JP2000049409A - Induction scattered light generator - Google Patents
Induction scattered light generatorInfo
- Publication number
- JP2000049409A JP2000049409A JP21362598A JP21362598A JP2000049409A JP 2000049409 A JP2000049409 A JP 2000049409A JP 21362598 A JP21362598 A JP 21362598A JP 21362598 A JP21362598 A JP 21362598A JP 2000049409 A JP2000049409 A JP 2000049409A
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- Prior art keywords
- stimulated
- scattered light
- light
- medium
- light generator
- Prior art date
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、レーザー光の生成技術
の、誘導散乱光の生成を行う装置に関するBACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for generating stimulated scattered light in a technique for generating laser light.
【０００２】[0002]
【従来の技術】従来の誘導散乱光発生器として、図５に
例を示すラマン散乱を用いて波長変換を行うストークス
光発振器や、図６に例を示すブリルアン散乱を用いた位
相共役鏡が製品として存在する。それらは、誘導散乱媒
質中に励起光を入射して誘導散乱光を発生させていた。
また、媒質は通常正の値の非線形屈折率を持っている。2. Description of the Related Art As a conventional stimulated scattered light generator, a Stokes light oscillator for performing wavelength conversion using Raman scattering as shown in FIG. 5 and a phase conjugate mirror using Brillouin scattering as shown in FIG. Exists as They generate excitation scattered light by injecting excitation light into the stimulated scattering medium.
In addition, the medium usually has a non-linear refractive index of a positive value.
【０００３】[0003]
【発明が解決しようとする課題】非線形屈折率の例とし
て電界強度の二乗に比例するものを考える。屈折率変化
をΔn、電界強度をE、非線形屈折率をn2とするとこれら
の関係は、Δn = n2|E|2の様に表される。従って、時間
的あるいは空間的に電界強度の高い部分の屈折率が増大
する。空間的にこの効果が働いた場合、励起光の強度分
布がレンズに相当する屈折率分布を引き起こし、自己集
束現象（図７）により空間的強度分布の不均一が加速す
る。パルスの時間的強度分布にこの効果が働いた場合、
パルスのピーク部分は強度が高いためその部分の速度が
低下しパルス波形が変型する自己位相変調現象（図８）
が生じる。As an example of the non-linear refractive index, consider a non-linear refractive index which is proportional to the square of the electric field strength. Assuming that the refractive index change is Δn, the electric field strength is E, and the nonlinear refractive index is n2, these relations are expressed as Δn = n2 | E | 2 . Therefore, the refractive index of the portion where the electric field strength is high temporally or spatially increases. When this effect spatially works, the intensity distribution of the excitation light causes a refractive index distribution corresponding to the lens, and the non-uniformity of the spatial intensity distribution is accelerated by the self-focusing phenomenon (FIG. 7). If this effect works on the temporal intensity distribution of the pulse,
Since the peak part of the pulse has high intensity, the speed of that part decreases, and the pulse waveform is deformed.
Occurs.
【０００４】上記の誘導散乱光発生器ではストークス光
を生成するしきい値を超えた励起光強度を実現するため
に媒質中に集光することが広く用いられている。この場
合、図９に示す様に励起光強度、あるいは媒質の非線形
屈折率の大きさによっては集光点付近で励起光は自己集
束を起こしフィラメント状になってしまう。励起光のビ
ーム強度分布の非一様性によってはフィラメントは単一
とは限らず、励起光のビーム内部の各部分で自己集束が
生じることにより局所的に強度が増し、誘導散乱光の発
生開始地点がビームの各部分でそれぞれ異なることにな
る。誘導後方ラマンストークス光発生器ではこの現象に
より得られるストークス光が多数個の短パルスに分裂し
てしまうという問題があった。In the above-mentioned stimulated scattered light generator, focusing on a medium is widely used in order to realize an excitation light intensity exceeding a threshold value for generating Stokes light. In this case, as shown in FIG. 9, depending on the intensity of the excitation light or the magnitude of the nonlinear refractive index of the medium, the excitation light is self-focused in the vicinity of the converging point and becomes a filament. Depending on the non-uniformity of the excitation light beam intensity distribution, the filament is not limited to a single filament, and self-focusing occurs in each part of the excitation light beam, which locally increases the intensity and starts the generation of stimulated scattered light. The points will be different for each part of the beam. In the stimulated backward Raman Stokes light generator, there is a problem that the Stokes light obtained by this phenomenon is split into many short pulses.
