Nhng tin b trong Quang hc, Quang ph vÃ ng dng VI ISSN 1859 - 4271

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Advances in Optics, Photonics, Spectroscopy & Applications VI ISSN 1859 - 4271Fig. 4. Oscilloscope traces of eye-safe 1 st Stokespulse, pump and depleted pump in ring Ramanlaser.Fig. 5. 3 rd Stokes pulse energy as a function offlashlamp energy (1) without and (2) withintracavity telescope and (3, 4) as a function ofoutput coupler reflectivity at different pumpenergy. The dots 5 show 3 rd Stokes pulse width(FWHM) as a function of flashlamp energy.The most essential characteristics of the eye-safe laser source based on the ring KTP-OPO areshown in Fig. 6 and 7. The source generates radiation pulses with energies up to 35 mJ andduration ~11 ns at electrical pumping energy which does not exceed 8 J. According to ourmeasurements, the output wavelength of the KTP-OPO with pumping by radiation with λ=1.064μm is1570.8nm.Thisagreeswelwiththecalculatedvalue(1571nm)obtainedusingthepublishedSelmeierequationforKTP.Thelong-termoperationofthesourcepumpedat6.5J.isas<strong>trong</strong>caseforitsreliability.Thepulseenergyhasbeenmonitoredfortwointervalsofmorethanthreehoursofcon<s<strong>trong</strong>>tin</s<strong>trong</strong>>uousoperationthathavebeenseparatedbyanone-hourpause.ItcanbeseenthattheaverageOPO pulseenergyof~24.7mJremainspracticalyconstantwithprolongedoperation.Onlysmalrandom changesofoutputenergyduetothestatisticalpropertiesofNd:YAG-lasergenerationandthenoisepropertiesofOPOgenerationareobserved.Thechangesoccurwithastandarddeviationof0.74mJ.Fig. 6. Output energy of travelling-waveOPO as a function of electrical pump energyof Nd:YAG laser. Insert shows spectrum ofeye-safe radiation.Fig. 7. Behaviour of eye-safe radiation energy forlong-term source operation at repetition rate of 10Hz. Insert shows one-dimensional energy densitydistributions for (1) near and (2) far fields.38
Những tiến bộ <strong>trong</strong> <strong>Quang</strong> học, <strong>Quang</strong> <strong>ph</strong>ổ và Ứng dụng VI ISSN 1859 - 4271Forthetraveling-waveOPO,ac<s<strong>trong</strong>>tin</s<strong>trong</strong>>gasanaturaldia<strong>ph</strong>ragm,narowerpumpingbeamsdecreasetheapertureoftheOPOresonator(inotherwords,theefectivevalueoftheFresnelnumber)andtherebyhelptodecreasethedivergenceoftheOPO radiation,evenwithhighintrinsicdivergence.InthecauseofKTPcrystals,three-mirorringcavityisresonantonlyforthesignalwaveandthelargepumpingbeamdivergenceisreflectedmainlyintheidlerwaveradiation.One-dimensionalenergydensitydistributions1and2havebeenrecordedinthenear(~60cmfrom thesource)andfar(focalplaneofthes<strong>ph</strong>ericalmiror)fields,respectively.ThedivergenceoftheOPObeam withaverageoutputenergyof~25mJislesthansevendifractionlimits.ItshouldbenotedthatthefabricatedsourcemodelwiththeringOPOhasproduced2.5·10 6 pulseswithoutasubstantialchangeinthecharacteristicsoftheoutputradiation.IV. CONCLUSIONWehavedemonstrateddiferentapproachestodeveloppulsedeye-saferadiationsourcesinwhichRamanlasersbasedonNd:KGW crystalsandOPOwithKTPcrystalsconvertemisionofNd:KGW andNd:YAGlaserswiththe 4 F 3/2 – 4 I 13/2 and 4 F 3/2 – 4 I 13/2 workingtransitionsintothe1.5–1.57spectralrange.Independenceontheapproach,naturalcooledsourceswithRamanlaserconvertersensureeye-safewavelengths,pulseenergies,pulsewidthsandoutputbeamdivergencesbeingbetweenthelimits1.5and1.54μm,9and15mJ,3and25nsand5and15mrad,respectively.Basedonthetraveling-waveOPO,acompact,highlyefective,eye-safelasersourceradiatepulsesofupto35mJinenergy,11nsecinduration,and10Hzinrepetitionrateatelectricalpumpenergy≤ 8J.Atthe86.5% levelofthetotalpulseenergy,thesource-beamdivergenceisnotsomanyassevendifractionlimits.REFERENCES[1]V.I.Dashkevich,V.A.Orlovich and A.P.Shkadarevich,in CD-ROM Technical Digest onInternational conference ICONO/LAT 2007: Minsk,Belarus,28May–1Jun,2007,pp.LO1-58[2]V.I.Dashkevich,V.A.Orlovich,A.P.ShkadarevichandA.S.Shushpanov,,J. Appl. Spectrosc. Vol.75,2008,pp.539-545.[3]V.I.Dashkevich,V.A.OrlovichandA.P.Shkadarevich,J. Appl. Spectrosc. Vol.76,2009,pp.685-691.[4]V.I.Dashkevich,V.A.OrlovichandP.A.Apanacevich,in CD-ROM Technical Digest on 14 thInternational conference on Laser Optics «LO-2010»: St.Petersburg,Rusia,28Jun–2July,2010,pp.R1-436.39
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Nhng tin b trong Quang hc, Quang ph vÃ ng dng VI ISSN 1859 - 4271

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