1415激光原理与激光器.ppt
1.4 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 needed?,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,1897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。,Fabry-Perot Etalon,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,Loss：损耗,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，,*不同分子、原子及半导体材料中的电子有不同的E，其中半导体材料的E可变范围很大,Different types of lasers,Free electron laser,UCSB(63 mm 2.5 mm),VCSEL array:vertical cavitysurface emittinglaser(850 nm),Ti:Sapphire laser:ultrashort pulses(30 fs)(700-1000 nm),Laser characteristics II-Threshold,kink inoutput power,spectral narrowing,线宽压缩（线宽变窄）,扭结、弯曲,Laser history,1910,1920,1930,1940,1950,1960,1970,1980,1990,2000,Lasers in science-http:/,laser coolingand trapping,interferometrylength measurements,biological processes,ultrafast phenomena,http:/,Lasers in medicine-http:/,corrective eye surgery,removing blemishes,gallbladder surgeryusing fiber optics,Lasers in every day life,barcode scannershttp:/www.barcode-,laser printers,laser cutting laser welding.,CD players,barcode scannershttp:/www.barcode-,http:/,http:/,电吸收分布反馈,Lasers in communication systems,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掺铒光纤放大器,隔离器,隔离器,耦合器,Energy Lever of Er3+,980 nm,1550 nm,1550 nm,1550 nm,1550 nm,Chapter 7 Some Specific Laser Systems,Solid laser,Gas laser,Excimer laser（激基分子激光器）,Semiconductor laser,Ruby Laser,Nd3+:YAG Laser,Neodymium-Glass Laser,He-Ne Laser,CO2 Laser,（掺铒光纤放大激光器）,Quantum Well Laser,DFB Laser,VCSES Laser,GainMaterial,(EDFA),量子阱,分布反馈,垂直腔表面发射半导体,Fiber Laser,1.5.1,1.5.2,1.5.3,1.5.4,Active medium:Impurity ions in a transparent dielectric host ions:rare-earth(3+)or transition-metal ions(3+)concentrations:0.110%Hosts:crystals(oxides,garnets 石榴石or fluorides 氟化物)or glasses Pumping:optical pumping,Solid laser,(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:flashlamps(510-4 s)(two absorption bands),See Figure 7-4,692.5nm,R2 694.3nm,R1,See Figure 7-5,（螺旋状的）,Typical setup of a pulsed ruby laser,(1)Ruby Laser,+Circuit+Cooling system,Structure,(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 upper-state lifetime double pulse cooling problems low pulse rate poor efficiency,Optical flux;Absorb coefficient;Absorb quantum efficiency;,(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 laser;pulse or CW operation(lower threshold);pulse operation,Four-level laser,See figure 7-9,Figure 7-10,Structure,Pumping,(2)Nd3+:YAG&Nd3+:Glass Laser,Nd:YAG Laser:YAG most common host material typical values: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 optical crystals(KTP,BBO,),(2)Nd3+:YAG&Nd3+:Glass Laser,Applications:IndustryMaterial processingElectronics industryMedicine endoscope(内窥镜）Cataract surgery（白内障手术）ResearchMilitaryLaser rangingTarget designation,(2)Nd3+:YAG&Nd3+:Glass Laser,1.如何选择激光介质？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,Gas laser,Active medium:Gas,He-Ne Laser(atom)CO2 Laser(molecule)Ar+Laser(ion)Excimer Laser(excited atom/molecule)He-Cd Laser N2 Laser Copper vapor Laser Gold vapor Laser,First gas laser(1961,1.15um),Energy level,(1)He-Ne Laser,3S,2S,2P,3P,1S,Brewster window,Structure,(1)He-Ne Laser,(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:,(2)CO2 Laser,The 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 operation,3 relative motion,Total energy of the molecular:,Figure 7-17,Energy level,(2)CO2 Laser,He:buffer gas,4 types of Construction:,Closed discharge tube,wave guide,(2)CO2 Laser,slow axial flow fast axial flow,transverse flow+transverse discharge transverse excitation atmosphere pressure,(2)CO2 Laser,More power with gas circulation（循环）,(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(LIDAR)Laser chemistryPumping of FIR laserMilitary,(3)Ion laser:Ar+Laser,Visible(350nm 520nm),the most important laser Gas:Ar+(18)or Kr+(36)Pumping:electric discharge(电子放电）4-level laser;CW operation,(3)Ar+Laser,(3)Ar+Laser,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 shows,(4)Excimer laser,excimer(激基分子）=excited dimer（二聚物）,Structure:,Parameters:,(4)Excimer laser,(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）,Pulsed Nd3+:YAGPulsed CO2Excimer laser,EDFA,