【０００５】それ故、本発明は、上記従来の誘導散乱光
発生器の問題の原因であった励起光の自己集束や自己位
相変調現象を抑制して、誘導ラマン散乱により生成され
たストークス光、また誘導ブリルアン散乱を用いて生成
された位相共役光の品質を改善することを目的としてい
る。[0005] Therefore, the present invention suppresses the self-focusing and self-phase modulation phenomenon of the excitation light, which is a cause of the above-mentioned conventional stimulated scattered light generator, to reduce the Stokes light generated by stimulated Raman scattering. It is another object of the present invention to improve the quality of phase conjugate light generated by using stimulated Brillouin scattering.
【０００６】[0006]
【課題を解決するための手段】上記従来の課題を解決す
るため本発明は、誘導散乱媒質と逆の符号の負の非線形
屈折率を持つ媒質を混合した誘導散乱光発生器を用い
る。負の非線形屈折率を得る方法の例としては、媒質の
２光子共鳴吸収準位からわずかに低いエネルギー領域で
はその媒質は負の屈折率を持つ媒質として働くことを用
いる。負の非線形屈折率を持つ媒質を、誘導散乱発振器
に用いている媒質の正の非線形屈折率を補正しうる量だ
け混合することによって、励起光の自己集束や自己位相
変調現象を抑制できる。In order to solve the above-mentioned conventional problems, the present invention uses an stimulated scattered light generator in which a medium having a negative nonlinear refractive index having a sign opposite to that of the stimulated scatter medium is mixed. An example of a method for obtaining a negative nonlinear refractive index is to use a medium that functions as a medium having a negative refractive index in an energy region slightly lower than the two-photon resonance absorption level of the medium. By mixing a medium having a negative nonlinear refractive index by an amount that can correct the positive nonlinear refractive index of the medium used for the stimulated scattering oscillator, self-focusing and self-phase modulation of the pump light can be suppressed.
【０００７】[0007]
【発明の実施の形態】図１は本発明の誘導散乱光発生器
を誘導ラマン散乱発振器に適用した例を示す。励起レー
ザー光１はラマンセル３中に凸レンズ２を用いて集光さ
れている。生成されたストークス光５は励起レーザー光
１と同じ光路を逆向きに伝搬し波長選択鏡４により分離
される。焦点付近の励起レーザー光の強度が高くなるた
めキセノンガスを混合して自己集束や自己位相変調現象
を抑制する。FIG. 1 shows an example in which the stimulated scattered light generator of the present invention is applied to a stimulated Raman scattering oscillator. The excitation laser beam 1 is condensed in the Raman cell 3 using the convex lens 2. The generated Stokes light 5 propagates in the same optical path as the pump laser light 1 in the opposite direction, and is separated by the wavelength selection mirror 4. Since the intensity of the excitation laser light near the focal point increases, xenon gas is mixed to suppress self-focusing and self-phase modulation.
【０００８】また、図２は本発明の誘導散乱光発生器を
誘導ラマン散乱増幅器に適用した例を示す。励起レーザ
ー光１は高い強度で種ストークス光７と対向する配位で
ラマンセル３中に入射されている。セル３内で励起レー
ザー光１と種ストークス光７は相互作用しその結果増幅
されたストークス光６を得る。このとき励起レーザー光
１の強度によってはラマン媒質中で自己集束や自己位相
変調現象を起こすのでキセノンガスを混合してそれを抑
制する。FIG. 2 shows an example in which the stimulated scattered light generator of the present invention is applied to a stimulated Raman scattering amplifier. The excitation laser light 1 is incident on the Raman cell 3 with a high intensity and a configuration facing the seed Stokes light 7. In the cell 3, the excitation laser light 1 and the seed Stokes light 7 interact, and as a result, an amplified Stokes light 6 is obtained. At this time, depending on the intensity of the excitation laser light 1, self-focusing or self-phase modulation occurs in the Raman medium, so that xenon gas is mixed and suppressed.
