JP4052625B2

JP4052625B2 - Laser crystal manufacturing method

Info

Publication number: JP4052625B2
Application number: JP2001205069A
Authority: JP
Inventors: 高公柳谷; 秀喜八木; 仁久保; 智紀久保
Original assignee: Konoshima Chemical Co Ltd
Current assignee: Konoshima Chemical Co Ltd
Priority date: 2001-07-05
Filing date: 2001-07-05
Publication date: 2008-02-27
Anticipated expiration: 2021-07-05
Also published as: JP2003020288A

Description

【０００１】
【産業上の利用分野】
本発明は、複数の結晶を接合したレーザー結晶の製造方法に関する。
【０００２】
【従来技術】
固体レーザーの励起に伴う発熱は、レーザー結晶の機械的な歪みを引き起こし、結晶が破壊するばかりでなく、それ以前に熱複屈折効果や熱レンズ効果によるビーム品質の劣化や出力低下が生ずる為、レーザー出力を制限している。これを解消する為、Nd：YAG単結晶とYAG単結晶、Cr：アルミナ単結晶（ルビー）とアルミナ単結晶（サファイア）というように、レーザー結晶に附活剤無添加の結晶を接合することにより、放熱を促進するとともにレーザー結晶の均熱化が図られている。
【０００３】
結晶同士の接合には、光学接着剤を用いる方法やガラスを接着剤として用いる方法等の提案も有るが、接着剤やガラスは本来熱伝導性の悪いものであり十分な効果が望めないとして、米国特許第５,４４１,８０３にある拡散接合が多用されている。
【０００４】
また、レーザー結晶には非常に高度の品質が求められ、大型のレーザー用単結晶の作製は困難とされている。この対策として小さな結晶を複数個接合して大型結晶とすることも可能であり、この場合にも拡散接合は有効とされている（特開平４−２５９２６９）。
【０００５】
一方、近年の粉体技術やセラミックス技術の進歩により、光学応用可能な多結晶セラミックス（以下、多結晶体と呼ぶ）も比較的簡単に作製されるようになってきた。さらに、究極の品質を要求されるといわれるレーザー結晶としても、例えばオプトロニクス社のOPTRONICS，p168-173（2001）No.4に報告されているように、多結晶体の利用が可能となってきている。
【０００６】
多結晶体は、原料粉体を所望の形に成形して焼結すればよい。従って、複数の結晶が接合された多結晶体を得るには、目的とする複数の結晶原料を順次充填して、多層からなるセラミックス成形体を作製したのち焼結すればよいと考えられる。しかしながらこの手法では、結晶の接合界面での原料の混ざり込みが起こり易く、また、セラミックスの焼結収縮の為、各結晶の寸法精度にかける懸念が大である。従って、複数の結晶を接合してなるレーザー結晶の作製には、上記の拡散接合を用いるしかないのが現状である。
【０００７】
【発明が解決しようとする課題】
拡散接合では、光学研磨された結晶同士をオプティカルコンタクトさせた後に、結晶格子の再配列が起こる温度まで加熱して接合する。オプティカルコンタクトでは、接触面にレーザー波長域での輝点や散乱点が生じないように、２つの結晶を正確にコンタクトさせることが必要で、オプティカルコンタクトが可能な研磨は非常に高価となり、その産業応用を困難なものとしている。またオプティカルコンタクトを必要とするため、その接合面の形状は平面に限られている。この為、形状にとらわれない、安価な接合方法ならびに接合体が望まれている。
【０００８】
【課題を解決する為の手段】
本発明者らは上記問題を解決する為種々検討した結果、単結晶ないし多結晶体と多結晶の鋳込み成形体の自由面とを組み合わせた後に、ないしは多結晶の鋳込み成形体の自由面同士を組み合わせた後に焼結することにより、光学的に問題の無い接合体の作製が可能であることを見出し、本発明を完成した。
すなわち、本発明は、鋳込み成形体の成形時の自由面を接合面とし、この接合面を他の結晶の表面に接触させて焼結することにより、成形体を焼結して多結晶体とし、同時に多結晶体の接合面を他の結晶と接合する、レーザー結晶の製造方法にある。
好ましくは、鋳込み成形を排泥鋳込み成形とし、かつ前記自由面を鋳込み成形時に型に接触しない面とする。
特に好ましくは、円筒状の鋳込み成形体の内周面を自由面とし、レーザーロッドを鋳込み成形体の内周面に挿入し、鋳込み成形体をレーザーロッドと共に焼結して、鋳込み成形体の内周面をレーザーロッドの側面に接合する。
この明細書で鋳込み成形時の自由面は、鋳込み成形を行った際に型などに接触しない面を言い、例えば排泥面などが自由面である。
【０００９】
