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Solid State Pump Lasers with High Power and High Repetition Rate

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I'Proceedingrocecding~s orlhe oflhe 6th 6th International International SymposiumSymposiu m on onon Advanced AdvancedAdvanced Nuclcar Nuclear Energy Energy Rcsenrch Research -INNOVA-INNOVATIVTl VE E LASERLASE R TECHNOLOGIESTECHNOLOGIE S IN IN NUCLEARNUCLEA R ENERGY-ENERGY - SoSoli1i d State State PumpPum p LasersLaser s withwit h HighHig h PowerPowe r andan d HighHig h RepetitionRepetitio n RateRat e Masaki MasakiMasaki Oba ，, Masaaki Masaak i Kato Kato and and Takashi Takashi Ari Arisawsawa a Department Department ザof Cl Chemistrylemistry and and Fuel Fuel Research Research Japall Japall Japan Atomic Energy Research Institute[nsli 似， te Tokai-muraTokai-mura,， Ib Ibaraki-ken, araki 四 ke n， 319-11319-11,， Japan TeTel.0292-82-6085l. 0292-82-6085 ,， Fax.0292-82-5572 Fax.0292-82-557 2 Abstract Abstract Abstract WeW e built built a laser laser diode diode pumpedpumpe d solid solid state state green green laselaser r 仏(LDPSSGLDPSSGI ぷ) rated rated at at high high repetition repetition repetitio n rate. rate. TwoTw o laser laser heads heads are are placed placed in in one one cavity cavity with with a rotator rotator in in betweenbetween to to design design design to to avoid avoid thermal thermal lensing lensing and and thermal therma l birefringence birefringence effec effect t. AIthough Although average average green green green laser laser powerpowe r higher higher than than 10 10 W waswa s obtained obtained at at 1k kHHz z repetition repetition rate rate with with pulse pulse width width width of of 20-3020-3 0 nsec nsec,th ，the e beambea m quality quality waswa s so so muchmuc h deteriorated deteriorated that that energy energ y efficiency efficiency waswa s as as lowlo w as as 2 %. LeLearninaming g 企froomm this this experience experience that that high high powerpowe r osc oscillatoil1 ator r causes causes a lot lot ofof thermaI therma l distortion distortion not not only only in in the th e laser laser rod rod but bu t also also in in the the Q-switch Q-switch device device,w，we e proceeded proceeded proceeded to to bubuiliI ta a osc oscillator/amplifieiIl ator/amp 1i fier r system. system. A lowlo w powerpowe r oscillator oscillator has has a slab slab type type crystal crystal crystal in in the th e cavity. cavity. AsA s a result resul t spatial spatia l distribution distribution of of laser laser powerpowe r waswa s extremely extremely improved. improved. improved. AsA s wew e expect expect that that the the high hig h repetition repetition rate rate solid solid state state laser laser should should bebe CWCW operated operated operated Q-switchQ-switch type type laser laser 企froomm the the viewview point point of o f lifetime lifetime of of diode diode lasers ,， a conventional conventional conventional arc arc lamp lamp pumpedpumpe d CWCW Q-switch Q-switch green green YAGYA G laser laser of of which which the th e repetition repetition rate rate rate is is changeable changeable fromfrom 1k kHHz z to to 5k kHHz z and and the the pulse pulse width width is is 250-570250-57 0 nsec nsec waswa s also also tested tested tested to to obtain obtain pumpingpumpin g characteristics characteristics of of a dyedye laser laser as as a function function of of power ,， pulse puls e width width width etc. ，, and an d dyedye laser laser pulse pulse width width of o10 f 100-13Q.- 130 0 nsec nsec werewer e obtained. obtained. key keykey words:words : laser laser diode ，, solid soli d state state laser ,， slab ，, CWC W Q-switch ,， tunable tunabl e laser laser l. l.Introductio Introduction n TUnable TUnable Tunable lasers lasers in in the th e visible visible wavelength wavelength region ,， such suc h as a s Ti:sapphire Tirsapphire or or a dyedye laser laser laser are are generally generally pumpedpumpe d byb y green gree n lasers. lasers. SomeSom e ofof themthem have hav been e been developed developed for for carrying carrying carrying out out the the experiments experiments ono n chemical chemica l reaction reaction in in the th e reprocessing reprocessing of of nuclear nuclea r fuels fuels or or or uranium uranium enrichment enrichmen t process. process. ForFor the the implementation implementation of of these thes e applications applications high high power ,， high hig h repetition repetition rate ，, highhig h energy energy efficiency ,， reliability reliabilit y and and ∞compactnes mpactness s are are indispensable. indispensable. indispensable. GreenGreen YAGYA G lasers lasers excited excited by by laser laser diodes diodes are