【０００９】上記の媒質を主にラマン散乱を起こすもの
から六フッ化硫黄などのブリルアン散乱を起こすものに
置き換える、あるいはブリルアン利得を増すために媒質
の圧力を上げるなど行い、出力ストークス光の分離を波
長選択鏡から偏光子などに置き換えることによって同様
に誘導ブリルアン散乱を用いて誘導散乱光発生器が構成
できる。The above-mentioned medium is mainly replaced with one that causes Brillouin scattering such as sulfur hexafluoride from one that causes Raman scattering, or the pressure of the medium is increased to increase the Brillouin gain to separate output Stokes light. By replacing the wavelength selective mirror with a polarizer or the like, an stimulated scattered light generator can be similarly configured using stimulated Brillouin scattering.
【００１０】図３に示す様にキセノンガスはKrFレーザ
ー光の波長248.4nmに相当するエネルギーよりもわずか
に小さい２光子共鳴吸収の準位（波長に換算して249.6n
m）を持つため、KrFレーザー光に対して負の非線形屈折
率を持つ媒質として働く。同様な例はネオジウムガラス
レーザーの波長1.06μmに対するセシウムなどがある。
セル中に誘導散乱を起こす媒質を充填して、そこに入射
するレーザー光の波長に対して負の屈折率を持つ媒質を
混合する。例えばメタンガスを用いて誘導ラマン散乱に
よりストークス光を得ようとする場合、メタンガスの非
線形屈折率はKrF波長(248.4nm)、１気圧当たりおよそ2.
7ｘ10-16esuあるため、レーザービームパターンの一様
性、強度、集光条件によっては非線形光学効果によりビ
ームが自己収束を起こし、得られるストークス光の発散
角、パルス波形、スペクトル広がり等の品質が劣化す
る。他のラマン散乱を起こす媒質として二酸化炭素、窒
素、酸素などがありそれぞれKrF波長における１気圧当
たりの非線形屈折率は+1.6ｘ10-14esu、+1.8ｘ10-16es
u、+7.25ｘ10-16esuとなる。一方、KrF波長に対してキ
セノンは１気圧当たり-1.8ｘ10-14esuの非線形屈折率を
持つため少量メタンガスに混合することによって自己収
束等を抑制し得られるストークス光の品質を良く保つこ
とができる。As shown in FIG. 3, xenon gas has a two-photon resonance absorption level (249.6 n in terms of wavelength) slightly smaller than the energy corresponding to the wavelength of 248.4 nm of KrF laser light.
m), it acts as a medium with a negative nonlinear refractive index for KrF laser light. A similar example is cesium for a wavelength of 1.06 μm of a neodymium glass laser.
The cell is filled with a medium that causes stimulated scattering, and a medium having a negative refractive index with respect to the wavelength of the laser light incident thereon is mixed. For example, when trying to obtain Stokes light by stimulated Raman scattering using methane gas, the non-linear refractive index of methane gas is about KrF wavelength (248.4 nm) and about 2.
Due to the 7x10 -16 esu, the beam self-focuss due to the nonlinear optical effect depending on the uniformity, intensity, and focusing conditions of the laser beam pattern, and the quality of the obtained Stokes light, such as the divergence angle, pulse waveform, and spectrum spread, is improved. to degrade. Other media that cause Raman scattering include carbon dioxide, nitrogen, and oxygen. The nonlinear refractive indexes per atmospheric pressure at the KrF wavelength are + 1.6 × 10 -14 esu and + 1.8 × 10 -16 es, respectively.
u, + 7.25 × 10 -16 esu. On the other hand, xenon has a nonlinear refractive index of -1.8 × 10 -14 esu / atm for the KrF wavelength, so that by mixing it with a small amount of methane gas, it is possible to suppress self-convergence etc. and maintain the quality of the Stokes light obtained. .
