《激光原理与激光器》PPT课件.ppt

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1、Optical Electronics,Fall 20101.4 Laser characteristics spectrally broad divergent cant be focused tightly not very intense incoherent very monochromatic does not diverge as fast can be focused tightly can be extremely intense spatial coherence(interference)temporally coherent(beat notes)What is need

2、ed?More generally:gain medium pump-far from thermal equilibrium feedback(resonator,mirrors,cavity)发散非相干单色干涉反馈（谐振器，镜子，腔）：光束的选择性增益物质（激活物质）：单光泵浦源（激励源）：粒子数反转Optical Electronics,Fall 20101897年发明法布里珀罗空腔谐振器20世纪50年代中期，肖洛与美国著名物理学家汤斯共同研究微波激射问题。当汤斯提出受激辐射放大原理时，肖洛第一个提出运用没有侧壁的开放式法布里-珀罗腔作振荡器的设想。1960年，他和汤斯研制出第一台激光器

3、。Fabry-Perot EtalonOptical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,

4、Fall 2010Optical Electronics,Fall 2010增益饱和，粒子数不再反转的时候Gain?当受激辐射超过受激吸收和自发辐射的时候，即粒子数发生反转固体（气体、液体）增益物质：三能级，四能级半导体增益物质：直接带隙，间接带隙Optical Electronics,Fall 2010Loss：损耗：损耗Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,F

5、all 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010Optical Electronics,Fall 2010简称开腔，全称：开放式光学谐振腔共轴球面腔：稳定腔、不稳腔、临界腔，Optical Electronics,Fall 2010Optical Electronics,Fall 2010*不同分子、原子及半不同分子、原子及半导体材料中的电子有不导体材料中的电子有不同的同的E E，其中半导体，其中半导体材料的材料的E E可变范围很可变范围很大大Optical Electronics,Fall 2010Optic

6、al Electronics,Fall 2010Different types of lasersFree electron laser,UCSB(63 m mm 2.5 mm)VCSEL array:vertical cavitysurface emittinglaser(850 nm)Ti:Sapphire laser:ultrashort pulses(30 fs)(700-1000 nm)Fermi:10-15Picometer:10-12Nanometer:10-9Optical Electronics,Fall 2010Laser characteristics II-Thresh

7、oldkink inoutput powerspectral narrowing线宽压缩（线宽变窄）扭结、弯曲Optical Electronics,Fall 2010Laser history1910192019301940195019601970198019902000Einstein predictsstimulated emissionTownes invents and builds first MASERSchawlow and Townes propose LASERMaiman builds first(ruby)LASERJavan inventsHe-Ne laserFai

8、st builds quantumcascade laserNakamura builds blue laser diodenanowire laser builtat UCBAlferov builds first heterostructure laserCD playerIBM builds first laser printerHall buildssemiconductor laserSpectra introducesTi:Sapphire laserfirst fiber optic communication system(Chicago)Optical Electronics

9、,Fall 2010Lasers in science-http:/ coolingand trappinginterferometrylength measurementsbiological processesultrafast phenomenahttp:/ Electronics,Fall 2010Lasers in medicine-http:/ eye surgeryremoving blemishesgallbladder surgeryusing fiber opticsOptical Electronics,Fall 2010Lasers in every day lifeb

10、arcode scannershttp:/www.barcode- printers laser cutting laser welding.CD playersbarcode scannershttp:/www.barcode- Electronics,Fall 2010 电吸收分布反馈Lasers in communication systems 4 PIN receivers 160 km standard fibre boosteramplifier4 WDMEA-DFB lasers pre-amplifierattenuatorand powermeteroptical spect

11、rum analyserchannel separation:100 GHz(0.8 nm)DEMUXlaser as sourcelaser as amplifierPIN-diodePIN-diodeInput1550Monitor tapIsolator980/1550 couplerEr fibreIsolatorMonitor tapOutput 980 nmpump laser光功率放大器De-Multiplexer 分路器Wavelength Division Multiplexer 波分复用系统前置放大器Erbium-doped Optical Fiber Amplifer掺铒

