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1、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
2、 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
3、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 cavity surface emitting laser (850 nm),Ti:Sapphire
4、 laser: ultrashort pulses (30 fs) (700-1000 nm),Laser characteristics II -Threshold,kink in output 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- ,laser cooling and trapping,interferometry length measurements,biological pr
5、ocesses,ultrafast phenomena,Lasers in medicine- ,corrective eye surgery,removing blemishes,gallbladder surgery using fiber optics,Lasers in every day life,barcode scanners http:/www.barcode-,laser printers,laser cutting laser welding .,CD players,barcode scanners http:/www.barcode-,电吸收分布反馈,Lasers in
6、 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）,Semico
7、nductor 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,Gain Material,(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+) o
8、r 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
9、 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
10、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; Ab
11、sorb quantum efficiency;,(2) Nd3+:YAG pulse or CW operation (lower threshold) ; pulse operation,Four-level laser,See figure 7-9, Figure 7-10,Structure,Pumping,(2) Nd3+:YAG CW or pulse operation,3 relative motion,Total energy of the molecular:,Figure 7-17, Energy level,(2) CO2 Laser,He: buffer gas,4
12、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 processing Cutting and we
13、lding （焊接）of metals and non-metals Heat treatment of metals Scribing （雕合） Medicine no bleeding （止血） surgery ( water absorbs well in 10um) Research Spectroscopy (LIDAR) Laser chemistry Pumping of FIR laser Military,(3) Ion laser: Ar+ Laser,Visible( 350nm 520nm ), the most important laser Gas: Ar+ (18
14、) 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
15、 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+:YAG Pulsed CO2 Excimer laser, EDFA,