ar e greatly greatly promising promising to to beb e used used used as as a pumppum p laser laser for for tunable tunable laser lase r system. system. HiHiggh h powerpowe r laser laser diode diode makesmake s possible possible to to to bubuiliI t ∞compacmpact t aalIl l so soli1i d state state Iasers lasers with with high high powerpowe r and and high hig h repetition repetition rate. rate. In In atomic atomic atomic vapor vapor Iaser laser isotope isotop e separation separation (A(AVLIS VLIS) ) process ,， CCVL VLs s are are used used for for pumpingpumpin g dye dyedye lasers ，, because becaus e ofo f their their high high powerpowe r and and high hig h repetition repetitio n rate. rate. ButBut energy energ y efficiency efficiency is is is as as lowlo w as as 1 % andand they they 0occup∞upy y muchmuc h space. space. LDLD pumpedpumpe d solid solid state state laser laser can can be be ∞compac mpact t andand moremor e than than 3 % of of energy energy eefficienc百iciency y is is expec expected包d. WeW e bubuiliI t twotwo types types ofof quasi quasi CWCW LDL D pumpedpumpe d Nd:YAGNd:YA G Iasers lasers operated operated at at the the repetition repetition repetition rate rate 1k kHHz z to to study study their thei r characteristics. characteristics . First First of of a11 all wew e built built a rod rod type type oscillator oscillator oscillator with with twotw o heads heads and and at at the the second second step step wcw e built built zig-zag zig-zag slab slab type type laser laser at at lowlo w - 686 686-ー powerpowe r reg regionlO n. CWCW pumpedpumpe d Q-switchQ-switch green green laser laser is is attractive attractive because because of of longer longe r lifetime lifetime ofof laser laser lase r diodes. diodes. But Bu t their their pulse pulse width width generated generated byb y AOAO Q-switchQ-switch is is normally normally longer longer than than EOEO Q-switchQ-switc h laser. laser. AsA s wew e are ar e interested interested in in the the dyedye laser laser pumpedpumpe d by by such such long long pu]se pulse,， wew e measured measured the the characteristics characteristics ofof dyedy e laser laser pumpedpumpe d byb y a conventional conventional CWCW Q-switch Q-switch YAGYA G green gree n Iaser. laser. 2.LD2.L D PuPumpemped d DoubleDoubl e RodRo d YAGYA G Laser Laser Fig.1 Fig.1 Fig.l showsshow s the the schematics schematics of of the th e laser laser in in whichwhic h 969 6 bars bars ofof LDsLD s werewer e used ,， and an d werewer e set set on on the the 8 faces faces around around the the YAGYA G rods.LDs rods.LDs werewer e operated operated with with 250μsec25 0 usee pulse pulse width width width at at 1k kHHz z repetition repetition rate. rate. A 90 °0 rotator rotator waswa s set set betweenbetween rods rods to to avoid avoid therma1 thermal birefringence birefringence birefringence effec effect t. GreenGreen (532 (532 nm)nm ) output output waswa s obtained obtained by by KTPKT P crystal crystal in in the the external external externa l cavity. cavity. AboutAbou t 505 0 W output output powerpowe r waswa s obtained obtained at at 1064106 4 nmnm (日 (fig.2)g.2). Energy Energy conversion conversion conversio n efficiency efficiency waswa s 2.5 2.5 % at at the the 50 50 W output output powerpowe r and and slope slop e efficiency efficiency waswa s 1212. .5 5 %. %. ButBu t its its green green output output powerpowe r converted converted by by KTPKT P waswa s lower lower than than 13 13 羽'.W. ThThi is s inefficient inefficient inefficient performance performance waswa s probably probably caused caused by by badbad beambea m quaquality Ii ty. Fig.3 Fig.3 showsshow s beambea m profile profile profile at at 1064 1064 nm.nm . TwoTw o peaks peaks appeared appeared at at high high powerpowe r region. region. WeW e considered considered that that the the cause cause cause waswa s attributed attributed to to thermal therma l distortion distortion not not only only in in a YAGYA G rod rod but but a1so also in in a Q-switch Q-switchQ-switch crysta crystal l. 3.Zig-zag 3.Zig-zag 3.Zig-zag YAGYA G Slab Slab Laser Laser 羽W'e e built built a zig-zag zig-zag YAGYA G slab slab laser laser at at 10wlo w powerpowe r region region to to improveimprove the the beambea m quality quality quality of of the the laser laser above above developed. developed. Laser Laser beam travels travels in in the the YAGYA G crystal crystal in in zig-zag ,， andan d to to compensate compensate the the thermal therma l distortion distortion in in a crysta crystal I. Fig.4 Fig.4 showsshow s the the schematics schematics schematics ofof zig-zag zig-zag slab slab YAGYA G laser.
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