尾松 孝茂

We present a quantitative comparison between thermal lenses under lasing and non-lasing conditions in a diode-laser pumped self-frequency-doubled Nd,Lu:YAl3(BO3)(4) laser using an interferometric technique. At the pump power of 1.5 W, the thermal lens under the non-lasing condition attained 8 m(-1), and this corresponded to 170% of that under the lasing condition. Validity of the measured thermal lenses was confirmed by investigating the dependence of output power on the cavity length. The difference between thermal lenses under lasing and non-lasing conditions is caused by the nonradiative loss process of the upper level due to the cross-relaxation.

We present a new technique for suppressing the self-frequency-scanning in a single-stripe high power laser diode, known as a broad-stripe laser diode (BS-LD) with phase conjugate feedback. The lasing frequency was locked at the central wavelength of 808.7 nm within 0.1 nm for 20 min. The BS-LD was then operated in a narrow-band with a nm line width and generated a single-lobed near-field radiation with a narrow divergence.

複数の音響導波モードが存在する光ファイバにおいて, 音響導波モードごとのブリルアン散乱現象の違いについて理論的に調べた. その結果, 以下のことが明らかとなった. (1)ブリルアン周波数シフトのひずみ感度は, 無ひずみ状態のファイバにおけるブリルアン周波数シフト量に比例し, モード依存性はごくわずかである. (2)光ファイバのコア径変動はブリルアン周波数シフト変動を伴い, その変動量は一般に高次モードほど大きい. したがって, 構造揺らぎの影響を受けないでひずみの分布を高精度に測定するためには, 低次モードに着目した測定を行うのが効果的である. また, 四つの音響導波モードが存在するファイバについて, 音響導波モードごとにブリルアン周波数シフトのファイバ長手方向分布とブリルアン散乱利得を調べた. その結果, (3)一般に高次音響導波モードほど散乱利得ピークが減少すること, (4)ひずみ感度のモード依存性は小さいことなどが実験的に確認された.

A broad-area laser is injection-locked by another broad-area laser that is also injection-locked by a single-mode diode laser. Two double-phase conjugate mirrors of photorefractive BaTaO3 are used to couple the master laser beams to the first slave laser, and the first slave laser output to the second slave laser. One of the double-phase conjugate mirrors is built up with the beams from two broad-area lasers. Two slave lasers are oscillating in single longitudinal mode at 808.5 nm and the spectral width is the same as that of the master laser. Final single-mode output power from the second slave broad-area laser is 840 mW, which is limited by the power of the injection beam. This work verifies the possibility of the multistage cascaded injection locking of high-power diode lasers with phase-conjugate injection.

ニアフィールドパターンを測定することによって、2モードファイバのモードパワ分布を分析する新しい方法を提案する。この方法は、基本モードと高次モードの対称性の違いを利用している。2モードファイバに軸ずれ入射したガウシアンビームによる基本モードと高次モードの励振効率の測定に本分析方法を適用し、理論的予測とよい一致を見た。

We present quantitative interferometric measurements of thermal lensing in diode-pumped Nd:YVO4 crystals with and without laser action. When laser action was inhibited the thermal loading was increased significantly. The fraction of absorbed power deposited as heat was found to be strongly dependent on upper laser-level loss mechanisms (ie. non-radiative decay, concentration-dependant quenching and Auger recombination).

We present quantitative interferometric measurements of thermal lensing in a diode-pumped Nd:YVO4 crystal with and without laser action. The thermal loading increased by two times when laser action was inhibited, The thermal loading was strongly dependent on upper laser-level loss mechanisms (e.g., nonradiative decay, quenching, and Auger recombination).

We present the first report to the best of our knowledge of highly efficient phase conjugation in a laser-pumped polymer-dye saturable amplifier. Phase-conjugate reflectivity of as much as 210% at 560 nm has been obtained. Moreover, efficient reflectivity has been obtained in the broad wavelength region from 556 to 567 nm. (C) 1998 Optical Society of America.