レーザー結晶は例えば固体レーザーのレーザーロッドとし、好ましくは附活剤（発振用不純物）を含んだ単結晶ロッドの端面や側面（周面）に、附活剤の含有量がより少ない、もしくは実質的に附活剤を含まない多結晶体を接合する。附活剤は、例えばYAGやY2O3の場合のネオジウムや、アルミナの場合のクロム等である。従来例では、接合面に散乱点等を生じずに単結晶ロッドの側面に多結晶体を接合することは不可能であるが、この発明では接合面が平面に限られないので、単結晶ロッドの側面に多結晶体を接合することもできる。また接合面にはオプティカルコンタクトが得られる程の研磨が必要でないので、接合が容易になる。
【００１０】
【発明の実施の形態】
実施例の複数の結晶を接合してなるレーザー結晶は、鋳込み成形体の自由面を接合面として用いて作製する。接合する結晶の組み合わせとしては、
（1）単結晶体ないしは多結晶体と多結晶の鋳込み成形体の自由面、あるいは
（2）多結晶の鋳込み成形体の自由面同士、の2通りがある。
【００１１】
まず、（1）の単結晶体ないしは多結晶体と鋳込み成形体の自由面との組み合わせにより、接合結晶を作成する方法について説明する。（2）の鋳込み成形体の自由面同士による接合では、単結晶ないし多結晶体のラップ面を鋳込み成形体の自由面で置き換えればよい。
【００１２】
単結晶体ないし多結晶体の接合面は、Ｒmaxが５μｍ以下となるまでラッピングしておくのが好ましく、２μｍ以下がより好ましく、０.５μｍ以下が最も好ましい。これ以上大きな場合にはセラミックスの焼結力をもってしても、結晶とセラミックスとの間に形成される空孔を取り除くことが出来ず、最終的に接合面にポアとして取り残され、光散乱の原因となる。
【００１３】
結晶に接合するセラミックスの材質は、基本的に結晶と同材質が好ましい。焼結により接合が完了するが、冷却時に熱膨張率の差に基づき接合界面に応力が働き、結果として接合後の結晶全体に歪みが生じて、透過波面に乱れが生じることになる。ただしイットリアとYAGのように熱膨張率が酷似している場合には問題無い。この種の制限は、拡散接合による場合と同等である。そして好ましくは、レーザーロッドが不純物含有量の高い単結晶のロッドで、その端面または側面に多結晶で不純物含有量が少ない、もしくはゼロのセラミックスを接合する。
【００１４】
接合に用いる成形体は、鋳込み成形により作製する。鋳込み成形には固形鋳込み方式と排泥鋳込み方式とが有るが、自由面が必要な為、排泥鋳込み方式を採用する。鋳込み成形に使用する泥漿は水系でも非水系でもよいが、水系の場合には通常の鋳込み成形で用いられる溶媒吸収性の型としての石膏型は使用しない方が好ましい。媒液として使用している水に石膏が溶解して、成形体中に石膏が混入し、光学特性に優れた多結晶体が得られなくなる。石膏を型として用いる場合にはアルコール系の泥漿が、また、水系の泥漿を用いる場合には溶媒吸収性の型として樹脂型やセラミックスの素焼き状態等にみられる多孔質セラミックスが推奨される。
【００１５】
実際の接合操作の例として、レーザーロッドとしてよく用いられる形状である単結晶円柱状結晶の、側面または端面に多結晶体を接合する方法について説明する。
【００１６】
側面に多結晶体を接合する場合には、セラミック成形体としてパイプを作製する。まず、溶媒吸収性の型に必要寸法の穴を貫通させてあけ、下部を閉じておく。この穴に作製しようとするセラミックスの泥漿を流し込み、、しばらく放置して着肉させる。目的とする肉厚まで着肉が起こった時点で下部を開放し、残っている泥漿を排泥する。これによってパイプ内面は排泥面となる。
【００１７】
乾燥機中でしばらく放置することにより、乾燥収縮により型から成形体が離れ、成形体を取り出すことが可能となる。このようにして得られた成形体に直接結晶を挿入して脱脂さらに焼結を行なうか、あるいは成形体は傷つき易いため、成形体のみで脱脂を行い、強度を持たせた後に結晶を挿入して焼結する。結晶とセラミック成形体を組み合わせた後、透光性セラミックスを得る為の通常の焼結を行なうことにより、レーザー品質の接合結晶が得られる。
【００１８】
結晶とセラミックパイプ成形体（鋳込み成形体）の外径及び内径の関係は、セラミック成形体の焼結による収縮量によって決める。焼結後にセラミックパイプの内径が結晶の外径よりも小さくなるようにすればよい。小さくなりすぎる場合には、セラミックスの破壊が考えられるが、驚くべきことに通常レーザーロッドとして用いられている１０ｍｍΦ程度の結晶へのセラミックスの接合では、結晶の外径と焼結前のセラミックパイプ成形体の内径とがほぼ同じであっても、焼結時に破壊に至ることはない。この現象により、結晶の外径寸法精度やセラミック成形体の内径寸法精度は、非常に自由度の高いものとなる。
【００１９】
次に円柱状結晶の端面に多結晶体を接合する方法を説明する。セラミック成形体は、焼結後に必要厚み以上のものとなる板材を用意すればよい。鋳込み成形により作製するのであれば手法に制限はないが、溶媒吸収性の型材の上に泥漿貯留部として塩ビパイプや硝子管等を切断したリングを乗せ、これに泥漿を注ぎ込んで成形し、自由面を得るのが最も簡単であろう。この成形法では、必要厚み分の泥漿しか用いない場合には特に排泥する必要はない。自由面は鋳込み成形時に型に接触しない表面のことで、排泥面は自由面であり、手法的に考えて排泥面と自由面に差異はない。
【００２０】
