pulse created in these systems make precise micro-machining possible with little thermal damages around the processed regions. It is demonstrated that micro-drilling and micro-scribing of metals and crystals such as tungsten, diamond-like-carbon (DLC) coating, stainless steel 304, silicon, sapphire and lithium-niobate. The microstructures of the processed specimens observed by a scanning electron micro-scope and an optical microscope are also introduced in this paper.

The first successful experimental demonstration of spherical implosion of cannonball targets is reported. The cannonball target was irradiated by two 1.052-$\mu$m laser beams. The pusher containing DT fuel gas was imploded, with excellent spherical symmetry, by the pressure of the plasma confined between the tamper and the pusher. Both high compression density and high neutron yield were obtained.

雑音状パルスの持つ特性は、ナノ秒に広がる広い包絡線内に、サブピコ秒と考えられる多数のパルスが群を成している点にある。これにより高い非線形性と共に高い安定性と低い可干渉性が得られていることが徐々に明らかになりつつある。今年度の成果として、パルス発生機序の解明と発振条件の特定を進めてきた。 今回用いているレーザー共振器は、極めて斬新な構成を有しており、従来の考え方では連続波はもとよりパルス発振すら難しいとレーザーに詳しい研究者であれば考えざるを得ない構成となっている。この構成の中では、高度に非線形性を発揮する、時間的にエネルギーの集中した高強度短パルスが必要であることがわかる。しかしながら、高強度であるが故に内部の偏光子によってパルス分離が生じ、これを繰り返すことによりパルス群を形成していることが予想される。 具体的なパルスの数がどの程度になっているのかはわからないが、スペクトルの広がりからパルス幅500フェムト秒程度のパルスの集合体であることが予想される。さらに、短パルスの集合体であるため、その立ち上がりが有する特性によって非線形性が強く生じていることも確認できており、波長変換に用いる種光源として、従来の単パルスな短パルスレーザーでは得られない特性が発現している模様である。 現在、このパルスを二つの方法で高出力化することにより新しい用途範囲を探っている。一つは、高ピークパワー化とランダム性を利用し、現在知られているファイバレーザーよりも高い非線形効果を得ることにより、波長拡張などを効率よく発生させること。具体的には、高分散媒質を利用したパルスの拡張と、拡張後パルスの増幅と時間圧縮技術の開発。次には、パルスを直接増幅可能な低非線形な光増幅器の開発である。何れの方法も基礎的なデータが揃いつつあり、ファイバメーカーの協力も得ながら新規な構造の増幅器も検討を進めている。

Basic technologies of the phase coupled laser composed by 16 fiber laser modules were developed in this research. This number is the value that corresponds to twice the number reported with past papers. Coupling efficiency reached 94% in coupled 16-fiber-laser-modules. These technologies are high effective for high power fiber laser and precision machining. High resolution and practicable phase controlling technology was achieved by this research. As a result, high power fiber laser has been advanced by coexisting high beam quality.

産業界で導入が進められつつあるファイバレーザーの高出力化、高安定化、フェムト秒領域の短パルス発生、ナノ秒領域の10GW/cm^2の高輝度パルスの発生に関して、実用化を視野に入れた開発を進めている。

光ファイバを利用したファイバレーザー用途、通信用途の新しい光部品の開発を行うと同時に、測定技術の開発も進めている。