【００１１】効果を確かめるため下記の条件で予備的な
実験を行った。実験条件を以下に示す。 励起光波長 ：248.4 nm 励起光強度 ：6ｘ108 W メタンガス圧力 ：760 Torr キセノンガス圧力 ：50 Torr 集光レンズ焦点距離 ：2.0 mA preliminary experiment was conducted under the following conditions to confirm the effect. The experimental conditions are shown below. Excitation light wavelength: 248.4 nm Excitation light intensity: 6 × 10 8 W Methane gas pressure: 760 Torr Xenon gas pressure: 50 Torr Condensing lens focal length: 2.0 m
【００１２】後方誘導ラマン散乱光のパルス波形をスト
リークカメラにより計測した。自己集束によるレーザー
光の分裂は空間的に微小な領域で生じるためストリーク
カメラの時間分解性能を必要とする。図４に得られたス
トークス光のパルス波形の例を示す。メタンガスだけの
場合、数１０ピコ秒のパルス幅のストークス光が数１０
ピコ秒の間隔で２〜３個に分裂する現象が観測された
が、キセノンガスを50Torr添加することによって単一の
ストークス光パルスが得られた。このことは、メタンガ
スのみを用いた場合は自己集束現象で局所的に強度を増
した励起光がストークス光を発生させ、パルスが分裂し
ていたが、キセノンガスを添加することによって励起光
の自己集束現象を抑制することができ、単一のパルスを
得ることが可能になったことを示している。The pulse waveform of the backward stimulated Raman scattered light was measured by a streak camera. Since splitting of laser light due to self-focusing occurs in a spatially minute area, a time-resolved performance of a streak camera is required. FIG. 4 shows an example of the pulse waveform of the obtained Stokes light. In the case of only methane gas, Stokes light having a pulse width of several tens of picoseconds is several tens of seconds.
Although a phenomenon of splitting into two or three at picosecond intervals was observed, a single Stokes light pulse was obtained by adding 50 Torr of xenon gas. This means that when only methane gas was used, the excitation light locally increased in intensity due to the self-focusing phenomenon generated Stokes light, and the pulse was split. This shows that the focusing phenomenon can be suppressed and a single pulse can be obtained.
【００１３】[0013]
【発明の効果】本発明により、誘導ラマン散乱により生
成されたストークス光、また誘導ブリルアン散乱を用い
て生成された位相共役光の品質を改善することができ
る。According to the present invention, it is possible to improve the quality of Stokes light generated by stimulated Raman scattering and phase conjugate light generated by stimulated Brillouin scattering.
【図１】本発明の誘導散乱光発生器を誘導散乱発振器に
適用した例を示す。FIG. 1 shows an example in which the stimulated scattered light generator of the present invention is applied to an stimulated scatter oscillator.
【図２】本発明の誘導散乱光発生器を誘導散乱増幅器に
適用した例を示す。FIG. 2 shows an example in which the stimulated scattered light generator of the present invention is applied to an stimulated scatter amplifier.
【図３】キセノンの非線形屈折率を示す。FIG. 3 shows the nonlinear refractive index of xenon.
【図４】本発明の誘導ラマン散乱により得られたストー
クス光のパルス波形の例を示す。FIG. 4 shows an example of a pulse waveform of Stokes light obtained by stimulated Raman scattering according to the present invention.
【図５】従来の誘導散乱光発生器として、ラマン散乱を
用いて波長変換を行うストークス光発振器を示す図であ
る。FIG. 5 is a diagram showing a Stokes optical oscillator that performs wavelength conversion using Raman scattering as a conventional stimulated scattered light generator.
【図６】従来の誘導散乱光発生器として、ブリルアン散
乱を用いた位相共役鏡を示す図である。FIG. 6 is a diagram showing a phase conjugate mirror using Brillouin scattering as a conventional stimulated scattered light generator.
【図７】空間的強度分布の不均一が加速する自己集束現
象を説明するための図である。FIG. 7 is a diagram for explaining a self-focusing phenomenon in which unevenness of a spatial intensity distribution is accelerated.
【図８】パルス波形が変型する自己位相変調現象を説明
するための図である。FIG. 8 is a diagram for explaining a self-phase modulation phenomenon in which a pulse waveform changes.
【図９】自己集束による集光概形の変形を説明するため
の図である。FIG. 9 is a diagram for explaining deformation of a light-condensing schematic shape due to self-focusing.