セラミック成形体は前述のごとく、直接結晶体と組み合わせて脱脂、焼結を行なってもよいが、結晶体との接合前に脱脂を済ませて初期的強度を与え、特に結晶との擦り合わせで傷が付かない程度に加熱処理しておくのが好ましい。
【００２１】
セラミック成形体の自由面と結晶とを組み合わせ、焼結して接合が完了する。この際、焼成炉中で接合する結晶と成形体とを上下に重ねて配置するのが、焼成中の接合面のズレ等を防止するのに好適である。
【００２２】
焼成中に接合面に圧縮加重をかける手法が有効である。結晶の接合面の平坦度として、通常のラッピングが行われるならば３μｍ程度の面は簡単に得られる。この程度の平坦度であれば、セラミックスの焼成途上での変形により、セラミックスが結晶に倣う形で結晶とセラミックスとの間の空間が吸収され、完全な光学接合が可能である。通常のレーザー結晶の取り扱いではまずありえないが、仮にこれ以上の大きな平坦度の差があっても荷重を掛けることにより５０μｍ程度までは許容される。荷重の許容範囲は無荷重から、セラミック成形体の破壊荷重までである。
【００２３】
以上の説明の通り、本願発明によれば、現在結晶の接合方法として広く用いられている拡散接合に比較して、非常に簡単に接合結晶を作製することが可能となる。この理由は定かでないが、鋳込み成形体の自由面では、その表面粗さとして原料粒子数個分の乱れしかなく、またこの乱れは焼結途上におけるセラミックスの変形により吸収されてしまう為と考えられる。
【００２４】
【実施例】
実施例１
硝酸イットリウム水溶液と硝酸アルミニウム水溶液とをYAG組成となる様に混合し、水を加えて、YAG換算で０.００３mol/Lの酸性水溶液１０００Ｌとした。これにモル比で金属イオン濃度の１４.５倍量の尿素並びに１.６倍量の濃硫酸をそれぞれ添加し、また焼結助剤としてコロイダルシリカをYAGに対して酸化物換算で４００ｗｔｐｐｍとなるように加えた後、１００℃に加熱して撹袢下３時間反応させ沈殿を生成させた。反応後、３５℃まで冷却し、ろ過、水洗を６回繰り返した後に１５０℃で１２時間乾燥した。この沈澱を１２００℃で３時間仮焼することにより、TEMおよびSEMでの観察で平均一次粒子径０.２μｍ、二次粒子径０.３μｍのYAG粉末が得られた。
【００２５】
この粉末１kgに媒液として純水を２５０g、分散剤としてＡ−６１１４（東亜合成化学、ポリカルボン酸系、Ａ−６１１４は東亜合成化学の商品名）を純分換算で０.５ｗｔ％、更にバインダーとしてＷＦ−８０４（中京油脂社製、ポリビニルアルコール系、ＷＦ−８０４は中京油脂社の商品名）を０.５ｗｔ％添加して、一昼夜ボールミル粉砕ならびに混合を行い、鋳込み用泥漿を得た。
この泥漿を、泥漿貯留部として塩ビ製リングを乗せた素焼き状態の多孔質アルミナ板上に注ぎ込み、１日放置した後、６０℃の乾燥機中で１日、更に１２０℃の乾燥機で１日乾燥し、１０５Φ×５ｍｍｔの成形体７個を得た。なおこの明細書で、Φは直径をｍｍ単位で表す。
【００２６】
実施例２
実施例１で得られた成形体から、１０×１０×５ｍｍｔの成形体７０個を切出し、毎時２５℃の速度で昇温した後、１１００℃で５時間熱処理して脱脂した。熱処理後、２５個を１０−１Pa以下の真空度のもと、１８００℃で１０時間焼結して、透光性YAGセラミックスを得た。上下面を平行度１０秒で鏡面研磨した後、フィゾー干渉計で透過波面を観察したが、歪みは観察されなかった。
【００２７】
実施例３
実施例２で作製した焼結体の片面をSiCの遊離砥粒を用いて、Ｒmax１０.１、４.８、２.２、０.４５μmの各面粗さに５個ずつラップした。何れの試料の平坦度も約１μｍであった。このラップ面と、同じく実施例２で作製し熱処理した成形体の自由面とを向かい合わせに組み合わせて、真空炉にセットし焼結した。焼結体は接合面と向かい合う２面を平行度８から１０秒で鏡面に研磨し、肉眼で接合状態を確認したところ、何れの接合面も全面が接合されていた。Ｈｅ-Ｎｅレーザーを透過させて接合面に存在する散乱点（空隙、気孔）を観察し、更に透過波面の乱れも確認した。結果を表１に示す。
【００２８】
【表１】

【００２９】
ここでは脱脂済み板状の鋳込み成形体の自由面を、焼結後の鋳込み成形体に接合したが、実際の応用では、レーザーロッド、例えば単結晶レーザーロッド、の両端面に未焼結で脱脂済みの鋳込み成形体の自由面を接触させて、焼結することが好ましい。
【００３０】
比較例１
焼結体のラップ面（Ｒmax０.４５μｍ、平坦度１μｍ）と組み合わせる熱処理した成形体の面を、成形時にアルミナ型に向かい合った面（５個）ないしはカットした後旋盤で上仕上げした加工面（５個）とした以外は、実施例３と同様にして接合結晶を作製した。接合結晶の接合面と向かい合う２面を鏡面に研磨し、肉眼で接合状態を確認したところ、何れの接合面も全面が接合されていた。次いで５ｍＷのＨｅ-Ｎｅレーザーを透過させて接合面でのレーザー光散乱点を観察すると、全数に多数の散乱輝点が存在した。
【００３１】
比較例２
Ｒmax０.４５μm、平坦度０.８μｍにラップした焼結体のラップ面同士を組み合わせ、実施例３と同様に真空下１８００℃で熱処理した。接合面の面積のうち約２０％が接合されていなかった。
【００３２】
実施例４