光の偏光方向制御は偏光依存性を持つデバイスの特性評論やヘテロダイン検波の高効率化にとって重要である。従来、所望の偏光方向を得る為には、偏光子や1/2波長板を用いる方法がとられてきた。しかし、どちらも入射偏光方向が既知でかつ変化しないことが必要であり、入射偏光方向が揺らぐ場合には不都合を生じる。本論文は、この問題を原理的に解消する偏光前回転装置を提案する。また、種々の偏光状態の入射光に対する効果を実際に製作した装置を用いて示す。

A theoretical analysis involving ABCD ray transfer matrices is used to find the self-consistent fundamental spatial mode solutions of self-adaptive laser resonators. The resonators investigated consist of a nonlinear medium in a self-intersecting loop geometry together with a feedback output coupler mirror and additional intracavity elements. A simplified system without intracavity elements is analyzed initially, and an analytic expression for the mode solution is deduced. Addition of an intracavity lens is shown to permit enhancement of the quality of the phase-conjugation process as well as control of the mode size. The theoretical analysis is extended to model an experimental self-adaptive laser oscillator utilizing gain-grating formation in a solid state Nd:YAG laser amplifier. Good agreement is found between the theory and the experimental results. (C) 1998 Optical Society of America.

A new type of fiber Fabry-Perot interferometer buried in a fiber connector housing was proposed. The transmission spectra revealed double peaks due to birefringence in the fiber and the peak separation showed a temperature dependence as large as -7.7 MHz/deg, which was 2 orders of magnitude larger than that estimated from the thermal characteristics of its component materials.

Thermal lensing in compact neodymium yttrium aluminium garnet slabs and rods end pumped with a beam brought to a line focus has been measured using holographic lateral shearing interferometry. This powerful technique enabled us to directly measure thermal lenses with focal lengths in the range 0.02-12 m with an accuracy of 12% and good spatial resolution. It was found that the Line focused pump beam resulted in severe astigmatic thermal lensing. The measured thermal lens strongly deviated from the ideal parabolic profile along both axes, introducing an important additional consideration for laser-diode end-pumped laser resonator design. The degree of longitudinal heat flow was found to strongly influence thermal lens power. It is anticipated that results obtained from the measurement technique presented here will enable optimal design of high-power end-pumped solid-state laser cavities. (C) 1998 American Institute of Physics.

We demonstrate single-longitudinal-mode operation of a 160 mW broad-stripe laser diode (BS-LD) with 0.2 nm line-width using an external semi-linear phase conjugator. The lasing spectrum of the BS-LD was insensitive to reflectivity fluctuations of the phase conjugator and the lasing wavelength was locked at 805.5 nm to within 0.02 nm over a period of 20 min. The stability of the lasing spectrum was due to the feedback beam being incoherent with the internal radiation of the BS-LD. (C) 1998 Elsevier Science B.V.

Injection locking of a 1-W broad-area diode laser was achieved using a double phase-conjugate mirror (DPCM). The DPCM was build up for the first time using the broad-area laser beam and it coupled an elliptical-shaped beam of a single-mode master laser efficiently into a broad-area laser's slit-shaped output facet. Single longitudinal mode operation up to 550 mW output was achieved by an injection beam power of no more than 0.6% of the whole output. The lateral beam pattern was also improved and the measured M-2 value of the locked beam greatly decreased compared with that of the free-running beam. M-2 = 8 for low-power operation and M-2 = 28 for high-power operation were achieved. (C) 1998 Elsevier Science B.V.

A new technique for measuring a thermal lens, using a holographic shearing interferometer is presented. This technique was used to measure transient thermal lensing in a laser diode pumped NYAB laser. The measured thermal lensing power was proportional to the pumping laser diode intensity, with a gradient of 1.1 x 10(-1) m-l mm(2)/W. The transient response time of the thermal lens was 1.5 s, this value being consistent with the temporal decline of the second harmonic power. (C) 1997 Elsevier Science B.V.

従来のファイバ・ファブリ・ペロ・エタロンを光ファイバからの出射光に対して用いるためにはコリメート光学系を必要とし小型化に限界がある。本研究では, 小型でかつ光ファイバとの結合が容易で, 結合損失を小さくできる可能性のあるコネクタ埋め込み型ファイバ・ファブリ・ペロ・エタロン(FFPI)を提案し, その透過特性を明らかにする。さらに, 複屈折による透過周波数差の高感度温度依存性を用いた温度計測への適用可能性を示す。

A novel highly sensitive method to detect the concentration of trace gas for environmental purposes is proposed. This method includes the application of frequency modulation for stabilization of laser frequency, together with optical heterodyne measurement. The shift of resonance frequency of the Fabry-Perot cavity resonator is due to the change of refractive index, accompanied by the dispersion effect due to the presence of a target gas (e.g., methane, carbon dioxide or nitrogen dioxide) inside the Fabry-Perot cavity.