１ 励起レーザー ２ 凸レンズ ３ ラマンセル ４ 波長選択鏡 ５ ストークス光 ６ 増幅ストークス光 ７ 種ストークス光 DESCRIPTION OF SYMBOLS 1 Excitation laser 2 Convex lens 3 Raman cell 4 Wavelength selective mirror 5 Stokes light 6 Amplified Stokes light 7 kinds Stokes light
───────────────────────────────────────────────────── フロントページの続き (72)発明者 大和田野 芳郎 茨城県つくば市梅園１丁目１番４ 工業技 術院電子技術総合研究所内 (72)発明者 桑原 研爾 茨城県つくば市梅園１丁目１番４ 工業技 術院電子技術総合研究所内 Ｆターム(参考） 5F071 AA06 AA07 DD04 5F072 AA06 AA07 AB08 KK30 PP10 QQ06 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiro Owadano 1-1-4 Umezono, Tsukuba, Ibaraki Pref. Within the Institute of Electronics and Technology (72) Inventor Kenji Kuwahara 1-1-1, Umezono, Tsukuba, Ibaraki No. 4 F-term in the Electronic Technology Research Laboratory, National Institute of Industrial Science (reference) 5F071 AA06 AA07 DD04 5F072 AA06 AA07 AB08 KK30 PP10 QQ06
Claims (7)
より誘導散乱光を発生させる誘導散乱光発生器におい
て、 前記誘導散乱媒質として、所定の値の非線形屈折率を持
つ第一の誘導散乱媒質に、該第一の誘導散乱媒質とは逆
の符号の非線形屈折率を持つ第二の誘導散乱媒質を混合
して用いることを特徴とする誘導散乱光発生器。1. An induced scattered light generator that generates stimulated scattered light by injecting excitation light into the stimulated scatter medium, wherein the stimulated scatter medium has a first stimulated scatter having a nonlinear refractive index of a predetermined value. A stimulated scattered light generator characterized in that a medium is mixed with a second stimulated scattering medium having a non-linear refractive index having a sign opposite to that of the first stimulated scattering medium.
れもラマン散乱媒質又はブリルアン散乱媒質であること
を特徴とする請求項１に記載の誘導散乱光発生器。2. The stimulated scattered light generator according to claim 1, wherein said first and second stimulated scattering media are both Raman scattering media or Brillouin scattering media.
率を持つのに対して、前記第二の誘導散乱媒質が負の非
線形屈折率を持つことを特徴とする請求項１又は２に記
載の誘導散乱光発生器。3. The method according to claim 1, wherein the first stimulated scattering field has a positive nonlinear refractive index, and the second stimulated scattering medium has a negative nonlinear refractive index. 3. The stimulated scattered light generator according to 2.
である請求項１〜請求項３のいずれかに記載の誘導散乱
光発生器。4. The stimulated scattered light generator according to claim 1, wherein the stimulated scattered light generator is an stimulated scattered oscillator.
である請求項１〜請求項３のいずれかに記載の誘導散乱
光発生器。5. The stimulated scattered light generator according to claim 1, wherein said stimulated scattered light generator is an stimulated scattered light amplifier.
を用い、かつ前記第一の誘導散乱媒質としてメタンガス
を、また前記第二の誘導散乱媒質としてキセノンガスを
用いることを特徴とする請求項１に記載の誘導散乱光発
生器。6. The method according to claim 1, wherein a KrF excimer laser beam is used as said excitation light, methane gas is used as said first stimulated scattering medium, and xenon gas is used as said second stimulated scattering medium. A stimulated scattered light generator as described.
い、かつ前記第二の誘導散乱媒質としてセシウムガスを
用いることを特徴とする請求項１に記載の誘導散乱光発
生器。7. The stimulated scattered light generator according to claim 1, wherein Nd glass laser light is used as the excitation light, and cesium gas is used as the second stimulated scattering medium.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21362598A JP2000049409A (en) | 1998-07-29 | 1998-07-29 | Induction scattered light generator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21362598A JP2000049409A (en) | 1998-07-29 | 1998-07-29 | Induction scattered light generator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2000049409A true JP2000049409A (en) | 2000-02-18 |
Family
ID=16642267
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP21362598A Pending JP2000049409A (en) | 1998-07-29 | 1998-07-29 | Induction scattered light generator |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004325584A (en) * | 2003-04-22 | 2004-11-18 | Shinetsu Quartz Prod Co Ltd | Pulse compression device and pulse compression method |
| US7106776B1 (en) * | 2003-08-01 | 2006-09-12 | Sorokin Peter P | Discharge-pumped “dressed-atom” coherent light amplifier and generators |
-
1998
- 1998-07-29 JP JP21362598A patent/JP2000049409A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004325584A (en) * | 2003-04-22 | 2004-11-18 | Shinetsu Quartz Prod Co Ltd | Pulse compression device and pulse compression method |
| JP4574953B2 (en) * | 2003-04-22 | 2010-11-04 | 信越石英株式会社 | Pulse compression apparatus and pulse compression method |
| US7106776B1 (en) * | 2003-08-01 | 2006-09-12 | Sorokin Peter P | Discharge-pumped “dressed-atom” coherent light amplifier and generators |
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