８Φ×２０５ｍｍの０.６％Nd:YAG単結晶レーザーロッドから約１０ｍｍ長さの試料を１０個切出し、端面をＲmax０.４５μm、平坦度０.９μｍにラップした。このラップ面と、実施例２で作製した熱処理した成形体の自由面とを向かい合わせに組み合わせたものを５セット用意し、真空炉にセットして焼結した。結晶体は接合面と向かい合う２面を平行度８から１０秒で鏡面に研磨し、肉眼で接合状態を確認したところ、何れの接合面も単結晶側の全面が接合されていた。この面に５ｍＷ出力のＨｅ-Ｎｅレーザーを透過させて接合面に存在する散乱点（空隙、気孔）を観察したが、全く認められなかった。
【００３３】
比較例３
焼結体の替わりに実施例４で用意した８Φ×１０ｍｍの単結晶試料を用いた以外は比較例２と同様にして、単結晶の接合結晶を作製した。接合面の面積のうち約５０％が接合されていなかった。
【００３４】
実施例５
実施例１と同様にして作製したYAG原料粉末１０００ｇに、媒液として６６７ｇのエタノール、分散剤としてＥ−５０３（中京油脂社製、ポリカルボン酸系，Ｅ−５０３は中京油脂社の商品名）０.５ｗｔ％、バインダーとしてＰＶＢ−ＢＬ１（積水化学社製、ポリビニルアルコール系，ＰＶＢは積水化学の商品名）１ｗｔ％を添加して、１日ボールミルにて粉砕・混合して泥漿を得た。この泥漿を、あらかじめ１１.５Φ×７５ｍｍの貫通穴をあけたのち再度底部を塞いでおいた石膏型に流し込み、着肉厚みが１ｍｍになるまで放置した。目的の着肉厚みに達した後、残っている泥漿を石膏型の底部を開けて排泥した。こうして得られた成形体を乾燥することにより、内径９Φ−外径１１Φ−長さ７０ｍｍのYAGセラミックス成形体が得られた。
【００３５】
この成形体に傷を付けないよう十分に注意して、８Φ×５０ｍｍ長さのNd：YAG単結晶を内部に挿入した。この後、大気中で毎時２５℃の速度で１１００℃まで昇温し、この温度で５時間保持して十分に脱脂した。脱脂処理後、１０−１Pa以下の真空度のもと、１８００℃で１０時間焼結して透光性YAGセラミックス−Nd：YAG単結晶のロッド状接合結晶を得た。両端面を鏡面研磨した後、この面に５ｍＷ出力のＨｅ-Ｎｅレーザーを透過させて接合面に存在する散乱点（空隙、気孔）を観察したが、全く認められなかった。
【００３６】
比較例４
実施例５と同様にして作製した泥漿からスプレードライヤーを用いてＣＩＰ（冷間静水圧）成形に用いる顆粒を得た。この顆粒を用いてＣＩＰ成形によりパイプ状成形体を作製した以外は実施例５と同様にして接合結晶を作製した。両端面を鏡面研磨して接合面の状態を肉眼で確認したところ、明らかに単結晶外周にそって気孔が存在すると判断できる白いリングが認められた。
【００３７】
実施例６
硝酸イットリウム、尿素、硫酸アンモニウムならびに硝酸アルミニウムを、濃度がそれぞれ、[ Ｙ(NO３)３ ] = ０.２５ mol/L、[ Urea ] = １.５ mol/L、 [(NH４)２SO４ ] = ０.２５ mol/L、及び[ Al(NO３)３ ] = ６.７×１０-５ mol/Lとなる様に純水で溶解した。次に、該混合液１０Ｌをオートクレーブに入れ、温度を１２５℃、圧力を５×１０^５ Paにそれぞれ調節し、２時間保持してイットリウムの炭酸塩の沈殿を得た。得られた沈殿物の濾過洗浄を、５回繰り返し行い、１１０℃で２４時間乾燥した。次に、この乾燥粉をアルミナるつぼにて大気雰囲気で１２００℃，３時間仮焼して易焼結性イットリア粉末を得た。得られたイットリア原料粉末２００gに対して解膠剤として中京油脂製E−５０３とF−２１９(アミン系)を１２g及び４g添加し、更にバインダーとして積水化学製PVB-BL１を１g添加して、エタノール５０gと共にナイロンポット及びナイロンボールを用いて１２時間混合し、アルコールスラリーとした。
【００３８】
このアルコールスラリーを石膏型に流し込み、６０mm×６０mm×５mmの成形体を得た。この成形体から１０×１０×５ｍｍの成形体を２０個切出した。このうち５個を、毎時２５℃で昇温して１１００℃で５時間充分に脱脂した後、真空炉にて１６５０℃の温度で５時間焼結した。この際、昇温速度は１００℃／ｈｒ、真空度は１０-１Pa以下とした。こうして得られた焼結体の一端面をＲmax０.４５μｍ、平坦度０.８μｍにラップした。このラップ面と成形体の自由面とを組み合わせたもの５セットと、成形体の自由面同士を組み合わせたもの５セットとを再度、毎時２５℃で昇温して１１００℃で５時間充分に脱脂した後、真空炉にて１６５０℃の温度で５時間焼結した。この際、成形体の自由面同士を組み合わせたものは、脱脂時イットリア焼結体を５×１０^３Ｐａの荷重となるように乗せた。
【００３９】
得られた結晶体は、接合面と向かい合う２面を平行度８から１０秒で鏡面に研磨し、肉眼で接合状態を確認したところ、何れの接合面も全面が接合されていた。Ｈｅ-Ｎｅレーザーを透過させて接合面に存在する散乱点（空隙、気孔）を観察し、更に透過波面の乱れも確認したが、光学結晶として全く問題の無い物であった。[0001]
[Industrial application fields]
The present invention relates to a process for producing a laser crystal by joining a plurality of crystals.
