激光原理15激光器
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 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。 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, 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Optical Electronics, Fall 2010Optical Electronics, Fall 2010Optical Electronics, Fall 2010Optical Electronics, Fall 2010Optical Electronics, Fall 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 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Optical Electronics, Fall 2010Optical Electronics, Fall 2010Different types of lasersFree electron laser, UCSB (63 mm 2.5 mm)VCSEL array: vertical cavity surface emitting laser (850 nm)Ti:Sapphire laser: ultrashort pulses (30 fs) (700-1000 nm)Fermi: 10-15Picometer: 10-12Nanometer: 10-9Optical Electronics, Fall 2010Laser characteristics II -Thresholdkink in output powerspectral narrowing线宽压缩（线宽变窄）扭结、弯曲Optical Electronics, Fall 2010Laser history1910192019301940195019601970198019902000Einstein predicts stimulated emissionTownes invents and builds first MASERSchawlow and Townes propose LASERMaiman builds first (ruby) LASERJavan invents He-Ne laserFaist builds quantum cascade laserNakamura builds blue laser diodenanowire laser built at UCBAlferov builds first heterostructure laserCD playerIBM builds first laser printerHall builds semiconductor laserSpectra introduces Ti:Sapphire laserfirst fiber optic communication system (Chicago)Optical Electronics, Fall 2010Lasers in science- http:/33tt.com/print.php?articleid=599laser cooling and trappinginterferometry length measurementsbiological processesultrafast phenomenahttp:/www.ic160.com/bbs/2006-1-7/200617181220.htmOptical Electronics, Fall 2010Lasers in medicine- http:/33tt.com/print.php?articleid=599corrective eye surgeryremoving blemishesgallbladder surgery using fiber opticsOptical Electronics, Fall 2010Lasers in every day lifebarcode scanners http:/www.barcode-tech.cn/p_0_1.htmllaser printers laser cutting laser welding CD playersbarcode scanners http:/www.barcode-tech.cn/p_0_1.htmlhttp:/electronics.howstuffworks.com/cd.htm#http:/videos.howstuffworks.com/labratstv/2831-episode-57-printers-101-video.htmOptical Electronics, Fall 2010电吸收分布反馈Lasers in communication systems4 PIN receivers160 km standard fibrebooster amplifier 4 WDM EA-DFBlaserspre-amplifierattenuator and power meteroptical spectrum analyserchannel separation: 100 GHz (0.8 nm)D E M U Xlaser as sourcelaser as amplifierPIN-diodePIN-diodeInput1550Monitor tapIsolator980/1550couplerEr fibreIsolatorMonitor tapOutput980 nm pump 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 nm 1550 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 LaserHe-Ne LaserCO2 LaserIon laserAr+ Laser（掺铒光纤放大激光器）Quantum Well LaserDFB LaserVCSES LaserGainMaterial(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+) concentrations: 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: flashlamps ( 5×10-4 s) ( two absorption bands)See Figure 7-3吸收系数跃迁截面See Figure 7-4, 692.5nm, R2694.3nm, 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 systemExternal Mirror （螺旋状的） External Mirror (partiallytransmitting)Outp