12、光纤放大器 Positive-Instincive-Negative光电转换隔离器隔离器耦合器Optical Electronics,Fall 2010Energy Lever of Er3+980 nm1550 nm1550 nm1550 nm1550 nmOptical Electronics,Fall 2010Chapter 7 Some Specific Laser SystemsSolid laserGas laserExcimer laser（激基分子激光器）Semiconductor laserRuby LaserNd3+:YAG LaserNeodymium-Glass Las

13、erHe-Ne LaserCO2 LaserIon laserAr+Laser（掺铒光纤放大激光器）Quantum Well LaserDFB LaserVCSES Laser GainMaterial(EDFA)量子阱分布反馈垂直腔表面发射半导体Fiber Laser1.5.11.5.21.5.31.5.4Optical Electronics,Fall 2010Active medium:Impurity ions in a transparent dielectric host ions:rare-earth(3+)or transition-metal ions(3+)concentr

14、ations:0.110%Hosts:crystals(oxides,garnets 石榴石or fluorides 氟化物)or glasses Pumping:optical pumping Solid laserOptical Electronics,Fall 2010(1)Ruby Laser Ions:rare-earth(Cr 3+)concentrations:0.05%,Hosts:Al2O3(synthetic sapphire,人造蓝宝石)First laser(1960);3-level laser;pulse operation Optical Pumping:flas

15、hlamps(510-4 s)(two absorption bands)See Figure 7-3吸收系数跃迁截面See Figure 7-4,692.5nm,R2 694.3nm,R1three-level laser4F24F1R1See Figure 7-5,Optical Electronics,Fall 2010（螺旋状的）Typical setup of a pulsed ruby laser(1)Ruby Laser+Circuit+Cooling systemExternalMirror（螺旋状的）ExternalMirror(partially transmitting)

16、OutputBeam（聚光腔）StructureOptical Electronics,Fall 2010(1)Ruby Laser Parameters:t flash t 2 N0:N1+N2 N2:the number of atoms pumped into level 2 Applications:Holography（全息）Medical applications Large holograms Holographic interferometry Plasma diagnostics(等离子体诊断学）Comments:requires strong pumping long up

17、per-state lifetime double pulse cooling problems low pulse rate poor efficiency Optical flux;Absorb coefficient;Absorb quantum efficiency;Optical Electronics,Fall 2010(2)Nd3+:YAG&Nd3+:Glass Laser Ions:rare-earth(Nd 3+)concentrations:1%Hosts:Y3Al5O12(yttrium aluminum garnet,YAG,钇铝石榴石)Glass 4-level la

18、ser;pulse or CW operation(lower threshold);pulse operationFour-level laserSee figure 7-9,Figure 7-10Optical Pumping:(two absorption bands)Optical Electronics,Fall 2010 Structure Pumping(2)Nd3+:YAG&Nd3+:Glass Laser Optical Electronics,Fall 2010 Nd:YAG Laser:YAG most common host material typical value

19、s:pulse rate:10-100 Hz CW power:10-100W pulse energy:50mJ-10J Nd:glass Laser:Possible to fabricate large rods high pulse energy glass is a poor heat conductor low pulse rate Harmonic Generation:(fundamental :1.06um)2.harmonic:532 nm 3.harmonic:1.06um+532 nm 355 nm(UV)4.harmonic:266 nm(UV)Nonlinear o

20、ptical crystals(KTP,BBO,)(2)Nd3+:YAG&Nd3+:Glass Laser Optical Electronics,Fall 2010 Applications:IndustryMaterial processingElectronics industryMedicine endoscope(内窥镜）Cataract surgery（白内障手术）ResearchMilitaryLaser rangingTarget designation(2)Nd3+:YAG&Nd3+:Glass Laser Optical Electronics,Fall 20101.如何选