[0002]
[Prior art]
The heat generated by the excitation of the solid-state laser causes mechanical distortion of the laser crystal, which not only destroys the crystal, but also degrades the beam quality and decreases the output due to the thermal birefringence effect and thermal lens effect before that. The laser output is limited. In order to solve this problem, Nd: YAG single crystal and YAG single crystal, Cr: alumina single crystal (ruby) and alumina single crystal (sapphire) are joined to the laser crystal without adding an activator. In addition, heat dissipation is promoted and soaking of the laser crystal is achieved.
[0003]
There are proposals such as a method using an optical adhesive and a method using glass as an adhesive for bonding between crystals, but the adhesive and glass are inherently poor in thermal conductivity, and sufficient effects cannot be expected. Diffusion bonding in US Pat. No. 5,441,803 is frequently used.
[0004]
Laser crystals are required to have a very high quality, and it is difficult to produce a large single crystal for laser. As a countermeasure, it is possible to join a plurality of small crystals to make a large crystal. In this case, diffusion bonding is also effective (Japanese Patent Laid-Open No. 4-259269).
[0005]
On the other hand, with recent advances in powder technology and ceramic technology, polycrystalline ceramics (hereinafter referred to as polycrystals) that can be optically applied have been relatively easily produced. Furthermore, as a laser crystal that is said to require the ultimate quality, for example, as reported in OPTRONICS of Optronics, p168-173 (2001) No. 4, it has become possible to use polycrystals. Yes.
[0006]
The polycrystalline body may be sintered by forming the raw material powder into a desired shape. Therefore, in order to obtain a polycrystalline body in which a plurality of crystals are bonded, it is considered that a plurality of target crystal raw materials are sequentially filled to produce a multilayer ceramic molded body and then sintered. However, in this method, the raw materials are likely to be mixed at the crystal bonding interface, and there is a great concern about the dimensional accuracy of each crystal due to sintering shrinkage of the ceramic. Therefore, the present situation is that the above-mentioned diffusion bonding can only be used to manufacture a laser crystal formed by bonding a plurality of crystals.
[0007]
[Problems to be solved by the invention]
In diffusion bonding, optically polished crystals are optically contacted and then heated to a temperature at which crystal lattice rearrangement occurs and bonded. In optical contact, it is necessary to contact two crystals accurately so that no bright spot or scattering point in the laser wavelength region is generated on the contact surface. Polishing capable of optical contact is very expensive, and the industry Application is difficult. Further, since an optical contact is required, the shape of the joint surface is limited to a flat surface. For this reason, an inexpensive joining method and joined body that are not restricted by the shape are desired.
[0008]
[Means for solving the problems]
As a result of various studies to solve the above problems, the present inventors have determined that after combining a single crystal or a polycrystalline body and a free surface of a polycrystalline cast molding, or between the free surfaces of a polycrystalline cast molding. It was found that a joined body having no optical problem can be produced by sintering after combining, and the present invention was completed.
That is, the present invention uses a free surface at the time of molding of a cast molded body as a joint surface, and the joint surface is brought into contact with the surface of another crystal to sinter, thereby sintering the molded body into a polycrystalline body. , bonding the bonding surface of the polycrystalline body and another crystal simultaneously, Ru manufacturing method near the laser crystal.
Preferably , the casting is a waste mud casting, and the free surface is a surface that does not contact the mold during casting.
Particularly preferably, the inner peripheral surface of the cylindrical cast molded body is a free surface, the laser rod is inserted into the inner peripheral surface of the cast molded body, and the cast molded body is sintered together with the laser rod. Join the circumference to the side of the laser rod.
In this specification, the free surface at the time of casting molding refers to a surface that does not come into contact with a mold or the like when casting molding is performed, and for example, a drainage surface is a free surface.
[0009]
The laser crystal is, for example, a laser rod of a solid laser, and preferably contains less or substantially no activator on the end face or side surface (circumferential surface) of the single crystal rod containing the activator (oscillation impurity). A polycrystal which does not contain an activator is joined. The activator is, for example, neodymium in the case of YAG or Y2O3, or chromium in the case of alumina. In the conventional example, it is impossible to bond a polycrystalline body to the side surface of a single crystal rod without causing a scattering point or the like on the bonded surface. However, in this invention, the bonded surface is not limited to a flat surface. A polycrystalline body can be bonded to the side surface of the substrate. Further, since the bonding surface does not need to be polished enough to obtain an optical contact, the bonding becomes easy.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The laser crystal formed by bonding a plurality of crystals of the example is manufactured using the free surface of the cast molded body as the bonding surface. As a combination of crystals to be joined,
There are two ways: (1) the free surface of a single crystal or a polycrystalline body and a polycrystalline cast molding, or (2) the free surfaces of a polycrystalline cast molding.
[0011]
First, a method for producing a bonded crystal by combining the single crystal or polycrystal of (1) and the free surface of the cast molded body will be described. In the joining between the free surfaces of the cast molded body (2), the lap surface of the single crystal or polycrystalline body may be replaced with the free surface of the cast molded body.