We present what is, to our knowledge, the first report of thermal effects in the laser diode (LD) pumped NYAB laser. By blocking the pump energy periodically, we investigated temporal behavior of second harmonic (SH) intensity. During the laser oscillation, the SH power decreased and its beam pattern changed from a Gaussian shape to a bell one. Under lasing conditions, the optical distortion in the NYAB crystal was analyzed using a Michelson's interferometer. At the center of the pumped region, the phase shift of the laser rod had attained 2.05 rad compared with the edge of the rod. It was proved that these temporal behaviors of the second harmonics were caused by the temperature rise of the NYAB laser rod due to the local heating of the laser crystal.

We analyzed theoretically the conversion efficiency of a second harmonic generation (SHG) in a copper vapor laser (CVL) at 510.6 nm using the beta-BaB2 O-4 crystal and the anamorphic optics. It was found that a higher conversion efficiency compared with that of a conventional spherical focus can be achieved using several anamorphic systems with different anamorphicities.

The temporal behavior of the beam divergence of a copper vapor laser (CVL) equipped with on- or off-axis unstable resonators at 510.6 nm has been investigated experimentally and theoretically. The temporal change of the beam divergence is measured using a streak camera and is evaluated by the M2 factor. Narrowing of the beam divergence during the pulse is observed. Also is found that the difference of the narrowing ratio between the on-axis and off-axis unstable resonators resulted from the near-field pattern of the laser beam.

The temporal behavior of the conversion efficiency in the second harmonic generation (SHG) of a copper vapor laser (CVL) at 510.6 nm has been investigated experimentally and theoretically. We measured the temporal change of the beam divergence using a streak camera. We observed narrowing of the beam divergence during the pulse. We also found that the narrowing ratio depends on the lasing condition. The saturation of the conversion efficiency, that is, the deviation from the square law of SHG, was caused by the delay of the narrowing of the beam divergence during the pulse at higher laser average power.

パルスレーザーにおけるコヒーレンスの成立過程を知ることはレーザー物理の見地から見て非常に興味深い．われわれは大口径パルスレーザーである銅蒸気レーザーの空間的コヒーレンスがパルス内で成長する過程を実験，理論の両面から解析した．その結果，パルス内でのコヒーレンスの時間変化は，共振器滞在時間の異なるレーザー成分が時間的に入れ替わることで引き起こされることが明らかになった．小特集 光デバイス・光工学

We analyzed the pulse shape of a copper vapor laser (CVL) beam by solving the spatio-temporal rate equations, in which the propagation of the laser light in the cavity and the spatial distribution of the population inversion density along the optical axis were taken into consideration. We found that the pulse shape was determined by the fact that the gain saturates and recovers alternatively with the transit time of the laser cavity, 10 ns. We found that the dominant part of the laser pulse changes temporally in the pulse duration with the transit time of 10 ns. Furthermore, we investigated the histories of the parts of the laser pulse which were originated by the spontaneous emission radiated at different time. The temporal change of the spatial coherence can be fully explained by the change of the dominant part in the laser beam. We obtained good agreement between the calculation and the experiment. © 1992.

We have measured the temporal change of spatial coherence of a copper vapor laser (CVL) beam with an unstable resonator by a reversal shear interferometer and a streak camera. By this method, we can evaluate the temporal change of the spatial coherence function from a single-shot measurement. We have observed stepwise increase of the coherence width at intervals equal to the transit time of the resonator. The values of the first, second and third plateaus were 5 mm, 6.7 mm and 13 mm, respectively, when an unstable resonator of magnification factor 60 was used. Moreover we have verified the result by a theoretical calculation on the basis of a passive resonator model.

We measured the temporal change of the beam divergence of a copper vapor laser using the saturable absorber DASBTI. The recovery time of the absorption of the DASBTI (approximately 50 ps) is much shorter than the temporal change of the intensity of the copper vapor laser (approximately 20 ns). In this case, the transmissivity is a linear function of the instantaneous intensity. The beam divergence can be derived from the input and output power.

We measured the spatial coherence of a copper vapour laser (CVL) beam with an unstable resonator by the reversal shear interferometer. By this method, we can evaluate the spatial coherence function from a single-shot measurement. The spatial coherence width was 5 mm when an unstable resonator with a magnification factor of 60 was used. Moreover we verified the result by the theoretical calculation on the basis of the passive resonator model.