21、择激光介质？2.泵浦结构如何选择？泵浦结构主要包括端泵、侧泵、面泵等等 3.冷却方式如何选择？是水冷还是风冷，是空气自然冷却还是用TEC进行冷却或者用热管进行冷却 4.腔结构如何选择？腔大体上分稳定腔和非稳定腔；对腔设计还要考虑热透镜效用的补偿5.如何进行选模？一类是横模的选择，光阑；另一类是纵模的选择，光学元件6.整体结构如何选择？整体结构主要指就仅仅一个振荡器还是利用MOPA结构 补充内容：固体激光器设计步骤Optical Electronics,Fall 2010 Gas laserActive medium:Gas He-Ne Laser (atom)CO2 Laser (molecu

22、le)Ar+Laser (ion)Excimer Laser(excited atom/molecule)He-Cd Laser N2 Laser Copper vapor Laser Gold vapor LaserOptical Electronics,Fall 2010 First gas laser(1961,1.15um)Energy level(1)He-Ne Laser 3S 2S 2P 3P 1SBrewster window Optical Electronics,Fall 2010 Structure(1)He-Ne LaserOptical Electronics,Fal

23、l 2010(1)He-Ne Laser Applications:Bar code scanningThe standard was originally created by He-Ne Laser Holography only for non-moving objectsAlignment Laser pointers&laser printers(displaced by diode lasers)Medicine(acupuncture（针刺疗法）,cosmetology（美容）laser)Advantages:Optical Electronics,Fall 2010(2)CO2

24、 LaserThe high efficient()laser of large laser power,typical molecular laser Gas:CO2+N2+He(typically in ratios 1:1:8,Ptot 5-15 Torr)Pumping:plasma discharge(等离子体放电）Energy level:relative motion of the constituent atoms;CW or pulse operation3 relative motionTotal energy of the molecular:Optical Electr

25、onics,Fall 2010Figure 7-17,Energy level001100020010(2)CO2 LaserHe:buffer gasOptical Electronics,Fall 2010 4 types of Construction:Closed discharge tube wave guide(2)CO2 LaserOptical Electronics,Fall 2010 slow axial flow fast axial flow transverse flow+transverse discharge transverse excitation atmos

26、phere pressure(2)CO2 LaserMore power with gas circulation（循环）Optical Electronics,Fall 2010(2)CO2 Laser Applications:Material processingCutting and welding（焊接）of metals and non-metalsHeat treatment of metalsScribing（雕合）Medicine no bleeding（止血）surgery(water absorbs well in 10um)ResearchSpectroscopy(LI

27、DAR)Laser chemistryPumping of FIR laserMilitaryOptical Electronics,Fall 2010(3)Ion laser:Ar+LaserVisible(350nm 520nm),the most important laser Gas:Ar+(18)or Kr+(36)Pumping:electric discharge(电子放电）4-level laser;CW operation Optical Electronics,Fall 2010(3)Ar+LaserOptical Electronics,Fall 2010(3)Ar+La

28、ser Advantages:high power in blue materials typically more sensitive for blue than for red good quality output beam and long coherence length Applications:Laser printers CD-ROM mastering Holography Spectroscopy Pumping of other lasers Surgery(eye)photochemistry Light showsOptical Electronics,Fall 20

29、10(4)Excimer laserexcimer(激基分子）=excited dimer（二聚物）UV(200nm 400nm)激基状态:(RH)*=(AX)*Pumping:energetic e-beams(高能电子束）short pulse operation（卤化物）Optical Electronics,Fall 2010Structure:Parameters:(4)Excimer laserOptical Electronics,Fall 2010(4)Excimer laser Applications micromachining by laser ablation(polymers,biological materials,etc.)comeal sculpting(PRK,LASIK)photolithography（影印平版术）dye laser pumping（消融，切除）(a)Pulsed Nd3+:YAG(b)Pulsed CO2(c)Excimer laserOptical Electronics,Fall 2010 EDFA