[0012]
The bonding surface of the single crystal body or polycrystal body is preferably lapped until Rmax is 5 μm or less, more preferably 2 μm or less, and most preferably 0.5 μm or less. If it is larger than this, even if it has the sintering power of ceramics, the voids formed between the crystal and the ceramics cannot be removed and eventually left as a pore on the joint surface, causing light scattering. It becomes.
[0013]
The material of the ceramic bonded to the crystal is basically preferably the same material as the crystal. Joining is completed by sintering, but stress acts on the joining interface based on the difference in coefficient of thermal expansion during cooling, resulting in distortion of the entire crystal after joining and disturbance of the transmitted wavefront. However, there is no problem if the coefficients of thermal expansion are very similar, such as yttria and YAG. This kind of restriction is equivalent to that by diffusion bonding. Preferably, the laser rod is a single crystal rod having a high impurity content, and a polycrystalline ceramic with a low impurity content or zero is bonded to the end face or side face thereof.
[0014]
The compact used for joining is produced by casting. There are a solid casting method and a waste mud casting method for casting, but since a free surface is required, the waste mud casting method is adopted. The slurry used for casting may be aqueous or non-aqueous, but in the case of aqueous, it is preferable not to use a gypsum mold as a solvent-absorbing mold used in ordinary casting. The gypsum dissolves in the water used as the liquid medium, and gypsum is mixed into the molded body, so that a polycrystalline body having excellent optical properties cannot be obtained. When gypsum is used as a mold, alcohol-based mud is recommended, and when water-based mud is used, porous ceramics that can be seen in a resin mold or an unglazed state of ceramics are recommended as solvent-absorbing molds.
[0015]
As an example of actual bonding operation, a method of bonding a polycrystalline body to the side surface or end surface of a single crystal columnar crystal having a shape often used as a laser rod will be described.
[0016]
When joining a polycrystalline body to a side surface, a pipe is produced as a ceramic molded body. First, a hole having a required size is made to penetrate through a solvent-absorbing mold, and the lower part is closed. Pour the slurry of ceramic to be made into this hole and leave it for a while to make it thick. When inking reaches the desired thickness, the lower part is opened and the remaining mud is drained. As a result, the inner surface of the pipe becomes a mud discharge surface.
[0017]
By leaving it in the dryer for a while, the molded body is separated from the mold by drying shrinkage, and the molded body can be taken out. Degreasing and sintering are performed by directly inserting crystals into the molded body thus obtained, or since the molded body is easily damaged, degreasing is performed only with the molded body, and after adding strength, crystals are inserted. And sinter. After combining the crystal and the ceramic molded body, a laser-quality bonded crystal can be obtained by performing ordinary sintering to obtain a translucent ceramic.
[0018]
The relationship between the outer diameter and the inner diameter of the crystal and the ceramic pipe molded body (casting molded body) is determined by the amount of shrinkage due to sintering of the ceramic molded body. The inner diameter of the ceramic pipe may be made smaller than the outer diameter of the crystal after sintering. If it becomes too small, the ceramic may be destroyed. Surprisingly, in the joining of ceramics to a crystal of about 10mmΦ, which is usually used as a laser rod, the outer diameter of the crystal and ceramic pipe formation before sintering Even if the inner diameter of the body is almost the same, destruction does not occur during sintering. Due to this phenomenon, the outer diameter dimensional accuracy of the crystal and the inner diameter dimensional accuracy of the ceramic molded body are very high.
[0019]
Next, a method for joining a polycrystalline body to the end face of a columnar crystal will be described. As the ceramic molded body, a plate material having a thickness greater than the necessary thickness after sintering may be prepared. The method is not limited as long as it is made by casting, but a ring that cuts a PVC pipe or a glass tube as a slurry storage part is placed on a solvent-absorbing mold material, and slurry is poured into the mold to form it freely. It would be easiest to get a plane. In this molding method, it is not particularly necessary to discharge mud when only the necessary amount of slurry is used. The free surface is a surface that does not come into contact with the mold at the time of casting, and the drainage surface is a free surface.
[0020]
As described above, the ceramic molded body may be degreased and sintered directly in combination with the crystal body. However, before bonding with the crystal body, the ceramic body is degreased to give initial strength, and in particular, it is scratched by rubbing with the crystal. It is preferable to heat-treat to such an extent that no sticking occurs.
[0021]
The free surface of the ceramic molded body and the crystal are combined and sintered to complete the joining. At this time, it is preferable to dispose the crystals to be joined in the firing furnace and the molded body so as to be stacked one above the other in order to prevent misalignment of the joining surface during firing.
[0022]
It is effective to apply a compression load to the joint surface during firing. As the flatness of the crystal bonding surface, a surface of about 3 μm can be easily obtained if normal lapping is performed. With this level of flatness, the space between the crystal and the ceramic is absorbed in such a manner that the ceramic follows the crystal due to deformation during the firing of the ceramic, and complete optical joining is possible. Although it is unlikely to be handled by ordinary laser crystals, even if there is a greater difference in flatness than this, up to about 50 μm is allowed by applying a load. The allowable load range is from no load to the breaking load of the ceramic molded body.
[0023]
As described above, according to the present invention, it is possible to manufacture a bonded crystal very easily as compared with diffusion bonding that is widely used as a method for bonding crystals at present. The reason for this is not clear, but on the free surface of the cast molded body, there is only a disorder of several raw material particles as the surface roughness, and this disorder is absorbed by the deformation of the ceramics during sintering. .
[0024]
【Example】
Example 1
An aqueous yttrium nitrate solution and an aqueous aluminum nitrate solution were mixed so as to have a YAG composition, and water was added to make 1000 L of an acidic aqueous solution of 0.003 mol / L in terms of YAG. To this, urea of 14.5 times the metal ion concentration and 1.6 times of concentrated sulfuric acid are added in molar ratio, and colloidal silica as a sintering aid is 400 wtppm in terms of oxide with respect to YAG. Then, the mixture was heated to 100 ° C. and reacted for 3 hours with stirring to form a precipitate. After the reaction, the mixture was cooled to 35 ° C., filtered and washed with water six times, and then dried at 150 ° C. for 12 hours. This precipitate was calcined at 1200 ° C. for 3 hours to obtain a YAG powder having an average primary particle size of 0.2 μm and a secondary particle size of 0.3 μm as observed by TEM and SEM.
[0025]
To 1 kg of this powder, 250 g of pure water as a liquid, A-6114 (Toa Synthetic Chemical, polycarboxylic acid type, A-6114 is a trade name of Toa Synthetic Chemical) as a dispersant, 0.5 wt% in terms of pure content, and As a binder, WF-804 (manufactured by Chukyo Yushi Co., Ltd., polyvinyl alcohol type, WF-804 is a trade name of Chukyo Yushi Co., Ltd.) was added at 0.5 wt%, and ball milling and mixing were performed all day and night to obtain a slurry for casting.
This slurry is poured onto an unglazed porous alumina plate on which a vinyl ring is placed as a slurry storage part, and left for 1 day, then in a 60 ° C. dryer for 1 day, and further in a 120 ° C. dryer for 1 day. It dried and obtained seven compacts of 105Φ × 5 mmt. In this specification, Φ represents the diameter in mm.
[0026]
Example 2
70 molded bodies of 10 × 10 × 5 mmt were cut out from the molded body obtained in Example 1, heated at a rate of 25 ° C. per hour, and then heat treated at 1100 ° C. for 5 hours for degreasing. After the heat treatment, 25 pieces were sintered at 1800 ° C. for 10 hours under a vacuum degree of 10 −1 Pa or less to obtain translucent YAG ceramics. After the upper and lower surfaces were mirror-polished with a parallelism of 10 seconds, the transmitted wavefront was observed with a Fizeau interferometer, but no distortion was observed.
[0027]
Example 3
One side of the sintered body produced in Example 2 was lapped on each surface roughness of Rmax 10.1, 4.8, 2.2, 0.45 μm using SiC free abrasive grains. The flatness of any sample was about 1 μm. This lap surface was combined with the free surface of the molded body produced and heat-treated in the same manner as in Example 2, and set in a vacuum furnace and sintered. The sintered body was polished to a mirror surface on two surfaces facing the bonding surface at a parallelism of 8 to 10 seconds, and the bonding state was confirmed with the naked eye. All of the bonding surfaces were bonded together. The scattering points (voids and pores) present on the bonding surface were observed by transmitting a He—Ne laser, and the disturbance of the transmitted wavefront was also confirmed. The results are shown in Table 1.
[0028]
[Table 1]

[0029]
Here, the free surface of the degreased plate-like cast molded body is joined to the sintered cast molded body. However, in actual application, both ends of a laser rod such as a single crystal laser rod are unsintered and degreased. It is preferable to sinter by bringing the free surface of the cast molding into contact with each other.
[0030]
Comparative Example 1
The surface of the heat-treated molded body combined with the lapping surface (Rmax 0.45 μm, flatness 1 μm) of the sintered body is the surface facing the alumina mold at the time of molding (5 pieces) or the machined surface finished with a cut lathe (5 A bonded crystal was produced in the same manner as in Example 3 except that the above was used. Two surfaces facing the bonding surface of the bonding crystal were polished to a mirror surface, and the bonding state was confirmed with the naked eye. As a result, all the bonding surfaces were bonded together. Next, when a laser light scattering point on the bonding surface was observed through a 5 mW He—Ne laser, a large number of scattered bright spots existed in the total number.
[0031]
Comparative Example 2
The lap surfaces of the sintered bodies wrapped to Rmax 0.45 μm and flatness 0.8 μm were combined and heat-treated at 1800 ° C. under vacuum in the same manner as in Example 3. About 20% of the area of the joint surface was not joined.
[0032]
Example 4
Ten samples having a length of about 10 mm were cut out from an 8Φ × 205 mm 0.6% Nd: YAG single crystal laser rod, and the end face was wrapped to Rmax 0.45 μm and flatness 0.9 μm. Five sets of this lap surface combined with the free surface of the heat-treated molded body produced in Example 2 were prepared so as to face each other, set in a vacuum furnace, and sintered. As for the crystal, the two surfaces facing the bonding surface were polished to a mirror surface with a parallelism of 8 to 10 seconds, and the bonding state was confirmed with the naked eye. As a result, all the bonding surfaces were bonded to the single crystal side. A scattering point (voids and pores) existing on the bonding surface was observed by transmitting a He—Ne laser having a power of 5 mW through this surface, but no scattering point was observed.
[0033]
Comparative Example 3
A single crystal bonded crystal was produced in the same manner as in Comparative Example 2 except that the 8Φ × 10 mm single crystal sample prepared in Example 4 was used instead of the sintered body. About 50% of the area of the joint surface was not joined.
[0034]
Example 5
YAG raw material powder produced in the same manner as in Example 1, 1000 g, 667 g of ethanol as a medium, E-503 as a dispersant (manufactured by Chukyo Yushi Co., Ltd., polycarboxylic acid type, E-503 is a trade name of Chukyo Yushi Co., Ltd.) 0.5 wt% of PVB-BL1 (Sekisui Chemical Co., Ltd., polyvinyl alcohol type, PVB is a trade name of Sekisui Chemical) as a binder was added at 1 wt%, and pulverized and mixed in a ball mill for 1 day to obtain a slurry. This slurry was poured into a plaster mold having a 11.5Φ × 75 mm through-hole in advance and then closed at the bottom, and left until the thickness of the wall reached 1 mm. After reaching the desired thickness, the remaining mud was drained by opening the bottom of the plaster mold. By drying the molded body thus obtained, a YAG ceramic molded body having an inner diameter of 9Φ, an outer diameter of 11Φ, and a length of 70 mm was obtained.
[0035]
The Nd: YAG single crystal having a length of 8Φ × 50 mm was inserted into the molded body with sufficient care not to damage the molded body. Then, it heated up to 1100 degreeC in the air | atmosphere at the speed | rate of 25 degree-hour / hour, and hold | maintained at this temperature for 5 hours, and fully degreased | defatted. After the degreasing treatment, sintering was performed at 1800 ° C. for 10 hours under a vacuum of 10-1 Pa or less to obtain a rod-like bonded crystal of translucent YAG ceramics-Nd: YAG single crystal. After mirror-polishing both end surfaces, a 5 mW output He—Ne laser was transmitted through this surface, and scattering points (voids and pores) existing on the bonding surface were observed, but no surface was observed.
[0036]
Comparative Example 4
Granules used for CIP (cold isostatic pressing) molding were obtained from the slurry produced in the same manner as in Example 5 using a spray dryer. A bonded crystal was produced in the same manner as in Example 5 except that a pipe-like molded product was produced by CIP molding using this granule. When both ends were mirror-polished and the state of the joint surface was confirmed with the naked eye, a white ring was clearly recognized that pores were clearly present along the outer periphery of the single crystal.
[0037]
Example 6
Concentrations of yttrium nitrate, urea, ammonium sulfate, and aluminum nitrate were [Y (NO3) 3] = 0.25 mol / L, [Urea] = 1.5 mol / L, and [(NH4) 2SO4] = 0.5. It melt | dissolved with the pure water so that it might become 25 mol / L and [Al (NO3) 3] = 6.7 * 10 <-5> mol / L. Next, 10 L of the mixed solution was put into an autoclave, the temperature was adjusted to 125 ° C., the pressure was adjusted to 5 × 10 ⁵ Pa, and the mixture was maintained for 2 hours to obtain a precipitate of yttrium carbonate. The obtained precipitate was filtered and washed five times and dried at 110 ° C. for 24 hours. Next, this dried powder was calcined in an alumina crucible in the atmosphere at 1200 ° C. for 3 hours to obtain a readily sinterable yttria powder. To 200 g of the obtained yttria raw material powder, 12 g and 4 g of Chukyo Yushi E-503 and F-219 (amine system) were added as a peptizer, and 1 g of Sekisui Chemical PVB-BL1 was added as a binder. The mixture was mixed with 50 g of ethanol using a nylon pot and a nylon ball for 12 hours to obtain an alcohol slurry.
[0038]
This alcohol slurry was poured into a gypsum mold to obtain a molded body of 60 mm × 60 mm × 5 mm. Twenty 10 × 10 × 5 mm compacts were cut out from this compact. Five of them were heated at 25 ° C. per hour and sufficiently degreased at 1100 ° C. for 5 hours, and then sintered in a vacuum furnace at a temperature of 1650 ° C. for 5 hours. At this time, the heating rate was 100 ° C./hr and the degree of vacuum was 10 −1 Pa or less. One end face of the sintered body thus obtained was wrapped to Rmax 0.45 μm and flatness 0.8 μm. 5 sets of the combination of the lapping surface and the free surface of the molded body and 5 sets of the combined free surfaces of the molded body were again heated at 25 ° C. per hour and sufficiently degreased at 1100 ° C. for 5 hours. After that, it was sintered in a vacuum furnace at a temperature of 1650 ° C. for 5 hours. Under the present circumstances, what combined the free surfaces of the molded object put the yttria sintered compact at the time of degreasing | defatting so that it might become a load of 5 * 10 < ³ > Pa.
[0039]
The obtained crystal body was polished to a mirror surface on two surfaces facing the bonding surface at a parallelism of 8 to 10 seconds, and the bonding state was confirmed with the naked eye. All the bonding surfaces were bonded together. Scattering points (voids and pores) existing on the bonding surface were observed by transmitting a He—Ne laser, and disturbance of the transmitted wave front was also confirmed. However, the optical crystal had no problem at all.

Claims

A free surface at the time of molding of the cast molded body is used as a joint surface, and this joint surface is brought into contact with the surface of another crystal and sintered to sinter the molded body into a polycrystalline body. A method for producing a laser crystal, in which a bonding surface of a body is bonded to another crystal.

2. The method of manufacturing a laser crystal according to claim 1 , wherein casting molding is waste mud casting and the free surface is a surface that does not contact the mold during casting.

The inner peripheral surface of the cylindrical cast molded body is a free surface, the laser rod is inserted into the inner peripheral surface of the cast molded body, the cast molded body is sintered together with the laser rod, and the inner peripheral surface of the cast molded body is lasered. The method for producing a laser crystal according to claim 2 , wherein the method is joined to a side surface of the rod.